ATMEL ATMEGA325V-8AI

Features
• High Performance, Low Power AVR® 8-Bit Microcontroller
• Advanced RISC Architecture
•
•
•
•
•
•
•
– 130 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16 MHz
– On-Chip 2-cycle Multiplier
Non-volatile Program and Data Memories
– In-System Self-Programmable Flash, Endurance: 10,000 Write/Erase Cycles
32K bytes (ATmega325/ATmega3250)
64K bytes (ATmega645/ATmega6450)
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
– EEPROM, Endurance: 100,000 Write/Erase Cycles
1K bytes (ATmega325/ATmega3250)
2K bytes (ATmega645/ATmega6450)
– Internal SRAM
2K bytes (ATmega325/ATmega3250)
4K bytes (ATmega645/ATmega6450)
– Programming Lock for Software Security
JTAG (IEEE std. 1149.1 compliant) Interface
– Boundary-scan Capabilities According to the JTAG Standard
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescaler and Compare Mode
– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
Mode
– Real Time Counter with Separate Oscillator
– Four PWM Channels
– 8-channel, 10-bit ADC
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Universal Serial Interface with Start Condition Detector
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
– Interrupt and Wake-up on Pin Change
Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated Oscillator
– External and Internal Interrupt Sources
– Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and
Standby
I/O and Packages
– 53/68 Programmable I/O Lines
– 64-lead TQFP, 64-pad QFN/MLF, and 100-lead TQFP
Speed Grade:
– ATmega325V/ATmega3250V/ATmega645V/ATmega6450V:
0 - 4 MHz @ 1.8 - 5.5V, 0 - 8 MHz @ 2.7 - 5.5V
– ATmega325/3250/645/6450:
0 - 8 MHz @ 2.7 - 5.5V, 0 - 16 MHz @ 4.5 - 5.5V
Temperature range:
– -40°C to 85°C Industrial
8-bit
Microcontroller
with In-System
Programmable
Flash
ATmega325/V
ATmega3250/V
ATmega645/V
ATmega6450/V
Preliminary
2570J–AVR–11/06
Features (Continued)
• Ultra-Low Power Consumption
– Active Mode:
1 MHz, 1.8V: 350 µA
32 kHz, 1.8V: 20 µA (including Oscillator)
– Power-down Mode:
100 nA at 1.8V
2
AVCC
AGND
AREF
PF0 (ADC0)
PF1(ADC1)
PF2 (ADC2)
PF3 (ADC3)
PF4 (ADC4/TCK)
PF5 (ADC5/TMS)
PF6 (ADC6/TDO)
PF7 (ADC7/TDI)
DNC
DNC
PH7 (PCINT23)
PH6 (PCINT22)
PH5 (PCINT21)
PH4 (PCINT20)
DNC
DNC
GND
VCC
DNC
PA0
PA1
PA2
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
Figure 1. Pinout ATmega3250/6450
DNC
1
75
PA3
(RXD/PCINT0) PE0
2
74
PA4
(TXD/PCINT1) PE1
3
73
PA5
(XCK/AIN0/PCINT2) PE2
4
72
PA6
(AIN1/PCINT3) PE3
5
71
PA7
(USCK/SCL/PCINT4) PE4
6
70
PG2
(DI/SDA/PCINT5) PE5
7
69
PC7
(DO/PCINT6) PE6
8
68
PC6
(CLKO/PCINT7) PE7
9
67
DNC
VCC
10
66
PH3 (PCINT19)
GND
11
65
PH2 (PCINT18)
DNC
12
64
PH1 (PCINT17)
(PCINT24) PJ0
13
63
PH0 (PCINT16)
(PCINT25) PJ1
14
62
DNC
DNC
15
61
DNC
DNC
16
60
DNC
DNC
17
59
DNC
DNC
18
58
PC5
(SS/PCINT8) PB0
19
57
PC4
(SCK/PCINT9) PB1
20
56
PC3
(MOSI/PCINT10) PB2
21
55
PC2
(MISO/PCINT11) PB3
22
54
PC1
(OC0A/PCINT12) PB4
23
53
PC0
(OC1A/PCINT13) PB5
24
52
PG1
(OC1B/PCINT14) PB6
25
51
PG0
INDEX CORNER
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
DNC
(T1) PG3
(T0) PG4
RESET/PG5
VCC
GND
XTAL2 (TOSC2)
XTAL1 (TOSC1)
DNC
DNC
(PCINT26) PJ2
(PCINT27) PJ3
(PCINT28) PJ4
(PCINT29) PJ5
(PCINT30) PJ6
DNC
(ICP1) PD0
(INT0) PD1
PD2
PD3
PD4
PD5
PD6
PD7
ATmega3250/6450
(OC2A/PCINT15) PB7
Pin Configurations
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
DNC
1
(RXD/PCINT0) PE0
2
AVCC
GND
AREF
PF0 (ADC0)
PF1 (ADC1)
PF2 (ADC2)
PF3 (ADC3)
PF4 (ADC4/TCK)
PF5 (ADC5/TMS)
PF6 (ADC6/TDO)
PF7 (ADC7/TDI)
GND
VCC
PA0
PA1
PA2
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
Figure 2. Pinout ATmega325/645
48 PA3
47 PA4
INDEX CORNER
(TXD/PCINT1) PE1
3
46 PA5
(XCK/AIN0/PCINT2) PE2
4
45 PA6
(AIN1/PCINT3) PE3
5
44 PA7
(USCK/SCL/PCINT4) PE4
6
43 PG2
(DI/SDA/PCINT5) PE5
7
42 PC7
(DO/PCINT6) PE6
8
(CLKO/PCINT7) PE7
9
40 PC5
(SS/PCINT8) PB0
10
39 PC4
33 PG0
Disclaimer
PD7 32
16
PD6 31
(OC1B/PCINT14) PB6
PD5 30
34 PG1
PD4 29
15
PD3 28
(OC1A/PCINT13) PB5
PD2 27
35 PC0
PD1 (INT0) 26
14
(ICP1) PD0 25
(OC0A/PCINT12) PB4
XTAL1 (TOSC1) 24
36 PC1
GND 22
13
XTAL2 (TOSC2) 23
(MISO/PCINT11) PB3
VCC 21
37 PC2
(T0) PG4 19
38 PC3
12
RESET/PG5 20
11
(T1) PG3 18
(SCK/PCINT9) PB1
(MOSI/PCINT10) PB2
(OC2A/PCINT15) PB7 17
Note:
41 PC6
ATmega325/645
The large center pad underneath the QFN/MLF packages is made of metal and internally
connected to GND. It should be soldered or glued to the board to ensure good mechanical stability. If the center pad is left unconnected, the package might loosen from the
board.
Typical values contained in this datasheet are based on simulations and characterization of other AVR microcontrollers manufactured on the same process technology. Min
and Max values will be available after the device is characterized.
3
2570J–AVR–11/06
Overview
The ATmega325/3250/645/6450 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega325/3250/645/6450 achieves throughputs
approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.
Block Diagram
PF0 - PF7
VCC
DATA DIR.
REG. PORTF
DATA REGISTER
PORTF
PC0 - PC7
PA0 - PA7
PORTA DRIVERS
PORTF DRIVERS
PORTC DRIVERS
DATA DIR.
REG. PORTA
DATA REGISTER
PORTA
XTAL1
GND
XTAL2
Figure 3. Block Diagram
DATA REGISTER
PORTC
DATA DIR.
REG. PORTC
8-BIT DATA BUS
AVCC
AGND
CALIB. OSC
ADC
INTERNAL
OSCILLATOR
AREF
STACK
POINTER
WATCHDOG
TIMER
ON-CHIP DEBUG
PROGRAM
FLASH
SRAM
MCU CONTROL
REGISTER
BOUNDARYSCAN
INSTRUCTION
REGISTER
TIMER/
COUNTERS
GENERAL
PURPOSE
REGISTERS
X
PROGRAMMING
LOGIC
INSTRUCTION
DECODER
CONTROL
LINES
+
-
ANALOG
COMPARATOR
Z
INTERRUPT
UNIT
ALU
EEPROM
Y
STATUS
REGISTER
AVR CPU
USART
UNIVERSAL
SERIAL INTERFACE
DATA REGISTER
PORTE
DATA DIR.
REG. PORTE
PORTE DRIVERS
PE0 - PE7
4
TIMING AND
CONTROL
RESET
DATA DIR.
REG. PORTH
DATA REGISTER
PORTH
PROGRAM
COUNTER
DATA DIR.
REG. PORTJ
DATA REGISTER
PORTJ
PORTH DRIVERS
PORTJ DRIVERS
PJ0 - PJ6
PH0 - PH7
OSCILLATOR
JTAG TAP
SPI
DATA REGISTER
PORTB
DATA DIR.
REG. PORTB
PORTB DRIVERS
PB0 - PB7
DATA REGISTER
PORTD
DATA DIR.
REG. PORTD
PORTD DRIVERS
PD0 - PD7
DATA REG.
PORTG
DATA DIR.
REG. PORTG
PORTG DRIVERS
PG0 - PG4
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
The AVR core combines a rich instruction set with 32 general purpose working registers.
All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing
two independent registers to be accessed in one single instruction executed in one clock
cycle. The resulting architecture is more code efficient while achieving throughputs up to
ten times faster than conventional CISC microcontrollers.
The ATmega325/3250/645/6450 provides the following features: 32/64K bytes of InSystem Programmable Flash with Read-While-Write capabilities, 1/2K bytes EEPROM,
2/4K byte SRAM, 54/69 general purpose I/O lines, 32 general purpose working registers, a JTAG interface for Boundary-scan, On-chip Debugging support and
programming, three flexible Timer/Counters with compare modes, internal and external
interrupts, a serial programmable USART, Universal Serial Interface with Start Condition Detector, an 8-channel, 10-bit ADC, a programmable Watchdog Timer with internal
Oscillator, an SPI serial port, and five software selectable power saving modes. The Idle
mode stops the CPU while allowing the SRAM, Timer/Counters, SPI port, and interrupt
system to continue functioning. The Power-down mode saves the register contents but
freezes the Oscillator, disabling all other chip functions until the next interrupt or hardware reset. In Power-save mode, the asynchronous timer will continue to run, allowing
the user to maintain a timer base while the rest of the device is sleeping. The ADC Noise
Reduction mode stops the CPU and all I/O modules except asynchronous timer and
ADC to minimize switching noise during ADC conversions. In Standby mode, the crystal/resonator Oscillator is running while the rest of the device is sleeping. This allows
very fast start-up combined with low-power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology.
The On-chip In-System re-Programmable (ISP) Flash allows the program memory to be
reprogrammed In-System through an SPI serial interface, by a conventional non-volatile
memory programmer, or by an On-chip Boot program running on the AVR core. The
Boot program can use any interface to download the application program in the Application Flash memory. Software in the Boot Flash section will continue to run while the
Application Flash section is updated, providing true Read-While-Write operation. By
combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic
chip, the Atmel ATmega325/3250/645/6450 is a powerful microcontroller that provides a
highly flexible and cost effective solution to many embedded control applications.
The ATmega325/3250/645/6450 AVR is supported with a full suite of program and system development tools including: C Compilers, Macro Assemblers, Program
Debugger/Simulators, In-Circuit Emulators, and Evaluation kits.
5
2570J–AVR–11/06
Comparison between
ATmega325,
ATmega3250,
ATmega645 and
ATmega6450
The ATmega325, ATmega3250, ATmega645, and ATmega6450 differs only in memory
sizes, pin count and pinout. Table 1 on page 6 summarizes the different configurations
for the four devices.
Table 1. Configuration Summary
General Purpose
I/O Pins
Device
Flash
EEPROM
RAM
ATmega325
32K bytes
1K bytes
2K bytes
54
ATmega3250
32K bytes
1K bytes
2K bytes
69
ATmega645
64K bytes
2K bytes
4K bytes
54
ATmega6450
64K bytes
2K bytes
4K bytes
69
Pin Descriptions
The following section describes the I/O-pin special functions.
VCC
Digital supply voltage.
GND
Ground.
Port A (PA7..PA0)
Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port A output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port A pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port B output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port B pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port B has better driving capabilities than the other ports.
Port B also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 66.
Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port C output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port C pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port D (PD7..PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port D output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port D pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port D also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 69.
Port E (PE7..PE0)
6
Port E is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port E output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port E pins that are externally pulled low will source
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
current if the pull-up resistors are activated. The Port E pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port E also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 70.
Port F (PF7..PF0)
Port F serves as the analog inputs to the A/D Converter.
Port F also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used.
Port pins can provide internal pull-up resistors (selected for each bit). The Port F output
buffers have symmetrical drive characteristics with both high sink and source capability.
As inputs, Port F pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port F pins are tri-stated when a reset condition becomes
active, even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS), and PF4(TCK) will be activated even if a reset
occurs.
Port F also serves the functions of the JTAG interface.
Port G (PG5..PG0)
Port G is a 6-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port G output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port G pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port G pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port G also serves the functions of various special features of the
ATmega325/3250/645/6450 as listed on page 70.
Port H (PH7..PH0)
Port H is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port H output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port H pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port H pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port H also serves the functions of various special features of the ATmega3250/6450 as
listed on page 70.
Port J (PJ6..PJ0)
Port J is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port J output buffers have symmetrical drive characteristics with both high sink
and source capability. As inputs, Port J pins that are externally pulled low will source
current if the pull-up resistors are activated. The Port J pins are tri-stated when a reset
condition becomes active, even if the clock is not running.
Port J also serves the functions of various special features of the ATmega3250/6450 as
listed on page 70.
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in Table
16 on page 40. Shorter pulses are not guaranteed to generate a reset.
XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
XTAL2
Output from the inverting Oscillator amplifier.
AVCC
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally
connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.
7
2570J–AVR–11/06
AREF
This is the analog reference pin for the A/D Converter.
Resources
A comprehensive set of development tools, application notes and datasheets are available for download on http://www.atmel.com/avr.
About Code
Examples
This documentation contains simple code examples that briefly show how to use various
parts of the device. These code examples assume that the part specific header file is
included before compilation. Be aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please
confirm with the C compiler documentation for more details.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and
“SBI” instructions must be replaced with instructions that allow access to extended I/O.
Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
8
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
AVR CPU Core
Introduction
This section discusses the AVR core architecture in general. The main function of the
CPU core is to ensure correct program execution. The CPU must therefore be able to
access memories, perform calculations, control peripherals, and handle interrupts.
Architectural Overview
Figure 4. Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
Control Lines
Direct Addressing
Instruction
Decoder
Indirect Addressing
Instruction
Register
Interrupt
Unit
SPI
Unit
Watchdog
Timer
ALU
Analog
Comparator
I/O Module1
Data
SRAM
I/O Module 2
I/O Module n
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture
– with separate memories and buses for program and data. Instructions in the program
memory are executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept
enables instructions to be executed in every clock cycle. The program memory is InSystem Reprogrammable Flash memory.
The fast-access Register File contains 32 x 8-bit general purpose working registers with
a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU)
operation. In a typical ALU operation, two operands are output from the Register File,
9
2570J–AVR–11/06
the operation is executed, and the result is stored back in the Register File – in one
clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for
Data Space addressing – enabling efficient address calculations. One of the these
address pointers can also be used as an address pointer for look up tables in Flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register,
described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations can also be executed in the ALU. After
an arithmetic operation, the Status Register is updated to reflect information about the
result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions,
able to directly address the whole address space. Most AVR instructions have a single
16-bit word format. Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and
the Application Program section. Both sections have dedicated Lock bits for write and
read/write protection. The SPM instruction that writes into the Application Flash memory
section must reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is
stored on the Stack. The Stack is effectively allocated in the general data SRAM, and
consequently the Stack size is only limited by the total SRAM size and the usage of the
SRAM. All user programs must initialize the SP in the Reset routine (before subroutines
or interrupts are executed). The Stack Pointer (SP) is read/write accessible in the I/O
space. The data SRAM can easily be accessed through the five different addressing
modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional
Global Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt
Vector in the Interrupt Vector table. The interrupts have priority in accordance with their
Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control
Registers, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as
the Data Space locations following those of the Register File, 0x20 - 0x5F. In addition,
the ATmega325/3250/645/6450 has Extended I/O space from 0x60 - 0xFF in SRAM
where only the ST/STS/STD and LD/LDS/LDD instructions can be used.
ALU – Arithmetic Logic
Unit
10
The high-performance AVR ALU operates in direct connection with all the 32 general
purpose working registers. Within a single clock cycle, arithmetic operations between
general purpose registers or between a register and an immediate are executed. The
ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some implementations of the architecture also provide a powerful multiplier
supporting both signed/unsigned multiplication and fractional format. See the “Instruction Set” section for a detailed description.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
AVR Status Register
The Status Register contains information about the result of the most recently executed
arithmetic instruction. This information can be used for altering program flow in order to
perform conditional operations. Note that the Status Register is updated after all ALU
operations, as specified in the Instruction Set Reference. This will in many cases
remove the need for using the dedicated compare instructions, resulting in faster and
more compact code.
The Status Register is not automatically stored when entering an interrupt routine and
restored when returning from an interrupt. This must be handled by software.
SREG – AVR Status Register
The AVR Status Register – SREG – is defined as:
Bit
7
6
5
4
3
2
1
0
0x3F (0x5F)
I
T
H
S
V
N
Z
C
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SREG
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global
Interrupt Enable Register is cleared, none of the interrupts are enabled independent of
the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt
has occurred, and is set by the RETI instruction to enable subsequent interrupts. The Ibit can also be set and cleared by the application with the SEI and CLI instructions, as
described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or
destination for the operated bit. A bit from a register in the Register File can be copied
into T by the BST instruction, and a bit in T can be copied into a bit in a register in the
Register File by the BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is
useful in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N
⊕V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See
the “Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See
the “Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information.
11
2570J–AVR–11/06
General Purpose
Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to
achieve the required performance and flexibility, the following input/output schemes are
supported by the Register File:
•
One 8-bit output operand and one 8-bit result input
•
Two 8-bit output operands and one 8-bit result input
•
Two 8-bit output operands and one 16-bit result input
•
One 16-bit output operand and one 16-bit result input
Figure 5 shows the structure of the 32 general purpose working registers in the CPU.
Figure 5. AVR CPU General Purpose Working Registers
7
0
Addr.
R0
0x00
R1
0x01
R2
0x02
…
R13
0x0D
General
R14
0x0E
Purpose
R15
0x0F
Working
R16
0x10
Registers
R17
0x11
…
R26
0x1A
X-register Low Byte
R27
0x1B
X-register High Byte
R28
0x1C
Y-register Low Byte
R29
0x1D
Y-register High Byte
R30
0x1E
Z-register Low Byte
R31
0x1F
Z-register High Byte
Most of the instructions operating on the Register File have direct access to all registers,
and most of them are single cycle instructions.
As shown in Figure 5, each register is also assigned a data memory address, mapping
them directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great
flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to
index any register in the file.
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The X-register, Y-register, and
Z-register
The registers R26..R31 have some added functions to their general purpose usage.
These registers are 16-bit address pointers for indirect addressing of the data space.
The three indirect address registers X, Y, and Z are defined as described in Figure 6.
Figure 6. The X-, Y-, and Z-registers
15
X-register
XH
XL
7
0
R27 (0x1B)
YH
YL
7
0
R29 (0x1D)
Z-register
0
R26 (0x1A)
15
Y-register
0
7
0
7
0
R28 (0x1C)
15
ZH
7
0
ZL
7
R31 (0x1F)
0
0
R30 (0x1E)
In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set
reference for details).
Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for
storing return addresses after interrupts and subroutine calls. The Stack Pointer Register always points to the top of the Stack. Note that the Stack is implemented as growing
from higher memory locations to lower memory locations. This implies that a Stack
PUSH command decreases the Stack Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt Stacks are located. This Stack space in the data SRAM must be defined by the
program before any subroutine calls are executed or interrupts are enabled. The Stack
Pointer must be set to point above 0x60. The Stack Pointer is decremented by one
when data is pushed onto the Stack with the PUSH instruction, and it is decremented by
two when the return address is pushed onto the Stack with subroutine call or interrupt.
The Stack Pointer is incremented by one when data is popped from the Stack with the
POP instruction, and it is incremented by two when data is popped from the Stack with
return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is implementation dependent. Note that the data space in some
implementations of the AVR architecture is so small that only SPL is needed. In this
case, the SPH Register will not be present.
Bit
15
14
13
12
11
10
9
8
0x3E (0x5E)
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
0x3D (0x5D)
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
Read/Write
Initial Value
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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Instruction Execution
Timing
This section describes the general access timing concepts for instruction execution. The
AVR CPU is driven by the CPU clock clkCPU, directly generated from the selected clock
source for the chip. No internal clock division is used.
Figure 7 shows the parallel instruction fetches and instruction executions enabled by the
Harvard architecture and the fast-access Register File concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for
functions per cost, functions per clocks, and functions per power-unit.
Figure 7. The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 8 shows the internal timing concept for the Register File. In a single clock cycle
an ALU operation using two register operands is executed, and the result is stored back
to the destination register.
Figure 8. Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
Reset and Interrupt
Handling
The AVR provides several different interrupt sources. These interrupts and the separate
Reset Vector each have a separate program vector in the program memory space. All
interrupts are assigned individual enable bits which must be written logic one together
with the Global Interrupt Enable bit in the Status Register in order to enable the interrupt.
Depending on the Program Counter value, interrupts may be automatically disabled
when Boot Lock bits BLB02 or BLB12 are programmed. This feature improves software
security. See the section “Memory Programming” on page 259 for details.
The lowest addresses in the program memory space are by default defined as the Reset
and Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 48.
The list also determines the priority levels of the different interrupts. The lower the
address the higher is the priority level. RESET has the highest priority, and next is INT0
– the External Interrupt Request 0. The Interrupt Vectors can be moved to the start of
the Boot Flash section by setting the IVSEL bit in the MCU Control Register (MCUCR).
Refer to “Interrupts” on page 48 for more information. The Reset Vector can also be
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ATmega325/3250/645/6450
moved to the start of the Boot Flash section by programming the BOOTRST Fuse, see
“Boot Loader Support – Read-While-Write Self-Programming” on page 246.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts
are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine. The I-bit is
automatically set when a Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that
sets the Interrupt Flag. For these interrupts, the Program Counter is vectored to the
actual Interrupt Vector in order to execute the interrupt handling routine, and hardware
clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a
logic one to the flag bit position(s) to be cleared. If an interrupt condition occurs while the
corresponding interrupt enable bit is cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or
more interrupt conditions occur while the Global Interrupt Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the Global Interrupt
Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present.
These interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor restored when returning from an interrupt routine. This must be handled by
software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately
disabled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can be used to
avoid interrupts during the timed EEPROM write sequence.
Assembly Code Example
in r16, SREG
cli
; store SREG value
; disable interrupts during timed sequence
sbi EECR, EEMWE
; start EEPROM write
sbi EECR, EEWE
out SREG, r16
; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
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When using the SEI instruction to enable interrupts, the instruction following SEI will be
executed before any pending interrupts, as shown in this example.
Assembly Code Example
sei
; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
Interrupt Response Time
16
The interrupt execution response for all the enabled AVR interrupts is four clock cycles
minimum. After four clock cycles the program vector address for the actual interrupt
handling routine is executed. During this four clock cycle period, the Program Counter is
pushed onto the Stack. The vector is normally a jump to the interrupt routine, and this
jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle
instruction, this instruction is completed before the interrupt is served. If an interrupt
occurs when the MCU is in sleep mode, the interrupt execution response time is
increased by four clock cycles. This increase comes in addition to the start-up time from
the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four
clock cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack
Pointer is incremented by two, and the I-bit in SREG is set.
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
AVR Memories
This section describes the different memories in the ATmega325/3250/645/6450. The
AVR architecture has two main memory spaces, the Data Memory and the Program
Memory space. In addition, the ATmega325/3250/645/6450 features an EEPROM
Memory for data storage. All three memory spaces are linear.
In-System
Reprogrammable Flash
Program Memory
The ATmega325/3250/645/6450 contains 32/64K bytes On-chip In-System Reprogrammable Flash memory for program storage. Since all AVR instructions are 16 or 32 bits
wide, the Flash is organized as 16/32K x 16. For software security, the Flash Program
memory space is divided into two sections, Boot Program section and Application Program section.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The
ATmega325/3250/645/6450 Program Counter (PC) is 14/15 bits wide, thus addressing
the 16/32K program memory locations. The operation of Boot Program section and
associated Boot Lock bits for software protection are described in detail in “Boot Loader
Support – Read-While-Write Self-Programming” on page 246. “Memory Programming”
on page 259 contains a detailed description on Flash data serial downloading using the
SPI pins or the JTAG interface.
Constant tables can be allocated within the entire program memory address space (see
the LPM – Load Program Memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 14.
Figure 9. Program Memory Map
Program Memory
0x0000
Application Flash Section
Boot Flash Section
0x3FFF/0x7FFF
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SRAM Data Memory
Figure 10 shows how the ATmega325/3250/645/6450 SRAM Memory is organized.
The ATmega325/3250/645/6450 is a complex microcontroller with more peripheral units
than can be supported within the 64 locations reserved in the Opcode for the IN and
OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
The lower 2304/4352 data memory locations address both the Register File, the I/O
memory, Extended I/O memory, and the internal data SRAM. The first 32 locations
address the Register File, the next 64 location the standard I/O memory, then 160 locations of Extended I/O memory, and the next 2048/4096 locations address the internal
data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In
the Register File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base
address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and postincrement, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and the 2,048 bytes of internal data SRAM in the ATmega325/3250/645/6450 are
all accessible through all these addressing modes. The Register File is described in
“General Purpose Register File” on page 12.
Figure 10. Data Memory Map
Data Memory
32 Registers
64 I/O Registers
160 Ext I/O Reg.
Internal SRAM
(2048 x 8)/
(4096 x 8)
Data Memory Access Times
18
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
0x0100
0x08FF/0x10FF
This section describes the general access timing concepts for internal memory access.
The internal data SRAM access is performed in two clkCPU cycles as described in Figure
11.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 11. On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Compute Address
Address valid
Write
Data
WR
Read
Data
RD
Memory Access Instruction
EEPROM Data Memory
Next Instruction
The ATmega325/3250/645/6450 contains 1/2K bytes of data EEPROM memory. It is
organized as a separate data space, in which single bytes can be read and written. The
EEPROM has an endurance of at least 100,000 write/erase cycles. The access
between the EEPROM and the CPU is described in the following, specifying the
EEPROM Address Registers, the EEPROM Data Register, and the EEPROM Control
Register.
For a detailed description of SPI, JTAG and Parallel data downloading to the EEPROM,
see page 274, page 279, and page 262 respectively.
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 2. A self-timing function, however, lets the user software detect when the next byte can be written. If the user code
contains instructions that write the EEPROM, some precautions must be taken. In
heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This
causes the device for some period of time to run at a voltage lower than specified as
minimum for the clock frequency used. See “Preventing EEPROM Corruption” on page
23. for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next
instruction is executed. When the EEPROM is written, the CPU is halted for two clock
cycles before the next instruction is executed.
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EEARH and EEARL – The
EEPROM Address Register
Bit
15
14
13
12
11
10
9
8
0x22 (0x42)
–
–
–
–
–
EEAR10
EEAR9
EEAR8
EEARH
0x21 (0x41)
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
EEARL
7
6
5
4
3
2
1
0
Read/Write
Initial Value
R
R
R
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
X
X
X
X
X
X
X
X
X
X
X
• Bits 15..11 – Res: Reserved Bits
These bits are reserved bits in the ATmega325/3250/645/6450 and will always read as
zero.
• Bits 10..0 – EEAR10..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address
in the 1/2K bytes EEPROM space. The EEPROM data bytes are addressed linearly
between 0 and 1023/2047. The initial value of EEAR is undefined. A proper value must
be written before the EEPROM may be accessed.
Note:
EEDR – The EEPROM Data
Register
EEAR10 is only valid for ATmega645 and ATmega6450.
Bit
7
6
5
4
3
2
1
0
0x20 (0x40)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EEDR
• Bits 7..0 – EEDR7..0: EEPROM Data
For the EEPROM write operation, the EEDR Register contains the data to be written to
the EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address given by
EEAR.
EECR – The EEPROM Control
Register
Bit
7
6
5
4
3
2
1
0
0x1F (0x3F)
–
–
–
–
EERIE
EEMWE
EEWE
EERE
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
X
0
EECR
• Bits 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATmega325/3250/645/6450 and will always read as
zero.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set.
Writing EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a
constant interrupt when EEWE is cleared.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be
written. When EEMWE is set, setting EEWE within four clock cycles will write data to the
EEPROM at the selected address If EEMWE is zero, setting EEWE will have no effect.
When EEMWE has been written to one by software, hardware clears the bit to zero after
four clock cycles. See the description of the EEWE bit for an EEPROM write procedure.
• Bit 1 – EEWE: EEPROM Write Enable
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ATmega325/3250/645/6450
The EEPROM Write Enable Signal EEWE is the write strobe to the EEPROM. When
address and data are correctly set up, the EEWE bit must be written to one to write the
value into the EEPROM. The EEMWE bit must be written to one before a logical one is
written to EEWE, otherwise no EEPROM write takes place. The following procedure
should be followed when writing the EEPROM (the order of steps 3 and 4 is not
essential):
1. Wait until EEWE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.
6. Within four clock cycles after setting EEMWE, write a logical one to EEWE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The
software must check that the Flash programming is completed before initiating a new
EEPROM write. Step 2 is only relevant if the software contains a Boot Loader allowing
the CPU to program the Flash. If the Flash is never being updated by the CPU, step 2
can be omitted. See “Boot Loader Support – Read-While-Write Self-Programming” on
page 246 for details about Boot programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the
EEPROM is interrupting another EEPROM access, the EEAR or EEDR Register will be
modified, causing the interrupted EEPROM access to fail. It is recommended to have
the Global Interrupt Flag cleared during all the steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared by hardware. The
user software can poll this bit and wait for a zero before writing the next byte. When
EEWE has been set, the CPU is halted for two cycles before the next instruction is
executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the
correct address is set up in the EEAR Register, the EERE bit must be written to a logic
one to trigger the EEPROM read. The EEPROM read access takes one instruction, and
the requested data is available immediately. When the EEPROM is read, the CPU is
halted for four cycles before the next instruction is executed.
The user should poll the EEWE bit before starting the read operation. If a write operation
is in progress, it is neither possible to read the EEPROM, nor to change the EEAR
Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 2 lists the typical
programming time for EEPROM access from the CPU.
Table 2. EEPROM Programming Time
Symbol
EEPROM write (from CPU)
Number of Calibrated
RC Oscillator Cycles
27,072
Typical Programming Time
3.4 ms
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The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these functions. The
examples also assume that no Flash Boot Loader is present in the software. If such
code is present, the EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to Data Register
out EEDR,r16
; Write logical one to EEMWE
sbi EECR,EEMWE
; Start eeprom write by setting EEWE
sbi EECR,EEWE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
The next code examples show assembly and C functions for reading the EEPROM. The
examples assume that interrupts are controlled so that no interrupts will occur during
execution of these functions.
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ATmega325/3250/645/6450
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from Data Register
in
r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from Data Register */
return EEDR;
}
EEPROM Write During Powerdown Sleep Mode
When entering Power-down sleep mode while an EEPROM write operation is active, the
EEPROM write operation will continue, and will complete before the Write Access time
has passed. However, when the write operation is completed, the clock continues running, and as a consequence, the device does not enter Power-down entirely. It is
therefore recommended to verify that the EEPROM write operation is completed before
entering Power-down.
Preventing EEPROM
Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the EEPROM to operate properly. These issues are the
same as for board level systems using EEPROM, and the same design solutions should
be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too
low. First, a regular write sequence to the EEPROM requires a minimum voltage to
operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the
supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design
recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD). If the detection
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level of the internal BOD does not match the needed detection level, an external low
VCC reset Protection circuit can be used. If a reset occurs while a write operation is in
progress, the write operation will be completed provided that the power supply voltage is
sufficient.
I/O Memory
The I/O space definition of the ATmega325/3250/645/6450 is shown in “Register Summary” on page 328.
All ATmega325/3250/645/6450 I/Os and peripherals are placed in the I/O space. All I/O
locations may be accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32 general purpose working registers and the I/O space. I/O
Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI
and CBI instructions. In these registers, the value of single bits can be checked by using
the SBIS and SBIC instructions. Refer to the instruction set section for more details.
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F
must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The ATmega325/3250/645/6450 is a
complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the Extended I/O
space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions
can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike
most other AVRs, the CBI and SBI instructions will only operate on the specified bit, and
can therefore be used on registers containing such Status Flags. The CBI and SBI
instructions work with registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
General Purpose I/O Registers The ATmega325/3250/645/6450 contains three General Purpose I/O Registers. These
registers can be used for storing any information, and they are particularly useful for
storing global variables and Status Flags. General Purpose I/O Registers within the
address range 0x00 - 0x1F are directly bit-accessible using the SBI, CBI, SBIS, and
SBIC instructions.
GPIOR2 – General Purpose I/O
Register 2
GPIOR1 – General Purpose I/O
Register 1
GPIOR0 – General Purpose I/O
Register 0
24
Bit
7
6
5
4
3
2
1
0
0x2B (0x4B)
MSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
7
6
5
4
3
2
1
Bit
LSB
0
0x2A (0x4A)
MSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
7
6
5
4
3
2
1
Bit
GPIOR2
LSB
GPIOR1
0
0x1E (0x3E)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GPIOR0
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
System Clock and
Clock Options
Clock Systems and their
Distribution
Figure 12 presents the principal clock systems in the AVR and their distribution. All of
the clocks need not be active at a given time. In order to reduce power consumption, the
clocks to modules not being used can be halted by using different sleep modes, as
described in “Power Management and Sleep Modes” on page 33. The clock systems
are detailed below.
Figure 12. Clock Distribution
Asynchronous
Timer/Counter
General I/O
Modules
clkI/O
CPU Core
AVR Clock
Control Unit
clkASY
RAM
clkCPU
clkFLASH
Reset Logic
Source clock
Clock
Multiplexer
Timer/Counter
Oscillator
External Clock
Flash and
EEPROM
Crystal
Oscillator
Watchdog Timer
Watchdog clock
Watchdog
Oscillator
Low-frequency
Crystal Oscillator
Calibrated RC
Oscillator
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR
core. Examples of such modules are the General Purpose Register File, the Status Register and the data memory holding the Stack Pointer. Halting the CPU clock inhibits the
core from performing general operations and calculations.
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and
USART. The I/O clock is also used by the External Interrupt module, but note that some
external interrupts are detected by asynchronous logic, allowing such interrupts to be
detected even if the I/O clock is halted. Also note that start condition detection in the USI
module is carried out asynchronously when clkI/O is halted, enabling USI start condition
detection in all sleep modes.
Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually
active simultaneously with the CPU clock.
Asynchronous Timer Clock –
clkASY
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked
directly from an external clock or an external 32 kHz clock crystal. The dedicated clock
domain allows using this Timer/Counter as a real-time counter even when the device is
in sleep mode.
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2570J–AVR–11/06
ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and
I/O clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion results.
Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as
shown below. The clock from the selected source is input to the AVR clock generator,
and routed to the appropriate modules.
Table 3. Device Clocking Options Select(1)
Device Clocking Option
CKSEL3..0
External Crystal/Ceramic Resonator
1111 - 1000
External Low-frequency Crystal
0111 - 0110
Calibrated Internal RC Oscillator
0010
External Clock
0000
Reserved
Note:
0011, 0001, 0101, 0100
1. For all fuses “1” means unprogrammed while “0” means programmed.
The various choices for each clocking option is given in the following sections. When the
CPU wakes up from Power-down or Power-save, the selected clock source is used to
time the start-up, ensuring stable Oscillator operation before instruction execution starts.
When the CPU starts from reset, there is an additional delay allowing the power to reach
a stable level before commencing normal operation. The Watchdog Oscillator is used
for timing this real-time part of the start-up time. The number of WDT Oscillator cycles
used for each time-out is shown in Table 4. The frequency of the Watchdog Oscillator is
voltage dependent as shown in “Typical Characteristics – Preliminary Data” on page
298.
Table 4. Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V)
Typ Time-out (VCC = 3.0V)
Number of Cycles
4.1 ms
4.3 ms
4K (4,096)
65 ms
69 ms
64K (65,536)
Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed.
The default clock source setting is the Internal RC Oscillator with longest start-up time
and an initial system clock prescaling of 8. This default setting ensures that all users can
make their desired clock source setting using an In-System or Parallel programmer.
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an On-chip Oscillator, as shown in Figure 13. Either a quartz
crystal or a ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value
of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial guidelines for
choosing capacitors for use with crystals are given in Table 5. For ceramic resonators,
the capacitor values given by the manufacturer should be used.
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ATmega325/3250/645/6450
Figure 13. Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in
Table 5.
Table 5. Crystal Oscillator Operating Modes
CKSEL3:1
Frequency Range
(MHz)
Recommended Range for Capacitors C1
and C2 for Use with Crystals (pF)
100(1)
0.4 - 0.9
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 -
12 - 22
Notes:
1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown
in Table 6.
Table 6. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
SUT1:0
Start-up Time from
Power-down and
Power-save
0
00
258 CK(1)
14CK + 4.1 ms
Ceramic resonator,
fast rising power
0
01
258 CK(1)
14CK + 65 ms
Ceramic resonator,
slowly rising power
0
10
1K CK(2)
14CK
Ceramic resonator,
BOD enabled
0
11
1K CK(2)
14CK + 4.1 ms
Ceramic resonator,
fast rising power
1
00
1K CK(2)
14CK + 65 ms
Ceramic resonator,
slowly rising power
01
16K CK
14CK
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
11
16K CK
14CK + 65 ms
Crystal Oscillator,
slowly rising power
1
1
1
Additional Delay
from Reset
(VCC = 5.0V)
Recommended
Usage
Crystal Oscillator,
BOD enabled
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2570J–AVR–11/06
Notes:
Low-frequency Crystal
Oscillator
1. These options should only be used when not operating close to the maximum frequency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency
crystal Oscillator must be selected by setting the CKSEL Fuses to “0110” or “0111”. The
crystal should be connected as shown in Figure 13. When this Oscillator is selected,
start-up times are determined by the SUT Fuses as shown in Table 7 and CKSEL1..0 as
shown in Table 8.
Table 7. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0
Additional Delay from Reset (VCC = 5.0V)
00
14CK
01
14CK + 4.1 ms
Slowly rising power
10
14CK + 65 ms
Stable frequency at start-up
11
Recommended Usage
Fast rising power or BOD enabled
Reserved
Table 8. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL3..0
Start-up Time from
Power-down and Power-save
(1)
0110
0111
Note:
Calibrated Internal RC
Oscillator
Recommended Usage
1K CK
32K CK
Stable frequency at start-up
1. This option should only be used if frequency stability at start-up is not important for
the application
The calibrated Internal RC Oscillator by default provides a 8.0 MHz clock. The frequency is nominal value at 3V and 25°C. The device is shipped with the CKDIV8 Fuse
programmed. See “System Clock Prescaler” on page 31 for more details.
This clock may be selected as the system clock by programming the CKSEL Fuses as
shown in Table 9 on page 29. If selected, it will operate with no external components.
During reset, hardware loads the pre-programmed calibration value into the OSCCAL
Register and thereby automatically calibrates the RC Oscillator. The accuracy of this
calibration is shown as Factory calibration in Table 126 on page 297.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on page 29, it is possible to get a higher calibration accuracy than by using the
factory calibration. The accuracy of this calibration is shown as User calibration in Table
126 on page 297.
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used
for the Watchdog Timer and for the Reset Time-out. For more information on the preprogrammed calibration value, see the section “Calibration Byte” on page 262.
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ATmega325/3250/645/6450
Table 9. Internal Calibrated RC Oscillator Operating Modes(1)(3)
Notes:
Frequency Range(2) (MHz)
CKSEL3..0
7.3 - 8.1
0010
1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values. Actual values are TBD.
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the
CKDIV8 Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 10 on page 29.
Table 10. Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
SUT1..0
BOD enabled
6 CK
14CK
00
Fast rising power
6 CK
14CK + 4.1 ms
Power Conditions
Slowly rising power
6 CK
14CK + 65 ms
01
(1)
10
Reserved
Note:
OSCCAL – Oscillator
Calibration Register
11
1. The device is shipped with this option selected.
Bit
(0x66)
Read/Write
Initial Value
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
OSCCAL
Device Specific Calibration Value
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator
to remove process variations from the oscillator frequency. A pre-programmed calibration value is automatically written to this register during chip reset, giving the Factory
calibrated frequency as specified in Table 126 on page 297. The application software
can write this register to change the oscillator frequency. The oscillator can be calibrated
to frequencies as specified in Table 126 on page 297. Calibration outside that range is
not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these
write times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0
gives the lowest frequency range, setting this bit to 1 gives the highest frequency range.
The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F
gives a higher frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of
0x00 gives the lowest frequency in that range, and a setting of 0x7F gives the highest
frequency in the range.
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2570J–AVR–11/06
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in
Figure 14. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 14. External Clock Drive Configuration
NC
XTAL2
EXTERNAL
CLOCK
SIGNAL
XTAL1
GND
When this clock source is selected, start-up times are determined by the SUT Fuses as
shown in Table 12.
Table 11. Crystal Oscillator Clock Frequency
CKSEL3..0
Frequency Range
0000
0 - 16 MHz
Table 12. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
10
6 CK
14CK + 65 ms
Slowly rising power
11
Recommended Usage
BOD enabled
Reserved
When applying an external clock, it is required to avoid sudden changes in the applied
clock frequency to ensure stable operation of the MCU. A variation in frequency of more
than 2% from one clock cycle to the next can lead to unpredictable behavior. It is
required to ensure that the MCU is kept in Reset during such changes in the clock
frequency.
Note that the System Clock Prescaler can be used to implement run-time changes of
the internal clock frequency while still ensuring stable operation. Refer to “System Clock
Prescaler” on page 31 for details.
Clock Output Buffer
30
When the CKOUT Fuse is programmed, the system Clock will be output on CLKO. This
mode is suitable when the chip clock is used to drive other circuits on the system. The
clock will be output also during reset and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including internal RC Oscillator,
can be selected when CLKO serves as clock output. If the System Clock Prescaler is
used, it is the divided system clock that is output when the CKOUT Fuse is
programmed.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Timer/Counter Oscillator
ATmega325/3250/645/6450 share the Timer/Counter Oscillator Pins (TOSC1 and
TOSC2) with XTAL1 and XTAL2. This means that the Timer/Counter Oscillator can only
be used when the calibrated internal RC Oscillator is selected as system clock source.
The Oscillator is optimized for use with a 32.768 kHz watch crystal. See Figure 13 on
page 27 for crystal connection.
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR Register is written to logic one. See “Asynchronous operation of the Timer/Counter” on page
141 for further description on selecting external clock as input instead of a 32 kHz
crystal.
System Clock Prescaler
CLKPR – Clock Prescale
Register
The ATmega325/3250/645/6450 system clock can be divided by setting the Clock Prescale Register – CLKPR. This feature can be used to decrease power consumption when
the requirement for processing power is low. This can be used with all clock source
options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH are divided by a factor as shown in Table 13.
Bit
7
6
5
4
3
2
1
0
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
(0x61)
CLKPR
See Bit Description
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The
CLKPCE bit is only updated when the other bits in CLKPR are simultaneously written to
zero. CLKPCE is cleared by hardware four cycles after it is written or when CLKPS bits
are written. Rewriting the CLKPCE bit within this time-out period does neither extend the
time-out period, nor clear the CLKPCE bit.
• Bits 3:0 – CLKPS3:0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal
system clock. These bits can be written run-time to vary the clock frequency to suit the
application requirements. As the divider divides the master clock input to the MCU, the
speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given in Table 13.
To avoid unintentional changes of clock frequency, a special write procedure must be
followed to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits
in CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to
CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits
are reset to “0011”, giving a division factor of 8 at start up. This feature should be used if
the selected clock source has a higher frequency than the maximum frequency of the
device at the present operating conditions. Note that any value can be written to the
CLKPS bits regardless of the CKDIV8 Fuse setting. The Application software must
ensure that a sufficient division factor is chosen if the selected clock source has a higher
31
2570J–AVR–11/06
frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed.
Table 13. Clock Prescaler Select
Switching Time
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Clock Division Factor
0
0
0
0
1
0
0
0
1
2
0
0
1
0
4
0
0
1
1
8
0
1
0
0
16
0
1
0
1
32
0
1
1
0
64
0
1
1
1
128
1
0
0
0
256
1
0
0
1
Reserved
1
0
1
0
Reserved
1
0
1
1
Reserved
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
When switching between prescaler settings, the System Clock Prescaler ensures that
no glitches occur in the clock system and that no intermediate frequency is higher than
neither the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided
clock, which may be faster than the CPU’s clock frequency. Hence, it is not possible to
determine the state of the prescaler – even if it were readable, and the exact time it
takes to switch from one clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2
before the new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period corresponding to the
new prescaler setting.
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ATmega325/3250/645/6450
Power Management
and Sleep Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby
saving power. The AVR provides various sleep modes allowing the user to tailor the
power consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one
and a SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR
Register select which sleep mode (Idle, ADC Noise Reduction, Power-down, Powersave, or Standby) will be activated by the SLEEP instruction. See Table 15 for a summary. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes
up. The MCU is then halted for four cycles in addition to the start-up time, executes the
interrupt routine, and resumes execution from the instruction following SLEEP. The contents of the Register File and SRAM are unaltered when the device wakes up from
sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the
Reset Vector.
Figure 12 on page 25 presents the different clock systems in the
ATmega325/3250/645/6450, and their distribution. The figure is helpful in selecting an
appropriate sleep mode.
Table 14. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
Idle
X
ADC Noise
Reduction
Standby
Notes:
(1)
X
X
X(2)
X
X
X
X
X
X
X
X
X(2)
X(3)
X
X(2)
X
X
X(3)
X
X(3)
X
(3)
X
X(2)
X
X
X
Other I/O
ADC
SPM/EEPROM
Ready
Timer2
USI Start
Condition
X
Power-down
Power-save
INT0 and Pin
Change
Wake-up Sources
Timer Osc
Enabled
clkASY
Main Clock
Source
Enabled
Oscillators
clkADC
clkIO
clkFLASH
Sleep Mode
clkCPU
Active Clock Domains
X
X
1. Only recommended with external crystal or resonator selected as clock source.
2. If Timer/Counter2 is running in asynchronous mode.
3. For INT0, only level interrupt.
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2570J–AVR–11/06
Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter
Idle mode, stopping the CPU but allowing the SPI, USART, Analog Comparator, ADC,
USI, Timer/Counters, Watchdog, and the interrupt system to continue operating. This
sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as
internal ones like the Timer Overflow and USART Transmit Complete interrupts. If
wake-up from the Analog Comparator interrupt is not required, the Analog Comparator
can be powered down by setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will reduce power consumption in Idle mode. If the ADC is
enabled, a conversion starts automatically when this mode is entered.
ADC Noise Reduction
Mode
When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter
ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the USI start condition detection, Timer/Counter2, and the Watchdog to continue
operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while
allowing the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is
entered. Apart form the ADC Conversion Complete interrupt, only an External Reset, a
Watchdog Reset, a Brown-out Reset, a USI start condition interrupt, a Timer/Counter2
interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin
change interrupt can wake up the MCU from ADC Noise Reduction mode.
Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter
Power-down mode. In this mode, the external Oscillator is stopped, while the external
interrupts, the USI start condition detection, and the Watchdog continue operating (if
enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an external level interrupt on INT0, or a pin change interrupt can wake
up the MCU. This sleep mode basically halts all generated clocks, allowing operation of
asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the
changed level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 53 for details.
When waking up from Power-down mode, there is a delay from the wake-up condition
occurs until the wake-up becomes effective. This allows the clock to restart and become
stable after having been stopped. The wake-up period is defined by the same CKSEL
Fuses that define the Reset Time-out period, as described in “Clock Sources” on page
26.
Power-save Mode
When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter
Power-save mode. This mode is identical to Power-down, with one exception:
If Timer/Counter2 controller is enabled, it will keep running during sleep. The device can
wake up from either Timer Overflow or Output Compare event from Timer/Counter2 if
the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2, and the Global Interrupt Enable bit in SREG is set.
If the Timer/Counter2 is not running, Power-down mode is recommended instead of
Power-save mode.
The Timer/Counter2 can be clocked both synchronously and asynchronously in Powersave mode. If Timer/Counter2 is not using the asynchronous clock, the Timer/Counter
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ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Oscillator is stopped during sleep. If Timer/Counter2 is not using the synchronous clock,
the clock source is stopped during sleep. Note that even if the synchronous clock is running in Power-save, this clock is only available for Timer/Counter2.
Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected,
the SLEEP instruction makes the MCU enter Standby mode. This mode is identical to
Power-down with the exception that the Oscillator is kept running. From Standby mode,
the device wakes up in six clock cycles.
Power Reduction
Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page
37, provides a method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/O registers inaccessible.
Resources used by the peripheral when stopping the clock will remain occupied so the
peripheral should be disabled before stopping the clock. Waking up a module, which is
done by clearing the bit in PRR, puts the module in the same state as before shutdown.
Module shutdown can be used in IDLE mode and active mode to reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.
Minimizing Power
Consumption
There are several possibilities to consider when trying to minimize the power consumption in an AVR controlled system. In general, sleep modes should be used as much as
possible, and the sleep mode should be selected so that as few as possible of the
device’s functions are operating. All functions not needed should be disabled. In particular, the following modules may need special consideration when trying to achieve the
lowest possible power consumption.
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should
be disabled before entering any sleep mode. When the ADC is turned off and on again,
the next conversion will be an extended conversion. Refer to “Analog to Digital Converter” on page 197 for details on ADC operation.
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When
entering ADC Noise Reduction mode, the Analog Comparator should be disabled. In
other sleep modes, the Analog Comparator is automatically disabled. However, if the
Analog Comparator is set up to use the Internal Voltage Reference as input, the Analog
Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep mode. Refer to “Analog Comparator” on
page 194 for details on how to configure the Analog Comparator.
Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned
off. If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in
all sleep modes, and hence, always consume power. In the deeper sleep modes, this
will contribute significantly to the total current consumption. Refer to “Brown-out Detection” on page 41 for details on how to configure the Brown-out Detector.
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the Analog Comparator or the ADC. If these modules are disabled as described in
the sections above, the internal voltage reference will be disabled and it will not be consuming power. When turned on again, the user must allow the reference to start up
before the output is used. If the reference is kept on in sleep mode, the output can be
used immediately. Refer to “Internal Voltage Reference” on page 44 for details on the
start-up time.
35
2570J–AVR–11/06
Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off.
If the Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence,
always consume power. In the deeper sleep modes, this will contribute significantly to
the total current consumption. Refer to “Watchdog Timer” on page 44 for details on how
to configure the Watchdog Timer.
Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power.
The most important is then to ensure that no pins drive resistive loads. In sleep modes
where both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device will be disabled. This ensures that no power is consumed by the input
logic when not needed. In some cases, the input logic is needed for detecting wake-up
conditions, and it will then be enabled. Refer to the section “Digital Input Enable and
Sleep Modes” on page 63 for details on which pins are enabled. If the input buffer is
enabled and the input signal is left floating or have an analog signal level close to VCC/2,
the input buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog
signal level close to VCC/2 on an input pin can cause significant current even in active
mode. Digital input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and DIDR0). Refer to “DIDR1 – Digital Input Disable Register 1” on page
196 and “DIDR0 – Digital Input Disable Register 0” on page 213 for details.
JTAG Interface and
On-chip Debug System
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enter Power
down or Power save sleep mode, the main clock source remains enabled. In these
sleep modes, this will contribute significantly to the total current consumption. There are
three alternative ways to avoid this:
•
Disable OCDEN Fuse.
•
Disable JTAGEN Fuse.
•
Write one to the JTD bit in MCUCSR.
The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP
controller is not shifting data. If the hardware connected to the TDO pin does not pull up
the logic level, power consumption will increase. Note that the TDI pin for the next
device in the scan chain contains a pull-up that avoids this problem. Writing the JTD bit
in the MCUCSR register to one or leaving the JTAG fuse unprogrammed disables the
JTAG interface.
36
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Register Description
SMCR – Sleep Mode Control
Register
The Sleep Mode Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
0x33 (0x53)
–
–
–
–
SM2
SM1
SM0
SE
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SMCR
• Bits 3, 2, 1 – SM2:0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 15.
Table 15. Sleep Mode Select
SM2
SM1
SM0
0
0
0
Idle
0
0
1
ADC Noise Reduction
0
1
0
Power-down
0
1
1
Power-save
1
0
0
Reserved
1
0
1
Reserved
1
1
0
Standby(1)
1
1
1
Reserved
Note:
Sleep Mode
1. Standby mode is only recommended for use with external crystals or resonators.
• Bit 1 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the
SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is
the programmer’s purpose, it is recommended to write the Sleep Enable (SE) bit to one
just before the execution of the SLEEP instruction and to clear it immediately after waking up.
PRR – Power Reduction
Register
Bit
7
6
5
4
3
2
1
0
(0x64)
–
–
–
–
PRTIM1
PRSPI
PRUSART0
PRADC
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PRR
• Bits 7:4 - Res: Reserved bits
These bits are reserved bits in ATmega325/3250/645/6450 and will always read as
zero.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing logic one to this bit shuts down the Timer/Counter1 module. When
Timer/Counter1 is enabled, operation will continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing logic one to this bit shuts down the Serial Peripheral Interface by stopping the
clock to the module. When waking up the SPI again, the SPI should be re-initialized to
ensure proper operation.
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2570J–AVR–11/06
• Bit 1 - PRUSART: Power Reduction USART
Writing logic one to this bit shuts down the USART by stopping the clock to the module.
When waking up the USART again, the USART should be re-initialized to ensure proper
operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing logic one to this bit shuts down the ADC. The ADC must be disabled before shut
down. The analog comparator cannot use the ADC input MUX when the ADC is shut
down.
Note:
38
The Analog Comparator is disabled using the ACD-bit in the “ACSR – Analog Comparator Control and Status Register” on page 194.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
System Control and
Reset
Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution from the Reset Vector. The instruction placed at the Reset Vector must be a JMP
– Absolute Jump – instruction to the reset handling routine. If the program never
enables an interrupt source, the Interrupt Vectors are not used, and regular program
code can be placed at these locations. This is also the case if the Reset Vector is in the
Application section while the Interrupt Vectors are in the Boot section or vice versa. The
circuit diagram in Figure 15 shows the reset logic. Table 16 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source
goes active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the
internal reset. This allows the power to reach a stable level before normal operation
starts. The time-out period of the delay counter is defined by the user through the SUT
and CKSEL Fuses. The different selections for the delay period are presented in “Clock
Sources” on page 26.
Reset Sources
The ATmega325/3250/645/6450 has five sources of reset:
•
Power-on Reset. The MCU is reset when the supply voltage is below the Power-on
Reset threshold (VPOT).
•
External Reset. The MCU is reset when a low level is present on the RESET pin for
longer than the minimum pulse length.
•
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and
the Watchdog is enabled.
•
Brown-out Reset. The MCU is reset when the supply voltage VCC is below the
Brown-out Reset threshold (VBOT) and the Brown-out Detector is enabled.
•
JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset
Register, one of the scan chains of the JTAG system. Refer to the section “IEEE
1149.1 (JTAG) Boundary-scan” on page 220 for details.
39
2570J–AVR–11/06
Figure 15. Reset Logic
DATA BUS
PORF
BORF
EXTRF
WDRF
JTRF
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
Brown-out
Reset Circuit
BODLEVEL [1..0]
Pull-up Resistor
SPIKE
FILTER
JTAG Reset
Register
Watchdog
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
SUT[1:0]
Table 16. Reset Characteristics
Symbol
VPOT
Condition
Min
Typ
Max
Units
Power-on Reset Threshold
Voltage (rising)
TA = -40°C
to 85°C
0.7
1.0
1.4
V
Power-on Reset Threshold
Voltage (falling)(1)
TA = -40°C
to 85°C
0.6
0.9
1.3
V
0.2VCC
0.85VCC
V
VRST
RESET Pin Threshold Voltage
VCC = 3V
tRST
Minimum pulse width on
RESET Pin
VCC = 3V
Notes:
Power-on Reset
Parameter
800
ns
1. The Power-on Reset will not work unless the supply voltage has been below VPOT
(falling)
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level is defined in Table 16. The POR is activated whenever VCC is below the
detection level. The POR circuit can be used to trigger the start-up Reset, as well as to
detect a failure in supply voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the Power-on Reset threshold voltage invokes the delay counter, which determines
how long the device is kept in RESET after VCC rise. The RESET signal is activated
again, without any delay, when VCC decreases below the detection level.
40
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 16. MCU Start-up, RESET Tied to VCC
VCC
RESET
VPOT
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
Figure 17. MCU Start-up, RESET Extended Externally
VCC
RESET
VPOT
VRST
TIME-OUT
tTOUT
INTERNAL
RESET
External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer
than the minimum pulse width (see Table 16) will generate a reset, even if the clock is
not running. Shorter pulses are not guaranteed to generate a reset. When the applied
signal reaches the Reset Threshold Voltage – VRST – on its positive edge, the delay
counter starts the MCU after the Time-out period – tTOUT – has expired.
Figure 18. External Reset During Operation
CC
Brown-out Detection
ATmega325/3250/645/6450 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level during operation by comparing it to a fixed trigger level. The trigger
level for the BOD can be selected by the BODLEVEL Fuses. The trigger level has a hys-
41
2570J–AVR–11/06
teresis to ensure spike free Brown-out Detection. The hysteresis on the detection level
should be interpreted as VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
Table 17. BODLEVEL Fuse Coding(1)
BODLEVEL 2..0 Fuses
Note:
Min VBOT
Typ VBOT
Max VBOT
11
BOD Disabled
10
1.8
01
2.7
00
4.3
Units
V
1. VBOT may be below nominal minimum operating voltage for some devices. For
devices where this is the case, the device is tested down to VCC = VBOT during the
production test. This guarantees that a Brown-Out Reset will occur before VCC drops
to a voltage where correct operation of the microcontroller is no longer guaranteed.
The test is performed using BODLEVEL = 10 for ATmega325/3250/645/6450V and
BODLEVEL = 01 for ATmega325/3250/645/6450L.
Table 18. Brown-out Characteristics
Symbol
Parameter
Min
Typ
Max
Units
VHYST
Brown-out Detector Hysteresis
50
mV
tBOD
Min Pulse Width on Brown-out Reset
2
µs
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOTin Figure 19), the Brown-out Reset is immediately activated. When VCC increases above
the trigger level (VBOT+ in Figure 19), the delay counter starts the MCU after the Timeout period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level
for longer than tBOD given in Table 16.
Figure 19. Brown-out Reset During Operation
VCC
VBOT-
VBOT+
RESET
TIME-OUT
tTOUT
INTERNAL
RESET
Watchdog Reset
42
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out period
tTOUT. Refer to page 44 for details on operation of the Watchdog Timer.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 20. Watchdog Reset During Operation
CC
CK
MCUSR – MCU Status
Register
The MCU Status Register provides information on which reset source caused an MCU
reset.
Bit
7
6
5
4
3
2
1
0
0x35 (0x55)
–
–
–
JTRF
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
MCUSR
See Bit Description
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register
selected by the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or
by writing a logic zero to the flag.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by
writing a logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by
writing a logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by
writing a logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to
the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and
then Reset the MCUSR as early as possible in the program. If the register is cleared
before another reset occurs, the source of the reset can be found by examining the
Reset Flags.
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2570J–AVR–11/06
Internal Voltage
Reference
ATmega325/3250/645/6450 features an internal bandgap reference. This reference is
used for Brown-out Detection, and it can be used as an input to the Analog Comparator
or the ADC.
Voltage Reference Enable
Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used.
The start-up time is given in Table 19. To save power, the reference is not always turned
on. The reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [1..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting
the ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the
user must always allow the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in Power-down mode, the user
can avoid the three conditions above to ensure that the reference is turned off before
entering Power-down mode.
Table 19. Internal Voltage Reference Characteristics(1)
Symbol
VBG
tBG
IBG
Note:
Watchdog Timer
Parameter
Condition
Min
Typ
Max
Units
Bandgap reference voltage
VCC = 2.7V,
TA = 25°C
1.0
1.1
1.2
V
Bandgap reference start-up time
VCC = 2.7V,
TA = 25°C
40
70
µs
Bandgap reference current
consumption
VCC = 2.7V,
TA = 25°C
15
µA
1. Values are guidelines only. Actual values are TBD.
The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at
1 MHz. This is the typical value at VCC = 5V. See characterization data for typical values
at other VCC levels. By controlling the Watchdog Timer prescaler, the Watchdog Reset
interval can be adjusted as shown in Table 21 on page 46. The WDR – Watchdog Reset
– instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is
disabled and when a Chip Reset occurs. Eight different clock cycle periods can be
selected to determine the reset period. If the reset period expires without another
Watchdog Reset, the ATmega325/3250/645/6450 resets and executes from the Reset
Vector. For timing details on the Watchdog Reset, refer to Table 21 on page 46.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out
period, two different safety levels are selected by the fuse WDTON as shown in Table
20. Refer to “Timed Sequences for Changing the Configuration of the Watchdog Timer”
on page 47 for details.
Table 20. WDT Configuration as a Function of the Fuse Settings of WDTON
WDTON
44
Safety
Level
WDT Initial
State
How to Disable the
WDT
How to Change
Time-out
Unprogrammed
1
Disabled
Timed sequence
Timed sequence
Programmed
2
Enabled
Always enabled
Timed sequence
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 21. Watchdog Timer
WATCHDOG
OSCILLATOR
WDTCR – Watchdog Timer
Control Register
Bit
7
6
5
4
3
2
1
0
(0x60)
–
–
–
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
WDTCR
• Bits 7:5 – Res: Reserved Bits
These bits are reserved bits in the ATmega325/3250/645/6450 and will always read as
zero.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog
will not be disabled. Once written to one, hardware will clear this bit after four clock
cycles. Refer to the description of the WDE bit for a Watchdog disable procedure. This
bit must also be set when changing the prescaler bits. See “Timed Sequences for
Changing the Configuration of the Watchdog Timer” on page 47.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is
written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared
if the WDCE bit has logic level one. To disable an enabled Watchdog Timer, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be
written to WDE even though it is set to one before the disable operation starts.
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the
Watchdog.
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm described above. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 47.
• Bits 2:0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0
The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the
Watchdog Timer is enabled. The different prescaling values and their corresponding
Time-out Periods are shown in Table 21 on page 46.
45
2570J–AVR–11/06
Table 21. Watchdog Timer Prescale Select
WDP2
WDP1
WDP0
Number of WDT
Oscillator Cycles
Typical Time-out
at VCC = 3.0V
Typical Time-out
at VCC = 5.0V
0
0
0
16K cycles
17.1 ms
16.3 ms
0
0
1
32K cycles
34.3 ms
32.5 ms
0
1
0
64K cycles
68.5 ms
65 ms
0
1
1
128K cycles
0.14 s
0.13 s
1
0
0
256K cycles
0.27 s
0.26 s
1
0
1
512K cycles
0.55 s
0.52 s
1
1
0
1,024K cycles
1.1 s
1.0 s
1
1
1
2,048K cycles
2.2 s
2.1 s
The following code example shows one assembly and one C function for turning off the
WDT. The example assumes that interrupts are controlled (e.g. by disabling interrupts
globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example(1)
WDT_off:
; Reset WDT
wdr
; Write logical one to WDCE and WDE
in
r16, WDTCR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
C Code Example(1)
void WDT_off(void)
{
/* Reset WDT */
__watchdog_reset();
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
Note:
46
1. See “About Code Examples” on page 8.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Timed Sequences for
Changing the
Configuration of the
Watchdog Timer
The sequence for changing configuration differs slightly between the two safety levels.
Separate procedures are described for each level.
Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the
WDE bit to 1 without any restriction. A timed sequence is needed when changing the
Watchdog Time-out period or disabling an enabled Watchdog Timer. To disable an
enabled Watchdog Timer, and/or changing the Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be
written to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, in the same operation, write the WDE and WDP
bits as desired, but with the WDCE bit cleared.
Safety Level 2
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read
as one. A timed sequence is needed when changing the Watchdog Time-out period. To
change the Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the
WDE always is set, the WDE must be written to one to start the timed sequence.
Within the next four clock cycles, in the same operation, write the WDP bits as desired,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
47
2570J–AVR–11/06
Interrupts
This section describes the specifics of the interrupt handling as performed in
ATmega325/3250/645/6450. For a general explanation of the AVR interrupt handling,
refer to “Reset and Interrupt Handling” on page 14.
Interrupt Vectors in ATmega325/3250/645/6450
Table 22. Reset and Interrupt Vectors
Vector
No.
Program
Address(2)
Source
Interrupt Definition
1
0x0000(1)
RESET
External Pin, Power-on Reset, Brown-out Reset,
Watchdog Reset, and JTAG AVR Reset
2
0x0002
INT0
External Interrupt Request 0
3
0x0004
PCINT0
Pin Change Interrupt Request 0
4
0x0006
PCINT1
Pin Change Interrupt Request 1
5
0x0008
TIMER2 COMP
Timer/Counter2 Compare Match
6
0x000A
TIMER2 OVF
Timer/Counter2 Overflow
7
0x000C
TIMER1 CAPT
Timer/Counter1 Capture Event
8
0x000E
TIMER1 COMPA
Timer/Counter1 Compare Match A
9
0x0010
TIMER1 COMPB
Timer/Counter1 Compare Match B
10
0x0012
TIMER1 OVF
Timer/Counter1 Overflow
11
0x0014
TIMER0 COMP
Timer/Counter0 Compare Match
12
0x0016
TIMER0 OVF
Timer/Counter0 Overflow
13
0x0018
SPI, STC
SPI Serial Transfer Complete
14
0x001A
USART, RX
USART, Rx Complete
15
0x001C
USART, UDRE
USART Data Register Empty
16
0x001E
USART, TX
USART, Tx Complete
17
0x0020
USI START
USI Start Condition
18
0x0022
USI OVERFLOW
USI Overflow
19
0x0024
ANALOG COMP
Analog Comparator
20
0x0026
ADC
ADC Conversion Complete
21
0x0028
EE READY
EEPROM Ready
22
0x002A
SPM READY
Store Program Memory Ready
23
0x002C
NOT_USED
RESERVED
(3)
0x002E
PCINT2
Pin Change Interrupt Request 2
25(3)
0x0030
PCINT3
Pin Change Interrupt Request 3
24
Notes:
48
1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader
address at reset, see “Boot Loader Support – Read-While-Write Self-Programming”
on page 246.
2. When the IVSEL bit in MCUCR is set, Interrupt Vectors will be moved to the start of
the Boot Flash Section. The address of each Interrupt Vector will then be the address
in this table added to the start address of the Boot Flash Section.
3. PCINT2 and PCINT3 are only present in ATmega3250 and ATmega6450.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 23 shows reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the
Interrupt Vectors are not used, and regular program code can be placed at these locations. This is also the case if the Reset Vector is in the Application section while the
Interrupt Vectors are in the Boot section or vice versa.
Table 23. Reset and Interrupt Vectors Placement(1)
BOOTRST
IVSEL
1
Note:
Reset Address
Interrupt Vectors Start Address
0
0x0000
0x0002
1
1
0x0000
Boot Reset Address + 0x0002
0
0
Boot Reset Address
0x0002
0
1
Boot Reset Address
Boot Reset Address + 0x0002
1. The Boot Reset Address is shown in Table 104 on page 258. For the BOOTRST
Fuse “1” means unprogrammed while “0” means programmed.
The most typical and general program setup for the Reset and Interrupt Vector
Addresses in ATmega325/3250/645/6450 is:
Address
Labels
Code
Comments
0x0000
jmp
RESET
0x0002
jmp
EXT_INT0
; IRQ0 Handler
0x0004
jmp
PCINT0
; PCINT0 Handler
0x0006
jmp
PCINT1
; PCINT1 Handler
0x0008
jmp
TIM2_COMP
; Timer2 Compare Handler
0x000A
jmp
TIM2_OVF
; Timer2 Overflow Handler
0x000C
jmp
TIM1_CAPT
; Timer1 Capture Handler
0x000E
jmp
TIM1_COMPA
; Timer1 CompareA Handler
0x0010
jmp
TIM1_COMPB
; Timer1 CompareB Handler
0x0012
jmp
TIM1_OVF
; Timer1 Overflow Handler
0x0014
jmp
TIM0_COMP
; Timer0 Compare Handler
0x0016
jmp
TIM0_OVF
; Timer0 Overflow Handler
0X0018
jmp
SPI_STC
; SPI Transfer Complete Handler
0x001A
jmp
USART_RXC
; USART RX Complete Handler
0x001C
jmp
USART_UDRE
; USART,UDR Empty Handler
0x001E
jmp
USART_TXC
; USART TX Complete Handler
0x0020
jmp
USI_STRT
; USI Start Condition Handler
0x0022
jmp
USI_OVF
; USI Overflow Handler
0x0024
jmp
ANA_COMP
; Analog Comparator Handler
0x0026
jmp
ADC
; ADC Conversion Complete Handler
0x0028
jmp
EE_RDY
; EEPROM Ready Handler
0x002A
jmp
SPM_RDY
; SPM Ready Handler
;NOT_USED
; RESERVED
0x002C
; Reset Handler
0x002E
jmp
PCINT2
; PCINT2 Handler
0x0030
jmp
PCINT3
; PCINT3 Handler
;
0x0032
ldi
r16, high(RAMEND)
; Main program start
0x0033
RESET:
out
SPH,r16
; Set Stack Pointer to top of RAM
0x0034
ldi
r16, low(RAMEND)
0x0035
out
SPL,r16
0x0036
sei
0x0037
<instr> xxx
...
...
; Enable interrupts
...
49
2570J–AVR–11/06
When the BOOTRST Fuse is unprogrammed, the Boot section size set to 4K bytes and
the IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most
typical and general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code
Comments
0x0000
RESET: ldi
r16,high(RAMEND); Main program start
0x0001
RAM
out
SPH,r16
0x0002
ldi
r16,low(RAMEND)
0x0003
0x0004
out
sei
SPL,r16
0x0005
<instr> xxx
; Set Stack Pointer to top of
; Enable interrupts
;
.org 0x3802/0x7802
0x3804/0x7804
jmp
EXT_INT0
; IRQ0 Handler
0x3806/0x7806
jmp
PCINT0
; PCINT0 Handler
...
...
...
;
0x1C2C
Handler
jmp
SPM_RDY
; Store Program Memory Ready
When the BOOTRST Fuse is programmed and the Boot section size set to 4K bytes, the
most typical and general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code
Comments
.org 0x0002
0x0002
jmp
EXT_INT0
; IRQ0 Handler
0x0004
jmp
PCINT0
; PCINT0 Handler
...
...
...
;
0x002C
Handler
jmp
SPM_RDY
; Store Program Memory Ready
;
.org 0x3800/0x7800
0x3800/0x7801RESET:ldir16,high(RAMEND); Main program start
0x3801/0x7801
out
SPH,r16
; Set Stack Pointer to top of RAM
0x3802/0x7802
ldi
r16,low(RAMEND)
0x3803/0x7803
0x3804/0x7804
out
sei
SPL,r16
0x3805/0x7805
<instr>
; Enable interrupts
xxx
When the BOOTRST Fuse is programmed, the Boot section size set to 4K bytes and the
IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code
Comments
;
.org 0x3800/0x7800
0x3800/0x7800 jmp
0x3802/0x7802 jmp
RESET
EXT_INT0
; Reset handler
; IRQ0 Handler
0x3804/0x7804
jmp
PCINT0
; PCINT0 Handler
...
...
...
;
0x382C/0x782C
jmp
SPM_RDY
; Store Program Memory Ready Handler
;
50
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
0x382E/0x782ERESET:ldir16,high(RAMEND); Main program start
Moving Interrupts Between
Application and Boot Space
MCUCR – MCU Control
Register
0x382F/0x782F
out
SPH,r16
; Set Stack Pointer to top of RAM
0x3830/0x7830
ldi
r16,low(RAMEND)
0x3831/0x7831
0x3832/0x7832
out
sei
SPL,r16
0x3833/0x7833
<instr>
; Enable interrupts
xxx
The MCU Control Register controls the placement of the Interrupt Vector table.
Bit
7
6
5
4
3
2
1
0
0x35 (0x55)
JTD
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the
Flash memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot Loader section of the Flash. The actual address of the start of the Boot
Flash Section is determined by the BOOTSZ Fuses. Refer to the section “Boot Loader
Support – Read-While-Write Self-Programming” on page 246 for details. To avoid unintentional changes of Interrupt Vector tables, a special write procedure must be followed
to change the IVSEL bit:
1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to
IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are
disabled in the cycle IVCE is set, and they remain disabled until after the instruction following the write to IVSEL. If IVSEL is not written, interrupts remain disabled for four
cycles. The I-bit in the Status Register is unaffected by the automatic disabling.
Note:
If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed, interrupts are disabled while executing from the Application section. If
Interrupt Vectors are placed in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while executing from the Boot Loader section. Refer to
the section “Boot Loader Support – Read-While-Write Self-Programming” on page 246
for details on Boot Lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is
cleared by hardware four cycles after it is written or when IVSEL is written. Setting the
IVCE bit will disable interrupts, as explained in the IVSEL description above. See Code
Example below.
51
2570J–AVR–11/06
Assembly Code Example
Move_interrupts:
;Get MCUCR
in r16, MCUCR
mov r17, r16
; Enable change of Interrupt Vectors
ori r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ori r17, (1<<IVSEL)
out MCUCR, r17
ret
C Code Example
void Move_interrupts(void)
{
/* Enable change of Interrupt Vectors */
MCUCR |= (1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR |= (1<<IVSEL);
}
52
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT30..0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT0 or PCINT30..0 pins
are configured as outputs. This feature provides a way of generating a software interrupt. The pin change interrupt PCI1 will trigger if any enabled PCINT15..8 pin toggles.
Pin change interrupts PCI0 will trigger if any enabled PCINT7..0 pin toggles. The
PCMSK3, PCMSK2, PCMSK1, and PCMSK0 Registers control which pins contribute to
the pin change interrupts. Pin change interrupts on PCINT30..0 are detected asynchronously. This implies that these interrupts can be used for waking the part also from sleep
modes other than Idle mode.
The INT0 interrupts can be triggered by a falling or rising edge or a low level. This is set
up as indicated in the specification for the External Interrupt Control Register A –
EICRA. When the INT0 interrupt is enabled and is configured as level triggered, the
interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising
edge interrupts on INT0 requires the presence of an I/O clock, described in “Clock Systems and their Distribution” on page 25. Low level interrupt on INT0 is detected
asynchronously. This implies that this interrupt can be used for waking the part also
from sleep modes other than Idle mode. The I/O clock is halted in all sleep modes
except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the
required level must be held long enough for the MCU to complete the wake-up to trigger
the level interrupt. If the level disappears before the end of the Start-up Time, the MCU
will still wake up, but no interrupt will be generated. The start-up time is defined by the
SUT and CKSEL Fuses as described in “System Clock and Clock Options” on page 25.
Pin Change Interrupt
Timing
An example of timing of a pin change interrupt is shown in Figure 22.
Figure 22. Pin Change Interrupt
pin_lat
PCINT(0)
LE
clk
D
pcint_in_(0)
Q
0
pcint_syn
pcint_setflag
PCIF
pin_sync
x
PCINT(0) in PCMSK(x)
clk
clk
PCINT(n)
pin_lat
pin_sync
pcint_in_(n)
pcint_syn
pcint_setflag
PCIF
53
2570J–AVR–11/06
EICRA – External Interrupt
Control Register A
The External Interrupt Control Register A contains control bits for interrupt sense
control.
Bit
7
6
5
4
3
2
1
0
(0x69)
–
–
–
–
–
–
ISC01
ISC00
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EICRA
• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the
corresponding interrupt mask are set. The level and edges on the external INT0 pin that
activate the interrupt are defined in Table 24. The value on the INT0 pin is sampled
before detecting edges. If edge or toggle interrupt is selected, pulses that last longer
than one clock period will generate an interrupt. Shorter pulses are not guaranteed to
generate an interrupt. If low level interrupt is selected, the low level must be held until
the completion of the currently executing instruction to generate an interrupt.
Table 24. Interrupt 0 Sense Control
54
ISC01
ISC00
Description
0
0
The low level of INT0 generates an interrupt request.
0
1
Any logical change on INT0 generates an interrupt request.
1
0
The falling edge of INT0 generates an interrupt request.
1
1
The rising edge of INT0 generates an interrupt request.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
EIMSK – External Interrupt
Mask Register
Bit
7
6
5
4
3
2
1
0
PCIE3
PCIE2
PCIE1
PCIE0
–
–
–
INT0
Read/Write
R/W
R/W
R/W
R/W
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
0x1D (0x3D)
EIMSK
• Bit 7 – PCIE3: Pin Change Interrupt Enable 3
When the PCIE3 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
pin change interrupt 3 is enabled. Any change on any enabled PCINT30..24 pin will
cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT3 Interrupt Vector. PCINT30..24 pins are enabled individually by
the PCMSK3 Register.
This bit is reserved bit in ATmega325/645 and should always be written to zero.
• Bit 6 – PCIE2: Pin Change Interrupt Enable 2
When the PCIE2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
pin change interrupt 2 is enabled. Any change on any enabled PCINT23..16 pin will
cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT2 Interrupt Vector. PCINT23..16 pins are enabled individually by
the PCMSK2 Register.
This bit is reserved bit in ATmega325/645 and should always be written to zero.
• Bit 5 – PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
pin change interrupt 1 is enabled. Any change on any enabled PCINT15..8 pin will
cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT1 Interrupt Vector. PCINT15..8 pins are enabled individually by the
PCMSK1 Register.
• Bit 4 – PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
pin change interrupt 0 is enabled. Any change on any enabled PCINT7..0 pin will cause
an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed
from the PCINT0 Interrupt Vector. PCINT7..0 pins are enabled individually by the
PCMSK0 Register.
• Bit 0 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and
ISC00) in the External Interrupt Control Register A (EICRA) define whether the external
interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity
on the pin will cause an interrupt request even if INT0 is configured as an output. The
corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt Vector.
55
2570J–AVR–11/06
EIFR – External Interrupt Flag
Registe
Bit
7
6
5
4
3
2
1
0
PCIF3
PCIF2
PCIF1
PCIF0
–
–
–
INTF0
Read/Write
R/W
R/W
R/W
R/W
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
0x1C (0x3C)
EIFR
• Bit 7– PCIF3: Pin Change Interrupt Flag 3
When a logic change on any PCINT30..24 pin triggers an interrupt request, PCIF3
becomes set (one). If the I-bit in SREG and the PCIE3 bit in EIMSK are set (one), the
MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to
it.
This bit is reserved bit in ATmega325/645 and will always be read as zero.
• Bit 6– PCIF2: Pin Change Interrupt Flag 2
When a logic change on any PCINT24..16 pin triggers an interrupt request, PCIF2
becomes set (one). If the I-bit in SREG and the PCIE2 bit in EIMSK are set (one), the
MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to
it.
This bit is reserved bit in ATmega325/645 and will always be read as zero.
• Bit 5– PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT15..8 pin triggers an interrupt request, PCIF1
becomes set (one). If the I-bit in SREG and the PCIE1 bit in EIMSK are set (one), the
MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to
it.
• Bit 4– PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0
becomes set (one). If the I-bit in SREG and the PCIE0 bit in EIMSK are set (one), the
MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to
it.
• Bit 0 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0
becomes set (one). If the I-bit in SREG and the INT0 bit in EIMSK are set (one), the
MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to
it. This flag is always cleared when INT0 is configured as a level interrupt.
PCMSK3 – Pin Change Mask
Register 3(1)
Bit
7
6
5
4
3
2
1
0
(0x73)
–
PCINT30
PCINT29
PCINT28
PCINT27
PCINT26
PCINT25
PCINT24
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCMSK3
• Bit 6:0 – PCINT30:24: Pin Change Enable Mask 30:24
Each PCINT30:24-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT30:24 is set and the PCIE3 bit in EIMSK is set, pin change
interrupt is enabled on the corresponding I/O pin. If PCINT30:24 is cleared, pin change
interrupt on the corresponding I/O pin is disabled.
56
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
PCMSK2 – Pin Change Mask
Register 2(1)
Bit
(0x6D)
7
6
5
4
3
2
1
0
PCINT23
PCINT22
PCINT21
PCINT20
PCINT19
PCINT18
PCINT17
PCINT16
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
Read/Write
Initial
Value
PCMSK2
• Bit 7:0 – PCINT23:16: Pin Change Enable Mask 23..16
Each PCINT23:16 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT23:16 is set and the PCIE2 bit in EIMSK is set, pin change
interrupt is enabled on the corresponding I/O pin. If PCINT23:16 is cleared, pin change
interrupt on the corresponding I/O pin is disabled.
Note:
PCMSK1 – Pin Change Mask
Register 1
1. PCMSK3 and PCMSK2 are only present in ATmega3250/6450.
Bit
7
6
5
4
3
2
1
0
PCINT15
PCINT14
PCINT13
PCINT12
PCINT11
PCINT10
PCINT9
PCINT8
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x6C)
PCMSK1
• Bit 7:0 – PCINT15:8: Pin Change Enable Mask 15..8
Each PCINT15:8-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT15:8 is set and the PCIE1 bit in EIMSK is set, pin change interrupt is
enabled on the corresponding I/O pin. If PCINT15:8 is cleared, pin change interrupt on
the corresponding I/O pin is disabled.
PCMSK0 – Pin Change Mask
Register 0
Bit
7
6
5
4
3
2
1
0
(0x6B)
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PCMSK0
• Bit 7:0 – PCINT7:0: Pin Change Enable Mask 7..0
Each PCINT7:0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7:0 is set and the PCIE0 bit in EIMSK is set, pin change interrupt is
enabled on the corresponding I/O pin. If PCINT7:0 is cleared, pin change interrupt on
the corresponding I/O pin is disabled.
57
2570J–AVR–11/06
I/O-Ports
Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital
I/O ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The
same applies when changing drive value (if configured as output) or enabling/disabling
of pull-up resistors (if configured as input). Each output buffer has symmetrical drive
characteristics with both high sink and source capability. Port B has a higher pin driver
strength than the other ports, but all the pin drivers are strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supplyvoltage invariant resistance. All I/O pins have protection diodes to both VCC and Ground
as indicated in Figure 23. Refer to “Electrical Characteristics” on page 291 for a complete list of parameters. If exceeding the pin voltage “Absolute Maximum Ratings”,
resulting currents can harm the device if not limited accordingly. For segment pins used
as general I/O, the same situation can also influence the LCD voltage level.
Figure 23. I/O Pin Equivalent Schematic
Rpu
Logic
Pxn
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case
“x” represents the numbering letter for the port, and a lower case “n” represents the bit
number. However, when using the register or bit defines in a program, the precise form
must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally
as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description for I/O-Ports” on page 80.
Three I/O memory address locations are allocated for each port, one each for the Data
Register – PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The
Port Input Pins I/O location is read only, while the Data Register and the Data Direction
Register are read/write. However, writing a logic one to a bit in the PINx Register, will
result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up
Disable – PUD bit in MCUCR disables the pull-up function for all pins in all ports when
set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on
page 59. Most port pins are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes with the port pin is described
58
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
in “Alternate Port Functions” on page 64. Refer to the individual module sections for a
full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use
of the other pins in the port as general digital I/O.
Ports as General Digital
I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 24 shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 24. General Digital I/O(1)
PUD
Q
D
DDxn
Q CLR
WDx
RESET
DATA BUS
RDx
1
Q
Pxn
D
0
PORTxn
Q CLR
RESET
WPx
RRx
SLEEP
SYNCHRONIZER
D
Q
L
Q
D
WRx
RPx
Q
PINxn
Q
clk I/O
PUD:
SLEEP:
clkI/O:
Note:
Configuring the Pin
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port.
clkI/O, SLEEP, and PUD are common to all ports.
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in
“Register Description for I/O-Ports” on page 80, the DDxn bits are accessed at the
DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at
the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written
logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up
resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic
zero or the pin has to be configured as an output pin. The port pins are tri-stated when
reset condition becomes active, even if no clocks are running.
59
2570J–AVR–11/06
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is
driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).
Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of
DDRxn. Note that the SBI instruction can be used to toggle one single bit in a port.
Switching Between Input and
Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn,
PORTxn} = 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} =
0b01) or output low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up
enabled state is fully acceptable, as a high-impedant environment will not notice the difference between a strong high driver and a pull-up. If this is not the case, the PUD bit in
the MCUCR Register can be set to disable all pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The
user must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state
({DDxn, PORTxn} = 0b11) as an intermediate step.
Table 25 summarizes the control signals for the pin value.
Table 25. Port Pin Configurations
Reading the Pin Value
60
DDxn
PORTxn
PUD
(in MCUCR)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled
low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output Low (Sink)
1
1
X
Output
No
Output High (Source)
Comment
Independent of the setting of Data Direction bit DDxn, the port pin can be read through
the PINxn Register bit. As shown in Figure 24, the PINxn Register bit and the preceding
latch constitute a synchronizer. This is needed to avoid metastability if the physical pin
changes value near the edge of the internal clock, but it also introduces a delay. Figure
25 shows a timing diagram of the synchronization when reading an externally applied
pin value. The maximum and minimum propagation delays are denoted tpd,max and tpd,min
respectively.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 25. Synchronization when Reading an Externally Applied Pin value
SYSTEM CLK
INSTRUCTIONS
XXX
XXX
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd, max
t pd, min
61
2570J–AVR–11/06
Consider the clock period starting shortly after the first falling edge of the system clock.
The latch is closed when the clock is low, and goes transparent when the clock is high,
as indicated by the shaded region of the “SYNC LATCH” signal. The signal value is
latched when the system clock goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a
single signal transition on the pin will be delayed between ½ and 1½ system clock
period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as
indicated in Figure 26. The out instruction sets the “SYNC LATCH” signal at the positive
edge of the clock. In this case, the delay tpd through the synchronizer is 1 system clock
period.
Figure 26. Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
0xFF
out PORTx, r16
nop
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and
define the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The
resulting pin values are read back again, but as previously discussed, a nop instruction
is included to be able to read back the value recently assigned to some of the pins.
62
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi
r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out
PORTB,r16
out
DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in
r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
Note:
Digital Input Enable and Sleep
Modes
1. For the assembly program, two temporary registers are used to minimize the time
from pull-ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set,
defining bit 2 and 3 as low and redefining bits 0 and 1 as strong high drivers.
As shown in Figure 24, the digital input signal can be clamped to ground at the input of
the Schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep
Controller in Power-down mode, Power-save mode, and Standby mode to avoid high
power consumption if some input signals are left floating, or have an analog signal level
close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP is active also for these pins. SLEEP is also
overridden by various other alternate functions as described in “Alternate Port Functions” on page 64.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the
external interrupt is not enabled, the corresponding External Interrupt Flag will be set
when resuming from the above mentioned Sleep mode, as the clamping in these sleep
mode produces the requested logic change.
Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined
level. Even though most of the digital inputs are disabled in the deep sleep modes as
63
2570J–AVR–11/06
described above, floating inputs should be avoided to reduce current consumption in all
other modes where the digital inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal
pull-up. In this case, the pull-up will be disabled during reset. If low power consumption
during reset is important, it is recommended to use an external pull-up or pull-down.
Connecting unused pins directly to VCC or GND is not recommended, since this may
cause excessive currents if the pin is accidentally configured as an output.
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure
27 shows how the port pin control signals from the simplified Figure 24 can be overridden by alternate functions. The overriding signals may not be present in all port pins, but
the figure serves as a generic description applicable to all port pins in the AVR microcontroller family.
Figure 27. Alternate Port Functions(1)
PUOExn
PUOVxn
1
PUD
0
DDOExn
DDOVxn
1
Q D
DDxn
0
Q CLR
WDx
PVOExn
RESET
RDx
1
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
DIEOVxn
WPx
RESET
WRx
1
0
DATA BUS
PVOVxn
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
Q
D
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
Note:
64
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP CONTROL
Pxn, PORT TOGGLE OVERRIDE ENABLE
PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clkI/O:
DIxn:
AIOxn:
PULLUP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port.
clkI/O, SLEEP, and PUD are common to all ports. All other signals are unique for each
pin.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 26 summarizes the function of the overriding signals. The pin and port indexes
from Figure 27 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
Table 26. Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
PUOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the
PUOV signal. If this signal is cleared, the pull-up is
enabled when {DDxn, PORTxn, PUD} = 0b010.
PUOV
Pull-up Override
Value
If PUOE is set, the pull-up is enabled/disabled when
PUOV is set/cleared, regardless of the setting of the
DDxn, PORTxn, and PUD Register bits.
DDOE
Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled
by the DDOV signal. If this signal is cleared, the Output
driver is enabled by the DDxn Register bit.
DDOV
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled
when DDOV is set/cleared, regardless of the setting of
the DDxn Register bit.
PVOE
Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the
port value is controlled by the PVOV signal. If PVOE is
cleared, and the Output Driver is enabled, the port Value
is controlled by the PORTxn Register bit.
PVOV
Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless
of the setting of the PORTxn Register bit.
PTOE
Port Toggle
Override Enable
If PTOE is set, the PORTxn Register bit is inverted.
DIEOE
Digital Input
Enable Override
Enable
If this bit is set, the Digital Input Enable is controlled by
the DIEOV signal. If this signal is cleared, the Digital Input
Enable is determined by MCU state (Normal mode, sleep
mode).
DIEOV
Digital Input
Enable Override
Value
If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state
(Normal mode, sleep mode).
DI
Digital Input
This is the Digital Input to alternate functions. In the
figure, the signal is connected to the output of the schmitt
trigger but before the synchronizer. Unless the Digital
Input is used as a clock source, the module with the
alternate function will use its own synchronizer.
AIO
Analog
Input/Output
This is the Analog Input/output to/from alternate
functions. The signal is connected directly to the pad, and
can be used bi-directionally.
The following subsections shortly describe the alternate functions for each port, and
relate the overriding signals to the alternate function. Refer to the alternate function
description for further details.
65
2570J–AVR–11/06
MCUCR – MCU Control
Register
Bit
7
6
5
4
3
2
1
0
0x35 (0x55)
JTD
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 4 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn
and PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01).
See “Configuring the Pin” on page 59 for more details about this feature.
Alternate Functions of Port B
The Port B pins with alternate functions are shown in Table 27.
Table 27. Port B Pins Alternate Functions
Port Pin
Alternate Functions
PB7
OC2A/PCINT15 (Output Compare and PWM Output A for Timer/Counter2 or
Pin Change Interrupt15).
PB6
OC1B/PCINT14 (Output Compare and PWM Output B for Timer/Counter1 or
Pin Change Interrupt14).
PB5
OC1A/PCINT13 (Output Compare and PWM Output A for Timer/Counter1 or
Pin Change Interrupt13).
PB4
OC0A/PCINT12 (Output Compare and PWM Output A for Timer/Counter0 or
Pin Change Interrupt12).
PB3
MISO/PCINT11 (SPI Bus Master Input/Slave Output or Pin Change
Interrupt11).
PB2
MOSI/PCINT10 (SPI Bus Master Output/Slave Input or Pin Change
Interrupt10).
PB1
SCK/PCINT9 (SPI Bus Serial Clock or Pin Change Interrupt9).
PB0
SS/PCINT8 (SPI Slave Select input or Pin Change Interrupt8).
The alternate pin configuration is as follows:
• OC2A/PCINT15, Bit 7
OC2, Output Compare Match A output: The PB7 pin can serve as an external output for
the Timer/Counter2 Output Compare A. The pin has to be configured as an output
(DDB7 set (one)) to serve this function. The OC2A pin is also the output pin for the PWM
mode timer function.
PCINT15, Pin Change Interrupt source 15: The PB7 pin can serve as an external interrupt source.
• OC1B/PCINT14, Bit 6
OC1B, Output Compare Match B output: The PB6 pin can serve as an external output
for the Timer/Counter1 Output Compare B. The pin has to be configured as an output
(DDB6 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM
mode timer function.
PCINT14, Pin Change Interrupt Source 14: The PB6 pin can serve as an external interrupt source.
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ATmega325/3250/645/6450
• OC1A/PCINT13, Bit 5
OC1A, Output Compare Match A output: The PB5 pin can serve as an external output
for the Timer/Counter1 Output Compare A. The pin has to be configured as an output
(DDB5 set (one)) to serve this function. The OC1A pin is also the output pin for the PWM
mode timer function.
PCINT13, Pin Change Interrupt Source 13: The PB5 pin can serve as an external interrupt source.
• OC0A/PCINT12, Bit 4
OC0A, Output Compare Match A output: The PB4 pin can serve as an external output
for the Timer/Counter0 Output Compare A. The pin has to be configured as an output
(DDB4 set (one)) to serve this function. The OC0A pin is also the output pin for the PWM
mode timer function.
PCINT12, Pin Change Interrupt Source 12: The PB4 pin can serve as an external interrupt source.
• MISO/PCINT11 – Port B, Bit 3
MISO: Master Data input, Slave Data output pin for SPI. When the SPI is enabled as a
Master, this pin is configured as an input regardless of the setting of DDB3. When the
SPI is enabled as a Slave, the data direction of this pin is controlled by DDB3. When the
pin is forced to be an input, the pull-up can still be controlled by the PORTB3 bit.
PCINT11, Pin Change Interrupt Source 11: The PB3 pin can serve as an external interrupt source.
• MOSI/PCINT10 – Port B, Bit 2
MOSI: SPI Master Data output, Slave Data input for SPI. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB2. When the SPI
is enabled as a Master, the data direction of this pin is controlled by DDB2. When the pin
is forced to be an input, the pull-up can still be controlled by the PORTB2 bit.
PCINT10, Pin Change Interrupt Source 10: The PB2 pin can serve as an external interrupt source.
• SCK/PCINT9 – Port B, Bit 1
SCK: Master Clock output, Slave Clock input pin for SPI. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB1. When the SPI
is enabled as a Master, the data direction of this pin is controlled by DDB1. When the pin
is forced to be an input, the pull-up can still be controlled by the PORTB1 bit.
PCINT9, Pin Change Interrupt Source 9: The PB1 pin can serve as an external interrupt
source.
• SS/PCINT8 – Port B, Bit 0
SS: Slave Port Select input. When the SPI is enabled as a Slave, this pin is configured
as an input regardless of the setting of DDB0. As a Slave, the SPI is activated when this
pin is driven low. When the SPI is enabled as a Master, the data direction of this pin is
controlled by DDB0. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB0 bit
PCINT8, Pin Change Interrupt Source 8: The PB0 pin can serve as an external interrupt
source.
Table 28 and Table 29 relate the alternate functions of Port B to the overriding signals
shown in Figure 27 on page 64. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute
67
2570J–AVR–11/06
the MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE
INPUT.
Table 28. Overriding Signals for Alternate Functions in PB7:PB4
Signal
Name
PB7/OC2A/
PCINT15
PB6/OC1B/
PCINT14
PB5/OC1A/
PCINT13
PB4/OC0A/
PCINT12
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
OC2A ENABLE
OC1B ENABLE
OC1A ENABLE
OC0A ENABLE
PVOV
OC2A
OC1B
OC1A
OC0A
PTOE
–
–
–
–
DIEOE
PCINT15 •
PCIE1
PCINT14 •
PCIE1
PCINT13 •
PCIE1
PCINT12 •
PCIE1
DIEOV
1
1
1
1
DI
PCINT15 INPUT
PCINT14 INPUT
PCINT13 INPUT
PCINT12 INPUT
AIO
–
–
–
–
Table 29. Overriding Signals for Alternate Functions in PB3:PB0
68
Signal
Name
PB3/MISO/
PCINT11
PB2/MOSI/
PCINT10
PB1/SCK/
PCINT9
PB0/SS/
PCINT8
PUOE
SPE • MSTR
SPE • MSTR
SPE • MSTR
SPE • MSTR
PUOV
PORTB3 • PUD
PORTB2 • PUD
PORTB1 • PUD
PORTB0 • PUD
DDOE
SPE • MSTR
SPE • MSTR
SPE • MSTR
SPE • MSTR
DDOV
0
0
0
0
PVOE
SPE • MSTR
SPE • MSTR
SPE • MSTR
0
PVOV
SPI SLAVE
OUTPUT
SPI MSTR
OUTPUT
SCK OUTPUT
0
PTOE
–
–
–
–
DIEOE
PCINT11 •
PCIE1
PCINT10 •
PCIE1
PCINT9 • PCIE1
PCINT8 • PCIE1
DIEOV
1
1
1
1
DI
PCINT11 INPUT
SPI MSTR
INPUT
PCINT10 INPUT
SPI SLAVE
INPUT
PCINT9 INPUT
SCK INPUT
PCINT8 INPUT
SPI SS
AIO
–
–
–
–
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Alternate Functions of Port D
The Port D pins with alternate functions are shown in Table 30.
Table 30. Port D Pins Alternate Functions
Port Pin
Alternate Function
PD7
-
PD6
-
PD5
-
PD4
-
PD3
-
PD2
-
PD1
INT0 (External Interrupt0 Input)
PD0
ICP1 (Timer/Counter1 Input Capture pin)
The alternate pin configuration is as follows:
• INT0 – Port D, Bit 1
INT0, External Interrupt Source 0. The PD1 pin can serve as an external interrupt
source to the MCU.
• ICP1 – Port D, Bit 0
ICP1 – Input Capture pin1: The PD0 pin can act as an Input Capture pin for
Timer/Counter1.
Table 31 relates the alternate functions of Port D to the overriding signals shown in Figure 27 on page 64.
Table 31. Overriding Signals for Alternate Functions in PD3:PD0
Signal
Name
PD3
PD2
PD1/INT0
PD0/ICP1
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
PTOE
–
–
–
–
DIEOE
0
0
INT0 ENABLE
0
DIEOV
0
0
INT0 ENABLE
0
DI
–
–
INT0 INPUT
ICP1 INPUT
AIO
–
–
–
–
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2570J–AVR–11/06
Alternate Functions of Port E
The Port E pins with alternate functions are shown in Table 32.
Table 32. Port E Pins Alternate Functions
Port Pin
Alternate Function
PE7
PCINT7 (Pin Change Interrupt7)
CLKO (Divided System Clock)
PE6
DO/PCINT6 (USI Data Output or Pin Change Interrupt6)
PE5
DI/SDA/PCINT5 (USI Data Input or TWI Serial DAta or Pin Change Interrupt5)
PE4
USCK/SCL/PCINT4 (USART External Clock Input/Output or TWI Serial Clock
or Pin Change Interrupt4)
PE3
AIN1/PCINT3 (Analog Comparator Negative Input or Pin Change Interrupt3)
PE2
XCK/AIN0/ PCINT2 (USART External Clock or Analog Comparator Positive
Input or Pin Change Interrupt2)
PE1
TXD/PCINT1 (USART Transmit Pin or Pin Change Interrupt1)
PE0
RXD/PCINT0 (USART Receive Pin or Pin Change Interrupt0)
• PCINT7 – Port E, Bit 7
PCINT7, Pin Change Interrupt Source 7: The PE7 pin can serve as an external interrupt
source.
CLKO, Divided System Clock: The divided system clock can be output on the PE7 pin.
The divided system clock will be output if the CKOUT Fuse is programmed, regardless
of the PORTE7 and DDE7 settings. It will also be output during reset.
• DO/PCINT6 – Port E, Bit 6
DO, Universal Serial Interface Data output.
PCINT6, Pin Change Interrupt Source 6: The PE6 pin can serve as an external interrupt
source.
• DI/SDA/PCINT5 – Port E, Bit 5
DI, Universal Serial Interface Data input.
SDA, Two-wire Serial Interface Data:
PCINT5, Pin Change Interrupt Source 5: The PE5 pin can serve as an external interrupt
source.
• USCK/SCL/PCINT4 – Port E, Bit 4
USCK, Universal Serial Interface Clock.
SCL, Two-wire Serial Interface Clock.
PCINT4, Pin Change Interrupt Source 4: The PE4 pin can serve as an external interrupt
source.
• AIN1/PCINT3 – Port E, Bit 3
AIN1 – Analog Comparator Negative input. This pin is directly connected to the negative
input of the Analog Comparator.
PCINT3, Pin Change Interrupt Source 3: The PE3 pin can serve as an external interrupt
source.
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ATmega325/3250/645/6450
• XCK/AIN0/PCINT2 – Port E, Bit 2
XCK, USART External Clock. The Data Direction Register (DDE2) controls whether the
clock is output (DDE2 set) or input (DDE2 cleared). The XCK pin is active only when the
USART operates in synchronous mode.
AIN0 – Analog Comparator Positive input. This pin is directly connected to the positive
input of the Analog Comparator.
PCINT2, Pin Change Interrupt Source 2: The PE2 pin can serve as an external interrupt
source.
• TXD/PCINT1 – Port E, Bit 1
TXD0, UART0 Transmit pin.
PCINT1, Pin Change Interrupt Source 1: The PE1 pin can serve as an external interrupt
source.
• RXD/PCINT0 – Port E, Bit 0
RXD, USART Receive pin. Receive Data (Data input pin for the USART). When the
USART Receiver is enabled this pin is configured as an input regardless of the value of
DDE0. When the USART forces this pin to be an input, a logical one in PORTE0 will turn
on the internal pull-up.
PCINT0, Pin Change Interrupt Source 0: The PE0 pin can serve as an external interrupt
source.
Table 33 and Table 34 relates the alternate functions of Port E to the overriding signals
shown in Figure 27 on page 64.
Table 33. Overriding Signals for Alternate Functions PE7:PE4
Signal
Name
PE7/PCINT7
PE6/DO/
PCINT6
PE5/DI/SDA/
PCINT5
PE4/USCK/SCL/
PCINT4
PUOE
0
0
USI_TWO-WIRE
USI_TWO-WIRE
PUOV
0
0
0
0
0
USI_TWO-WIRE
USI_TWO-WIRE
(1)
DDOE
CKOUT
DDOV
1
0
(SDA +
PORTE5) •
DDE5
(USI_SCL_HOL
D + PORTE4) •
DDE4
PVOE
CKOUT(1)
USI_THREEWIRE
USI_TWO-WIRE
• DDE5
USI_TWO-WIRE
• DDE4
PVOV
clkI/O
DO
0
0
PTOE
–
–
0
USITC
DIEOE
PCINT7 • PCIE0
PCINT6 • PCIE0
(PCINT5 •
PCIE0) + USISIE
(PCINT4 •
PCIE0) + USISIE
DIEOV
1
1
1
1
DI
PCINT7 INPUT
PCINT6 INPUT
DI/SDA INPUT
PCINT5 INPUT
USCKL/SCL
INPUT
PCINT4 INPUT
AIO
–
–
–
–
Note:
1. CKOUT is one if the CKOUT Fuse is programmed
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2570J–AVR–11/06
Table 34. Overriding Signals for Alternate Functions in PE3:PE0
Signal
Name
PE3/AIN1/
PCINT3
PE2/XCK/AIN0/
PCINT2
PE1/TXD/
PCINT1
PE0/RXD/PCINT
0
PUOE
0
XCK OUTPUT
ENABLE
TXEN
RXEN
PUOV
0
XCK
0
PORTE0 • PUD
DDOE
0
0
TXEN
RXEN
DDOV
0
0
1
0
PVOE
0
0
TXEN
0
PVOV
0
0
TXD
0
PTOE
–
–
–
–
DIEOE
(PCINT3 •
PCIE0) +
AIN1D(1)
(PCINT2 •
PCIE0) +
AIN0D(1)
PCINT1 • PCIE0
PCINT0 • PCIE0
DIEOV
PCINT3 • PCIE0
PCINT2 • PCIE0
1
1
DI
PCINT3 INPUT
XCK/PCINT2
INPUT
PCINT1 INPUT
RXD/PCINT0
INPUT
AIO
AIN1 INPUT
AIN0 INPUT
–
–
Note:
Alternate Functions of Port F
1. AIN0D and AIN1D is described in “DIDR1 – Digital Input Disable Register 1” on page
196.
The Port F has an alternate function as analog input for the ADC as shown in Table 35.
If some Port F pins are configured as outputs, it is essential that these do not switch
when a conversion is in progress. This might corrupt the result of the conversion. If the
JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS) and
PF4(TCK) will be activated even if a reset occurs.
Table 35. Port F Pins Alternate Functions
Port Pin
Alternate Function
PF7
ADC7/TDI (ADC input channel 7 or JTAG Test Data Input)
PF6
ADC6/TDO (ADC input channel 6 or JTAG Test Data Output)
PF5
ADC5/TMS (ADC input channel 5 or JTAG Test mode Select)
PF4
ADC4/TCK (ADC input channel 4 or JTAG Test ClocK)
PF3
ADC3 (ADC input channel 3)
PF2
ADC2 (ADC input channel 2)
PF1
ADC1 (ADC input channel 1)
PF0
ADC0 (ADC input channel 0)
• TDI, ADC7 – Port F, Bit 7
ADC7, Analog to Digital Converter, Channel 7.
TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or
Data Register (scan chains). When the JTAG interface is enabled, this pin can not be
used as an I/O pin.
72
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ATmega325/3250/645/6450
• TDO, ADC6 – Port F, Bit 6
ADC6, Analog to Digital Converter, Channel 6.
TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When the JTAG interface is enabled, this pin can not be used as an I/O pin. In TAP
states that shift out data, the TDO pin drives actively. In other states the pin is pulled
high.
• TMS, ADC5 – Port F, Bit 5
ADC5, Analog to Digital Converter, Channel 5.
TMS, JTAG Test mode Select: This pin is used for navigating through the TAP-controller
state machine. When the JTAG interface is enabled, this pin can not be used as an I/O
pin.
• TCK, ADC4 – Port F, Bit 4
ADC4, Analog to Digital Converter, Channel 4.
TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is enabled, this pin can not be used as an I/O pin.
• ADC3 - ADC0 – Port F, Bit 3:0
Analog to Digital Converter, Channel 3-0.
Table 36. Overriding Signals for Alternate Functions in PF7:PF4
Signal
Name
PF7/ADC7/TDI
PF6/ADC6/TDO
PF5/ADC5/TMS
PF4/ADC4/TCK
PUOE
JTAGEN
JTAGEN
JTAGEN
JTAGEN
PUOV
1
1
1
1
DDOE
JTAGEN
JTAGEN
JTAGEN
JTAGEN
DDOV
0
SHIFT_IR +
SHIFT_DR
0
0
PVOE
0
JTAGEN
0
0
PVOV
0
TDO
0
0
PTOE
–
–
–
–
DIEOE
JTAGEN
JTAGEN
JTAGEN
JTAGEN
DIEOV
0
0
0
0
DI
–
–
–
–
AIO
TDI
ADC7 INPUT
ADC6 INPUT
TMS
ADC5 INPUT
TCK
ADC4 INPUT
73
2570J–AVR–11/06
Table 37. Overriding Signals for Alternate Functions in PF3:PF0
Alternate Functions of Port G
Signal
Name
PF3/ADC3
PF2/ADC2
PF1/ADC1
PF0/ADC0
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
PTOE
–
–
–
–
DIEOE
0
0
0
0
DIEOV
0
0
0
0
DI
–
–
–
–
AIO
ADC3 INPUT
ADC2 INPUT
ADC1 INPUT
ADC0 INPUT
The alternate pin configuration is as follows:
Table 38. Port G Pins Alternate Functions
Port Pin
Note:
Alternate Function
PG5
RESET(1)
PG4
T0 (Timer/Counter0 Clock Inpu)
PG3
T1 (Timer/Counter1 Clock Input)
PG2
-
PG1
-
PG0
-
1. Port G, PG5 is input only. Pull-up is always on.
See Table 109 on page 260 for RSTDISBL fuse.
The alternate pin configuration is as follows:
• RESET – Port G, Bit 5
RESET: External Reset input. When the RSTDISBL Fuse is programmed ('0'), PG5 will
function as input with pull-up always on.
• T0 – Port G, Bit 4
T0, Timer/Counter0 Counter Source.
• T1 – Port G, Bit 3
T1, Timer/Counter1 Counter Source.
Table 38 and Table 39 relates the alternate functions of Port G to the overriding signals
shown in Figure 27 on page 64.
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ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Table 39. Overriding Signals for Alternate Functions in PG4 and PG3
Signal Name
PG4/T0
PG3/T1
PUOE
0
0
PUOV
0
0
DDOE
0
0
DDOV
0
0
PVOE
0
0
PVOV
0
0
PTOE
–
–
DIEOE
0
0
DIEOV
0
0
DI
T0 INPUT
T1 INPUT
AIO
-
-
75
2570J–AVR–11/06
Alternate Functions of Port H
Port H is only present in ATmega3250/6450. The alternate pin configuration is as
follows:
Table 40. Port H Pins Alternate Functions
Port Pin
Alternate Function
PH7
PCINT23 (Pin Change Interrupt23)
PH6
PCINT22 (Pin Change Interrupt22)
PH5
PCINT21 (Pin Change Interrupt21)
PH4
PCINT20 (Pin Change Interrupt20)
PH3
PCINT19 (Pin Change Interrupt19)
PH2
PCINT18 (Pin Change Interrupt18)
PH1
PCINT17 (Pin Change Interrupt17)
PH0
PCINT16 (Pin Change Interrupt16)
The alternate pin configuration is as follows:
• PCINT23 – Port H, Bit 7
PCINT23, Pin Change Interrupt Source 23: The PH7 pin can serve as an external interrupt source.
• PCINT22 – Port H, Bit 6
PCINT22, Pin Change Interrupt Source 22: The PH6 pin can serve as an external interrupt source.
• PCINT21 – Port H, Bit 5
PCINT21, Pin Change Interrupt Source 21: The PH5 pin can serve as an external interrupt source.
• PCINT20 – Port H, Bit 4
PCINT20, Pin Change Interrupt Source 20: The PH4 pin can serve as an external interrupt source.
• PCINT19 – Port H, Bit 3
PCINT19, Pin Change Interrupt Source 19: The PH3 pin can serve as an external interrupt source.
• PCINT18 – Port H, Bit 2
PCINT18, Pin Change Interrupt Source 18: The PH2 pin can serve as an external interrupt source.
• PCINT17 – Port H, Bit 1
PCINT17, Pin Change Interrupt Source 17: The P1 pin can serve as an external interrupt source.
• PCINT16 – Port H, Bit 0
PCINT16, Pin Change Interrupt Source 16: The PH0 pin can serve as an external interrupt source.
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Table 41 and Table 42 relates the alternate functions of Port H to the overriding signals
shown in Figure 27 on page 64.
Table 41. Overriding Signals for Alternate Functions in PH7:4
Signal
Name
PH7/PCINT23
PH6/PCINT22
PH5/PCINT21
PH4/PCINT20
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
PTOE
–
–
–
–
DIEOE
PCINT23 •
PCIE0
PCINT22 •
PCIE0
PCINT21 •
PCIE0
PCINT20 •
PCIE0
DIEOV
0
0
0
0
DI
PCINT23 INPUT
PCINT22 INPUT
PCINT21 INPUT
PCINT20 INPUT
AIO
–
–
–
–
Table 42. Overriding Signals for Alternate Functions in PH3:0
Signal
Name
PH3/PCINT19
PH2/PCINT18
PH1/PCINT17
PH0/PCINT16
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
PTOE
–
–
–
–
DIEOE
PCINT19 •
PCIE0
PCINT18 •
PCIE0
PCINT17 •
PCIE0
PCINT16 •
PCIE0
DIEOV
0
0
0
0
DI
PCINT19 INPUT
PCINT18 INPUT
PCINT17 INPUT
PCINT16 INPUT
AIO
–
–
–
–
77
2570J–AVR–11/06
Alternate Functions of Port J
Port J is only present in ATmega3250/6450. The alternate pin configuration is as
follows:
Table 43. Port J Pins Alternate Functions
Port Pin
Alternate Function
PJ6
PCINT30 (Pin Change Interrupt30)
PJ5
PCINT29 (Pin Change Interrupt29)
PJ4
PCINT28 (Pin Change Interrupt28)
PJ3
PCINT27 (Pin Change Interrupt27)
PJ2
PCINT26(Pin Change Interrupt26)
PJ1
PCINT25(Pin Change Interrupt25)
PJ0
PCINT24 (Pin Change Interrupt26)
The alternate pin configuration is as follows:
• PCINT30 – Port J, Bit 6
PCINT30, Pin Change Interrupt Source 30: The PE30 pin can serve as an external interrupt source.
• PCINT29 – Port J, Bit 5
PCINT29, Pin Change Interrupt Source 29: The PE29 pin can serve as an external interrupt source.
• PCINT28 – Port J, Bit 4
PCINT28, Pin Change Interrupt Source 28: The PE28 pin can serve as an external interrupt source.
• PCINT27 – Port J, Bit 3
PCINT27, Pin Change Interrupt Source 27: The PE27 pin can serve as an external interrupt source.
• PCINT26 – Port J, Bit 2
PCINT26, Pin Change Interrupt Source 26: The PE26 pin can serve as an external interrupt source.
• PCINT25 – Port J, Bit 1
PCINT25, Pin Change Interrupt Source 25: The PE25 pin can serve as an external interrupt source.
• PCINT24 – Port J, Bit 0
PCINT24, Pin Change Interrupt Source 24: The PE24 pin can serve as an external interrupt source.
Table 44 and Table 45 relates the alternate functions of Port J to the overriding signals
shown in Figure 27 on page 64.
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ATmega325/3250/645/6450
Table 44. Overriding Signals for Alternate Functions in PJ7:4
Signal
Name
PJ6/PCINT30
PJ5/PCINT29
PJ4/PCINT28
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
0
0
DDOV
0
0
0
PVOE
0
0
0
PVOV
0
0
0
PTOE
–
–
–
DIEOE
PCINT30 •
PCIE0
PCINT29 •
PCIE0
PCINT28 •
PCIE0
DIEOV
0
0
0
DI
–
–
–
AIO
–
–
–
Table 45. Overriding Signals for Alternate Functions in PH3:0
Signal
Name
PJ3/PCINT27
PJ2/PCINT26
PJ1/PCINT25
PJ0/PCINT24
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
0
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
0
PVOV
0
0
0
0
PTOE
–
–
–
–
DIEOE
PCINT27 •
PCIE0
PCINT26 •
PCIE0
PCINT25 •
PCIE0
PCINT24 •
PCIE0
DIEOV
0
0
0
0
DI
–
–
–
–
AIO
–
–
–
–
79
2570J–AVR–11/06
Register Description for I/O-Ports
PORTA – Port A Data Register
Bit
DDRA – Port A Data Direction
Register
PINA – Port A Input Pins
Address
7
6
5
4
3
2
1
0
0x02 (0x22)
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x01 (0x21)
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x00 (0x20)
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTA
DDRA
PINA
PORTB – Port B Data Register
Bit
DDRB – Port B Data Direction
Register
PINB – Port B Input Pins
Address
7
6
5
4
3
2
1
0
0x05 (0x25)
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x04 (0x24)
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x03 (0x23)
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTB
DDRB
PINB
PORTC – Port C Data Register
Bit
DDRC – Port C Data Direction
Register
PINC – Port C Input Pins
Address
80
7
6
5
4
3
2
1
0
0x08 (0x28)
PORTC7
PORTC6
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x07 (0x27)
DDC7
DDC6
DDC5
DDC4
DDC3
DDC2
DDC1
DDC0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x06 (0x26)
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTC
DDRC
PINC
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
PORTD – Port D Data Register
Bit
DDRD – Port D Data Direction
Register
PIND – Port D Input Pins
Address
7
6
5
4
3
2
1
0
0x0B (0x2B)
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x0A (0x2A)
DDD7
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x09 (0x29)
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTD
DDRD
PIND
PORTE – Port E Data Register
Bit
DDRE – Port E Data Direction
Register
7
6
5
4
3
2
1
0
0x0E (0x2E)
PORTE7
PORTE6
PORTE5
PORTE4
PORTE3
PORTE2
PORTE1
PORTE0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
DDE7
DDE6
DDE5
DDE4
DDE3
DDE2
DDE1
DDE0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
0x0D (0x2D)
PINE – Port E Input Pins
Address
Bit
7
6
5
4
3
2
1
0
PINE7
PINE6
PINE5
PINE4
PINE3
PINE2
PINE1
PINE0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0x0C (0x2C)
PORTE
DDRE
PINE
PORTF – Port F Data Register
Bit
DDRF – Port F Data Direction
Register
PINF – Port F Input Pins
Address
7
6
5
4
3
2
1
0
0x11 (0x31)
PORTF7
PORTF6
PORTF5
PORTF4
PORTF3
PORTF2
PORTF1
PORTF0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x10 (0x30)
DDF7
DDF6
DDF5
DDF4
DDF3
DDF2
DDF1
DDF0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x0F (0x2F)
PINF7
PINF6
PINF5
PINF4
PINF3
PINF2
PINF1
PINF0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PORTF
DDRF
PINF
81
2570J–AVR–11/06
PORTG – Port G Data Register
DDRG – Port G Data Direction
Register
PING – Port G Input Pins
Address
PORTH – Port H Data
Register(1)
Bit
7
6
5
4
3
2
1
0
0x14 (0x34)
–
–
–
PORTG4
PORTG3
PORTG2
PORTG1
PORTG0
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x13 (0x33)
–
–
–
DDG4
DDG3
DDG2
DDG1
DDG0
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
0x12 (0x32)
–
–
PING5
PING4
PING3
PING2
PING1
PING0
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
N/A
N/A
N/A
N/A
N/A
Bit
7
6
5
4
3
2
1
0
PORTH7
PORTH6
PORTH5
PORTH4
PORTH3
PORTH2
PORTH1
PORTH0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0xDA)
DDRH – Port H Data Direction
Register(1)
Bit
7
6
5
4
3
2
1
0
DDH7
DDH6
DDH5
DDH4
DDH3
DDH2
DDH1
DDH0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0xD9)
PINH – Port H Input Pins
Address(1)
Bit
7
6
5
4
3
2
1
0
PINH7
PINH6
PINH5
PINH4
PINH3
PINH2
PINH1
PINH0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
(0xD8)
PORTJ – Port J Data
Register(1)
DDRJ – Port J Data Direction
Register(1)
PINJ – Port J Input Pins
Address(1)
Bit
7
6
5
4
3
2
1
0
(0xDD)
–
PORTJ6
PORTJ5
PORTJ4
PORTJ3
PORTJ2
PORTJ1
PORTJ0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
(0xDC)
–
DDJ6
DDJ5
DDJ4
DDJ3
DDJ2
DDJ1
DDJ0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
(0xDB)
–
PINJ6
PINJ5
PINJ4
PINJ3
PINJ2
PINJ1
PINJ0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Note:
82
PORTG
DDRG
PING
PORTH
DDRH
PINH
PORTJ
DDRJ
PINJ
1. Register only available in ATmega3250/6450.
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ATmega325/3250/645/6450
8-bit Timer/Counter0
with PWM
Timer/Counter0 is a general purpose, single compare unit, 8-bit Timer/Counter module.
The main features are:
• Single Compare Unit Counter
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Frequency Generator
• External Event Counter
• 10-bit Clock Prescaler
• Overflow and Compare Match Interrupt Sources (TOV0 and OCF0A)
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 28. For the
actual placement of I/O pins, refer to “Pinout ATmega3250/6450” on page 2 and “Pinout
ATmega325/645” on page 3. CPU accessible I/O Registers, including I/O bits and I/O
pins, are shown in bold. The device-specific I/O Register and bit locations are listed in
the “8-bit Timer/Counter Register Description” on page 93.
Figure 28. 8-bit Timer/Counter Block Diagram
TCCRn
count
TOVn
(Int.Req.)
clear
Control Logic
direction
clk Tn
Clock Select
Edge
Detector
DATA BUS
BOTTOM
Tn
TOP
( From Prescaler )
Timer/Counter
TCNTn
=
=0
= 0xFF
OCn
(Int.Req.)
Waveform
Generation
OCn
OCRn
Registers
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers.
Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer
Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer
Interrupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock
source on the T0 pin. The Clock Select logic block controls which clock source and edge
the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is
inactive when no clock source is selected. The output from the Clock Select logic is
referred to as the timer clock (clkT0).
The double buffered Output Compare Register (OCR0A) is compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare
pin (OC0A). See “Output Compare Unit” on page 85. for details. The compare match
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event will also set the Compare Flag (OCF0A) which can be used to generate an Output
Compare interrupt request.
Definitions
Many register and bit references in this section are written in general form. A lower case
“n” replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the
Output Compare unit number, in this case unit A. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in Table 46 are also used extensively throughout the document.
Table 46. Definitions of Timer/Counter values.
BOTTOM
MAX
TOP
The counter reaches the BOTTOM when it becomes 0x00.
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR0A Register. The
assignment is dependent on the mode of operation.
Timer/Counter Clock
Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock
source is selected by the Clock Select logic which is controlled by the Clock Select
(CS02:0) bits located in the Timer/Counter Control Register (TCCR0A). For details on
clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on
page 97.
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.
Figure 29 shows a block diagram of the counter and its surroundings.
Figure 29. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
count
TCNTn
clear
Control Logic
clkTn
Edge
Detector
Tn
direction
( From Prescaler )
bottom
top
Signal description (internal signals):
84
count
Increment or decrement TCNT0 by 1.
direction
Select between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT0 in the following.
top
Signalize that TCNT0 has reached maximum value.
bottom
Signalize that TCNT0 has reached minimum value (zero).
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ATmega325/3250/645/6450
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT0). clkT0 can be generated from an external or internal
clock source, selected by the Clock Select bits (CS02:0). When no clock source is
selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed
by the CPU, regardless of whether clkT0 is present or not. A CPU write overrides (has
priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits
located in the Timer/Counter Control Register (TCCR0A). There are close connections
between how the counter behaves (counts) and how waveforms are generated on the
Output Compare output OC0A. For more details about advanced counting sequences
and waveform generation, see “Modes of Operation” on page 88.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation
selected by the WGM01:0 bits. TOV0 can be used for generating a CPU interrupt.
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Register
(OCR0A). Whenever TCNT0 equals OCR0A, the comparator signals a match. A match
will set the Output Compare Flag (OCF0A) at the next timer clock cycle. If enabled
(OCIE0A = 1 and Global Interrupt Flag in SREG is set), the Output Compare Flag generates an Output Compare interrupt. The OCF0A Flag is automatically cleared when the
interrupt is executed. Alternatively, the OCF0A Flag can be cleared by software by writing a logical one to its I/O bit location. The Waveform Generator uses the match signal
to generate an output according to operating mode set by the WGM01:0 bits and Compare Output mode (COM0A1:0) bits. The max and bottom signals are used by the
Waveform Generator for handling the special cases of the extreme values in some
modes of operation (See “Modes of Operation” on page 88.).
Figure 30 shows a block diagram of the Output Compare unit.
Figure 30. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator )
OCFnx (Int.Req.)
top
bottom
Waveform Generator
OCnx
FOCn
WGMn1:0
COMnX1:0
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The OCR0A Register is double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the normal and Clear Timer on Compare (CTC) modes of operation,
the double buffering is disabled. The double buffering synchronizes the update of the
OCR0 Compare Register to either top or bottom of the counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby
making the output glitch-free.
The OCR0A Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR0A Buffer Register, and if double
buffering is disabled the CPU will access the OCR0A directly.
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be
forced by writing a one to the Force Output Compare (FOC0A) bit. Forcing compare
match will not set the OCF0A Flag or reload/clear the timer, but the OC0A pin will be
updated as if a real compare match had occurred (the COM0A1:0 bits settings define
whether the OC0A pin is set, cleared or toggled).
Compare Match Blocking by
TCNT0 Write
All CPU write operations to the TCNT0 Register will block any compare match that
occur in the next timer clock cycle, even when the timer is stopped. This feature allows
OCR0A to be initialized to the same value as TCNT0 without triggering an interrupt
when the Timer/Counter clock is enabled.
Using the Output Compare
Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one
timer clock cycle, there are risks involved when changing TCNT0 when using the Output
Compare unit, independently of whether the Timer/Counter is running or not. If the value
written to TCNT0 equals the OCR0A value, the compare match will be missed, resulting
in incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is counting down.
The setup of the OC0A should be performed before setting the Data Direction Register
for the port pin to output. The easiest way of setting the OC0A value is to use the Force
Output Compare (FOC0A) strobe bits in Normal mode. The OC0A Register keeps its
value even when changing between Waveform Generation modes.
Be aware that the COM0A1:0 bits are not double buffered together with the compare
value. Changing the COM0A1:0 bits will take effect immediately.
Compare Match Output
Unit
86
The Compare Output mode (COM0A1:0) bits have two functions. The Waveform Generator uses the COM0A1:0 bits for defining the Output Compare (OC0A) state at the next
compare match. Also, the COM0A1:0 bits control the OC0A pin output source. Figure 31
shows a simplified schematic of the logic affected by the COM0A1:0 bit setting. The I/O
Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the
general I/O port control registers (DDR and PORT) that are affected by the COM0A1:0
bits are shown. When referring to the OC0A state, the reference is for the internal OC0A
Register, not the OC0A pin. If a System Reset occur, the OC0A Register is reset to “0”.
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ATmega325/3250/645/6450
Figure 31. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCn
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC0A) from the
Waveform Generator if either of the COM0A1:0 bits are set. However, the OC0A pin
direction (input or output) is still controlled by the Data Direction Register (DDR) for the
port pin. The Data Direction Register bit for the OC0A pin (DDR_OC0A) must be set as
output before the OC0A value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0A state
before the output is enabled. Note that some COM0A1:0 bit settings are reserved for
certain modes of operation. See “8-bit Timer/Counter Register Description” on page 93.
Compare Output Mode and
Waveform Generation
The Waveform Generator uses the COM0A1:0 bits differently in Normal, CTC, and
PWM modes. For all modes, setting the COM0A1:0 = 0 tells the Waveform Generator
that no action on the OC0A Register is to be performed on the next compare match. For
compare output actions in the non-PWM modes refer to Table 48 on page 94. For fast
PWM mode, refer to Table 49 on page 94, and for phase correct PWM refer to Table 50
on page 95.
A change of the COM0A1:0 bits state will have effect at the first compare match after the
bits are written. For non-PWM modes, the action can be forced to have immediate effect
by using the FOC0A strobe bits.
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Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare
pins, is defined by the combination of the Waveform Generation mode (WGM01:0) and
Compare Output mode (COM0A1:0) bits. The Compare Output mode bits do not affect
the counting sequence, while the Waveform Generation mode bits do. The COM0A1:0
bits control whether the PWM output generated should be inverted or not (inverted or
non-inverted PWM). For non-PWM modes the COM0A1:0 bits control whether the output should be set, cleared, or toggled at a compare match (See “Compare Match Output
Unit” on page 86.).
For detailed timing information refer to Figure 35, Figure 36, Figure 37 and Figure 38 in
“Timer/Counter Timing Diagrams” on page 92.
Normal Mode
The simplest mode of operation is the Normal mode (WGM01:0 = 0). In this mode the
counting direction is always up (incrementing), and no counter clear is performed. The
counter simply overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then
restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag
(TOV0) will be set in the same timer clock cycle as the TCNT0 becomes zero. The
TOV0 Flag in this case behaves like a ninth bit, except that it is only set, not cleared.
However, combined with the timer overflow interrupt that automatically clears the TOV0
Flag, the timer resolution can be increased by software. There are no special cases to
consider in the Normal mode, a new counter value can be written anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using
the Output Compare to generate waveforms in Normal mode is not recommended,
since this will occupy too much of the CPU time.
Clear Timer on Compare
Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM01:0 = 2), the OCR0A Register is used
to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for
the counter, hence also its resolution. This mode allows greater control of the compare
match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 32. The counter value
(TCNT0) increases until a compare match occurs between TCNT0 and OCR0A, and
then counter (TCNT0) is cleared.
Figure 32. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCn
(Toggle)
Period
(COMnx1:0 = 1)
1
2
3
4
An interrupt can be generated each time the counter value reaches the TOP value by
using the OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be
used for updating the TOP value. However, changing TOP to a value close to BOTTOM
when the counter is running with none or a low prescaler value must be done with care
since the CTC mode does not have the double buffering feature. If the new value written
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to OCR0A is lower than the current value of TCNT0, the counter will miss the compare
match. The counter will then have to count to its maximum value (0xFF) and wrap
around starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle
its logical level on each compare match by setting the Compare Output mode bits to toggle mode (COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the
data direction for the pin is set to output. The waveform generated will have a maximum
frequency of fOC0 = fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency
is defined by the following equation:
f clk_I/O
f OCnx = ------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnx )
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x00.
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM01:0 = 3) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM
option by its single-slope operation. The counter counts from BOTTOM to MAX then
restarts from BOTTOM. In non-inverting Compare Output mode, the Output Compare
(OC0A) is cleared on the compare match between TCNT0 and OCR0A, and set at BOTTOM. In inverting Compare Output mode, the output is set on compare match and
cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the
fast PWM mode can be twice as high as the phase correct PWM mode that use dualslope operation. This high frequency makes the fast PWM mode well suited for power
regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the MAX
value. The counter is then cleared at the following timer clock cycle. The timing diagram
for the fast PWM mode is shown in Figure 33. The TCNT0 value is in the timing diagram
shown as a histogram for illustrating the single-slope operation. The diagram includes
non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0
slopes represent compare matches between OCR0A and TCNT0.
Figure 33. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
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The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches MAX. If
the interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the
OC0A pin. Setting the COM0A1:0 bits to two will produce a non-inverted PWM and an
inverted PWM output can be generated by setting the COM0A1:0 to three (See Table 49
on page 94). The actual OC0A value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or
clearing) the OC0A Register at the compare match between OCR0A and TCNT0, and
clearing (or setting) the OC0A Register at the timer clock cycle the counter is cleared
(changes from MAX to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating
a PWM waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM,
the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A
equal to MAX will result in a constantly high or low output (depending on the polarity of
the output set by the COM0A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved
by setting OC0A to toggle its logical level on each compare match (COM0A1:0 = 1). The
waveform generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is
set to zero. This feature is similar to the OC0A toggle in CTC mode, except the double
buffer feature of the Output Compare unit is enabled in the fast PWM mode.
Phase Correct PWM Mode
The phase correct PWM mode (WGM01:0 = 1) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dualslope operation. The counter counts repeatedly from BOTTOM to MAX and then from
MAX to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC0A)
is cleared on the compare match between TCNT0 and OCR0A while counting up, and
set on the compare match while counting down. In inverting Output Compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency
than single slope operation. However, due to the symmetric feature of the dual-slope
PWM modes, these modes are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase
correct PWM mode the counter is incremented until the counter value matches MAX.
When the counter reaches MAX, it changes the count direction. The TCNT0 value will
be equal to MAX for one timer clock cycle. The timing diagram for the phase correct
PWM mode is shown on Figure 34. The TCNT0 value is in the timing diagram shown as
a histogram for illustrating the dual-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0A and TCNT0.
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Figure 34. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCn
(COMnx1:0 = 2)
OCn
(COMnx1:0 = 3)
Period
1
2
3
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The Interrupt Flag can be used to generate an interrupt each time the counter
reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on
the OC0A pin. Setting the COM0A1:0 bits to two will produce a non-inverted PWM. An
inverted PWM output can be generated by setting the COM0A1:0 to three (See Table 50
on page 95). The actual OC0A value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by clearing (or
setting) the OC0A Register at the compare match between OCR0A and TCNT0 when
the counter increments, and setting (or clearing) the OC0A Register at compare match
between OCR0A and TCNT0 when the counter decrements. The PWM frequency for
the output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = ----------------N ⋅ 510
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases when generating a
PWM waveform output in the phase correct PWM mode. If the OCR0A is set equal to
BOTTOM, the output will be continuously low and if set equal to MAX the output will be
continuously high for non-inverted PWM mode. For inverted PWM the output will have
the opposite logic values.
At the very start of period 2 in Figure 34 OCn has a transition from high to low even
though there is no Compare Match. The point of this transition is to guarantee symmetry
around BOTTOM. There are two cases that give a transition without Compare Match.
•
OCR0A changes its value from MAX, like in Figure 34. When the OCR0A value is
MAX the OCn pin value is the same as the result of a down-counting Compare
Match. To ensure symmetry around BOTTOM the OCn value at MAX must
correspond to the result of an up-counting Compare Match.
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2570J–AVR–11/06
•
Timer/Counter Timing
Diagrams
The timer starts counting from a value higher than the one in OCR0A, and for that
reason misses the Compare Match and hence the OCn change that would have
happened on the way up.
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore
shown as a clock enable signal in the following figures. The figures include information
on when Interrupt Flags are set. Figure 35 contains timing data for basic Timer/Counter
operation. The figure shows the count sequence close to the MAX value in all modes
other than phase correct PWM mode.
Figure 35. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 36 shows the same timing data, but with the prescaler enabled.
Figure 36. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 37 shows the setting of OCF0A in all modes except CTC mode.
Figure 37. Timer/Counter Timing Diagram, Setting of OCF0A, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
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Figure 38 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode.
Figure 38. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with
Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
TOP - 1
TOP
OCRnx
BOTTOM
BOTTOM + 1
TOP
OCFnx
8-bit Timer/Counter
Register Description
TCCR0A – Timer/Counter
Control Register A
Bit
7
6
5
4
3
2
1
0
0x24 (0x44)
FOC0A
WGM00
COM0A1
COM0A0
WGM01
CS02
CS01
CS00
Read/Write
W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM00 bit specifies a non-PWM mode. However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0 is written when operating in PWM mode. When writing a logical one to the
FOC0A bit, an immediate compare match is forced on the Waveform Generation unit.
The OC0A output is changed according to its COM0A1:0 bits setting. Note that the
FOC0A bit is implemented as a strobe. Therefore it is the value present in the
COM0A1:0 bits that determines the effect of the forced compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode
using OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6, 3 – WGM01:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum
(TOP) counter value, and what type of waveform generation to be used. Modes of operation supported by the Timer/Counter unit are: Normal mode, Clear Timer on Compare
match (CTC) mode, and two types of Pulse Width Modulation (PWM) modes. See Table
47 and “Modes of Operation” on page 88.
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Table 47. Waveform Generation Mode Bit Description(1)
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter
Mode of Operation
TOP
Update of
OCR0A at
TOV0 Flag
Set on
0
0
0
Normal
0xFF
Immediate
MAX
1
0
1
PWM, Phase Correct
0xFF
TOP
BOTTOM
2
1
0
CTC
OCR0A
Immediate
MAX
3
1
1
Fast PWM
0xFF
BOTTOM
MAX
Note:
1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 definitions. However, the functionality and location of these bits are compatible with
previous versions of the timer.
• Bit 5:4 – COM01:0: Compare Match Output Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the
COM0A1:0 bits are set, the OC0A output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0A pin must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM01:0 bit setting. Table 48 shows the COM0A1:0 bit functionality when the
WGM01:0 bits are set to a normal or CTC mode (non-PWM).
Table 48. Compare Output Mode, non-PWM Mode
COM0A1
COM0A0
Description
0
0
Normal port operation, OC0A disconnected.
0
1
Toggle OC0A on compare match
1
0
Clear OC0A on compare match
1
1
Set OC0A on compare match
Table 49 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast
PWM mode.
Table 49. Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
Reserved
1
0
Clear OC0A on compare match, set OC0A at BOTTOM,
(non-inverting mode)
1
1
Set OC0A on compare match, clear OC0A at BOTTOM,
(inverting mode.)
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case,
the compare match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 89 for more details.
Table 50 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to
phase correct PWM mode.
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Table 50. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
Reserved
1
0
Clear OC0A on compare match when up-counting. Set OC0A on
compare match when counting down.
1
1
Set OC0A on compare match when up-counting. Clear OC0A on
compare match when counting down.
Note:
Description
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case,
the compare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page 90 for more details.
• Bit 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 51. Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
No clock source (Timer/Counter stopped)
0
0
1
clkI/O/(No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on T0 pin. Clock on falling edge.
1
1
1
External clock source on T0 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will
clock the counter even if the pin is configured as an output. This feature allows software
control of the counting.
TCNT0 – Timer/Counter
Register
Bit
7
6
5
0x26 (0x46)
4
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to
the Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes)
the compare match on the following timer clock. Modifying the counter (TCNT0) while
the counter is running, introduces a risk of missing a compare match between TCNT0
and the OCR0A Register.
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OCR0A – Output Compare
Register A
Bit
7
6
5
0x27 (0x47)
4
3
2
1
0
OCR0A[7:0]
OCR0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared
with the counter value (TCNT0). A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the OC0A pin.
TIMSK0 – Timer/Counter 0
Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0
(0x6E)
–
–
–
–
–
–
OCIE0A
TOIE0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK0
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set (one),
the Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt
is executed if a compare match in Timer/Counter0 occurs, i.e., when the OCF0A bit is
set in the Timer/Counter 0 Interrupt Flag Register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if
an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR0.
TIFR0 – Timer/Counter 0
Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x15 (0x35)
–
–
–
–
–
–
OCF0A
TOV0
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR0
• Bit 1 – OCF0A: Output Compare Flag 0 A
The OCF0A bit is set (one) when a compare match occurs between the Timer/Counter0
and the data in OCR0A – Output Compare Register0. OCF0A is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, OCF0A is
cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0A
(Timer/Counter0 Compare match Interrupt Enable), and OCF0A are set (one), the
Timer/Counter0 Compare match Interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared
by hardware when executing the corresponding interrupt handling vector. Alternatively,
TOV0 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0
(Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set (one), the
Timer/Counter0 Overflow interrupt is executed. In phase correct PWM mode, this bit is
set when Timer/Counter0 changes counting direction at 0x00.
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Timer/Counter0 and
Timer/Counter1
Prescalers
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the
Timer/Counters can have different prescaler settings. The description below applies to
both Timer/Counter1 and Timer/Counter0.
Internal Clock Source
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 =
1). This provides the fastest operation, with a maximum Timer/Counter clock frequency
equal to system clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a clock source. The prescaled clock has a frequency of either
fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024.
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of
the Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. Since the
prescaler is not affected by the Timer/Counter’s clock select, the state of the prescaler
will have implications for situations where a prescaled clock is used. One example of
prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 >
CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to the
first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program
execution. However, care must be taken if the other Timer/Counter that shares the
same prescaler also uses prescaling. A prescaler reset will affect the prescaler period
for all Timer/Counters it is connected to.
External Clock Source
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge
detector. Figure 39 shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector logic. The registers are clocked at the positive edge of the
internal system clock (clkI/O). The latch is transparent in the high period of the internal
system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0 = 6) edge it detects.
Figure 39. T1/T0 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system
clock cycles from an edge has been applied to the T1/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T1/T0 has been stable for
at least one system clock cycle, otherwise it is a risk that a false Timer/Counter clock
pulse is generated.
Each half period of the external clock applied must be longer than one system clock
cycle to ensure correct sampling. The external clock must be guaranteed to have less
than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since
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the edge detector uses sampling, the maximum frequency of an external clock it can
detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system clock frequency and duty cycle caused by Oscillator source (crystal,
resonator, and capacitors) tolerances, it is recommended that maximum frequency of an
external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 40. Prescaler for Timer/Counter0 and Timer/Counter1(1)
clk I/O
Clear
PSR10
T0
Synchronization
T1
Synchronization
clkT1
Note:
GTCCR – General
Timer/Counter Control
Register
clkT0
1. The synchronization logic on the input pins (T1/T0) is shown in Figure 39.
Bit
7
6
5
4
3
2
1
0
0x23 (0x43)
TSM
–
–
–
–
–
PSR2
PSR10
Read/Write
R/W
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this
mode, the value that is written to the PSR2 and PSR10 bits is kept, hence keeping the
corresponding prescaler reset signals asserted. This ensures that the corresponding
Timer/Counters are halted and can be configured to the same value without the risk of
one of them advancing during configuration. When the TSM bit is written to zero, the
PSR2 and PSR10 bits are cleared by hardware, and the Timer/Counters start counting
simultaneously.
• Bit 0 – PSR10: Prescaler Reset Timer/Counter1 and Timer/Counter0
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This
bit is normally cleared immediately by hardware, except if the TSM bit is set. Note that
Timer/Counter1 and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both timers.
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16-bit
Timer/Counter1
The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave generation, and signal timing measurement. The main features are:
•
•
•
•
•
•
•
•
•
•
•
Overview
True 16-bit Design (i.e., Allows 16-bit PWM)
Two independent Output Compare Units
Double Buffered Output Compare Registers
One Input Capture Unit
Input Capture Noise Canceler
Clear Timer on Compare Match (Auto Reload)
Glitch-free, Phase Correct Pulse Width Modulator (PWM)
Variable PWM Period
Frequency Generator
External Event Counter
Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1)
Most register and bit references in this section are written in general form. A lower case
“n” replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit. However, when using the register or bit defines in a program, the precise form
must be used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 41. For the
actual placement of I/O pins, refer to “Pinout ATmega3250/6450” on page 2. CPU
accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The devicespecific I/O Register and bit locations are listed in the “16-bit Timer/Counter Register
Description” on page 120.
The PRTIM1 bit in “Power Reduction Register” on page 35 must be written to zero to
enable the Timer/Counter1 module.
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Figure 41. 16-bit Timer/Counter Block Diagram(1)
Count
Clear
Direction
TOVn
(Int.Req.)
Control Logic
clkTn
Clock Select
Edge
Detector
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCnA
DATA BUS
OCRnA
OCnB
(Int.Req.)
Fixed
TOP
Values
Waveform
Generation
=
OCRnB
OCnB
( From Analog
Comparator Ouput )
ICFn (Int.Req.)
Edge
Detector
ICRn
Noise
Canceler
ICPn
TCCRnA
Note:
Registers
TCCRnB
1. Refer to Figure 1 on page 2, “Alternate Functions of Port D” on page 69, and “Alternate Functions of Port G” on page 74for Timer/Counter1 pin placement and
description.
The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture
Register (ICR1) are all 16-bit registers. Special procedures must be followed when
accessing the 16-bit registers. These procedures are described in the section “Accessing 16-bit Registers” on page 102. The Timer/Counter Control Registers (TCCR1A/B)
are 8-bit registers and have no CPU access restrictions. Interrupt requests (abbreviated
to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register
(TIFR1). All interrupts are individually masked with the Timer Interrupt Mask Register
(TIMSK1). TIFR1 and TIMSK1 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock
source on the T1 pin. The Clock Select logic block controls which clock source and edge
the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is
inactive when no clock source is selected. The output from the Clock Select logic is
referred to as the timer clock (clkT1).
The double buffered Output Compare Registers (OCR1A/B) are compared with the
Timer/Counter value at all time. The result of the compare can be used by the Waveform
Generator to generate a PWM or variable frequency output on the Output Compare pin
(OC1A/B). See “Output Compare Units” on page 108. The compare match event will
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also set the Compare Match Flag (OCF1A/B) which can be used to generate an Output
Compare interrupt request.
The Input Capture Register can capture the Timer/Counter value at a given external
(edge triggered) event on either the Input Capture pin (ICP1) or on the Analog Comparator pins (See “Analog Comparator” on page 194.) The Input Capture unit includes a
digital filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be
defined by either the OCR1A Register, the ICR1 Register, or by a set of fixed values.
When using OCR1A as TOP value in a PWM mode, the OCR1A Register can not be
used for generating a PWM output. However, the TOP value will in this case be double
buffered allowing the TOP value to be changed in run time. If a fixed TOP value is
required, the ICR1 Register can be used as an alternative, freeing the OCR1A to be
used as PWM output.
Definitions
The following definitions are used extensively throughout the section:
Table 52. Definitions of Timer/Counter values.
Compatibility
BOTTOM
The counter reaches the BOTTOM when it becomes 0x0000.
MAX
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be one of the fixed values:
0x00FF, 0x01FF, or 0x03FF, or to the value stored in the OCR1A or ICR1 Register. The assignment is dependent of the mode of operation.
The 16-bit Timer/Counter has been updated and improved from previous versions of the
16-bit AVR Timer/Counter. This 16-bit Timer/Counter is fully compatible with the earlier
version regarding:
•
All 16-bit Timer/Counter related I/O Register address locations, including Timer
Interrupt Registers.
•
Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt
Registers.
•
Interrupt Vectors.
The following control bits have changed name, but have same functionality and register
location:
•
PWM10 is changed to WGM10.
•
PWM11 is changed to WGM11.
•
CTC1 is changed to WGM12.
The following bits are added to the 16-bit Timer/Counter Control Registers:
•
FOC1A and FOC1B are added to TCCR1C.
•
WGM13 is added to TCCR1B.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some
special cases.
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Accessing 16-bit
Registers
The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR
CPU via the 8-bit data bus. The 16-bit register must be byte accessed using two read or
write operations. Each 16-bit timer has a single 8-bit register for temporary storing of the
high byte of the 16-bit access. The same temporary register is shared between all 16-bit
registers within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write
operation. When the low byte of a 16-bit register is written by the CPU, the high byte
stored in the temporary register, and the low byte written are both copied into the 16-bit
register in the same clock cycle. When the low byte of a 16-bit register is read by the
CPU, the high byte of the 16-bit register is copied into the temporary register in the
same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the
OCR1A/B 16-bit registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read,
the low byte must be read before the high byte.
The following code examples show how to access the 16-bit Timer Registers assuming
that no interrupts updates the temporary register. The same principle can be used
directly for accessing the OCR1A/B and ICR1 Registers. Note that when using “C”, the
compiler handles the 16-bit access.
Assembly Code Examples(1)
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
C Code Examples(1)
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
Note:
1. See “About Code Examples” on page 8.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two instructions accessing the 16-bit register, and the interrupt
code updates the temporary register by accessing the same or any other of the 16-bit
Timer Registers, then the result of the access outside the interrupt will be corrupted.
Therefore, when both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during the 16-bit access.
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The following code examples show how to do an atomic read of the TCNT1 Register
contents. Reading any of the OCR1A/B or ICR1 Registers can be done by using the
same principle.
Assembly Code Example(1)
TIM16_ReadTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
unsigned int TIM16_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
__disable_interrupt();
/* Read TCNT1 into i */
i = TCNT1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
1. See “About Code Examples” on page 8.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
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The following code examples show how to do an atomic write of the TCNT1 Register
contents. Writing any of the OCR1A/B or ICR1 Registers can be done by using the
same principle.
Assembly Code Example(1)
TIM16_WriteTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TCNT1H,r17
out TCNT1L,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
void TIM16_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
__disable_interrupt();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
1. See “About Code Examples” on page 8.
The assembly code example requires that the r17:r16 register pair contains the value to
be written to TCNT1.
Reusing the Temporary High
Byte Register
104
If writing to more than one 16-bit register where the high byte is the same for all registers
written, then the high byte only needs to be written once. However, note that the same
rule of atomic operation described previously also applies in this case.
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ATmega325/3250/645/6450
Timer/Counter Clock
Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock
source is selected by the Clock Select logic which is controlled by the Clock Select
(CS12:0) bits located in the Timer/Counter control Register B (TCCR1B). For details on
clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on
page 97.
Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional
counter unit. Figure 42 shows a block diagram of the counter and its surroundings.
Figure 42. Counter Unit Block Diagram
DATA BUS
(8-bit)
TOVn
(Int.Req.)
TEMP (8-bit)
Clock Select
Count
TCNTnH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
Clear
Direction
Control Logic
clkTn
Edge
Detector
Tn
( From Prescaler )
TOP
BOTTOM
Signal description (internal signals):
Count
Increment or decrement TCNT1 by 1.
Direction
Select between increment and decrement.
Clear
Clear TCNT1 (set all bits to zero).
clkT1
Timer/Counter clock.
TOP
Signalize that TCNT1 has reached maximum value.
BOTTOM
Signalize that TCNT1 has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High
(TCNT1H) containing the upper eight bits of the counter, and Counter Low (TCNT1L)
containing the lower eight bits. The TCNT1H Register can only be indirectly accessed
by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU
accesses the high byte temporary register (TEMP). The temporary register is updated
with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with the
temporary register value when TCNT1L is written. This allows the CPU to read or write
the entire 16-bit counter value within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1 Register when the
counter is counting that will give unpredictable results. The special cases are described
in the sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT1). The clkT1 can be generated from an external or
internal clock source, selected by the Clock Select bits (CS12:0). When no clock source
is selected (CS12:0 = 0) the timer is stopped. However, the TCNT1 value can be
accessed by the CPU, independent of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the Waveform Generation mode
bits (WGM13:0) located in the Timer/Counter Control Registers A and B (TCCR1A and
TCCR1B). There are close connections between how the counter behaves (counts) and
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how waveforms are generated on the Output Compare outputs OC1x. For more details
about advanced counting sequences and waveform generation, see “Modes of Operation” on page 111.
The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation
selected by the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt.
Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events
and give them a time-stamp indicating time of occurrence. The external signal indicating
an event, or multiple events, can be applied via the ICP1 pin or alternatively, via the
analog-comparator unit. The time-stamps can then be used to calculate frequency, dutycycle, and other features of the signal applied. Alternatively the time-stamps can be
used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 43. The elements of the block diagram that are not directly a part of the Input Capture unit are gray
shaded. The small “n” in register and bit names indicates the Timer/Counter number.
Figure 43. Input Capture Unit Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
ICRnH (8-bit)
WRITE
ICRnL (8-bit)
TCNTnH (8-bit)
ICRn (16-bit Register)
ACO*
Analog
Comparator
ACIC*
TCNTnL (8-bit)
TCNTn (16-bit Counter)
ICNC
ICES
Noise
Canceler
Edge
Detector
ICFn (Int.Req.)
ICPn
When a change of the logic level (an event) occurs on the Input Capture pin (ICP1),
alternatively on the Analog Comparator output (ACO), and this change confirms to the
setting of the edge detector, a capture will be triggered. When a capture is triggered, the
16-bit value of the counter (TCNT1) is written to the Input Capture Register (ICR1). The
Input Capture Flag (ICF1) is set at the same system clock as the TCNT1 value is copied
into ICR1 Register. If enabled (ICIE1 = 1), the Input Capture Flag generates an Input
Capture interrupt. The ICF1 Flag is automatically cleared when the interrupt is executed.
Alternatively the ICF1 Flag can be cleared by software by writing a logical one to its I/O
bit location.
Reading the 16-bit value in the Input Capture Register (ICR1) is done by first reading the
low byte (ICR1L) and then the high byte (ICR1H). When the low byte is read the high
byte is copied into the high byte temporary register (TEMP). When the CPU reads the
ICR1H I/O location it will access the TEMP Register.
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The ICR1 Register can only be written when using a Waveform Generation mode that
utilizes the ICR1 Register for defining the counter’s TOP value. In these cases the
Waveform Generation mode (WGM13:0) bits must be set before the TOP value can be
written to the ICR1 Register. When writing the ICR1 Register the high byte must be written to the ICR1H I/O location before the low byte is written to ICR1L.
For more information on how to access the 16-bit registers refer to “Accessing 16-bit
Registers” on page 102.
Input Capture Trigger Source
The main trigger source for the Input Capture unit is the Input Capture pin (ICP1).
Timer/Counter1 can alternatively use the Analog Comparator output as trigger source
for the Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog Comparator Input Capture (ACIC) bit in the Analog Comparator Control
and Status Register (ACSR). Be aware that changing trigger source can trigger a capture. The Input Capture Flag must therefore be cleared after the change.
Both the Input Capture pin (ICP1) and the Analog Comparator output (ACO) inputs are
sampled using the same technique as for the T1 pin (Figure 39 on page 97). The edge
detector is also identical. However, when the noise canceler is enabled, additional logic
is inserted before the edge detector, which increases the delay by four system clock
cycles. Note that the input of the noise canceler and edge detector is always enabled
unless the Timer/Counter is set in a Waveform Generation mode that uses ICR1 to
define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP1 pin.
Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme.
The noise canceler input is monitored over four samples, and all four must be equal for
changing the output that in turn is used by the edge detector.
The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNC1) bit
in Timer/Counter Control Register B (TCCR1B). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied to the input, to
the update of the ICR1 Register. The noise canceler uses the system clock and is therefore not affected by the prescaler.
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor
capacity for handling the incoming events. The time between two events is critical. If the
processor has not read the captured value in the ICR1 Register before the next event
occurs, the ICR1 will be overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICR1 Register should be read as early in the
interrupt handler routine as possible. Even though the Input Capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the maximum
number of clock cycles it takes to handle any of the other interrupt requests.
Using the Input Capture unit in any mode of operation when the TOP value (resolution)
is actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed
after each capture. Changing the edge sensing must be done as early as possible after
the ICR1 Register has been read. After a change of the edge, the Input Capture Flag
(ICF1) must be cleared by software (writing a logical one to the I/O bit location). For
measuring frequency only, the clearing of the ICF1 Flag is not required (if an interrupt
handler is used).
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Output Compare Units
The 16-bit comparator continuously compares TCNT1 with the Output Compare Register (OCR1x). If TCNT equals OCR1x the comparator signals a match. A match will set
the Output Compare Flag (OCF1x) at the next timer clock cycle. If enabled (OCIE1x =
1), the Output Compare Flag generates an Output Compare interrupt. The OCF1x Flag
is automatically cleared when the interrupt is executed. Alternatively the OCF1x Flag
can be cleared by software by writing a logical one to its I/O bit location. The Waveform
Generator uses the match signal to generate an output according to operating mode set
by the Waveform Generation mode (WGM13:0) bits and Compare Output mode
(COM1x1:0) bits. The TOP and BOTTOM signals are used by the Waveform Generator
for handling the special cases of the extreme values in some modes of operation (See
“Modes of Operation” on page 111.)
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP
value (i.e., counter resolution). In addition to the counter resolution, the TOP value
defines the period time for waveforms generated by the Waveform Generator.
Figure 44 shows a block diagram of the Output Compare unit. The small “n” in the register and bit names indicates the device number (n = 1 for Timer/Counter 1), and the “x”
indicates Output Compare unit (A/B). The elements of the block diagram that are not
directly a part of the Output Compare unit are gray shaded.
Figure 44. Output Compare Unit, Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
OCRnxH Buf. (8-bit)
OCRnxL Buf. (8-bit)
TCNTnH (8-bit)
OCRnx Buffer (16-bit Register)
OCRnxH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
OCRnxL (8-bit)
OCRnx (16-bit Register)
= (16-bit Comparator )
OCFnx (Int.Req.)
TOP
BOTTOM
Waveform Generator
WGMn3:0
OCnx
COMnx1:0
The OCR1x Register is double buffered when using any of the twelve Pulse Width Modulation (PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of
operation, the double buffering is disabled. The double buffering synchronizes the
update of the OCR1x Compare Register to either TOP or BOTTOM of the counting
sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical
PWM pulses, thereby making the output glitch-free.
The OCR1x Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR1x Buffer Register, and if double
buffering is disabled the CPU will access the OCR1x directly. The content of the OCR1x
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(Buffer or Compare) Register is only changed by a write operation (the Timer/Counter
does not update this register automatically as the TCNT1 and ICR1 Register). Therefore
OCR1x is not read via the high byte temporary register (TEMP). However, it is a good
practice to read the low byte first as when accessing other 16-bit registers. Writing the
OCR1x Registers must be done via the TEMP Register since the compare of all 16 bits
is done continuously. The high byte (OCR1xH) has to be written first. When the high
byte I/O location is written by the CPU, the TEMP Register will be updated by the value
written. Then when the low byte (OCR1xL) is written to the lower eight bits, the high byte
will be copied into the upper 8-bits of either the OCR1x buffer or OCR1x Compare Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit
Registers” on page 102.
Force Output Compare
In non-PWM Waveform Generation modes, the match output of the comparator can be
forced by writing a one to the Force Output Compare (FOC1x) bit. Forcing compare
match will not set the OCF1x Flag or reload/clear the timer, but the OC1x pin will be
updated as if a real compare match had occurred (the COM11:0 bits settings define
whether the OC1x pin is set, cleared or toggled).
Compare Match Blocking by
TCNT1 Write
All CPU writes to the TCNT1 Register will block any compare match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR1x to be
initialized to the same value as TCNT1 without triggering an interrupt when the
Timer/Counter clock is enabled.
Using the Output Compare
Unit
Since writing TCNT1 in any mode of operation will block all compare matches for one
timer clock cycle, there are risks involved when changing TCNT1 when using any of the
Output Compare units, independent of whether the Timer/Counter is running or not. If
the value written to TCNT1 equals the OCR1x value, the compare match will be missed,
resulting in incorrect waveform generation. Do not write the TCNT1 equal to TOP in
PWM modes with variable TOP values. The compare match for the TOP will be ignored
and the counter will continue to 0xFFFF. Similarly, do not write the TCNT1 value equal
to BOTTOM when the counter is counting down.
The setup of the OC1x should be performed before setting the Data Direction Register
for the port pin to output. The easiest way of setting the OC1x value is to use the Force
Output Compare (FOC1x) strobe bits in Normal mode. The OC1x Register keeps its
value even when changing between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare
value. Changing the COM1x1:0 bits will take effect immediately.
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Compare Match Output
Unit
The Compare Output mode (COM1x1:0) bits have two functions. The Waveform Generator uses the COM1x1:0 bits for defining the Output Compare (OC1x) state at the next
compare match. Secondly the COM1x1:0 bits control the OC1x pin output source. Figure 45 shows a simplified schematic of the logic affected by the COM1x1:0 bit setting.
The I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of
the general I/O Port Control Registers (DDR and PORT) that are affected by the
COM1x1:0 bits are shown. When referring to the OC1x state, the reference is for the
internal OC1x Register, not the OC1x pin. If a system reset occur, the OC1x Register is
reset to “0”.
Figure 45. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC1x) from the
Waveform Generator if either of the COM1x1:0 bits are set. However, the OC1x pin
direction (input or output) is still controlled by the Data Direction Register (DDR) for the
port pin. The Data Direction Register bit for the OC1x pin (DDR_OC1x) must be set as
output before the OC1x value is visible on the pin. The port override function is generally
independent of the Waveform Generation mode, but there are some exceptions. Refer
to Table 53, Table 54 and Table 55 for details.
The design of the Output Compare pin logic allows initialization of the OC1x state before
the output is enabled. Note that some COM1x1:0 bit settings are reserved for certain
modes of operation. See “16-bit Timer/Counter Register Description” on page 120.
The COM1x1:0 bits have no effect on the Input Capture unit.
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Compare Output Mode and
Waveform Generation
The Waveform Generator uses the COM1x1:0 bits differently in normal, CTC, and PWM
modes. For all modes, setting the COM1x1:0 = 0 tells the Waveform Generator that no
action on the OC1x Register is to be performed on the next compare match. For compare output actions in the non-PWM modes refer to Table 53 on page 120. For fast
PWM mode refer to Table 54 on page 121, and for phase correct and phase and frequency correct PWM refer to Table 55 on page 121.
A change of the COM1x1:0 bits state will have effect at the first compare match after the
bits are written. For non-PWM modes, the action can be forced to have immediate effect
by using the FOC1x strobe bits.
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare
pins, is defined by the combination of the Waveform Generation mode (WGM13:0) and
Compare Output mode (COM1x1:0) bits. The Compare Output mode bits do not affect
the counting sequence, while the Waveform Generation mode bits do. The COM1x1:0
bits control whether the PWM output generated should be inverted or not (inverted or
non-inverted PWM). For non-PWM modes the COM1x1:0 bits control whether the output should be set, cleared or toggle at a compare match (See “Compare Match Output
Unit” on page 110.)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 118.
Normal Mode
The simplest mode of operation is the Normal mode (WGM13:0 = 0). In this mode the
counting direction is always up (incrementing), and no counter clear is performed. The
counter simply overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and
then restarts from the BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOV1) will be set in the same timer clock cycle as the TCNT1 becomes zero.
The TOV1 Flag in this case behaves like a 17th bit, except that it is only set, not cleared.
However, combined with the timer overflow interrupt that automatically clears the TOV1
Flag, the timer resolution can be increased by software. There are no special cases to
consider in the Normal mode, a new counter value can be written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum interval between the external events must not exceed the resolution of the counter.
If the interval between events are too long, the timer overflow interrupt or the prescaler
must be used to extend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using
the Output Compare to generate waveforms in Normal mode is not recommended,
since this will occupy too much of the CPU time.
Clear Timer on Compare
Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1
Register are used to manipulate the counter resolution. In CTC mode the counter is
cleared to zero when the counter value (TCNT1) matches either the OCR1A (WGM13:0
= 4) or the ICR1 (WGM13:0 = 12). The OCR1A or ICR1 define the top value for the
counter, hence also its resolution. This mode allows greater control of the compare
match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 46. The counter value
(TCNT1) increases until a compare match occurs with either OCR1A or ICR1, and then
counter (TCNT1) is cleared.
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Figure 46. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnA
(Toggle)
Period
(COMnA1:0 = 1)
1
2
3
4
An interrupt can be generated at each time the counter value reaches the TOP value by
either using the OCF1A or ICF1 Flag according to the register used to define the TOP
value. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing the TOP to a value close to BOTTOM when the
counter is running with none or a low prescaler value must be done with care since the
CTC mode does not have the double buffering feature. If the new value written to
OCR1A or ICR1 is lower than the current value of TCNT1, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFFFF) and
wrap around starting at 0x0000 before the compare match can occur. In many cases
this feature is not desirable. An alternative will then be to use the fast PWM mode using
OCR1A for defining TOP (WGM13:0 = 15) since the OCR1A then will be double
buffered.
For generating a waveform output in CTC mode, the OC1A output can be set to toggle
its logical level on each compare match by setting the Compare Output mode bits to toggle mode (COM1A1:0 = 1). The OC1A value will not be visible on the port pin unless the
data direction for the pin is set to output (DDR_OC1A = 1). The waveform generated will
have a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The
waveform frequency is defined by the following equation:
f clk_I/O
f OCnA = -------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnA )
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV1 Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x0000.
Fast PWM Mode
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The fast Pulse Width Modulation or fast PWM mode (WGM13:0 = 5, 6, 7, 14, or 15) provides a high frequency PWM waveform generation option. The fast PWM differs from
the other PWM options by its single-slope operation. The counter counts from BOTTOM
to TOP then restarts from BOTTOM. In non-inverting Compare Output mode, the Output
Compare (OC1x) is cleared on the compare match between TCNT1 and OCR1x, and
set at BOTTOM. In inverting Compare Output mode output is set on compare match and
cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the
fast PWM mode can be twice as high as the phase correct and phase and frequency
correct PWM modes that use dual-slope operation. This high frequency makes the fast
PWM mode well suited for power regulation, rectification, and DAC applications. High
frequency allows physically small sized external components (coils, capacitors), hence
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The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either
ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to
0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM
resolution in bits can be calculated by using the following equation:
log ( TOP + 1 )
R FPWM = ---------------------------------log ( 2 )
In fast PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in
ICR1 (WGM13:0 = 14), or the value in OCR1A (WGM13:0 = 15). The counter is then
cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is
shown in Figure 47. The figure shows fast PWM mode when OCR1A or ICR1 is used to
define TOP. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and inverted PWM
outputs. The small horizontal line marks on the TCNT1 slopes represent compare
matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be set when a compare match occurs.
Figure 47. Fast PWM Mode, Timing Diagram
OCRnx / TOP Update
and TOVn Interrupt Flag
Set and OCnA Interrupt
Flag Set or ICFn
Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
8
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. In
addition the OC1A or ICF1 Flag is set at the same timer clock cycle as TOV1 is set
when either OCR1A or ICR1 is used for defining the TOP value. If one of the interrupts
are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is
higher or equal to the value of all of the Compare Registers. If the TOP value is lower
than any of the Compare Registers, a compare match will never occur between the
TCNT1 and the OCR1x. Note that when using fixed TOP values the unused bits are
masked to zero when any of the OCR1x Registers are written.
The procedure for updating ICR1 differs from updating OCR1A when used for defining
the TOP value. The ICR1 Register is not double buffered. This means that if ICR1 is
changed to a low value when the counter is running with none or a low prescaler value,
there is a risk that the new ICR1 value written is lower than the current value of TCNT1.
The result will then be that the counter will miss the compare match at the TOP value.
The counter will then have to count to the MAX value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. The OCR1A Register however, is
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double buffered. This feature allows the OCR1A I/O location to be written anytime.
When the OCR1A I/O location is written the value written will be put into the OCR1A
Buffer Register. The OCR1A Compare Register will then be updated with the value in
the Buffer Register at the next timer clock cycle the TCNT1 matches TOP. The update is
done at the same timer clock cycle as the TCNT1 is cleared and the TOV1 Flag is set.
Using the ICR1 Register for defining TOP works well when using fixed TOP values. By
using ICR1, the OCR1A Register is free to be used for generating a PWM output on
OC1A. However, if the base PWM frequency is actively changed (by changing the TOP
value), using the OCR1A as TOP is clearly a better choice due to its double buffer
feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the
OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and an
inverted PWM output can be generated by setting the COM1x1:0 to three (see Table 54
on page 121). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by
setting (or clearing) the OC1x Register at the compare match between OCR1x and
TCNT1, and clearing (or setting) the OC1x Register at the timer clock cycle the counter
is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ---------------------------------N ⋅ ( 1 + TOP )
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represents special cases when generating
a PWM waveform output in the fast PWM mode. If the OCR1x is set equal to BOTTOM
(0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle. Setting the
OCR1x equal to TOP will result in a constant high or low output (depending on the polarity of the output set by the COM1x1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved
by setting OC1A to toggle its logical level on each compare match (COM1A1:0 = 1).
This applies only if OCR1A is used to define the TOP value (WGM13:0 = 15). The waveform generated will have a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to
zero (0x0000). This feature is similar to the OC1A toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGM13:0 = 1,
2, 3, 10, or 11) provides a high resolution phase correct PWM waveform generation
option. The phase correct PWM mode is, like the phase and frequency correct PWM
mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output
mode, the Output Compare (OC1x) is cleared on the compare match between TCNT1
and OCR1x while counting up, and set on the compare match while counting down. In
inverting Output Compare mode, the operation is inverted. The dual-slope operation has
lower maximum operation frequency than single slope operation. However, due to the
symmetric feature of the dual-slope PWM modes, these modes are preferred for motor
control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or
defined by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or
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OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to
MAX). The PWM resolution in bits can be calculated by using the following equation:
( TOP + 1 )
R PCPWM = log
----------------------------------log ( 2 )
In phase correct PWM mode the counter is incremented until the counter value matches
either one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the
value in ICR1 (WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter
has then reached the TOP and changes the count direction. The TCNT1 value will be
equal to TOP for one timer clock cycle. The timing diagram for the phase correct PWM
mode is shown on Figure 48. The figure shows phase correct PWM mode when OCR1A
or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram shown as a
histogram for illustrating the dual-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be
set when a compare match occurs.
Figure 48. Phase Correct PWM Mode, Timing Diagram
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM. When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or
ICF1 Flag is set accordingly at the same timer clock cycle as the OCR1x Registers are
updated with the double buffer value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is
higher or equal to the value of all of the Compare Registers. If the TOP value is lower
than any of the Compare Registers, a compare match will never occur between the
TCNT1 and the OCR1x. Note that when using fixed TOP values, the unused bits are
masked to zero when any of the OCR1x Registers are written. As the third period shown
in Figure 48 illustrates, changing the TOP actively while the Timer/Counter is running in
the phase correct mode can result in an unsymmetrical output. The reason for this can
be found in the time of update of the OCR1x Register. Since the OCR1x update occurs
at TOP, the PWM period starts and ends at TOP. This implies that the length of the fall-
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ing slope is determined by the previous TOP value, while the length of the rising slope is
determined by the new TOP value. When these two values differ the two slopes of the
period will differ in length. The difference in length gives the unsymmetrical result on the
output.
It is recommended to use the phase and frequency correct mode instead of the phase
correct mode when changing the TOP value while the Timer/Counter is running. When
using a static TOP value there are practically no differences between the two modes of
operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on
the OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and
an inverted PWM output can be generated by setting the COM1x1:0 to three (See Table
1 on page 121). The actual OC1x value will only be visible on the port pin if the data
direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at the compare match between OCR1x
and TCNT1 when the counter increments, and clearing (or setting) the OC1x Register at
compare match between OCR1x and TCNT1 when the counter decrements. The PWM
frequency for the output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = --------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represent special cases when generating a
PWM waveform output in the phase correct PWM mode. If the OCR1x is set equal to
BOTTOM the output will be continuously low and if set equal to TOP the output will be
continuously high for non-inverted PWM mode. For inverted PWM the output will have
the opposite logic values. If OCR1A is used to define the TOP value (WGM13:0 = 11)
and COM1A1:0 = 1, the OC1A output will toggle with a 50% duty cycle.
Phase and Frequency Correct
PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM mode (WGM13:0 = 8 or 9) provides a high resolution phase and frequency
correct PWM waveform generation option. The phase and frequency correct PWM
mode is, like the phase correct PWM mode, based on a dual-slope operation. The
counter counts repeatedly from BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC1x) is cleared
on the compare match between TCNT1 and OCR1x while counting up, and set on the
compare match while counting down. In inverting Compare Output mode, the operation
is inverted. The dual-slope operation gives a lower maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the dualslope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct
PWM mode is the time the OCR1x Register is updated by the OCR1x Buffer Register,
(see Figure 48 and Figure 49).
The PWM resolution for the phase and frequency correct PWM mode can be defined by
either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to
0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM
resolution in bits can be calculated using the following equation:
log ( TOP + 1 )
R PFCPWM = ----------------------------------log ( 2 )
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In phase and frequency correct PWM mode the counter is incremented until the counter
value matches either the value in ICR1 (WGM13:0 = 8), or the value in OCR1A
(WGM13:0 = 9). The counter has then reached the TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The timing
diagram for the phase correct and frequency correct PWM mode is shown on Figure 49.
The figure shows phase and frequency correct PWM mode when OCR1A or ICR1 is
used to define TOP. The TCNT1 value is in the timing diagram shown as a histogram for
illustrating the dual-slope operation. The diagram includes non-inverted and inverted
PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare
matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be set when a compare match occurs.
Figure 49. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/TOP Updateand
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOV1) is set at the same timer clock cycle as the
OCR1x Registers are updated with the double buffer value (at BOTTOM). When either
OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 Flag set when
TCNT1 has reached TOP. The Interrupt Flags can then be used to generate an interrupt
each time the counter reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is
higher or equal to the value of all of the Compare Registers. If the TOP value is lower
than any of the Compare Registers, a compare match will never occur between the
TCNT1 and the OCR1x.
As Figure 49 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the OCR1x Registers are updated at BOTTOM, the length
of the rising and the falling slopes will always be equal. This gives symmetrical output
pulses and is therefore frequency correct.
Using the ICR1 Register for defining TOP works well when using fixed TOP values. By
using ICR1, the OCR1A Register is free to be used for generating a PWM output on
OC1A. However, if the base PWM frequency is actively changed by changing the TOP
value, using the OCR1A as TOP is clearly a better choice due to its double buffer
feature.
In phase and frequency correct PWM mode, the compare units allow generation of
PWM waveforms on the OC1x pins. Setting the COM1x1:0 bits to two will produce a
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non-inverted PWM and an inverted PWM output can be generated by setting the
COM1x1:0 to three (See Table 1 on page 121). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OC1x). The
PWM waveform is generated by setting (or clearing) the OC1x Register at the compare
match between OCR1x and TCNT1 when the counter increments, and clearing (or setting) the OC1x Register at compare match between OCR1x and TCNT1 when the
counter decrements. The PWM frequency for the output when using phase and frequency correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPFCPWM = --------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represents special cases when generating
a PWM waveform output in the phase correct PWM mode. If the OCR1x is set equal to
BOTTOM the output will be continuously low and if set equal to TOP the output will be
set to high for non-inverted PWM mode. For inverted PWM the output will have the
opposite logic values. If OCR1A is used to define the TOP value (WGM13:0 = 9) and
COM1A1:0 = 1, the OC1A output will toggle with a 50% duty cycle.
Timer/Counter Timing
Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT1) is therefore
shown as a clock enable signal in the following figures. The figures include information
on when Interrupt Flags are set, and when the OCR1x Register is updated with the
OCR1x buffer value (only for modes utilizing double buffering). Figure 50 shows a timing
diagram for the setting of OCF1x.
Figure 50. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 51 shows the same timing data, but with the prescaler enabled.
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Figure 51. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCRnx
OCFnx
Figure 52 shows the count sequence close to TOP in various modes. When using phase
and frequency correct PWM mode the OCR1x Register is updated at BOTTOM. The
timing diagrams will be the same, but TOP should be replaced by BOTTOM, TOP-1 by
BOTTOM+1 and so on. The same renaming applies for modes that set the TOV1 Flag
at BOTTOM.
Figure 52. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
Old OCRnx Value
New OCRnx Value
Figure 53 shows the same timing data, but with the prescaler enabled.
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Figure 53. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICF n (if used
as TOP)
OCRnx
Old OCRnx Value
(Update at TOP)
New OCRnx Value
16-bit Timer/Counter
Register Description
TCCR1A – Timer/Counter1
Control Register A
Bit
7
6
5
4
3
2
1
0
COM1A1
COM1A0
COM1B1
COM1B0
–
–
WGM11
WGM10
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x80)
TCCR1A
• Bit 7:6 – COM1A1:0: Compare Output Mode for Unit A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Unit B
The COM1A1:0 and COM1B1:0 control the Output Compare pins (OC1A and OC1B
respectively) behavior. If one or both of the COM1A1:0 bits are written to one, the OC1A
output overrides the normal port functionality of the I/O pin it is connected to. If one or
both of the COM1B1:0 bit are written to one, the OC1B output overrides the normal port
functionality of the I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to the OC1A or OC1B pin must be set in order to enable
the output driver.
When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is
dependent of the WGM13:0 bits setting. Table 53 shows the COM1x1:0 bit functionality
when the WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 53. Compare Output Mode, non-PWM
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COM1A1/COM1B1
COM1A0/COM1B0
Description
0
0
Normal port operation, OC1A/OC1B
disconnected.
0
1
Toggle OC1A/OC1B on Compare Match.
1
0
Clear OC1A/OC1B on Compare Match (Set
output to low level).
1
1
Set OC1A/OC1B on Compare Match (Set output
to high level).
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Table 54 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the
fast PWM mode.
Table 54. Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1
COM1A0/COM1B0
0
0
Normal port operation, OC1A/OC1B
disconnected.
0
1
WGM13:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation). For all other WGM1 settings, normal
port operation, OC1A/OC1B disconnected.
1
0
Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at BOTTOM (non-inverting mode).
1
1
Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at BOTTOM (inverting mode).
Note:
Description
1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is
set. In this case the compare match is ignored, but the set or clear is done at BOTTOM. See “Fast PWM Mode” on page 112. for more details.
Table 55 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the
phase correct or the phase and frequency correct, PWM mode.
Table 55. Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
COM1A1/COM1B1
COM1A0/COM1B0
0
0
Normal port operation, OC1A/OC1B
disconnected.
0
1
WGM13:0 = 9 or 11: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation). For all other WGM1 settings, normal
port operation, OC1A/OC1B disconnected.
1
0
Clear OC1A/OC1B on Compare Match when upcounting. Set OC1A/OC1B on Compare Match
when counting down.
1
1
Set OC1A/OC1B on Compare Match when upcounting. Clear OC1A/OC1B on Compare Match
when counting down.
Note:
Description
1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is
set. See “Phase Correct PWM Mode” on page 114. for more details.
• Bit 1:0 – WGM11:0: Waveform Generation Mode
Combined with the WGM13:2 bits found in the TCCR1B Register, these bits control the
counting sequence of the counter, the source for maximum (TOP) counter value, and
what type of waveform generation to be used, see Table 56. Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare
match (CTC) mode, and three types of Pulse Width Modulation (PWM) modes. (See
“Modes of Operation” on page 111.).
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Table 56. Waveform Generation Mode Bit Description(1)
Mode
WGM13
WGM12
(CTC1)
WGM11
(PWM11)
WGM10
(PWM10)
Timer/Counter Mode of
Operation
TOP
Update of
OCR1x at
TOV1 Flag
Set on
0
0
0
0
0
Normal
0xFFFF
Immediate
MAX
1
0
0
0
1
PWM, Phase Correct, 8-bit
0x00FF
TOP
BOTTOM
2
0
0
1
0
PWM, Phase Correct, 9-bit
0x01FF
TOP
BOTTOM
3
0
0
1
1
PWM, Phase Correct, 10-bit
0x03FF
TOP
BOTTOM
4
0
1
0
0
CTC
OCR1A
Immediate
MAX
5
0
1
0
1
Fast PWM, 8-bit
0x00FF
BOTTOM
TOP
6
0
1
1
0
Fast PWM, 9-bit
0x01FF
BOTTOM
TOP
7
0
1
1
1
Fast PWM, 10-bit
0x03FF
BOTTOM
TOP
8
1
0
0
0
PWM, Phase and Frequency
Correct
ICR1
BOTTOM
BOTTOM
9
1
0
0
1
PWM, Phase and Frequency
Correct
OCR1A
BOTTOM
BOTTOM
10
1
0
1
0
PWM, Phase Correct
ICR1
TOP
BOTTOM
11
1
0
1
1
PWM, Phase Correct
OCR1A
TOP
BOTTOM
12
1
1
0
0
CTC
ICR1
Immediate
MAX
13
1
1
0
1
(Reserved)
–
–
–
14
1
1
1
0
Fast PWM
ICR1
BOTTOM
TOP
15
1
1
1
1
Fast PWM
OCR1A
BOTTOM
TOP
Note:
1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
TCCR1B – Timer/Counter1
Control Register B
Bit
7
6
5
4
3
2
1
0
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x81)
TCCR1B
• Bit 7 – ICNC1: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is activated, the input from the Input Capture pin (ICP1) is filtered. The filter
function requires four successive equal valued samples of the ICP1 pin for changing its
output. The Input Capture is therefore delayed by four Oscillator cycles when the noise
canceler is enabled.
• Bit 6 – ICES1: Input Capture Edge Select
This bit selects which edge on the Input Capture pin (ICP1) that is used to trigger a capture event. When the ICES1 bit is written to zero, a falling (negative) edge is used as
trigger, and when the ICES1 bit is written to one, a rising (positive) edge will trigger the
capture.
When a capture is triggered according to the ICES1 setting, the counter value is copied
into the Input Capture Register (ICR1). The event will also set the Input Capture Flag
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(ICF1), and this can be used to cause an Input Capture Interrupt, if this interrupt is
enabled.
When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in
the TCCR1A and the TCCR1B Register), the ICP1 is disconnected and consequently
the Input Capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit
must be written to zero when TCCR1B is written.
• Bit 4:3 – WGM13:2: Waveform Generation Mode
See TCCR1A Register description.
• Bit 2:0 – CS12:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Figure 50 and Figure 51.
Table 57. Clock Select Bit Description
CS12
CS11
CS10
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clkI/O/1 (No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on T1 pin. Clock on falling edge.
1
1
1
External clock source on T1 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will
clock the counter even if the pin is configured as an output. This feature allows software
control of the counting.
TCCR1C – Timer/Counter1
Control Register C
Bit
7
6
5
4
3
2
1
FOC1A
FOC1B
–
–
–
–
–
–
Read/Write
R/W
R/W
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
(0x82)
0
TCCR1C
• Bit 7 – FOC1A: Force Output Compare for Unit A
• Bit 6 – FOC1B: Force Output Compare for Unit B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM
mode. However, for ensuring compatibility with future devices, these bits must be set to
zero when TCCR1A is written when operating in a PWM mode. When writing a logical
one to the FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform
Generation unit. The OC1A/OC1B output is changed according to its COM1x1:0 bits
setting. Note that the FOC1A/FOC1B bits are implemented as strobes. Therefore it is
the value present in the COM1x1:0 bits that determine the effect of the forced compare.
A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in Clear
Timer on Compare match (CTC) mode using OCR1A as TOP. The FOC1A/FOC1B bits
are always read as zero.
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TCNT1H and TCNT1L –
Timer/Counter1
Bit
7
6
5
4
3
(0x85)
TCNT1[15:8]
(0x84)
TCNT1[7:0]
2
1
0
TCNT1H
TCNT1L
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give
direct access, both for read and for write operations, to the Timer/Counter unit 16-bit
counter. To ensure that both the high and low bytes are read and written simultaneously
when the CPU accesses these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 102.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing
a compare match between TCNT1 and one of the OCR1x Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following
timer clock for all compare units.
OCR1AH and OCR1AL –
Output Compare Register 1 A
OCR1BH and OCR1BL –
Output Compare Register 1 B
Bit
7
6
5
4
3
(0x89)
OCR1A[15:8]
(0x88)
OCR1A[7:0]
2
1
0
OCR1AH
OCR1AL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
(0x8B)
OCR1B[15:8]
(0x8A)
OCR1B[7:0]
OCR1BH
OCR1BL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Registers contain a 16-bit value that is continuously compared
with the counter value (TCNT1). A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the OC1x pin.
The Output Compare Registers are 16-bit in size. To ensure that both the high and low
bytes are written simultaneously when the CPU writes to these registers, the access is
performed using an 8-bit temporary High Byte Register (TEMP). This temporary register
is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 102.
ICR1H and ICR1L – Input
Capture Register 1
Bit
7
6
5
4
3
(0x87)
ICR1[15:8]
(0x86)
ICR1[7:0]
2
1
0
ICR1H
ICR1L
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Input Capture is updated with the counter (TCNT1) value each time an event occurs
on the ICP1 pin (or optionally on the Analog Comparator output for Timer/Counter1).
The Input Capture can be used for defining the counter TOP value.
The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes
are read simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is
shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 102.
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TIMSK1 – Timer/Counter1
Interrupt Mask Register
Bit
7
6
5
4
3
2
1
0
(0x6F)
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK1
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Input Capture interrupt is enabled. The
corresponding Interrupt Vector (See “Interrupts” on page 48.) is executed when the
ICF1 Flag, located in TIFR1, is set.
• Bit 2 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Output Compare B Match interrupt is enabled. The
corresponding Interrupt Vector (See “Interrupts” on page 48.) is executed when the
OCF1B Flag, located in TIFR1, is set.
• Bit 1 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Output Compare A Match interrupt is enabled. The
corresponding Interrupt Vector (See “Interrupts” on page 48.) is executed when the
OCF1A Flag, located in TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Overflow interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 48.) is executed when the TOV1 Flag, located
in TIFR1, is set.
TIFR1 – Timer/Counter1
Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x16 (0x36)
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR1
• Bit 5 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture
Register (ICR1) is set by the WGM13:0 to be used as the TOP value, the ICF1 Flag is
set when the counter reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively, ICF1 can be cleared by writing a logic one to its bit location.
• Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output Compare Register B (OCR1B).
Note that a Forced Output Compare (FOC1B) strobe will not set the OCF1B Flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is
executed. Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
• Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output Compare Register A (OCR1A).
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Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is
executed. Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGM13:0 bits setting. In Normal and CTC
modes, the TOV1 Flag is set when the timer overflows. Refer to Table 56 on page 122
for the TOV1 Flag behavior when using another WGM13:0 bit setting.
TOV1 is automatically cleared when the Timer/Counter1 Overflow Interrupt Vector is
executed. Alternatively, TOV1 can be cleared by writing a logic one to its bit location.
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ATmega325/3250/645/6450
8-bit Timer/Counter2
with PWM and
Asynchronous
Operation
Timer/Counter2 is a general purpose, single compare unit, 8-bit Timer/Counter module.
The main features are:
• Single Compare Unit Counter
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Frequency Generator
• 10-bit Clock Prescaler
• Overflow and Compare Match Interrupt Sources (TOV2 and OCF2A)
• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 54. For the
actual placement of I/O pins, refer to “Pinout ATmega3250/6450” on page 2. CPU
accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The devicespecific I/O Register and bit locations are listed in the “8-bit Timer/Counter Register
Description” on page 138.
Figure 54. 8-bit Timer/Counter Block Diagram
TCCRnx
count
TOVn
(Int.Req.)
clear
Control Logic
direction
clkTn
TOSC1
BOTTOM
TOP
Prescaler
T/C
Oscillator
TOSC2
Timer/Counter
TCNTn
=0
= 0xFF
OCnx
(Int.Req.)
Waveform
Generation
=
clkI/O
OCnx
DATA BUS
OCRnx
Synchronized Status flags
clkI/O
Synchronization Unit
clkASY
Status flags
ASSRn
asynchronous mode
select (ASn)
Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers.
Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag
Register (TIFR2). All interrupts are individually masked with the Timer Interrupt Mask
Register (TIMSK2). TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously
clocked from the TOSC1/2 pins, as detailed later in this section. The asynchronous
operation is controlled by the Asynchronous Status Register (ASSR). The Clock Select
logic block controls which clock source the Timer/Counter uses to increment (or decre-
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ment) its value. The Timer/Counter is inactive when no clock source is selected. The
output from the Clock Select logic is referred to as the timer clock (clkT2).
The double buffered Output Compare Register (OCR2A) is compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare
pin (OC2A). See “Output Compare Unit” on page 129. for details. The compare match
event will also set the Compare Flag (OCF2A) which can be used to generate an Output
Compare interrupt request.
Definitions
Many register and bit references in this document are written in general form. A lower
case “n” replaces the Timer/Counter number, in this case 2. However, when using the
register or bit defines in a program, the precise form must be used, i.e., TCNT2 for
accessing Timer/Counter2 counter value and so on.
The definitions in Table 58 are also used extensively throughout the section.
Table 58. Definitions of Timer/Counter values.
BOTTOM
MAX
TOP
The counter reaches the BOTTOM when it becomes zero (0x00).
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR2A Register. The
assignment is dependent on the mode of operation.
Timer/Counter Clock
Sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source clkT2 is by default equal to the MCU clock, clkI/O.
When the AS2 bit in the ASSR Register is written to logic one, the clock source is taken
from the Timer/Counter Oscillator connected to TOSC1 and TOSC2. For details on
asynchronous operation, see “ASSR – Asynchronous Status Register” on page 141. For
details on clock sources and prescaler, see “Timer/Counter Prescaler” on page 144.
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.
Figure 55 shows a block diagram of the counter and its surrounding environment.
Figure 55. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
TOSC1
count
TCNTn
clear
clk Tn
Control Logic
Prescaler
T/C
Oscillator
direction
bottom
TOSC2
top
clkI/O
Signal description (internal signals):
128
count
Increment or decrement TCNT2 by 1.
direction
Selects between increment and decrement.
clear
Clear TCNT2 (set all bits to zero).
clkT2
Timer/Counter clock.
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top
Signalizes that TCNT2 has reached maximum value.
bottom
Signalizes that TCNT2 has reached minimum value (zero).
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT2). clkT2 can be generated from an external or internal
clock source, selected by the Clock Select bits (CS22:0). When no clock source is
selected (CS22:0 = 0) the timer is stopped. However, the TCNT2 value can be accessed
by the CPU, regardless of whether clkT2 is present or not. A CPU write overrides (has
priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits
located in the Timer/Counter Control Register (TCCR2A). There are close connections
between how the counter behaves (counts) and how waveforms are generated on the
Output Compare output OC2A. For more details about advanced counting sequences
and waveform generation, see “Modes of Operation” on page 132.
The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation
selected by the WGM21:0 bits. TOV2 can be used for generating a CPU interrupt.
Output Compare Unit
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register
(OCR2A). Whenever TCNT2 equals OCR2A, the comparator signals a match. A match
will set the Output Compare Flag (OCF2A) at the next timer clock cycle. If enabled
(OCIE2A = 1), the Output Compare Flag generates an Output Compare interrupt. The
OCF2A Flag is automatically cleared when the interrupt is executed. Alternatively, the
OCF2A Flag can be cleared by software by writing a logical one to its I/O bit location.
The Waveform Generator uses the match signal to generate an output according to
operating mode set by the WGM21:0 bits and Compare Output mode (COM2A1:0) bits.
The max and bottom signals are used by the Waveform Generator for handling the special cases of the extreme values in some modes of operation (“Modes of Operation” on
page 132).
Figure 56 shows a block diagram of the Output Compare unit.
Figure 56. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator )
OCFnx (Int.Req.)
top
bottom
Waveform Generator
OCnx
FOCn
WGMn1:0
COMnX1:0
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The OCR2A Register is double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of operation,
the double buffering is disabled. The double buffering synchronizes the update of the
OCR2A Compare Register to either top or bottom of the counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses,
thereby making the output glitch-free.
The OCR2A Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR2A Buffer Register, and if double
buffering is disabled the CPU will access the OCR2A directly.
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be
forced by writing a one to the Force Output Compare (FOC2A) bit. Forcing compare
match will not set the OCF2A Flag or reload/clear the timer, but the OC2A pin will be
updated as if a real compare match had occurred (the COM2A1:0 bits settings define
whether the OC2A pin is set, cleared or toggled).
Compare Match Blocking by
TCNT2 Write
All CPU write operations to the TCNT2 Register will block any compare match that
occurs in the next timer clock cycle, even when the timer is stopped. This feature allows
OCR2A to be initialized to the same value as TCNT2 without triggering an interrupt
when the Timer/Counter clock is enabled.
Using the Output Compare
Unit
Since writing TCNT2 in any mode of operation will block all compare matches for one
timer clock cycle, there are risks involved when changing TCNT2 when using the Output
Compare unit, independently of whether the Timer/Counter is running or not. If the value
written to TCNT2 equals the OCR2A value, the compare match will be missed, resulting
in incorrect waveform generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is counting down.
The setup of the OC2A should be performed before setting the Data Direction Register
for the port pin to output. The easiest way of setting the OC2A value is to use the Force
Output Compare (FOC2A) strobe bit in Normal mode. The OC2A Register keeps its
value even when changing between Waveform Generation modes.
Be aware that the COM2A1:0 bits are not double buffered together with the compare
value. Changing the COM2A1:0 bits will take effect immediately.
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Compare Match Output
Unit
The Compare Output mode (COM2A1:0) bits have two functions. The Waveform Generator uses the COM2A1:0 bits for defining the Output Compare (OC2A) state at the next
compare match. Also, the COM2A1:0 bits control the OC2A pin output source. Figure 57
shows a simplified schematic of the logic affected by the COM2A1:0 bit setting. The I/O
Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the
general I/O Port Control Registers (DDR and PORT) that are affected by the COM2A1:0
bits are shown. When referring to the OC2A state, the reference is for the internal OC2A
Register, not the OC2A pin.
Figure 57. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC2A) from the
Waveform Generator if either of the COM2A1:0 bits are set. However, the OC2A pin
direction (input or output) is still controlled by the Data Direction Register (DDR) for the
port pin. The Data Direction Register bit for the OC2A pin (DDR_OC2A) must be set as
output before the OC2A value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC2A state
before the output is enabled. Note that some COM2A1:0 bit settings are reserved for
certain modes of operation. See “8-bit Timer/Counter Register Description” on page
138.
Compare Output Mode and
Waveform Generation
The Waveform Generator uses the COM2A1:0 bits differently in normal, CTC, and PWM
modes. For all modes, setting the COM2A1:0 = 0 tells the Waveform Generator that no
action on the OC2A Register is to be performed on the next compare match. For compare output actions in the non-PWM modes refer to Table 60 on page 139. For fast
PWM mode, refer to Table 61 on page 139, and for phase correct PWM refer to Table
62 on page 139.
A change of the COM2A1:0 bits state will have effect at the first compare match after the
bits are written. For non-PWM modes, the action can be forced to have immediate effect
by using the FOC2A strobe bits.
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Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare
pins, is defined by the combination of the Waveform Generation mode (WGM21:0) and
Compare Output mode (COM2A1:0) bits. The Compare Output mode bits do not affect
the counting sequence, while the Waveform Generation mode bits do. The COM2A1:0
bits control whether the PWM output generated should be inverted or not (inverted or
non-inverted PWM). For non-PWM modes the COM2A1:0 bits control whether the output should be set, cleared, or toggled at a compare match (See “Compare Match Output
Unit” on page 131.).
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 136.
Normal Mode
The simplest mode of operation is the Normal mode (WGM21:0 = 0). In this mode the
counting direction is always up (incrementing), and no counter clear is performed. The
counter simply overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then
restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag
(TOV2) will be set in the same timer clock cycle as the TCNT2 becomes zero. The
TOV2 Flag in this case behaves like a ninth bit, except that it is only set, not cleared.
However, combined with the timer overflow interrupt that automatically clears the TOV2
Flag, the timer resolution can be increased by software. There are no special cases to
consider in the Normal mode, a new counter value can be written anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using
the Output Compare to generate waveforms in Normal mode is not recommended,
since this will occupy too much of the CPU time.
Clear Timer on Compare
Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM21:0 = 2), the OCR2A Register is used
to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNT2) matches the OCR2A. The OCR2A defines the top value for
the counter, hence also its resolution. This mode allows greater control of the compare
match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 58. The counter value
(TCNT2) increases until a compare match occurs between TCNT2 and OCR2A, and
then counter (TCNT2) is cleared.
Figure 58. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCnx
(Toggle)
Period
(COMnx1:0 = 1)
1
2
3
4
An interrupt can be generated each time the counter value reaches the TOP value by
using the OCF2A Flag. If the interrupt is enabled, the interrupt handler routine can be
used for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with
care since the CTC mode does not have the double buffering feature. If the new value
written to OCR2A is lower than the current value of TCNT2, the counter will miss the
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compare match. The counter will then have to count to its maximum value (0xFF) and
wrap around starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC2A output can be set to toggle
its logical level on each compare match by setting the Compare Output mode bits to toggle mode (COM2A1:0 = 1). The OC2A value will not be visible on the port pin unless the
data direction for the pin is set to output. The waveform generated will have a maximum
frequency of fOC2A = fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following equation:
f clk_I/O
f OCnx = ------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnx )
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the Normal mode of operation, the TOV2 Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x00.
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM21:0 = 3) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM
option by its single-slope operation. The counter counts from BOTTOM to MAX then
restarts from BOTTOM. In non-inverting Compare Output mode, the Output Compare
(OC2A) is cleared on the compare match between TCNT2 and OCR2A, and set at BOTTOM. In inverting Compare Output mode, the output is set on compare match and
cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the
fast PWM mode can be twice as high as the phase correct PWM mode that uses dualslope operation. This high frequency makes the fast PWM mode well suited for power
regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the MAX
value. The counter is then cleared at the following timer clock cycle. The timing diagram
for the fast PWM mode is shown in Figure 59. The TCNT2 value is in the timing diagram
shown as a histogram for illustrating the single-slope operation. The diagram includes
non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT2
slopes represent compare matches between OCR2A and TCNT2.
Figure 59. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
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The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches MAX. If
the interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the
OC2A pin. Setting the COM2A1:0 bits to two will produce a non-inverted PWM and an
inverted PWM output can be generated by setting the COM2A1:0 to three (See Table 61
on page 139). The actual OC2A value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or
clearing) the OC2A Register at the compare match between OCR2A and TCNT2, and
clearing (or setting) the OC2A Register at the timer clock cycle the counter is cleared
(changes from MAX to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a
PWM waveform output in the fast PWM mode. If the OCR2A is set equal to BOTTOM,
the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR2A
equal to MAX will result in a constantly high or low output (depending on the polarity of
the output set by the COM2A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved
by setting OC2A to toggle its logical level on each compare match (COM2A1:0 = 1). The
waveform generated will have a maximum frequency of foc2 = fclk_I/O/2 when OCR2A is
set to zero. This feature is similar to the OC2A toggle in CTC mode, except the double
buffer feature of the Output Compare unit is enabled in the fast PWM mode.
Phase Correct PWM Mode
The phase correct PWM mode (WGM21:0 = 1) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dualslope operation. The counter counts repeatedly from BOTTOM to MAX and then from
MAX to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC2A)
is cleared on the compare match between TCNT2 and OCR2A while counting up, and
set on the compare match while counting down. In inverting Output Compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency
than single slope operation. However, due to the symmetric feature of the dual-slope
PWM modes, these modes are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase
correct PWM mode the counter is incremented until the counter value matches MAX.
When the counter reaches MAX, it changes the count direction. The TCNT2 value will
be equal to MAX for one timer clock cycle. The timing diagram for the phase correct
PWM mode is shown on Figure 60. The TCNT2 value is in the timing diagram shown as
a histogram for illustrating the dual-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare matches between OCR2A and TCNT2.
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Figure 60. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches BOTTOM. The Interrupt Flag can be used to generate an interrupt each time the counter
reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on
the OC2A pin. Setting the COM2A1:0 bits to two will produce a non-inverted PWM. An
inverted PWM output can be generated by setting the COM2A1:0 to three (See Table 62
on page 139). The actual OC2A value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by clearing (or
setting) the OC2A Register at the compare match between OCR2A and TCNT2 when
the counter increments, and setting (or clearing) the OC2A Register at compare match
between OCR2A and TCNT2 when the counter decrements. The PWM frequency for
the output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = ----------------N ⋅ 510
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a
PWM waveform output in the phase correct PWM mode. If the OCR2A is set equal to
BOTTOM, the output will be continuously low and if set equal to MAX the output will be
continuously high for non-inverted PWM mode. For inverted PWM the output will have
the opposite logic values.
At the very start of period 2 in Figure 60 OCn has a transition from high to low even
though there is no Compare Match. The point of this transition is to guarantee symmetry
around BOTTOM. There are two cases that give a transition without Compare Match.
•
OCR2A changes its value from MAX, like in Figure 60. When the OCR2A value is
MAX the OCn pin value is the same as the result of a down-counting compare
match. To ensure symmetry around BOTTOM the OCn value at MAX must
correspond to the result of an up-counting Compare Match.
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•
Timer/Counter Timing
Diagrams
The timer starts counting from a value higher than the one in OCR2A, and for that
reason misses the Compare Match and hence the OCn change that would have
happened on the way up.
The following figures show the Timer/Counter in synchronous mode, and the timer clock
(clkT2) is therefore shown as a clock enable signal. In asynchronous mode, clkI/O should
be replaced by the Timer/Counter Oscillator clock. The figures include information on
when Interrupt Flags are set. Figure 61 contains timing data for basic Timer/Counter
operation. The figure shows the count sequence close to the MAX value in all modes
other than phase correct PWM mode.
Figure 61. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 62 shows the same timing data, but with the prescaler enabled.
Figure 62. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 63 shows the setting of OCF2A in all modes except CTC mode.
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Figure 63. Timer/Counter Timing Diagram, Setting of OCF2A, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCRnx
OCFnx
Figure 64 shows the setting of OCF2A and the clearing of TCNT2 in CTC mode.
Figure 64. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with
Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
OCRnx
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP
OCFnx
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8-bit Timer/Counter
Register Description
TCCR2A – Timer/Counter
Control Register A
Bit
7
6
5
4
3
2
1
0
FOC2A
WGM20
COM2A1
COM2A0
WGM21
CS22
CS21
CS20
Read/Write
W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0xB0)
TCCR2A
• Bit 7 – FOC2A: Force Output Compare A
The FOC2A bit is only active when the WGM bits specify a non-PWM mode. However,
for ensuring compatibility with future devices, this bit must be set to zero when TCCR2A
is written when operating in PWM mode. When writing a logical one to the FOC2A bit,
an immediate compare match is forced on the Waveform Generation unit. The OC2A
output is changed according to its COM2A1:0 bits setting. Note that the FOC2A bit is
implemented as a strobe. Therefore it is the value present in the COM2A1:0 bits that
determines the effect of the forced compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode
using OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6, 3 – WGM21:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum
(TOP) counter value, and what type of waveform generation to be used. Modes of operation supported by the Timer/Counter unit are: Normal mode, Clear Timer on Compare
match (CTC) mode, and two types of Pulse Width Modulation (PWM) modes. See Table
59 and “Modes of Operation” on page 132.
Table 59. Waveform Generation Mode Bit Description(1)
Mode
WGM21
(CTC2)
WGM20
(PWM2)
Timer/Counter Mode
of Operation
TOP
Update of
OCR2A at
TOV2 Flag
Set on
0
0
0
Normal
0xFF
Immediate
MAX
1
0
1
PWM, Phase Correct
0xFF
TOP
BOTTOM
2
1
0
CTC
OCR2A
Immediate
MAX
3
1
1
Fast PWM
0xFF
BOTTOM
MAX
Note:
138
1. The CTC2 and PWM2 bit definition names are now obsolete. Use the WGM21:0 definitions. However, the functionality and location of these bits are compatible with
previous versions of the timer.
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• Bit 5:4 – COM2A1:0: Compare Match Output Mode A
These bits control the Output Compare pin (OC2A) behavior. If one or both of the
COM2A1:0 bits are set, the OC2A output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to OC2A pin must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the
WGM21:0 bit setting. Table 60 shows the COM2A1:0 bit functionality when the
WGM21:0 bits are set to a normal or CTC mode (non-PWM).
Table 60. Compare Output Mode, non-PWM Mode
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
0
1
Toggle OC2A on compare match.
1
0
Clear OC2A on compare match.
1
1
Set OC2A on compare match.
Table 61 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast
PWM mode.
Table 61. Compare Output Mode, Fast PWM Mode(1)
COM2A1
COM2A0
0
0
Normal port operation, OC2A disconnected.
0
1
Reserved
1
0
Clear OC2A on compare match, set OC2A at BOTTOM,
(non-inverting mode).
1
1
Set OC2A on compare match, clear OC2A at BOTTOM,
(inverting mode).
Note:
Description
1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case,
the compare match is ignored, but the set or clear is done at BOTTOM. See “Fast
PWM Mode” on page 133 for more details.
Table 62 shows the COM21:0 bit functionality when the WGM21:0 bits are set to phase
correct PWM mode.
Table 62. Compare Output Mode, Phase Correct PWM Mode(1)
COM2A1
COM2A0
0
0
Normal port operation, OC2A disconnected.
0
1
Reserved
1
0
Clear OC2A on compare match when up-counting. Set OC2A on
compare match when counting down.
1
1
Set OC2A on compare match when up-counting. Clear OC2A on
compare match when counting down.
Note:
Description
1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case,
the compare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page 134 for more details.
• Bit 2:0 – CS22:0: Clock Select
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The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Table 63.
Table 63. Clock Select Bit Description
TCNT2 – Timer/Counter
Register
CS22
CS21
CS20
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clkT2S/(No prescaling)
0
1
0
clkT2S/8 (From prescaler)
0
1
1
clkT2S/32 (From prescaler)
1
0
0
clkT2S/64 (From prescaler)
1
0
1
clkT2S/128 (From prescaler)
1
1
0
clkT2S/256 (From prescaler)
1
1
1
clkT2S/1024 (From prescaler)
Bit
7
6
5
Description
4
3
2
1
0
TCNT2[7:0]
(0xB2)
TCNT2
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to
the Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes)
the compare match on the following timer clock. Modifying the counter (TCNT2) while
the counter is running, introduces a risk of missing a compare match between TCNT2
and the OCR2A Register.
OCR2A – Output Compare
Register A
Bit
7
6
5
4
3
2
1
0
OCR2A[7:0]
(0xB3)
OCR2A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared
with the counter value (TCNT2). A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the OC2A pin.
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Asynchronous operation
of the Timer/Counter
ASSR – Asynchronous Status
Register
Bit
7
6
5
4
3
2
1
0
(0xB6)
–
–
–
EXCLK
AS2
TCN2UB
OCR2UB
TCR2UB
Read/Write
R
R
R
R/W
R/W
R
R
R
Initial Value
0
0
0
0
0
0
0
0
ASSR
• Bit 4 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock
input buffer is enabled and an external clock can be input on Timer Oscillator 1 (TOSC1)
pin instead of a 32 kHz crystal. Writing to EXCLK should be done before asynchronous
operation is selected. Note that the crystal Oscillator will only run when this bit is zero.
• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When
AS2 is written to one, Timer/Counter2 is clocked from a crystal Oscillator connected to
the Timer Oscillator 1 (TOSC1) pin. When the value of AS2 is changed, the contents of
TCNT2, OCR2A, and TCCR2A might be corrupted.
• Bit 2 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes
set. When TCNT2 has been updated from the temporary storage register, this bit is
cleared by hardware. A logical zero in this bit indicates that TCNT2 is ready to be
updated with a new value.
• Bit 1 – OCR2UB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes
set. When OCR2A has been updated from the temporary storage register, this bit is
cleared by hardware. A logical zero in this bit indicates that OCR2A is ready to be
updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2A is written, this bit
becomes set. When TCCR2A has been updated from the temporary storage register,
this bit is cleared by hardware. A logical zero in this bit indicates that TCCR2A is ready
to be updated with a new value.
If a write is performed to any of the three Timer/Counter2 Registers while its update
busy flag is set, the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2A, and TCCR2A are different. When reading TCNT2, the actual timer value is read. When reading OCR2A or TCCR2A, the value
in the temporary storage register is read.
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Asynchronous Operation of
Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
•
Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2A, and TCCR2A might be
corrupted. A safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2A and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2A, and TCCR2A.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and
TCR2UB.
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
•
The CPU main clock frequency must be more than four times the Oscillator
frequency.
•
When writing to one of the registers TCNT2, OCR2A, or TCCR2A, the value is
transferred to a temporary register, and latched after two positive edges on TOSC1.
The user should not write a new value before the contents of the temporary register
have been transferred to its destination. Each of the three mentioned registers have
their individual temporary register, which means that e.g. writing to TCNT2 does not
disturb an OCR2A write in progress. To detect that a transfer to the destination
register has taken place, the Asynchronous Status Register – ASSR has been
implemented.
•
When entering Power-save or ADC Noise Reduction mode after having written to
TCNT2, OCR2A, or TCCR2A, the user must wait until the written register has been
updated if Timer/Counter2 is used to wake up the device. Otherwise, the MCU will
enter sleep mode before the changes are effective. This is particularly important if
the Output Compare2 interrupt is used to wake up the device, since the Output
Compare function is disabled during writing to OCR2A or TCNT2. If the write cycle
is not finished, and the MCU enters sleep mode before the OCR2UB bit returns to
zero, the device will never receive a compare match interrupt, and the MCU will not
wake up.
•
If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise
Reduction mode, precautions must be taken if the user wants to re-enter one of
these modes: The interrupt logic needs one TOSC1 cycle to be reset. If the time
between wake-up and re-entering sleep mode is less than one TOSC1 cycle, the
interrupt will not occur, and the device will fail to wake up. If the user is in doubt
whether the time before re-entering Power-save or ADC Noise Reduction mode is
sufficient, the following algorithm can be used to ensure that one TOSC1 cycle has
elapsed:
1. Write a value to TCCR2A, TCNT2, or OCR2A.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or ADC Noise Reduction mode.
•
142
When the asynchronous operation is selected, the 32.768 kHz Oscillator for
Timer/Counter2 is always running, except in Power-down and Standby modes. After
a Power-up Reset or wake-up from Power-down or Standby mode, the user should
be aware of the fact that this Oscillator might take as long as one second to stabilize.
The user is advised to wait for at least one second before using Timer/Counter2
after power-up or wake-up from Power-down or Standby mode. The contents of all
Timer/Counter2 Registers must be considered lost after a wake-up from Powerdown or Standby mode due to unstable clock signal upon start-up, no matter
whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
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ATmega325/3250/645/6450
•
Description of wake up from Power-save or ADC Noise Reduction mode when the
timer is clocked asynchronously: When the interrupt condition is met, the wake up
process is started on the following cycle of the timer clock, that is, the timer is
always advanced by at least one before the processor can read the counter value.
After wake-up, the MCU is halted for four cycles, it executes the interrupt routine,
and resumes execution from the instruction following SLEEP.
•
Reading of the TCNT2 Register shortly after wake-up from Power-save may give an
incorrect result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading
TCNT2 must be done through a register synchronized to the internal I/O clock
domain. Synchronization takes place for every rising TOSC1 edge. When waking up
from Power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will
read as the previous value (before entering sleep) until the next rising TOSC1 edge.
The phase of the TOSC clock after waking up from Power-save mode is essentially
unpredictable, as it depends on the wake-up time. The recommended procedure for
reading TCNT2 is thus as follows:
1. Write any value to either of the registers OCR2A or TCCR2A.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
•
TIMSK2 – Timer/Counter2
Interrupt Mask Register
During asynchronous operation, the synchronization of the Interrupt Flags for the
asynchronous timer takes 3 processor cycles plus one timer cycle. The timer is
therefore advanced by at least one before the processor can read the timer value
causing the setting of the Interrupt Flag. The Output Compare pin is changed on the
timer clock and is not synchronized to the processor clock.
Bit
7
6
5
4
3
2
1
0
(0x70)
–
–
–
–
–
–
OCIE2A
TOIE2
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK2
• Bit 1 – OCIE2A: Timer/Counter2 Output Compare Match A Interrupt Enable
When the OCIE2A bit is written to one and the I-bit in the Status Register is set (one),
the Timer/Counter2 Compare Match A interrupt is enabled. The corresponding interrupt
is executed if a compare match in Timer/Counter2 occurs, i.e., when the OCF2A bit is
set in the Timer/Counter 2 Interrupt Flag Register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if
an overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the
Timer/Counter2 Interrupt Flag Register – TIFR2.
TIFR2 – Timer/Counter2
Interrupt Flag Register
Bit
7
6
5
4
3
2
1
0
0x17 (0x37)
–
–
–
–
–
–
OCF2A
TOV2
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR2
• Bit 1 – OCF2A: Output Compare Flag 2 A
The OCF2A bit is set (one) when a compare match occurs between the Timer/Counter2
and the data in OCR2A – Output Compare Register2. OCF2A is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, OCF2A is
cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE2A
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(Timer/Counter2 Compare match Interrupt Enable), and OCF2A are set (one), the
Timer/Counter2 Compare match Interrupt is executed.
• Bit 0 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared
by hardware when executing the corresponding interrupt handling vector. Alternatively,
TOV2 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE2A
(Timer/Counter2 Overflow Interrupt Enable), and TOV2 are set (one), the
Timer/Counter2 Overflow interrupt is executed. In PWM mode, this bit is set when
Timer/Counter2 changes counting direction at 0x00.
Figure 65. Prescaler for Timer/Counter2
clkT2S
PSR2
clkT2S/1024
clkT2S/256
AS2
clkT2S/128
10-BIT T/C PRESCALER
Clear
clkT2S/64
TOSC1
clkT2S/32
clkI/O
clkT2S/8
Timer/Counter Prescaler
0
CS20
CS21
CS22
TIMER/COUNTER2 CLOCK SOURCE
clkT2
The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to
the main system I/O clock clkIO. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real
Time Counter (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from
Port C. A crystal can then be connected between the TOSC1 and TOSC2 pins to serve
as an independent clock source for Timer/Counter2. The Oscillator is optimized for use
with a 32.768 kHz crystal. If applying an external clock on TOSC1, the EXCLK bit in
ASSR must be set.
For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64,
clkT2S/128, clkT2S/256, and clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be
selected. Setting the PSR2 bit in GTCCR resets the prescaler. This allows the user to
operate with a predictable prescaler.
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GTCCR – General
Timer/Counter Control
Register
Bit
7
6
5
4
3
2
1
0
0x23 (0x43)
TSM
–
–
–
–
–
PSR2
PSR10
Read/Write
R/W
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally
cleared immediately by hardware. If the bit is written when Timer/Counter2 is operating
in asynchronous mode, the bit will remain one until the prescaler has been reset. The bit
will not be cleared by hardware if the TSM bit is set. Refer to the description of the “Bit 7
– TSM: Timer/Counter Synchronization Mode” on page 98 for a description of the
Timer/Counter Synchronization mode.
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SPI – Serial
Peripheral Interface
The ATmega325/3250/645/6450 SPI includes the following features:
• Full-duplex, Three-wire Synchronous Data Transfer
• Master or Slave Operation
• LSB First or MSB First Data Transfer
• Seven Programmable Bit Rates
• End of Transmission Interrupt Flag
• Write Collision Flag Protection
• Wake-up from Idle Mode
• Double Speed (CK/2) Master SPI Mode
Overview
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer
between the ATmega325/3250/645/6450 and peripheral devices or between several
AVR devices.
The PRSPI bit in “Power Reduction Register” on page 35 must be written to zero to
enable the SPI module.
Figure 66. SPI Block Diagram(1)
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128
Note:
1. Refer to Figure 1 on page 2, and Table 27 on page 66 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 67.
The system consists of two shift Registers, and a Master clock generator. The SPI Master initiates the communication cycle when pulling low the Slave Select SS pin of the
desired Slave. Master and Slave prepare the data to be sent in their respective shift
Registers, and the Master generates the required clock pulses on the SCK line to interchange data. Data is always shifted from Master to Slave on the Master Out – Slave In,
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ATmega325/3250/645/6450
MOSI, line, and from Slave to Master on the Master In – Slave Out, MISO, line. After
each data packet, the Master will synchronize the Slave by pulling high the Slave Select,
SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line.
This must be handled by user software before communication can start. When this is
done, writing a byte to the SPI Data Register starts the SPI clock generator, and the
hardware shifts the eight bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of Transmission Flag (SPIF). If the SPI Interrupt Enable bit
(SPIE) in the SPCR Register is set, an interrupt is requested. The Master may continue
to shift the next byte by writing it into SPDR, or signal the end of packet by pulling high
the Slave Select, SS line. The last incoming byte will be kept in the Buffer Register for
later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated
as long as the SS pin is driven high. In this state, software may update the contents of
the SPI Data Register, SPDR, but the data will not be shifted out by incoming clock
pulses on the SCK pin until the SS pin is driven low. As one byte has been completely
shifted, the end of Transmission Flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE,
in the SPCR Register is set, an interrupt is requested. The Slave may continue to place
new data to be sent into SPDR before reading the incoming data. The last incoming byte
will be kept in the Buffer Register for later use.
Figure 67. SPI Master-slave Interconnection
SHIFT
ENABLE
The system is single buffered in the transmit direction and double buffered in the receive
direction. This means that bytes to be transmitted cannot be written to the SPI Data
Register before the entire shift cycle is completed. When receiving data, however, a
received character must be read from the SPI Data Register before the next character
has been completely shifted in. Otherwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To
ensure correct sampling of the clock signal, the minimum low and high period should be:
Low period: longer than 2 CPU clock cycles.
High period: longer than 2 CPU clock cycles.
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When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is
overridden according to Table 64. For more details on automatic port overrides, refer to
“Alternate Port Functions” on page 64.
Table 64. SPI Pin Overrides(1)
Pin
Direction, Master SPI
Direction, Slave SPI
MOSI
User Defined
Input
MISO
Input
User Defined
SCK
User Defined
Input
SS
User Defined
Input
Note:
148
1. See “Alternate Functions of Port B” on page 66 for a detailed description of how to
define the direction of the user defined SPI pins.
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ATmega325/3250/645/6450
The following code examples show how to initialize the SPI as a Master and how to perform a simple transmission. DDR_SPI in the examples must be replaced by the actual
Data Direction Register controlling the SPI pins. DD_MOSI, DD_MISO and DD_SCK
must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed
on pin PB5, replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi
r17,(1<<DD_MOSI)|(1<<DD_SCK)
out
DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi
r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out
SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out
SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}
Note:
1. See “About Code Examples” on page 8.
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The following code examples show how to initialize the SPI as a Slave and how to perform a simple reception.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi
r17,(1<<DD_MISO)
out
DDR_SPI,r17
; Enable SPI
ldi
r17,(1<<SPE)
out
SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in
r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return Data Register */
return SPDR;
}
Note:
150
1. See “About Code Examples” on page 8.
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SS Pin Functionality
Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When
SS is held low, the SPI is activated, and MISO becomes an output if configured so by
the user. All other pins are inputs. When SS is driven high, all pins are inputs, and the
SPI is passive, which means that it will not receive incoming data. Note that the SPI
logic will be reset once the SS pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the master clock generator. When the SS pin is driven high, the SPI slave
will immediately reset the send and receive logic, and drop any partially received data in
the Shift Register.
Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine
the direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the
SPI system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If
the SS pin is driven low by peripheral circuitry when the SPI is configured as a Master
with the SS pin defined as an input, the SPI system interprets this as another master
selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the
SPI system takes the following actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a
result of the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF Flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in
SREG is set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a
possibility that SS is driven low, the interrupt should always check that the MSTR bit is
still set. If the MSTR bit has been cleared by a slave select, it must be set by the user to
re-enable SPI Master mode.
SPCR – SPI Control Register
Bit
7
6
5
4
3
2
1
0
0x2C (0x4C)
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPCR
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set
and the if the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable
any SPI operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written
logic zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will
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be cleared, and SPIF in SPSR will become set. The user will then have to set MSTR to
re-enable SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero,
SCK is low when idle. Refer to Figure 68 and Figure 69 for an example. The CPOL functionality is summarized below:
Table 65. CPOL Functionality
CPOL
Leading Edge
Trailing Edge
0
Rising
Falling
1
Falling
Rising
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading
(first) or trailing (last) edge of SCK. Refer to Figure 68 and Figure 69 for an example.
The CPOL functionality is summarized below:
Table 66. CPHA Functionality
CPHA
Leading Edge
Trailing Edge
0
Sample
Setup
1
Setup
Sample
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and
SPR0 have no effect on the Slave. The relationship between SCK and the Oscillator
Clock frequency fosc is shown in the following table:
Table 67. Relationship Between SCK and the Oscillator Frequency
152
SPI2X
SPR1
SPR0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
SCK Frequency
fosc/4
fosc/16
fosc/64
fosc/128
fosc/2
fosc/8
fosc/32
fosc/64
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SPSR – SPI Status Register
Bit
7
6
5
4
3
2
1
0
SPIF
WCOL
–
–
–
–
–
SPI2X
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
0x2D (0x4D)
SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if
SPIE in SPCR is set and global interrupts are enabled. If SS is an input and is driven low
when the SPI is in Master mode, this will also set the SPIF Flag. SPIF is cleared by
hardware when executing the corresponding interrupt handling vector. Alternatively, the
SPIF bit is cleared by first reading the SPI Status Register with SPIF set, then accessing
the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer.
The WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register
with WCOL set, and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the ATmega325/3250/645/6450 and will always read as
zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when
the SPI is in Master mode (see Table 67). This means that the minimum SCK period will
be two CPU clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4 or lower.
The SPI interface on the ATmega325/3250/645/6450 is also used for program memory
and EEPROM downloading or uploading. See page 274 for serial programming and
verification.
SPDR – SPI Data Register
Bit
7
6
5
4
3
2
1
0
0x2E (0x4E)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
X
X
X
X
X
X
X
X
SPDR
Undefined
The SPI Data Register is a read/write register used for data transfer between the Register File and the SPI Shift Register. Writing to the register initiates data transmission.
Reading the register causes the Shift Register Receive buffer to be read.
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Data Modes
There are four combinations of SCK phase and polarity with respect to serial data,
which are determined by control bits CPHA and CPOL. The SPI data transfer formats
are shown in Figure 68 and Figure 69. Data bits are shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is
clearly seen by summarizing Table 65 and Table 66, as done below:
Table 68. CPOL Functionality
Leading Edge
Trailing eDge
SPI Mode
CPOL=0, CPHA=0
Sample (Rising)
Setup (Falling)
0
CPOL=0, CPHA=1
Setup (Rising)
Sample (Falling)
1
CPOL=1, CPHA=0
Sample (Falling)
Setup (Rising)
2
CPOL=1, CPHA=1
Setup (Falling)
Sample (Rising)
3
Figure 68. SPI Transfer Format with CPHA = 0
SCK (CPOL = 0)
mode 0
SCK (CPOL = 1)
mode 2
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0) MSB
LSB first (DORD = 1) LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
Figure 69. SPI Transfer Format with CPHA = 1
SCK (CPOL = 0)
mode 1
SCK (CPOL = 1)
mode 3
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0)
LSB first (DORD = 1)
154
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
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USART0
The Universal Synchronous and Asynchronous serial Receiver and Transmitter
(USART) is a highly flexible serial communication device. The main features are:
• Full Duplex Operation (Independent Serial Receive and Transmit Registers)
• Asynchronous or Synchronous Operation
• Master or Slave Clocked Synchronous Operation
• High Resolution Baud Rate Generator
• Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
• Odd or Even Parity Generation and Parity Check Supported by Hardware
• Data OverRun Detection
• Framing Error Detection
• Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
• Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete
• Multi-processor Communication Mode
• Double Speed Asynchronous Communication Mode
Overview
A simplified block diagram of the USART Transmitter is shown in Figure 70. CPU accessible I/O Registers and I/O pins are shown in bold.
The Power Reduction USART bit, PRUSART0, in “Power Reduction Register” on page
35 must be written to zero to enable the USART0 module.
Figure 70. USART Block Diagram(1)
Clock Generator
UBRR[H:L]
OSC
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCK
Transmitter
TX
CONTROL
UDR (Transmit)
DATA BUS
PARITY
GENERATOR
TxD
Receiver
UCSRA
Note:
PIN
CONTROL
TRANSMIT SHIFT REGISTER
CLOCK
RECOVERY
RX
CONTROL
RECEIVE SHIFT REGISTER
DATA
RECOVERY
PIN
CONTROL
UDR (Receive)
PARITY
CHECKER
UCSRB
RxD
UCSRC
1. Refer to Figure 1 on page 2, Figure 2 on page 3 and “Alternate Functions of Port E”
on page 70 for USART pin placement.
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The dashed boxes in the block diagram separate the three main parts of the USART
(listed from the top): Clock Generator, Transmitter and Receiver. Control Registers are
shared by all units. The Clock Generation logic consists of synchronization logic for
external clock input used by synchronous slave operation, and the baud rate generator.
The XCK (Transfer Clock) pin is only used by synchronous transfer mode. The Transmitter consists of a single write buffer, a serial Shift Register, Parity Generator and
Control logic for handling different serial frame formats. The write buffer allows a continuous transfer of data without any delay between frames. The Receiver is the most
complex part of the USART module due to its clock and data recovery units. The recovery units are used for asynchronous data reception. In addition to the recovery units, the
Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDRn). The Receiver supports the same frame formats as the Transmitter, and can detect Frame Error, Data OverRun and Parity Errors.
AVR USART vs. AVR UART –
Compatibility
The USART is fully compatible with the AVR UART regarding:
•
Bit locations inside all USART Registers.
•
Baud Rate Generation.
•
Transmitter Operation.
•
Transmit Buffer Functionality.
•
Receiver Operation.
However, the receive buffering has two improvements that will affect the compatibility in
some special cases:
•
A second Buffer Register has been added. The two Buffer Registers operate as a
circular FIFO buffer. Therefore the UDRn must only be read once for each incoming
data! More important is the fact that the Error Flags (FEn and DORn) and the ninth
data bit (RXB8n) are buffered with the data in the receive buffer. Therefore the
status bits must always be read before the UDRn Register is read. Otherwise the
error status will be lost since the buffer state is lost.
•
The Receiver Shift Register can now act as a third buffer level. This is done by
allowing the received data to remain in the serial Shift Register (see Figure 70) if the
Buffer Registers are full, until a new start bit is detected. The USART is therefore
more resistant to Data OverRun (DORn) error conditions.
The following control bits have changed name, but have same functionality and register
location:
Clock Generation
•
CHR9 is changed to UCSZn2.
•
OR is changed to DORn.
The Clock Generation logic generates the base clock for the Transmitter and Receiver.
The USART supports four modes of clock operation: Normal asynchronous, Double
Speed asynchronous, Master synchronous and Slave synchronous mode. The UMSELn
bit in USART Control and Status Register C (UCSRnC) selects between asynchronous
and synchronous operation. Double Speed (asynchronous mode only) is controlled by
the U2Xn found in the UCSRnA Register. When using synchronous mode (UMSELn =
1), the Data Direction Register for the XCK pin (DDR_XCK) controls whether the clock
source is internal (Master mode) or external (Slave mode). The XCK pin is only active
when using synchronous mode.
Figure 71 shows a block diagram of the clock generation logic.
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Figure 71. Clock Generation Logic, Block Diagram
UBRR
U2X
fosc
Prescaling
Down-Counter
UBRR+1
/2
/4
/2
0
1
0
OSC
DDR_XCK
xcki
XCK
Pin
Sync
Register
Edge
Detector
0
UCPOL
txclk
UMSEL
1
xcko
DDR_XCK
1
1
0
rxclk
Signal description:
Internal Clock Generation –
The Baud Rate Generator
txclk
Transmitter clock (Internal Signal).
rxclk
Receiver base clock (Internal Signal).
xcki
Input from XCK pin (internal Signal). Used for synchronous slave operation.
xcko
Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
fosc
XTAL pin frequency (System Clock).
Internal clock generation is used for the asynchronous and the synchronous master
modes of operation. The description in this section refers to Figure 71.
The USART Baud Rate Register (UBRR) and the down-counter connected to it function
as a programmable prescaler or baud rate generator. The down-counter, running at system clock (fosc), is loaded with the UBRR value each time the counter has counted down
to zero or when the UBRRL Register is written. A clock is generated each time the
counter reaches zero. This clock is the baud rate generator clock output (=
fosc/(UBRR+1)). The Transmitter divides the baud rate generator clock output by 2, 8 or
16 depending on mode. The baud rate generator output is used directly by the
Receiver’s clock and data recovery units. However, the recovery units use a state
machine that uses 2, 8 or 16 states depending on mode set by the state of the UMSELn,
U2Xn and DDR_XCK bits.
Table 69 contains equations for calculating the baud rate (in bits per second) and for
calculating the UBRR value for each mode of operation using an internally generated
clock source.
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Table 69. Equations for Calculating Baud Rate Register Setting
Equation for Calculating
Baud Rate(1)
Equation for Calculating
UBRR Value
Asynchronous Normal
mode (U2Xn = 0)
f OSC
BAUD = -------------------------------------16 ( UBRR + 1 )
f OSC
UBRR = -----------------------–1
16BAUD
Asynchronous Double
Speed mode
(U2Xn = 1)
f OSC
BAUD = ---------------------------------8 ( UBRR + 1 )
f OSC
UBRR = -------------------–1
8BAUD
Synchronous Master
mode
f OSC
BAUD = ---------------------------------2 ( UBRR + 1 )
f OSC
UBRR = -------------------–1
2BAUD
Operating Mode
Note:
1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD Baud rate (in bits per second, bps)
fOSC
System Oscillator clock frequency
UBRR Contents of the UBRRH and UBRRL Registers, (0-4095)
Some examples of UBRR values for some system clock frequencies are found in Table
77 (see page 177).
Double Speed Operation
(U2Xn)
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit
only has effect for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively
doubling the transfer rate for asynchronous communication. Note however that the
Receiver will in this case only use half the number of samples (reduced from 16 to 8) for
data sampling and clock recovery, and therefore a more accurate baud rate setting and
system clock are required when this mode is used. For the Transmitter, there are no
downsides.
External Clock
External clocking is used by the synchronous slave modes of operation. The description
in this section refers to Figure 71 for details.
External clock input from the XCK pin is sampled by a synchronization register to minimize the chance of meta-stability. The output from the synchronization register must
then pass through an edge detector before it can be used by the Transmitter and
Receiver. This process introduces a two CPU clock period delay and therefore the maximum external XCK clock frequency is limited by the following equation:
f OSC
f XCK < ----------4
Note that fosc depends on the stability of the system clock source. It is therefore recommended to add some margin to avoid possible loss of data due to frequency variations.
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Synchronous Clock Operation When synchronous mode is used (UMSELn = 1), the XCK pin will be used as either
clock input (Slave) or clock output (Master). The dependency between the clock edges
and data sampling or data change is the same. The basic principle is that data input (on
RxD) is sampled at the opposite XCK clock edge of the edge the data output (TxD) is
changed.
Figure 72. Synchronous Mode XCK Timing.
UCPOL = 1
XCK
RxD / TxD
Sample
UCPOL = 0
XCK
RxD / TxD
Sample
The UCPOLn bit in UCSRnC selects which XCK clock edge is used for data sampling
and which is used for data change. As Figure 72 shows, when UCPOLn is zero the data
will be changed at rising XCK edge and sampled at falling XCK edge. If UCPOLn is set,
the data will be changed at falling XCK edge and sampled at rising XCK edge.
Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start
and stop bits), and optionally a parity bit for error checking. The USART accepts all 30
combinations of the following as valid frame formats:
•
1 start bit
•
5, 6, 7, 8, or 9 data bits
•
no, even or odd parity bit
•
1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next
data bits, up to a total of nine, are succeeding, ending with the most significant bit. If
enabled, the parity bit is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can be directly followed by a new frame, or the
communication line can be set to an idle (high) state. Figure 73 illustrates the possible
combinations of the frame formats. Bits inside brackets are optional.
Figure 73. Frame Formats
FRAME
(IDLE)
St
0
1
2
3
4
St
Start bit, always low.
(n)
Data bits (0 to 8).
P
Parity bit. Can be odd or even.
[5]
[6]
[7]
[8]
[P]
Sp1 [Sp2]
(St / IDLE)
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Sp
Stop bit, always high.
IDLE
No transfers on the communication line (RxD or TxD). An IDLE line must be
high.
The frame format used by the USART is set by the UCSZn2:0, UPMn1:0 and USBSn
bits in UCSRnB and UCSRnC. The Receiver and Transmitter use the same setting.
Note that changing the setting of any of these bits will corrupt all ongoing communication for both the Receiver and Transmitter.
The USART Character SiZe (UCSZn2:0) bits select the number of data bits in the frame.
The USART Parity mode (UPMn1:0) bits enable and set the type of parity bit. The selection between one or two stop bits is done by the USART Stop Bit Select (USBSn) bit.
The Receiver ignores the second stop bit. An FEn (Frame Error) will therefore only be
detected in the cases where the first stop bit is zero.
Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is
used, the result of the exclusive or is inverted. The relation between the parity bit and
data bits is as follows:
P even = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 0
P odd = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 1
Peven
Parity bit using even parity
Podd
Parity bit using odd parity
dn
Data bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial
frame.
USART Initialization
The USART has to be initialized before any communication can take place. The initialization process normally consists of setting the baud rate, setting frame format and
enabling the Transmitter or the Receiver depending on the usage. For interrupt driven
USART operation, the Global Interrupt Flag should be cleared (and interrupts globally
disabled) when doing the initialization.
Before doing a re-initialization with changed baud rate or frame format, be sure that
there are no ongoing transmissions during the period the registers are changed. The
TXCn Flag can be used to check that the Transmitter has completed all transfers, and
the RXCn Flag can be used to check that there are no unread data in the receive buffer.
Note that the TXCn Flag must be cleared before each transmission (before UDRn is
written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one
C function that are equal in functionality. The examples assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format. The baud rate is
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given as a function parameter. For the assembly code, the baud rate parameter is
assumed to be stored in the r17:r16 Registers.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out
UBRRH, r17
out
UBRRL, r16
; Enable receiver and transmitter
ldi
r16, (1<<RXEN0)|(1<<TXEN0)
out
UCSR0B,r16
; Set frame format: 8data, 2stop bit
ldi
r16, (1<<USBS0)|(3<<UCSZ0)
out
UCSR0C,r16
ret
C Code Example(1)
#define FOSC 1843200 // Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
void main( void )
{
...
USART_Init(MYUBRR)
...
}
void USART_Init( unsigned int ubrr)
{
/* Set baud rate */
UBRRH = (unsigned char)(ubrr>>8);
UBRRL = (unsigned char)ubrr;
/* Enable receiver and transmitter */
UCSR0B = (1<<RXEN0)|(1<<TXEN0);
/* Set frame format: 8data, 2stop bit */
UCSR0C = (1<<USBS0)|(3<<UCSZ0);
}
Note:
1. See “About Code Examples” on page 8.
More advanced initialization routines can be made that include frame format as parameters, disable interrupts and so on. However, many applications use a fixed setting of the
baud and control registers, and for these types of applications the initialization code can
be placed directly in the main routine, or be combined with initialization code for other
I/O modules.
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Data Transmission – The
USART Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXENn) bit in the
UCSRnB Register. When the Transmitter is enabled, the normal port operation of the
TxD pin is overridden by the USART and given the function as the Transmitter’s serial
output. The baud rate, mode of operation and frame format must be set up once before
doing any transmissions. If synchronous operation is used, the clock on the XCK pin will
be overridden and used as transmission clock.
Sending Frames with 5 to 8
Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The CPU can load the transmit buffer by writing to the UDRn I/O location. The
buffered data in the transmit buffer will be moved to the Shift Register when the Shift
Register is ready to send a new frame. The Shift Register is loaded with new data if it is
in idle state (no ongoing transmission) or immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is loaded with new data, it will transfer
one complete frame at the rate given by the Baud Register, U2Xn bit or by XCK depending on mode of operation.
The following code examples show a simple USART transmit function based on polling
of the Data Register Empty (UDREn) Flag. When using frames with less than eight bits,
the most significant bits written to the UDRn are ignored. The USART has to be initialized before the function can be used. For the assembly code, the data to be sent is
assumed to be stored in Register R16.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSR0A,UDRE0
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out
UDR0,r16
ret
C Code Example(1)
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE0)) )
;
/* Put data into buffer, sends the data */
UDR0 = data;
}
Note:
1. See “About Code Examples” on page 8.
The function simply waits for the transmit buffer to be empty by checking the UDREn
Flag, before loading it with new data to be transmitted. If the Data Register Empty interrupt is utilized, the interrupt routine writes the data into the buffer.
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Sending Frames with 9 Data
Bit
If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8n bit in
UCSRnB before the low byte of the character is written to UDRn. The following code
examples show a transmit function that handles 9-bit characters. For the assembly
code, the data to be sent is assumed to be stored in registers R17:R16.
Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSR0A,UDRE0
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB80
cbi
UCSR0B,TXB80
sbrc r17,0
sbi
UCSR0B,TXB80
; Put LSB data (r16) into buffer, sends the data
out
UDR0,r16
ret
C Code Example(1)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE0))) )
;
/* Copy 9th bit to TXB80 */
UCSR0B &= ~(1<<TXB80);
if ( data & 0x0100 )
UCSR0B |= (1<<TXB80);
/* Put data into buffer, sends the data */
UDR0 = data;
}
Notes:
1. These transmit functions are written to be general functions. They can be optimized if
the contents of the UCSRnB is static. For example, only the TXB8n bit of the UCSRnB Register is used after initialization.
2. See “About Code Examples” on page 8.
The ninth bit can be used for indicating an address frame when using multi processor
communication mode or for other protocol handling as for example synchronization.
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Transmitter Flags and
Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register
Empty (UDREn) and Transmit Complete (TXCn). Both flags can be used for generating
interrupts.
The Data Register Empty (UDREn) Flag indicates whether the transmit buffer is ready to
receive new data. This bit is set when the transmit buffer is empty, and cleared when the
transmit buffer contains data to be transmitted that has not yet been moved into the Shift
Register. For compatibility with future devices, always write this bit to zero when writing
the UCSRnA Register.
When the Data Register Empty Interrupt Enable (UDRIEn) bit in UCSRnB is written to
one, the USART Data Register Empty Interrupt will be executed as long as UDREn is
set (provided that global interrupts are enabled). UDREn is cleared by writing UDRn.
When interrupt-driven data transmission is used, the Data Register Empty interrupt routine must either write new data to UDRn in order to clear UDREn or disable the Data
Register Empty interrupt, otherwise a new interrupt will occur once the interrupt routine
terminates.
The Transmit Complete (TXCn) Flag bit is set one when the entire frame in the Transmit
Shift Register has been shifted out and there are no new data currently present in the
transmit buffer. The TXCn Flag bit is automatically cleared when a transmit complete
interrupt is executed, or it can be cleared by writing a one to its bit location. The TXCn
Flag is useful in half-duplex communication interfaces (like the RS-485 standard), where
a transmitting application must enter receive mode and free the communication bus
immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIEn) bit in UCSRnB is set, the
USART Transmit Complete Interrupt will be executed when the TXCn Flag becomes set
(provided that global interrupts are enabled). When the transmit complete interrupt is
used, the interrupt handling routine does not have to clear the TXCn Flag, this is done
automatically when the interrupt is executed.
Parity Generator
The Parity Generator calculates the parity bit for the serial frame data. When parity bit is
enabled (UPMn1 = 1), the transmitter control logic inserts the parity bit between the last
data bit and the first stop bit of the frame that is sent.
Disabling the Transmitter
The disabling of the Transmitter (setting the TXENn to zero) will not become effective
until ongoing and pending transmissions are completed, i.e., when the Transmit Shift
Register and Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter will no longer override the TxD pin.
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Data Reception – The
USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXENn) bit in the UCSRnB Register to one. When the Receiver is enabled, the normal pin operation of the
RxD pin is overridden by the USART and given the function as the Receiver’s serial
input. The baud rate, mode of operation and frame format must be set up once before
any serial reception can be done. If synchronous operation is used, the clock on the
XCK pin will be used as transfer clock.
Receiving Frames with 5 to 8
Data Bits
The Receiver starts data reception when it detects a valid start bit. Each bit that follows
the start bit will be sampled at the baud rate or XCK clock, and shifted into the Receive
Shift Register until the first stop bit of a frame is received. A second stop bit will be
ignored by the Receiver. When the first stop bit is received, i.e., a complete serial frame
is present in the Receive Shift Register, the contents of the Shift Register will be moved
into the receive buffer. The receive buffer can then be read by reading the UDRn I/O
location.
The following code example shows a simple USART receive function based on polling
of the Receive Complete (RXCn) Flag. When using frames with less than eight bits the
most significant bits of the data read from the UDRn will be masked to zero. The USART
has to be initialized before the function can be used.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get and return received data from buffer
in
r16, UDR0
ret
C Code Example(1)
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get and return received data from buffer */
return UDR0;
}
Note:
1. See “About Code Examples” on page 8.
The function simply waits for data to be present in the receive buffer by checking the
RXCn Flag, before reading the buffer and returning the value.
Receiving Frames with 9 Data
Bits
If 9-bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8n bit in
UCSRnB before reading the low bits from the UDRn. This rule applies to the FEn,
DORn and UPEn Status Flags as well. Read status from UCSRnA, then data from
UDRn. Reading the UDRn I/O location will change the state of the receive buffer FIFO
and consequently the TXB8n, FEn, DORn and UPEn bits, which all are stored in the
FIFO, will change.
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The following code example shows a simple USART receive function that handles both
nine bit characters and the status bits.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
in
r18, UCSR0A
in
r17, UCSR0B
in
r16, UDR0
; If error, return -1
andi r18,(1<<FE0)|(1<<DOR0)|(1<<UPE0)
breq USART_ReceiveNoError
ldi
r17, HIGH(-1)
ldi
r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr
r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSR0A;
resh = UCSR0B;
resl = UDR0;
/* If error, return -1 */
if ( status & (1<<FE0)|(1<<DOR0)|(1<<UPE0) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
Note:
1. See “About Code Examples” on page 8.
The receive function example reads all the I/O Registers into the Register File before
any computation is done. This gives an optimal receive buffer utilization since the buffer
location read will be free to accept new data as early as possible.
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Receive Compete Flag and
Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXCn) Flag indicates if there are unread data present in the
receive buffer. This flag is one when unread data exist in the receive buffer, and zero
when the receive buffer is empty (i.e., does not contain any unread data). If the Receiver
is disabled (RXENn = 0), the receive buffer will be flushed and consequently the RXCn
bit will become zero.
When the Receive Complete Interrupt Enable (RXCIEn) in UCSRnB is set, the USART
Receive Complete interrupt will be executed as long as the RXCn Flag is set (provided
that global interrupts are enabled). When interrupt-driven data reception is used, the
receive complete routine must read the received data from UDRn in order to clear the
RXCn Flag, otherwise a new interrupt will occur once the interrupt routine terminates.
Receiver Error Flags
The USART Receiver has three Error Flags: Frame Error (FEn), Data OverRun (DORn)
and Parity Error (UPEn). All can be accessed by reading UCSRnA. Common for the
Error Flags is that they are located in the receive buffer together with the frame for which
they indicate the error status. Due to the buffering of the Error Flags, the UCSRnA must
be read before the receive buffer (UDRn), since reading the UDRn I/O location changes
the buffer read location. Another equality for the Error Flags is that they can not be
altered by software doing a write to the flag location. However, all flags must be set to
zero when the UCSRnA is written for upward compatibility of future USART implementations. None of the Error Flags can generate interrupts.
The Frame Error (FEn) Flag indicates the state of the first stop bit of the next readable
frame stored in the receive buffer. The FEn Flag is zero when the stop bit was correctly
read (as one), and the FEn Flag will be one when the stop bit was incorrect (zero). This
flag can be used for detecting out-of-sync conditions, detecting break conditions and
protocol handling. The FEn Flag is not affected by the setting of the USBSn bit in UCSRnC since the Receiver ignores all, except for the first, stop bits. For compatibility with
future devices, always set this bit to zero when writing to UCSRnA.
The Data OverRun (DORn) Flag indicates data loss due to a receiver buffer full condition. A Data OverRun occurs when the receive buffer is full (two characters), it is a new
character waiting in the Receive Shift Register, and a new start bit is detected. If the
DORn Flag is set there was one or more serial frame lost between the frame last read
from UDRn, and the next frame read from UDRn. For compatibility with future devices,
always write this bit to zero when writing to UCSRnA. The DORn Flag is cleared when
the frame received was successfully moved from the Shift Register to the receive buffer.
The Parity Error (UPEn) Flag indicates that the next frame in the receive buffer had a
Parity Error when received. If Parity Check is not enabled the UPEn bit will always be
read zero. For compatibility with future devices, always set this bit to zero when writing
to UCSRnA. For more details see “Parity Bit Calculation” on page 160 and “Parity
Checker” on page 167.
Parity Checker
The Parity Checker is active when the high USART Parity mode (UPMn1) bit is set.
Type of Parity Check to be performed (odd or even) is selected by the UPMn0 bit. When
enabled, the Parity Checker calculates the parity of the data bits in incoming frames and
compares the result with the parity bit from the serial frame. The result of the check is
stored in the receive buffer together with the received data and stop bits. The Parity
Error (UPEn) Flag can then be read by software to check if the frame had a Parity Error.
The UPEn bit is set if the next character that can be read from the receive buffer had a
Parity Error when received and the Parity Checking was enabled at that point (UPMn1 =
1). This bit is valid until the receive buffer (UDRn) is read.
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Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from
ongoing receptions will therefore be lost. When disabled (i.e., the RXENn is set to zero)
the Receiver will no longer override the normal function of the RxD port pin. The
Receiver buffer FIFO will be flushed when the Receiver is disabled. Remaining data in
the buffer will be lost
Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer
will be emptied of its contents. Unread data will be lost. If the buffer has to be flushed
during normal operation, due to for instance an error condition, read the UDRn I/O location until the RXCn Flag is cleared. The following code example shows how to flush the
receive buffer.
Assembly Code Example(1)
USART_Flush:
sbis UCSR0A, RXC0
ret
in
r16, UDR0
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSR0A & (1<<RXC0) ) dummy = UDR0;
}
Note:
1. See “About Code Examples” on page 8.
Asynchronous Data
Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data reception. The clock recovery logic is used for synchronizing the internally
generated baud rate clock to the incoming asynchronous serial frames at the RxD pin.
The data recovery logic samples and low pass filters each incoming bit, thereby improving the noise immunity of the Receiver. The asynchronous reception operational range
depends on the accuracy of the internal baud rate clock, the rate of the incoming
frames, and the frame size in number of bits.
Asynchronous Clock
Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 74 illustrates the sampling process of the start bit of an incoming frame. The sample
rate is 16 times the baud rate for Normal mode, and eight times the baud rate for Double
Speed mode. The horizontal arrows illustrate the synchronization variation due to the
sampling process. Note the larger time variation when using the Double Speed mode
(U2Xn = 1) of operation. Samples denoted zero are samples done when the RxD line is
idle (i.e., no communication activity).
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Figure 74. Start Bit Sampling
RxD
IDLE
START
BIT 0
Sample
(U2X = 0)
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
Sample
(U2X = 1)
0
1
2
3
4
5
6
7
8
1
2
When the clock recovery logic detects a high (idle) to low (start) transition on the RxD
line, the start bit detection sequence is initiated. Let sample 1 denote the first zero-sample as shown in the figure. The clock recovery logic then uses samples 8, 9, and 10 for
Normal mode, and samples 4, 5, and 6 for Double Speed mode (indicated with sample
numbers inside boxes on the figure), to decide if a valid start bit is received. If two or
more of these three samples have logical high levels (the majority wins), the start bit is
rejected as a noise spike and the Receiver starts looking for the next high to low-transition. If however, a valid start bit is detected, the clock recovery logic is synchronized and
the data recovery can begin. The synchronization process is repeated for each start bit.
Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin.
The data recovery unit uses a state machine that has 16 states for each bit in Normal
mode and eight states for each bit in Double Speed mode. Figure 75 shows the sampling of the data bits and the parity bit. Each of the samples is given a number that is
equal to the state of the recovery unit.
Figure 75. Sampling of Data and Parity Bit
RxD
BIT n
Sample
(U2X = 0)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
Sample
(U2X = 1)
1
2
3
4
5
6
7
8
1
The decision of the logic level of the received bit is taken by doing a majority voting of
the logic value to the three samples in the center of the received bit. The center samples
are emphasized on the figure by having the sample number inside boxes. The majority
voting process is done as follows: If two or all three samples have high levels, the
received bit is registered to be a logic 1. If two or all three samples have low levels, the
received bit is registered to be a logic 0. This majority voting process acts as a low pass
filter for the incoming signal on the RxD pin. The recovery process is then repeated until
a complete frame is received. Including the first stop bit. Note that the Receiver only
uses the first stop bit of a frame.
Figure 76 shows the sampling of the stop bit and the earliest possible beginning of the
start bit of the next frame.
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Figure 76. Stop Bit Sampling and Next Start Bit Sampling
RxD
STOP 1
(A)
(B)
(C)
Sample
(U2X = 0)
1
2
3
4
5
6
7
8
9
10
0/1
0/1
0/1
Sample
(U2X = 1)
1
2
3
4
5
6
0/1
The same majority voting is done to the stop bit as done for the other bits in the frame. If
the stop bit is registered to have a logic 0 value, the Frame Error (FEn) Flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after
the last of the bits used for majority voting. For Normal Speed mode, the first low level
sample can be at point marked (A) in Figure 76. For Double Speed mode the first low
level must be delayed to (B). (C) marks a stop bit of full length. The early start bit detection influences the operational range of the Receiver.
Asynchronous Operational
Range
The operational range of the Receiver is dependent on the mismatch between the
received bit rate and the internally generated baud rate. If the Transmitter is sending
frames at too fast or too slow bit rates, or the internally generated baud rate of the
Receiver does not have a similar (see Table 70) base frequency, the Receiver will not
be able to synchronize the frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and
internal receiver baud rate.
( D + 1 )S
R slow = -----------------------------------------S – 1 + D ⋅ S + SF
( D + 2 )S
R fast = ----------------------------------( D + 1 )S + S M
D
Sum of character size and parity size (D = 5 to 10 bit)
S
Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
SF
First sample number used for majority voting. SF = 8 for normal speed and SF = 4
for Double Speed mode.
SM
Middle sample number used for majority voting. SM = 9 for normal speed and
SM = 5 for Double Speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
Table 70 and Table 71 list the maximum receiver baud rate error that can be tolerated.
Note that Normal Speed mode has higher toleration of baud rate variations.
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Table 70. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode
(U2Xn = 0)
D
# (Data+Parity Bit)
Rslow (%)
Rfast (%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
93.20
106.67
+6.67/-6.8
± 3.0
6
94.12
105.79
+5.79/-5.88
± 2.5
7
94.81
105.11
+5.11/-5.19
± 2.0
8
95.36
104.58
+4.58/-4.54
± 2.0
9
95.81
104.14
+4.14/-4.19
± 1.5
10
96.17
103.78
+3.78/-3.83
± 1.5
Table 71. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2Xn = 1)
D
# (Data+Parity Bit)
Rslow (%)
Rfast (%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
94.12
105.66
+5.66/-5.88
± 2.5
6
94.92
104.92
+4.92/-5.08
± 2.0
7
95.52
104,35
+4.35/-4.48
± 1.5
8
96.00
103.90
+3.90/-4.00
± 1.5
9
96.39
103.53
+3.53/-3.61
± 1.5
10
96.70
103.23
+3.23/-3.30
± 1.0
The recommendations of the maximum receiver baud rate error was made under the
assumption that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The Receiver’s system
clock (XTAL) will always have some minor instability over the supply voltage range and
the temperature range. When using a crystal to generate the system clock, this is rarely
a problem, but for a resonator the system clock may differ more than 2% depending of
the resonators tolerance. The second source for the error is more controllable. The baud
rate generator can not always do an exact division of the system frequency to get the
baud rate wanted. In this case an UBRR value that gives an acceptable low error can be
used if possible.
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Multi-processor
Communication Mode
Setting the Multi-processor Communication mode (MPCMn) bit in UCSRnA enables a
filtering function of incoming frames received by the USART Receiver. Frames that do
not contain address information will be ignored and not put into the receive buffer. This
effectively reduces the number of incoming frames that has to be handled by the CPU,
in a system with multiple MCUs that communicate via the same serial bus. The Transmitter is unaffected by the MPCMn setting, but has to be used differently when it is a
part of a system utilizing the Multi-processor Communication mode.
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop
bit indicates if the frame contains data or address information. If the Receiver is set up
for frames with nine data bits, then the ninth bit (RXB8n) is used for identifying address
and data frames. When the frame type bit (the first stop or the ninth bit) is one, the frame
contains an address. When the frame type bit is zero the frame is a data frame.
The Multi-processor Communication mode enables several slave MCUs to receive data
from a master MCU. This is done by first decoding an address frame to find out which
MCU has been addressed. If a particular slave MCU has been addressed, it will receive
the following data frames as normal, while the other slave MCUs will ignore the received
frames until another address frame is received.
Using MPCMn
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZ =
7). The ninth bit (TXB8n) must be set when an address frame (TXB8n = 1) or cleared
when a data frame (TXB = 0) is being transmitted. The slave MCUs must in this case be
set to use a 9-bit character frame format.
The following procedure should be used to exchange data in Multi-processor Communication mode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCMn in UCSRnA is set).
2. The Master MCU sends an address frame, and all slaves receive and read this
frame. In the Slave MCUs, the RXCn Flag in UCSRnA will be set as normal.
3. Each Slave MCU reads the UDRn Register and determines if it has been
selected. If so, it clears the MPCMn bit in UCSRnA, otherwise it waits for the next
address byte and keeps the MPCMn setting.
4. The addressed MCU will receive all data frames until a new address frame is
received. The other Slave MCUs, which still have the MPCMn bit set, will ignore
the data frames.
5. When the last data frame is received by the addressed MCU, the addressed
MCU sets the MPCMn bit and waits for a new address frame from master. The
process then repeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the
Receiver must change between using n and n+1 character frame formats. This makes
full-duplex operation difficult since the Transmitter and Receiver uses the same character size setting. If 5- to 8-bit character frames are used, the Transmitter must be set to
use two stop bit (USBSn = 1) since the first stop bit is used for indicating the frame type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCMn bit.
The MPCMn bit shares the same I/O location as the TXCn Flag and this might accidentally be cleared when using SBI or CBI instructions.
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USART Register
Description
UDRn – USART I/O Data
Register n
Bit
7
6
5
4
3
2
1
0
RXB[7:0]
UDRn (Read)
TXB[7:0]
UDRn (Write)
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers
share the same I/O address referred to as USART Data Register or UDRn. The Transmit Data Buffer Register (TXB) will be the destination for data written to the UDRn
Register location. Reading the UDRn Register location will return the contents of the
Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter
and set to zero by the Receiver.
The transmit buffer can only be written when the UDREn Flag in the UCSRnA Register
is set. Data written to UDRn when the UDREn Flag is not set, will be ignored by the
USART Transmitter. When data is written to the transmit buffer, and the Transmitter is
enabled, the Transmitter will load the data into the Transmit Shift Register when the
Shift Register is empty. Then the data will be serially transmitted on the TxD pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever
the receive buffer is accessed. Due to this behavior of the receive buffer, do not use
Read-Modify-Write instructions (SBI and CBI) on this location. Be careful when using bit
test instructions (SBIC and SBIS), since these also will change the state of the FIFO.
UCSRnA – USART Control
and Status Register n A
Bit
7
6
5
4
3
2
1
0
RXCn
TXCn
UDREn
FEn
DORn
UPEn
U2Xn
MPCMn
Read/Write
R
R/W
R
R
R
R
R/W
R/W
Initial Value
0
0
1
0
0
0
0
0
UCSRnA
• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the
receive buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive buffer will be flushed and consequently the RXCn bit will become
zero. The RXCn Flag can be used to generate a Receive Complete interrupt (see
description of the RXCIEn bit).
• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted
out and there are no new data currently present in the transmit buffer (UDRn). The
TXCn Flag bit is automatically cleared when a transmit complete interrupt is executed,
or it can be cleared by writing a one to its bit location. The TXCn Flag can generate a
Transmit Complete interrupt (see description of the TXCIEn bit).
• Bit 5 – UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If
UDREn is one, the buffer is empty, and therefore ready to be written. The UDREn Flag
can generate a Data Register Empty interrupt (see description of the UDRIEn bit).
UDREn is set after a reset to indicate that the Transmitter is ready.
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• Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when
received. I.e., when the first stop bit of the next character in the receive buffer is zero.
This bit is valid until the receive buffer (UDRn) is read. The FEn bit is zero when the stop
bit of received data is one. Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the
receive buffer is full (two characters), it is a new character waiting in the Receive Shift
Register, and a new start bit is detected. This bit is valid until the receive buffer (UDRn)
is read. Always set this bit to zero when writing to UCSRnA.
• Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received
and the Parity Checking was enabled at that point (UPMn1 = 1). This bit is valid until the
receive buffer (UDRn) is read. Always set this bit to zero when writing to UCSRnA.
• Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using
synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written to one, all the incoming frames received by the USART Receiver that do not contain
address information will be ignored. The Transmitter is unaffected by the MPCMn setting. For more detailed information see “Multi-processor Communication Mode” on page
172.
UCSRnB – USART Control
and Status Register n B
Bit
7
6
5
4
3
2
1
0
RXCIEn
TXCIEn
UDRIEn
RXENn
TXENn
UCSZn2
RXB8n
TXB8n
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
R/W
Initial Value
0
0
0
0
0
0
0
0
UCSRnB
• Bit 7 – RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete
interrupt will be generated only if the RXCIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete
interrupt will be generated only if the TXCIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty
interrupt will be generated only if the UDRIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXENn: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal
port operation for the RxD pin when enabled. Disabling the Receiver will flush the
receive buffer invalidating the FEn, DORn, and UPEn Flags.
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• Bit 3 – TXENn: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port operation for the TxD pin when enabled. The disabling of the Transmitter
(writing TXENn to zero) will not become effective until ongoing and pending transmissions are completed, i.e., when the Transmit Shift Register and Transmit Buffer Register
do not contain data to be transmitted. When disabled, the Transmitter will no longer
override the TxD port.
• Bit 2 – UCSZn2: Character Size
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data
bits (Character SiZe) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8n: Receive Data Bit 8
RXB8n is the ninth data bit of the received character when operating with serial frames
with nine data bits. Must be read before reading the low bits from UDRn.
• Bit 0 – TXB8n: Transmit Data Bit 8
TXB8n is the ninth data bit in the character to be transmitted when operating with serial
frames with nine data bits. Must be written before writing the low bits to UDRn.
UCSRnC – USART Control
and Status Register n C
Bit
7
6
5
4
3
2
1
0
–
UMSELn
UPMn1
UPMn0
USBSn
UCSZn1
UCSZn0
UCPOLn
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
1
1
0
UCSRnC
• Bit 6 – UMSELn: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
Table 72. UMSEL Bit Settings
UMSELn
Mode
0
Asynchronous Operation
1
Synchronous Operation
• Bit 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter will automatically generate and send the parity of the transmitted data bits within
each frame. The Receiver will generate a parity value for the incoming data and compare it to the UPMn0 setting. If a mismatch is detected, the UPEn Flag in UCSRnA will
be set.
Table 73. UPM Bits Settings
UPMn1
UPMn0
Parity Mode
0
0
Disabled
0
1
Reserved
1
0
Enabled, Even Parity
1
1
Enabled, Odd Parity
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• Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver
ignores this setting.
Table 74. USBS Bit Settings
USBSn
Stop Bit(s)
0
1-bit
1
2-bit
• Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data
bits (Character SiZe) in a frame the Receiver and Transmitter use.
Table 75. UCSZ Bits Settings
UCSZn2
UCSZn1
UCSZn0
Character Size
0
0
0
5-bit
0
0
1
6-bit
0
1
0
7-bit
0
1
1
8-bit
1
0
0
Reserved
1
0
1
Reserved
1
1
0
Reserved
1
1
1
9-bit
• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous
mode is used. The UCPOLn bit sets the relationship between data output change and
data input sample, and the synchronous clock (XCK).
Table 76. UCPOL Bit Settings
Transmitted Data Changed
(Output of TxD Pin)
Received Data Sampled
(Input on RxD Pin)
0
Rising XCK Edge
Falling XCK Edge
1
Falling XCK Edge
Rising XCK Edge
UCPOLn
UBRRnL and UBRRnH –
USART Baud Rate Registers
Bit
15
14
13
12
–
–
–
–
11
10
9
8
UBRRn[11:8]
UBRRnH
UBRRn[7:0]
7
Read/Write
Initial Value
176
6
5
UBRRnL
4
3
2
1
0
R
R
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit
must be written to zero when UBRRH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the
four most significant bits, and the UBRRL contains the eight least significant bits of the
USART baud rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate is changed. Writing UBRRL will trigger an immediate update of
the baud rate prescaler.
Examples of Baud Rate
Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for
asynchronous operation can be generated by using the UBRR settings in Table 77.
UBRR values which yield an actual baud rate differing less than 0.5% from the target
baud rate, are bold in the table. Higher error ratings are acceptable, but the Receiver will
have less noise resistance when the error ratings are high, especially for large serial
frames (see “Asynchronous Operational Range” on page 170). The error values are calculated using the following equation:
BaudRate Closest Match
- – 1⎞ • 100%
Error[%] = ⎛ ------------------------------------------------------⎝
⎠
BaudRate
Table 77. Examples of UBRR Settings for Commonly Used Oscillator Frequencies
fosc = 1.0000 MHz
fosc = 1.8432 MHz
fosc = 2.0000 MHz
Baud
Rate
(bps)
UBRR
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
51
0.2%
103
0.2%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
25
0.2%
51
0.2%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
12
0.2%
25
0.2%
14.4k
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
19.2k
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
28.8k
1
8.5%
3
8.5%
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
38.4k
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
57.6k
0
8.5%
1
8.5%
1
0.0%
3
0.0%
1
8.5%
3
8.5%
76.8k
–
–
1
-18.6%
1
-25.0%
2
0.0%
1
-18.6%
2
8.5%
115.2k
–
–
0
8.5%
0
0.0%
1
0.0%
0
8.5%
1
8.5%
230.4k
–
–
–
–
–
–
0
0.0%
–
–
–
–
250k
–
–
–
–
–
–
–
–
–
–
0
0.0%
Max.
1.
U2Xn = 0
(1)
Error
U2Xn = 1
UBRR
62.5 kbps
Error
125 kbps
U2Xn = 0
UBRR
Error
115.2 kbps
U2Xn = 1
UBRR
Error
230.4 kbps
U2Xn = 0
UBRR
Error
125 kbps
U2Xn = 1
UBRR
Error
250 kbps
UBRR = 0, Error = 0.0%
177
2570J–AVR–11/06
Table 78. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 3.6864 MHz
fosc = 4.0000 MHz
fosc = 7.3728 MHz
Baud
Rate
(bps)
UBRR
2400
95
0.0%
191
0.0%
103
0.2%
207
0.2%
191
0.0%
383
0.0%
4800
47
0.0%
95
0.0%
51
0.2%
103
0.2%
95
0.0%
191
0.0%
9600
23
0.0%
47
0.0%
25
0.2%
51
0.2%
47
0.0%
95
0.0%
14.4k
15
0.0%
31
0.0%
16
2.1%
34
-0.8%
31
0.0%
63
0.0%
19.2k
11
0.0%
23
0.0%
12
0.2%
25
0.2%
23
0.0%
47
0.0%
28.8k
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
15
0.0%
31
0.0%
38.4k
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
57.6k
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
76.8k
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
115.2k
1
0.0%
3
0.0%
1
8.5%
3
8.5%
3
0.0%
7
0.0%
230.4k
0
0.0%
1
0.0%
0
8.5%
1
8.5%
1
0.0%
3
0.0%
250k
0
-7.8%
1
-7.8%
0
0.0%
1
0.0%
1
-7.8%
3
-7.8%
0.5M
–
–
0
-7.8%
–
–
0
0.0%
0
-7.8%
1
-7.8%
–
–
–
–
–
–
–
–
–
–
0
-7.8%
1M
Max.
1.
178
(1)
U2Xn = 0
U2Xn = 1
Error
UBRR
230.4 kbps
U2Xn = 0
Error
460.8 kbps
UBRR
U2Xn = 1
Error
250 kbps
UBRR
U2Xn = 0
Error
0.5 Mbps
UBRR
U2Xn = 1
Error
460.8 kbps
UBRR
Error
921.6 kbps
UBRR = 0, Error = 0.0%
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 79. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 11.0592 MHz
fosc = 8.0000 MHz
fosc = 14.7456 MHz
Baud
Rate
(bps)
UBRR
2400
207
0.2%
416
-0.1%
287
0.0%
575
0.0%
383
0.0%
767
0.0%
4800
103
0.2%
207
0.2%
143
0.0%
287
0.0%
191
0.0%
383
0.0%
9600
51
0.2%
103
0.2%
71
0.0%
143
0.0%
95
0.0%
191
0.0%
14.4k
34
-0.8%
68
0.6%
47
0.0%
95
0.0%
63
0.0%
127
0.0%
19.2k
25
0.2%
51
0.2%
35
0.0%
71
0.0%
47
0.0%
95
0.0%
28.8k
16
2.1%
34
-0.8%
23
0.0%
47
0.0%
31
0.0%
63
0.0%
38.4k
12
0.2%
25
0.2%
17
0.0%
35
0.0%
23
0.0%
47
0.0%
57.6k
8
-3.5%
16
2.1%
11
0.0%
23
0.0%
15
0.0%
31
0.0%
76.8k
6
-7.0%
12
0.2%
8
0.0%
17
0.0%
11
0.0%
23
0.0%
115.2k
3
8.5%
8
-3.5%
5
0.0%
11
0.0%
7
0.0%
15
0.0%
230.4k
1
8.5%
3
8.5%
2
0.0%
5
0.0%
3
0.0%
7
0.0%
250k
1
0.0%
3
0.0%
2
-7.8%
5
-7.8%
3
-7.8%
6
5.3%
0.5M
0
0.0%
1
0.0%
–
–
2
-7.8%
1
-7.8%
3
-7.8%
–
–
0
0.0%
–
–
–
–
0
-7.8%
1
-7.8%
U2Xn = 0
1M
Max.
1.
(1)
Error
U2Xn = 1
UBRR
0.5 Mbps
Error
1 Mbps
U2Xn = 0
UBRR
Error
691.2 kbps
U2Xn = 1
UBRR
Error
1.3824 Mbps
U2Xn = 0
UBRR
Error
921.6 kbps
U2Xn = 1
UBRR
Error
1.8432 Mbps
UBRR = 0, Error = 0.0%
179
2570J–AVR–11/06
Table 80. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 16.0000 MHz
fosc = 18.4320 MHz
fosc = 20.0000 MHz
Baud
Rate
(bps)
UBRR
2400
416
-0.1%
832
0.0%
479
0.0%
959
0.0%
520
0.0%
1041
0.0%
4800
207
0.2%
416
-0.1%
239
0.0%
479
0.0%
259
0.2%
520
0.0%
9600
103
0.2%
207
0.2%
119
0.0%
239
0.0%
129
0.2%
259
0.2%
14.4k
68
0.6%
138
-0.1%
79
0.0%
159
0.0%
86
-0.2%
173
-0.2%
19.2k
51
0.2%
103
0.2%
59
0.0%
119
0.0%
64
0.2%
129
0.2%
28.8k
34
-0.8%
68
0.6%
39
0.0%
79
0.0%
42
0.9%
86
-0.2%
38.4k
25
0.2%
51
0.2%
29
0.0%
59
0.0%
32
-1.4%
64
0.2%
57.6k
16
2.1%
34
-0.8%
19
0.0%
39
0.0%
21
-1.4%
42
0.9%
76.8k
12
0.2%
25
0.2%
14
0.0%
29
0.0%
15
1.7%
32
-1.4%
115.2k
8
-3.5%
16
2.1%
9
0.0%
19
0.0%
10
-1.4%
21
-1.4%
230.4k
3
8.5%
8
-3.5%
4
0.0%
9
0.0%
4
8.5%
10
-1.4%
250k
3
0.0%
7
0.0%
4
-7.8%
8
2.4%
4
0.0%
9
0.0%
0.5M
1
0.0%
3
0.0%
–
–
4
-7.8%
–
–
4
0.0%
0
0.0%
1
0.0%
–
–
–
–
–
–
–
–
1M
Max.
1.
180
(1)
U2Xn = 0
Error
U2Xn = 1
UBRR
1 Mbps
Error
2 Mbps
U2Xn = 0
UBRR
Error
1.152 Mbps
U2Xn = 1
UBRR
Error
2.304 Mbps
U2Xn = 0
UBRR
Error
1.25 Mbps
U2Xn = 1
UBRR
Error
2.5 Mbps
UBRR = 0, Error = 0.0%
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
USI – Universal Serial
Interface
The Universal Serial Interface, or USI, provides the basic hardware resources needed
for serial communication. Combined with a minimum of control software, the USI allows
significantly higher transfer rates and uses less code space than solutions based on
software only. Interrupts are included to minimize the processor load. The main features
of the USI are:
• Two-wire Synchronous Data Transfer (Master or Slave)
• Three-wire Synchronous Data Transfer (Master or Slave)
• Data Received Interrupt
• Wake up from Idle Mode
• In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
• Two-wire Start Condition Detector with Interrupt Capability
Overview
A simplified block diagram of the USI is shown on Figure 77. For the actual placement of
I/O pins, refer to “Pinout ATmega3250/6450” on page 2 and “Pinout ATmega325/645”
on page 3. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in
bold. The device-specific I/O Register and bit locations are listed in the “USI Register
Descriptions” on page 188.
Figure 77. Universal Serial Interface, Block Diagram
USIPF
1
0
4-bit Counter
USIDC
USIOIF
USISIF
(Output only)
DI/SDA
(Input/Open Drain)
USCK/SCL
(Input/Open Drain)
3
2
USIDR
DATA BUS
DO
Bit0
Bit7
D Q
LE
TIM0 COMP
3
2
0
1
1
0
CLOCK
HOLD
[1]
Two-wire Clock
Control Unit
USISR
USITC
USICLK
USICS0
USICS1
USIWM0
USIWM1
USISIE
USIOIE
2
USICR
The 8-bit Shift Register is directly accessible via the data bus and contains the incoming
and outgoing data. The register has no buffering so the data must be read as quickly as
possible to ensure that no data is lost. The most significant bit is connected to one of two
output pins depending of the wire mode configuration. A transparent latch is inserted
between the Serial Register Output and output pin, which delays the change of data output to the opposite clock edge of the data input sampling. The serial input is always
sampled from the Data Input (DI) pin independent of the configuration.
The 4-bit counter can be both read and written via the data bus, and can generate an
overflow interrupt. Both the Serial Register and the counter are clocked simultaneously
by the same clock source. This allows the counter to count the number of bits received
or transmitted and generate an interrupt when the transfer is complete. Note that when
an external clock source is selected the counter counts both clock edges. In this case
the counter counts the number of edges, and not the number of bits. The clock can be
181
2570J–AVR–11/06
selected from three different sources: The USCK pin, Timer/Counter0 Compare Match
or from software.
The Two-wire clock control unit can generate an interrupt when a start condition is
detected on the Two-wire bus. It can also generate wait states by holding the clock pin
low after a start condition is detected, or after the counter overflows.
Functional Descriptions
Three-wire Mode
The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0
and 1, but does not have the slave select (SS) pin functionality. However, this feature
can be implemented in software if necessary. Pin names used by this mode are: DI, DO,
and USCK.
Figure 78. Three-wire Mode Operation, Simplified Diagram
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
SLAVE
DO
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
DI
Bit0
USCK
PORTxn
MASTER
Figure 78 shows two USI units operating in Three-wire mode, one as Master and one as
Slave. The two Shift Registers are interconnected in such way that after eight USCK
clocks, the data in each register are interchanged. The same clock also increments the
USI’s 4-bit counter. The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be
used to determine when a transfer is completed. The clock is generated by the Master
device software by toggling the USCK pin via the PORT Register or by writing a one to
the USITC bit in USICR.
182
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 79. Three-wire Mode, Timing Diagram
CYCLE
( Reference )
1
2
3
4
5
6
7
8
USCK
USCK
DO
MSB
DI
MSB
A
B
C
6
5
4
3
2
1
LSB
6
5
4
3
2
1
LSB
D
E
The Three-wire mode timing is shown in Figure 79. At the top of the figure is a USCK
cycle reference. One bit is shifted into the USI Shift Register (USIDR) for each of these
cycles. The USCK timing is shown for both external clock modes. In External Clock
mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (Data Register is shifted by one) at negative edges. External Clock mode 1 (USICS0 = 1) uses the
opposite edges versus mode 0, i.e., samples data at negative and changes the output at
positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 79.), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on
the protocol used, enables its output driver (mark A and B). The output is set up
by writing the data to be transmitted to the Serial Data Register. Enabling of the
output is done by setting the corresponding bit in the port Data Direction Register. Note that point A and B does not have any specific order, but both must be at
least one half USCK cycle before point C where the data is sampled. This must
be done to ensure that the data setup requirement is satisfied. The 4-bit counter
is reset to zero.
2. The Master generates a clock pulse by software toggling the USCK line twice (C
and D). The bit value on the slave and master’s data input (DI) pin is sampled by
the USI on the first edge (C), and the data output is changed on the opposite
edge (D). The 4-bit counter will count both edges.
3. Step 2. is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that the transfer is completed. The data bytes transferred must now be
processed before a new transfer can be initiated. The overflow interrupt will wake
up the processor if it is set to Idle mode. Depending of the protocol used the
slave device can now set its output to high impedance.
SPI Master Operation
Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
ldi
r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
sts
USICR,r16
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SPITransfer_loop
lds
r16,USIDR
183
2570J–AVR–11/06
ret
The code is size optimized using only eight instructions (+ ret). The code example
assumes that the DO and USCK pins are enabled as output in the DDRE Register. The
value stored in register r16 prior to the function is called is transferred to the Slave
device, and when the transfer is completed the data received from the Slave is stored
back into the r16 Register.
The second and third instructions clears the USI Counter Overflow Flag and the USI
counter value. The fourth and fifth instruction set Three-wire mode, positive edge Shift
Register clock, count at USITC strobe, and toggle USCK. The loop is repeated 16 times.
184
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
The following code demonstrates how to use the USI module as a SPI Master with maximum speed (fsck = fck/4):
SPITransfer_Fast:
sts
USIDR,r16
ldi
r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi
r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
sts
USICR,r16 ; MSB
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16
sts
USICR,r17
sts
USICR,r16 ; LSB
sts
USICR,r17
lds
r16,USIDR
ret
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi
r16,(1<<USIWM0)|(1<<USICS1)
sts
USICR,r16
...
SlaveSPITransfer:
sts
USIDR,r16
ldi
r16,(1<<USIOIF)
sts
USISR,r16
SlaveSPITransfer_loop:
lds
r16, USISR
sbrs
r16, USIOIF
rjmp
SlaveSPITransfer_loop
lds
r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example
assumes that the DO is configured as output and USCK pin is configured as input in the
DDR Register. The value stored in register r16 prior to the function is called is trans-
185
2570J–AVR–11/06
ferred to the master device, and when the transfer is completed the data received from
the Master is stored back into the r16 Register.
Note that the first two instructions is for initialization only and needs only to be executed
once.These instructions sets Three-wire mode and positive edge Shift Register clock.
The loop is repeated until the USI Counter Overflow Flag is set.
Two-wire Mode
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew
rate limiting on outputs and input noise filtering. Pin names used by this mode are SCL
and SDA.
Figure 80. Two-wire Mode Operation, Simplified Diagram
VCC
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
HOLD
SCL
Two-wire Clock
Control Unit
SLAVE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
SDA
Bit0
SCL
PORTxn
MASTER
Figure 80 shows two USI units operating in Two-wire mode, one as Master and one as
Slave. It is only the physical layer that is shown since the system operation is highly
dependent of the communication scheme used. The main differences between the Master and Slave operation at this level, is the serial clock generation which is always done
by the Master, and only the Slave uses the clock control unit. Clock generation must be
implemented in software, but the shift operation is done automatically by both devices.
Note that only clocking on negative edge for shifting data is of practical use in this mode.
The slave can insert wait states at start or end of transfer by forcing the SCL clock low.
This means that the Master must always check if the SCL line was actually released
after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate
that the transfer is completed. The clock is generated by the master by toggling the
USCK pin via the PORT Register.
The data direction is not given by the physical layer. A protocol, like the one used by the
TWI-bus, must be implemented to control the data flow.
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Figure 81. Two-wire Mode, Typical Timing Diagram
SDA
SCL
S
A
B
1-7
8
9
1-8
9
1-8
9
ADDRESS
R/W
ACK
DATA
ACK
DATA
ACK
C
D
E
P
F
Referring to the timing diagram (Figure 81.), a bus transfer involves the following steps:
1. The a start condition is generated by the Master by forcing the SDA low line while
the SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of
the Shift Register, or by setting the corresponding bit in the PORT Register to
zero. Note that the Data Direction Register bit must be set to one for the output to
be enabled. The slave device’s start detector logic (Figure 82.) detects the start
condition and sets the USISIF Flag. The flag can generate an interrupt if
necessary.
2. In addition, the start detector will hold the SCL line low after the Master has
forced an negative edge on this line (B). This allows the Slave to wake up from
sleep or complete its other tasks before setting up the Shift Register to receive
the address. This is done by clearing the start condition flag and reset the
counter.
3. The Master set the first bit to be transferred and releases the SCL line (C). The
Slave samples the data and shift it into the Serial Register at the positive edge of
the SCL clock.
4. After eight bits are transferred containing slave address and data direction (read
or write), the Slave counter overflows and the SCL line is forced low (D). If the
slave is not the one the Master has addressed, it releases the SCL line and waits
for a new start condition.
5. If the Slave is addressed it holds the SDA line low during the acknowledgment
cycle before holding the SCL line low again (i.e., the Counter Register must be
set to 14 before releasing SCL at (D)). Depending of the R/W bit the Master or
Slave enables its output. If the bit is set, a master read operation is in progress
(i.e., the slave drives the SDA line) The slave can hold the SCL line low after the
acknowledge (E).
6. Multiple bytes can now be transmitted, all in same direction, until a stop condition
is given by the Master (F). Or a new start condition is given.
If the Slave is not able to receive more data it does not acknowledge the data byte it has
last received. When the Master does a read operation it must terminate the operation by
force the acknowledge bit low after the last byte transmitted.
Figure 82. Start Condition Detector, Logic Diagram
USISIF
D Q
D Q
CLR
CLR
SDA
CLOCK
HOLD
SCL
Write( USISIF)
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Start Condition Detector
The start condition detector is shown in Figure 82. The SDA line is delayed (in the range
of 50 to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is
only enabled in Two-wire mode.
The start condition detector is working asynchronously and can therefore wake up the
processor from the Power-down sleep mode. However, the protocol used might have
restrictions on the SCL hold time. Therefore, when using this feature in this case the
Oscillator start-up time set by the CKSEL Fuses (see “Clock Systems and their Distribution” on page 25) must also be taken into the consideration. Refer to the USISIF bit
description on page 189 for further details.
Clock speed considerations.
Maximum frequency for SCL and SCK is fCK /4. This is also the maximum data transmit
and receieve rate in both two- and three-wire mode. In two-wire slave mode the Twowire Clock Control Unit will hold the SCL low until the slave is ready to receive more
data. This may reduce the actual data rate in two-wire mode.
Alternative USI Usage
When the USI unit is not used for serial communication, it can be set up to do alternative
tasks due to its flexible design.
Half-duplex Asynchronous
Data Transfer
By utilizing the Shift Register in Three-wire mode, it is possible to implement a more
compact and higher performance UART than by software only.
4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note
that if the counter is clocked externally, both clock edges will generate an increment.
12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
Edge Triggered External
Interrupt
By setting the counter to maximum value (F) it can function as an additional external
interrupt. The Overflow Flag and Interrupt Enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.
Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock
strobe.
USI Register
Descriptions
USIDR – USI Data Register
Bit
7
6
5
4
3
2
1
0
(0xBA)
MSB
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
USIDR
The USI uses no buffering of the Serial Register, i.e., when accessing the Data Register
(USIDR) the Serial Register is accessed directly. If a serial clock occurs at the same
cycle the register is written, the register will contain the value written and no shift is performed. A (left) shift operation is performed depending of the USICS1..0 bits setting. The
shift operation can be controlled by an external clock edge, by a Timer/Counter0 Compare Match, or directly by software using the USICLK strobe bit. Note that even when no
wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the
external clock input (USCK/SCL) can still be used by the Shift Register.
The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the Data Register. The output latch is open
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(transparent) during the first half of a serial clock cycle when an external clock source is
selected (USICS1 = 1), and constantly open when an internal clock source is used
(USICS1 = 0). The output will be changed immediately when a new MSB written as long
as the latch is open. The latch ensures that data input is sampled and data output is
changed on opposite clock edges.
Note that the corresponding Data Direction Register to the pin must be set to one for
enabling data output from the Shift Register.
USISR – USI Status Register
Bit
7
6
5
4
3
2
1
0
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
Read/Write
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0xB9)
USISR
The Status Register contains Interrupt Flags, line Status Flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When Two-wire mode is selected, the USISIF Flag is set (to one) when a start condition
is detected. When output disable mode or Three-wire mode is selected, the flag is set
when the 4-bit counter is incremented.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the
Global Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one
to the USISIF bit. Clearing this bit will release the start detection hold of USCL in Twowire mode.
A start condition interrupt will wake up the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to
0). An interrupt will be generated when the flag is set while the USIOIE bit in USICR and
the Global Interrupt Enable Flag are set. The flag will only be cleared if a one is written
to the USIOIF bit. Clearing this bit will release the counter overflow hold of SCL in Twowire mode.
A counter overflow interrupt will wake up the processor from Idle sleep mode.
• Bit 5 – USIPF: Stop Condition Flag
When Two-wire mode is selected, the USIPF Flag is set (one) when a stop condition is
detected. The flag is cleared by writing a one to this bit. Note that this is not an Interrupt
Flag. This signal is useful when implementing Two-wire bus master arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the Shift Register differs from the physical pin value.
The flag is only valid when Two-wire mode is used. This signal is useful when implementing Two-wire bus master arbitration.
• Bits 3:0 – USICNT3:0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be
read or written by the CPU.
The 4-bit counter increments by one for each clock generated either by the external
clock edge detector, by a Timer/Counter0 Compare Match, or by software using USICLK or USITC strobe bits. The clock source depends of the setting of the USICS1..0
bits. For external clock operation a special feature is added that allows the clock to be
generated by writing to the USITC strobe bit. This feature is enabled by write a one to
the USICLK bit while setting an external clock source (USICS1 = 1).
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Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) are can still be used by the counter.
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USICR – USI Control Register
Bit
7
6
5
4
3
2
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
W
W
Initial Value
0
0
0
0
0
0
0
0
(0xB8)
USICR
The Control Register includes interrupt enable control, wire mode setting, Clock Select
setting, and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending
interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will
immediately be executed. Refer to the USISIF bit description on page 189 for further
details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when the USIOIE and the Global Interrupt Enable Flag is set to one, this will
immediately be executed. Refer to the USIOIF bit description on page 189 for further
details.
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are affected by these bits. Data and clock inputs are not affected by the mode
selected and will always have the same function. The counter and Shift Register can
therefore be clocked externally, and data input sampled, even when outputs are disabled. The relations between USIWM1:0 and the USI operation is summarized in Table
81.
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Table 81. Relations between USIWM1..0 and the USI Operation
USIWM1
USIWM0
0
0
Outputs, clock hold, and start detector disabled. Port pins operates as
normal.
0
1
Three-wire mode. Uses DO, DI, and USCK pins.
The Data Output (DO) pin overrides the corresponding bit in the PORT
Register in this mode. However, the corresponding DDR bit still
controls the data direction. When the port pin is set as input the pins
pull-up is controlled by the PORT bit.
The Data Input (DI) and Serial Clock (USCK) pins do not affect the
normal port operation. When operating as master, clock pulses are
software generated by toggling the PORT Register, while the data
direction is set to output. The USITC bit in the USICR Register can be
used for this purpose.
1
0
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).
The Serial Data (SDA) and the Serial Clock (SCL) pins are bidirectional and uses open-collector output drives. The output drivers
are enabled by setting the corresponding bit for SDA and SCL in the
DDR Register.
When the output driver is enabled for the SDA pin, the output driver will
force the line SDA low if the output of the Shift Register or the
corresponding bit in the PORT Register is zero. Otherwise the SDA
line will not be driven (i.e., it is released). When the SCL pin output
driver is enabled the SCL line will be forced low if the corresponding bit
in the PORT Register is zero, or by the start detector. Otherwise the
SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition
and the output is enabled. Clearing the Start Condition Flag (USISIF)
releases the line. The SDA and SCL pin inputs is not affected by
enabling this mode. Pull-ups on the SDA and SCL port pin are
disabled in Two-wire mode.
1
1
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the Two-wire mode described above, except
that the SCL line is also held low when a counter overflow occurs, and
is held low until the Counter Overflow Flag (USIOIF) is cleared.
Note:
192
Description
1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL)
respectively to avoid confusion between the modes of operation.
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• Bit 3:2 – USICS1:0: Clock Source Select
These bits set the clock source for the Shift Register and counter. The data output latch
ensures that the output is changed at the opposite edge of the sampling of the data
input (DI/SDA) when using external clock source (USCK/SCL). When software strobe or
Timer/Counter0 Compare Match clock option is selected, the output latch is transparent
and therefore the output is changed immediately. Clearing the USICS1..0 bits enables
software strobe option. When using this option, writing a one to the USICLK bit clocks
both the Shift Register and the counter. For external clock source (USICS1 = 1), the
USICLK bit is no longer used as a strobe, but selects between external clocking and
software clocking by the USITC strobe bit.
Table 82 shows the relationship between the USICS1..0 and USICLK setting and clock
source used for the Shift Register and the 4-bit counter.
Table 82. Relations between the USICS1..0 and USICLK Setting
Shift Register Clock
Source
4-bit Counter Clock
Source
0
No Clock
No Clock
0
1
Software clock strobe
(USICLK)
Software clock strobe
(USICLK)
0
1
X
Timer/Counter0 Compare
Match
Timer/Counter0 Compare
Match
1
0
0
External, positive edge
External, both edges
1
1
0
External, negative edge
External, both edges
1
0
1
External, positive edge
Software clock strobe
(USITC)
1
1
1
External, negative edge
Software clock strobe
(USITC)
USICS1
USICS0
USICLK
0
0
0
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the Shift Register to shift one step and the
counter to increment by one, provided that the USICS1..0 bits are set to zero and by
doing so the software clock strobe option is selected. The output will change immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value
shifted into the Shift Register is sampled the previous instruction cycle. The bit will be
read as zero.
When an external clock source is selected (USICS1 = 1), the USICLK function is
changed from a clock strobe to a Clock Select Register. Setting the USICLK bit in this
case will select the USITC strobe bit as clock source for the 4-bit counter (see Table 82).
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from
1 to 0. The toggling is independent of the setting in the Data Direction Register, but if the
PORT value is to be shown on the pin the DDRE4 must be set as output (to one). This
feature allows easy clock generation when implementing master devices. The bit will be
read as zero.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to
one, writing to the USITC strobe bit will directly clock the 4-bit counter. This allows an
early detection of when the transfer is done when operating as a master device.
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Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on
the negative pin AIN1, the Analog Comparator output, ACO, is set. The comparator’s
output can be set to trigger the Timer/Counter1 Input Capture function. In addition, the
comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The
user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 83.
The Power Reduction ADC bit, PRADC, in “Power Reduction Register” on page 35 must
be disabled by writing a logical zero to be able to use the ADC module.
Figure 83. Analog Comparator Block Diagram(2)
BANDGAP
REFERENCE
ACBG
ACME
ADEN
ADC MULTIPLEXER
OUTPUT (1)
Notes:
ADCSRB – ADC Control and
Status Register B
1. See Table 84 on page 196.
2. Refer to Figure 1 on page 2, Figure 2 on page 3, and “Alternate Functions of Port E”
on page 70 for Analog Comparator pin placement.
Bit
7
6
5
4
3
2
1
0
(0x7B)
–
ACME
–
–
–
ADTS2
ADTS1
ADTS0
Read/Write
R
R/W
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is
zero), the ADC multiplexer selects the negative input to the Analog Comparator. When
this bit is written logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed description of this bit, see “Analog Comparator Multiplexed Input” on
page 196.
ACSR – Analog Comparator
Control and Status Register
194
Bit
7
6
5
4
3
2
1
0
0x30 (0x50)
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
N/A
0
0
0
0
0
ACSR
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• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off.
This bit can be set at any time to turn off the Analog Comparator. This will reduce power
consumption in Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt
can occur when the bit is changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the
Analog Comparator. When this bit is cleared, AIN0 is applied to the positive input of the
Analog Comparator. When the bandgap reference is used as input to the analog comparator, it will take a certain time for the voltage to stabilize. If not stabilized, the the first
converison may give a wrong value. See “Internal Voltage Reference” on page 44.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to
ACO. The synchronization introduces a delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode
defined by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if
the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a
logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Comparator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the Input Capture function in Timer/Counter1 to
be triggered by the Analog Comparator. The comparator output is in this case directly
connected to the Input Capture front-end logic, making the comparator utilize the noise
canceler and edge select features of the Timer/Counter1 Input Capture interrupt. When
written logic zero, no connection between the Analog Comparator and the Input Capture
function exists. To make the comparator trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask Register (TIMSK1) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings are shown in Table 83.
Table 83. ACIS1/ACIS0 Settings
ACIS1
ACIS0
Interrupt Mode
0
0
Comparator Interrupt on Output Toggle.
0
1
Reserved
1
0
Comparator Interrupt on Falling Output Edge.
1
1
Comparator Interrupt on Rising Output Edge.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt
can occur when the bits are changed.
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Analog Comparator
Multiplexed Input
It is possible to select any of the ADC7..0 pins to replace the negative input to the Analog Comparator. The ADC multiplexer is used to select this input, and consequently, the
ADC must be switched off to utilize this feature. If the Analog Comparator Multiplexer
Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is
zero), MUX2..0 in ADMUX select the input pin to replace the negative input to the Analog Comparator, as shown in Table 84. If ACME is cleared or ADEN is set, AIN1 is
applied to the negative input to the Analog Comparator.
Table 84. Analog Comparator Multiplexed Input
DIDR1 – Digital Input Disable
Register 1
ACME
ADEN
MUX2..0
Analog Comparator Negative Input
0
x
xxx
AIN1
1
1
xxx
AIN1
1
0
000
ADC0
1
0
001
ADC1
1
0
010
ADC2
1
0
011
ADC3
1
0
100
ADC4
1
0
101
ADC5
1
0
110
ADC6
1
0
111
ADC7
Bit
7
6
5
4
3
2
1
0
(0x7F)
–
–
–
–
–
–
AIN1D
AIN0D
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR1
• Bit 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled.
The corresponding PIN Register bit will always read as zero when this bit is set. When
an analog signal is applied to the AIN1/0 pin and the digital input from this pin is not
needed, this bit should be written logic one to reduce power consumption in the digital
input buffer.
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Analog to Digital
Converter
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
10-bit Resolution
0.5 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
13 µs - 260 µs Conversion Time (50 kHz to 1 MHz ADC clock)
Up to 76.9 kSPS at Maximum Resolution (200 kHz ADC clock)
Eight Multiplexed Single Ended Input Channels
Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
Selectable 1.1V ADC Reference Voltage
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
The ATmega325/3250/645/6450 features a 10-bit successive approximation ADC. The
ADC is connected to an 8-channel Analog Multiplexer which allows eight single-ended
voltage inputs constructed from the pins of Port F. The single-ended voltage inputs refer
to 0V (GND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the
ADC is held at a constant level during conversion. A block diagram of the ADC is shown
in Figure 84.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more
than ± 0.3V from VCC. See the paragraph “ADC Noise Canceler” on page 203 on how to
connect this pin.
Internal reference voltages of nominally 1.1V or AVCC are provided On-chip. The voltage reference may be externally decoupled at the AREF pin by a capacitor for better
noise performance.
The Power Reduction ADC bit, PRADC, in “Power Reduction Register” on page 35 must
be disabled by writing a logical zero to be able to use the ADC module.
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Figure 84. Analog to Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
INTERRUPT
FLAGS
ADTS[2:0]
15
TRIGGER
SELECT
ADC[9:0]
ADPS1
ADPS0
ADPS2
ADIF
ADEN
ADSC
ADATE
0
ADC DATA REGISTER
(ADCH/ADCL)
ADC CTRL. & STATUS
REGISTER (ADCSRA)
MUX0
MUX2
MUX1
MUX4
MUX3
ADLAR
REFS0
REFS1
ADC MULTIPLEXER
SELECT (ADMUX)
ADIE
ADIF
8-BIT DATA BUS
AVCC
PRESCALER
START
GAIN SELECTION
CHANNEL SELECTION
MUX DECODER
CONVERSION LOGIC
INTERNAL
REFERENCE
SAMPLE & HOLD
COMPARATOR
AREF
10-BIT DAC
+
GND
BANDGAP
REFERENCE
ADC7
SINGLE ENDED / DIFFERENTIAL SELECTION
ADC6
ADC5
ADC MULTIPLEXER
OUTPUT
POS.
INPUT
MUX
ADC4
ADC3
+
ADC2
DIFFERENTIAL
AMPLIFIER
ADC1
ADC0
NEG.
INPUT
MUX
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive
approximation. The minimum value represents GND and the maximum value represents
the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or an internal 1.1V reference voltage may be connected to the AREF pin by writing to the REFSn bits in the
ADMUX Register. The internal voltage reference may thus be decoupled by an external
capacitor at the AREF pin to improve noise immunity.
The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the
ADC input pins, as well as GND and a fixed bandgap voltage reference, can be selected
as single ended inputs to the ADC. The ADC is enabled by setting the ADC Enable bit,
ADEN in ADCSRA. Voltage reference and input channel selections will not go into effect
until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is
recommended to switch off the ADC before entering power saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers,
ADCH and ADCL. By default, the result is presented right adjusted, but can optionally
be presented left adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to
read ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content
of the Data Registers belongs to the same conversion. Once ADCL is read, ADC access
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to Data Registers is blocked. This means that if ADCL has been read, and a conversion
completes before ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the ADCH and ADCL Registers is
re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes.
When ADC access to the Data Registers is prohibited between reading of ADCH and
ADCL, the interrupt will trigger even if the result is lost.
Starting a Conversion
A single conversion is started by writing a logical one to the ADC Start Conversion bit,
ADSC. This bit stays high as long as the conversion is in progress and will be cleared by
hardware when the conversion is completed. If a different data channel is selected while
a conversion is in progress, the ADC will finish the current conversion before performing
the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The
trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB
(See description of the ADTS bits for a list of the trigger sources). When a positive edge
occurs on the selected trigger signal, the ADC prescaler is reset and a conversion is
started. This provides a method of starting conversions at fixed intervals. If the trigger
signal still is set when the conversion completes, a new conversion will not be started. If
another positive edge occurs on the trigger signal during conversion, the edge will be
ignored. Note that an Interrupt Flag will be set even if the specific interrupt is disabled or
the Global Interrupt Enable bit in SREG is cleared. A conversion can thus be triggered
without causing an interrupt. However, the Interrupt Flag must be cleared in order to trigger a new conversion at the next interrupt event.
Figure 85. ADC Auto Trigger Logic
ADTS[2:0]
PRESCALER
START
ADIF
CLKADC
ADATE
SOURCE 1
.
.
.
.
SOURCE n
CONVERSION
LOGIC
EDGE
DETECTOR
ADSC
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion
as soon as the ongoing conversion has finished. The ADC then operates in Free Running mode, constantly sampling and updating the ADC Data Register. The first
conversion must be started by writing a logical one to the ADSC bit in ADCSRA. In this
mode the ADC will perform successive conversions independently of whether the ADC
Interrupt Flag, ADIF is cleared or not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in
ADCSRA to one. ADSC can also be used to determine if a conversion is in progress.
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The ADSC bit will be read as one during a conversion, independently of how the conversion was started.
Prescaling and
Conversion Timing
Figure 86. ADC Prescaler
ADEN
START
Reset
7-BIT ADC PRESCALER
CK/128
CK/64
CK/32
CK/16
CK/8
CK/4
CK/2
CK
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
By default, the successive approximation circuitry requires an input clock frequency
between 50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10
bits is needed, the input clock frequency to the ADC can be higher than 200 kHz to get a
higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits
in ADCSRA. The prescaler starts counting from the moment the ADC is switched on by
setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the ADEN
bit is set, and is continuously reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is
switched on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize
the analog circuitry.
When the bandgap reference voltage is used as input to the ADC, it will take a certain
time for the voltage to stabilize. If not stabilized the first value read after the first conversion may be wrong.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal
conversion and 13.5 ADC clock cycles after the start of an first conversion. When a conversion is complete, the result is written to the ADC Data Registers, and ADIF is set. In
Single Conversion mode, ADSC is cleared simultaneously. The software may then set
ADSC again, and a new conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This
assures a fixed delay from the trigger event to the start of conversion. In this mode, the
sample-and-hold takes place two ADC clock cycles after the rising edge on the trigger
source signal. Three additional CPU clock cycles are used for synchronization logic.
When using Differential mode, along with Auto triggering from a source other than the
ADC Conversion Complete, each conversion will require 25 ADC clocks. This is
because the ADC must be disabled and re-enabled after every conversion.
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In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. For a summary of conversion times, see
Table 85.
Figure 87. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
Cycle Number
1
2
12
13
14
16
15
17
18
19
20
21
22
23
24
25
1
2
3
ADC Clock
ADEN
ADSC
ADIF
Sign and MSB of Result
ADCH
LSB of Result
ADCL
MUX and REFS
Update
Conversion
Complete
Sample & Hold
MUX and REFS
Update
Figure 88. ADC Timing Diagram, Single Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
3
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
MUX and REFS
Update
MUX and REFS
Update
Figure 89. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
9
Next Conversion
10
11
12
13
1
2
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Prescaler
Reset
Sample &
Hold
Conversion
Complete
Prescaler
Reset
MUX and REFS
Update
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Figure 90. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
11
12
Next Conversion
13
1
2
3
4
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
MUX and REFS
Update
Table 85. ADC Conversion Time
Sample & Hold (Cycles
from Start of Conversion)
Conversion Time
(Cycles)
First conversion
13.5
25
Normal conversions, single ended
1.5
13
2
13.5
Condition
Auto Triggered conversions
Changing Channel or
Reference Selection
The MUXn and REFS1:0 bits in the ADMUX Register are single buffered through a temporary register to which the CPU has random access. This ensures that the channels
and reference selection only takes place at a safe point during the conversion. The
channel and reference selection is continuously updated until a conversion is started.
Once the conversion starts, the channel and reference selection is locked to ensure a
sufficient sampling time for the ADC. Continuous updating resumes in the last ADC
clock cycle before the conversion completes (ADIF in ADCSRA is set). Note that the
conversion starts on the following rising ADC clock edge after ADSC is written. The user
is thus advised not to write new channel or reference selection values to ADMUX until
one ADC clock cycle after ADSC is written.
If Auto Triggering is used, the exact time of the triggering event can be indeterministic.
Special care must be taken when updating the ADMUX Register, in order to control
which conversion will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If
the ADMUX Register is changed in this period, the user cannot tell if the next conversion
is based on the old or the new settings. ADMUX can be safely updated in the following
ways:
1. When ADATE or ADEN is cleared.
2. During conversion, minimum one ADC clock cycle after the trigger event.
3. After a conversion, before the Interrupt Flag used as trigger source is
cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next
ADC conversion.
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ADC Input Channels
When changing channel selections, the user should observe the following guidelines to
ensure that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion.
The channel selection may be changed one ADC clock cycle after writing one to ADSC.
However, the simplest method is to wait for the conversion to complete before changing
the channel selection.
In Free Running mode, always select the channel before starting the first conversion.
The channel selection may be changed one ADC clock cycle after writing one to ADSC.
However, the simplest method is to wait for the first conversion to complete, and then
change the channel selection. Since the next conversion has already started automatically, the next result will reflect the previous channel selection. Subsequent conversions
will reflect the new channel selection.
ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC.
Single ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be
selected as either AVCC, internal 1.1V reference, or external AREF pin.
AVCC is connected to the ADC through a passive switch. The internal 1.1V reference is
generated from the internal bandgap reference (VBG) through an internal buffer. In either
case, the external AREF pin is directly connected to the ADC, and the reference voltage
can be made more immune to noise by connecting a capacitor between the AREF pin
and ground. VREF can also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high impedant source, and only a capacitive load should be
connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use
the other reference voltage options in the application, as they will be shorted to the
external voltage. If no external voltage is applied to the AREF pin, the user may switch
between AVCC and 1.1V as reference selection. The first ADC conversion result after
switching reference voltage source may be inaccurate, and the user is advised to discard this result.
ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to
reduce noise induced from the CPU core and other I/O peripherals. The noise canceler
can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the
following procedure should be used:
1. Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be selected and the ADC conversion complete interrupt
must be enabled.
2. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted.
3. If no other interrupts occur before the ADC conversion completes, the ADC
interrupt will wake up the CPU and execute the ADC Conversion Complete
interrupt routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion
Complete interrupt request will be generated when the ADC conversion
completes. The CPU will remain in active mode until a new sleep command
is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes
than Idle mode and ADC Noise Reduction mode. The user is advised to write zero to
ADEN before entering such sleep modes to avoid excessive power consumption.
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Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 91. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that
pin, regardless of whether that channel is selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance
(combined resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately
10 kΩ or less. If such a source is used, the sampling time will be negligible. If a source
with higher impedance is used, the sampling time will depend on how long time the
source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources with slowly varying signals, since this
minimizes the required charge transfer to the S/H capacitor.
Signal components higher than the Nyquist frequency (fADC/2) should not be present for
either kind of channels, to avoid distortion from unpredictable signal convolution. The
user is advised to remove high frequency components with a low-pass filter before
applying the signals as inputs to the ADC.
Figure 91. Analog Input Circuitry
IIH
ADCn
1..100 kΩ
CS/H= 14 pF
IIL
VCC/2
Analog Noise Canceling
Techniques
Digital circuitry inside and outside the device generates EMI which might affect the
accuracy of analog measurements. If conversion accuracy is critical, the noise level can
be reduced by applying the following techniques:
1. Keep analog signal paths as short as possible. Make sure analog tracks run
over the analog ground plane, and keep them well away from high-speed
switching digital tracks.
2. The AVCC pin on the device should be connected to the digital VCC supply
voltage via an LC network as shown in Figure 92.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC port pins are used as digital outputs, it is essential that these do
not switch while a conversion is in progress.
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Figure 92. ADC Power Connections
VCC
GND
52
53
(ADC7) PF7
54
(ADC6) PF6
55
(ADC5) PF5
56
(ADC4) PF4
57
(ADC3) PF3
58
(ADC2) PF2
59
(ADC1) PF1
60
(ADC0) PF0
61
AREF
62
10μΗ
GND
AVCC
100nF
Analog Ground Plane
ADC Accuracy Definitions
51
63
64
1
DNC
PA0
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n
steps (LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior:
•
Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal
transition (at 0.5 LSB). Ideal value: 0 LSB.
Figure 93. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
VREF Input Voltage
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•
Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the
last transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below
maximum). Ideal value: 0 LSB
Figure 94. Gain Error
Gain
Error
Output Code
Ideal ADC
Actual ADC
VREF Input Voltage
•
Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the
maximum deviation of an actual transition compared to an ideal transition for any
code. Ideal value: 0 LSB.
Figure 95. Integral Non-linearity (INL)
Output Code
INL
Ideal ADC
Actual ADC
VREF
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•
Differential Non-linearity (DNL): The maximum deviation of the actual code width
(the interval between two adjacent transitions) from the ideal code width (1 LSB).
Ideal value: 0 LSB.
Figure 96. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
ADC Conversion Result
VREF Input Voltage
•
Quantization Error: Due to the quantization of the input voltage into a finite number
of codes, a range of input voltages (1 LSB wide) will code to the same value. Always
± 0.5 LSB.
•
Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition
compared to an ideal transition for any code. This is the compound effect of offset,
gain error, differential error, non-linearity, and quantization error. Ideal value: ± 0.5
LSB.
After the conversion is complete (ADIF is high), the conversion result can be found in
the ADC Result Registers (ADCL, ADCH).
For single ended conversion, the result is
V IN ⋅ 1024
ADC = -------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 87 on page 209 and Table 88 on page 210). 0x000 represents analog
ground, and 0x3FF represents the selected reference voltage minus one LSB.
( V POS – V NEG ) ⋅ 512
ADC = ---------------------------------------------------V REF
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Figure 97. Differential Measurement Range
Output Code
0x1FF
0x000
- VREF
0x3FF
0
VREF
Differential Input
Voltage (Volts)
0x200
Table 86. Correlation Between Input Voltage and Output Codes
VADCn
Read Code
VADCm + VREF
0x1FF
511
VADCm + 511/512 VREF
0x1FF
511
510
0x1FE
510
VADCm +
/512 VREF
Corresponding Decimal Value
...
...
...
VADCm + 1/512 VREF
0x001
1
VADCm
0x000
0
VADCm - /512 VREF
0x3FF
-1
...
...
...
VADCm - 511/512 VREF
0x201
-511
VADCm - VREF
0x200
-512
1
ADMUX = 0xFB (ADC3 - ADC2, 1.1V reference, left adjusted result)
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
ADCR = 512 * (300 - 500) / 1100 = -93 = 0x3A3.
ADCL will thus read 0xC0, and ADCH will read 0xD8. Writing zero to ADLAR right
adjusts the result: ADCL = 0xA3, ADCH = 0x03.
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ADMUX – ADC Multiplexer
Selection Register
Bit
7
6
5
4
3
2
1
0
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x7C)
ADMUX
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 87. If these bits
are changed during a conversion, the change will not go in effect until this conversion is
complete (ADIF in ADCSRA is set). The internal voltage reference options may not be
used if an external reference voltage is being applied to the AREF pin.
Table 87. Voltage Reference Selections for ADC
•
REFS1
REFS0
Voltage Reference Selection
0
0
AREF, Internal Vref turned off
0
1
AVCC with external capacitor at AREF pin
1
0
Reserved
1
1
Internal 1.1V Voltage Reference with external capacitor at AREF pin
Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data
Register. Write one to ADLAR to left adjust the result. Otherwise, the result is right
adjusted. Changing the ADLAR bit will affect the ADC Data Register immediately,
regardless of any ongoing conversions. For a complete description of this bit, see
“ADCL and ADCH – The ADC Data Register” on page 212.
• Bits 4:0 – MUX4:0: Analog Channel Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. See Table 88 for details. If these bits are changed during a conversion, the
change will not go in effect until this conversion is complete (ADIF in ADCSRA is set).
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Table 88. Input Channel Selections
MUX4..0
Single Ended Input
00000
ADC0
00001
ADC1
00010
ADC2
00011
ADC3
00100
ADC4
00101
ADC5
00110
ADC6
00111
ADC7
Positive Differential Input
Negative Differential Input
N/A
01000
01001
01010
01011
01100
01101
01110
01111
10000
ADC0
ADC1
10001
ADC1
ADC1
ADC2
ADC1
10011
ADC3
ADC1
10100
ADC4
ADC1
10101
ADC5
ADC1
10110
ADC6
ADC1
10111
ADC7
ADC1
11000
ADC0
ADC2
11001
ADC1
ADC2
11010
ADC2
ADC2
11011
ADC3
ADC2
11100
ADC4
ADC2
11101
ADC5
ADC2
10010
210
N/A
11110
1.1V (VBG)
11111
0V (GND)
N/A
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ADCSRA – ADC Control and
Status Register A
Bit
7
6
5
4
3
2
1
0
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x7A)
ADCSRA
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode, write this bit to one to start the first conversion. The first conversion after
ADSC has been written after the ADC has been enabled, or if ADSC is written at the
same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal
13. This first conversion performs initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is
complete, it returns to zero. Writing zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start
a conversion on a positive edge of the selected trigger signal. The trigger source is
selected by setting the ADC Trigger Select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the Data Registers are updated.
The ADC Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in
SREG are set. ADIF is cleared by hardware when executing the corresponding interrupt
handling vector. Alternatively, ADIF is cleared by writing a logical one to the flag.
Beware that if doing a Read-Modify-Write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete Interrupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the XTAL frequency and the input
clock to the ADC.
Table 89. ADC Prescaler Selections
ADPS2
ADPS1
ADPS0
Division Factor
0
0
0
2
0
0
1
2
0
1
0
4
0
1
1
8
1
0
0
16
1
0
1
32
1
1
0
64
1
1
1
128
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ADCL and ADCH – The ADC
Data Register
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
(0x79)
–
–
–
–
–
–
ADC9
ADC8
ADCH
(0x78)
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Read/Write
Initial Value
ADLAR = 1
Bit
15
14
13
12
11
10
9
8
(0x79)
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
(0x78)
ADC1
ADC0
–
–
–
–
–
–
ADCL
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Read/Write
Initial Value
When an ADC conversion is complete, the result is found in these two registers. When
ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently,
if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to
read ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is
read from the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared
(default), the result is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion
Result” on page 207.
ADCSRB – ADC Control and
Status Register B
Bit
7
6
5
4
3
2
1
0
(0x7B)
–
ACME
–
–
–
ADTS2
ADTS1
ADTS0
Read/Write
R
R/W
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 7 – Res: Reserved Bit
This bit is reserved for future use. To ensure compatibility with future devices, this bit
must be written to zero when ADCSRB is written.
• Bit 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will
trigger an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no
effect. A conversion will be triggered by the rising edge of the selected Interrupt Flag.
Note that switching from a trigger source that is cleared to a trigger source that is set,
will generate a positive edge on the trigger signal. If ADEN in ADCSRA is set, this will
start a conversion. Switching to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set.
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Table 90. ADC Auto Trigger Source Selections
DIDR0 – Digital Input Disable
Register 0
ADTS2
ADTS1
ADTS0
0
0
0
Free Running mode
0
0
1
Analog Comparator
0
1
0
External Interrupt Request 0
0
1
1
Timer/Counter0 Compare MatchA
1
0
0
Timer/Counter0 Overflow
1
0
1
Timer/Counter1 Compare Match B
1
1
0
Timer/Counter1 Overflow
1
1
1
Timer/Counter1 Capture Event
Bit
Trigger Source
7
6
5
4
3
2
1
0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
(0x7E)
DIDR0
• Bit 7:0 – ADC7D:ADC0D: ADC7:0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is
disabled. The corresponding PIN Register bit will always read as zero when this bit is
set. When an analog signal is applied to the ADC7..0 pin and the digital input from this
pin is not needed, this bit should be written logic one to reduce power consumption in
the digital input buffer.
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JTAG Interface and
On-chip Debug
System
Features
• JTAG (IEEE std. 1149.1 Compliant) Interface
• Boundary-scan Capabilities According to the IEEE std. 1149.1 (JTAG) Standard
• Debugger Access to:
– All Internal Peripheral Units
– Internal and External RAM
– The Internal Register File
– Program Counter
– EEPROM and Flash Memories
• Extensive On-chip Debug Support for Break Conditions, Including
– AVR Break Instruction
– Break on Change of Program Memory Flow
– Single Step Break
– Program Memory Break Points on Single Address or Address Range
– Data Memory Break Points on Single Address or Address Range
• Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
• On-chip Debugging Supported by AVR Studio®
Overview
The AVR IEEE std. 1149.1 compliant JTAG interface can be used for
•
Testing PCBs by using the JTAG Boundary-scan capability
•
Programming the non-volatile memories, Fuses and Lock bits
•
On-chip debugging
A brief description is given in the following sections. Detailed descriptions for Programming via the JTAG interface, and using the Boundary-scan Chain can be found in the
sections “Programming via the JTAG Interface” on page 279 and “IEEE 1149.1 (JTAG)
Boundary-scan” on page 220, respectively. The On-chip Debug support is considered
being private JTAG instructions, and distributed within ATMEL and to selected third
party vendors only.
Figure 98 shows a block diagram of the JTAG interface and the On-chip Debug system.
The TAP Controller is a state machine controlled by the TCK and TMS signals. The TAP
Controller selects either the JTAG Instruction Register or one of several Data Registers
as the scan chain (Shift Register) between the TDI – input and TDO – output. The
Instruction Register holds JTAG instructions controlling the behavior of a Data Register.
The ID-Register, Bypass Register, and the Boundary-scan Chain are the Data Registers
used for board-level testing. The JTAG Programming Interface (actually consisting of
several physical and virtual Data Registers) is used for serial programming via the JTAG
interface. The Internal Scan Chain and Break Point Scan Chain are used for On-chip
debugging only.
TAP – Test Access Port
214
The JTAG interface is accessed through four of the AVR’s pins. In JTAG terminology,
these pins constitute the Test Access Port – TAP. These pins are:
•
TMS: Test mode select. This pin is used for navigating through the TAP-controller
state machine.
•
TCK: Test Clock. JTAG operation is synchronous to TCK.
•
TDI: Test Data In. Serial input data to be shifted in to the Instruction Register or Data
Register (Scan Chains).
•
TDO: Test Data Out. Serial output data from Instruction Register or Data Register.
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The IEEE std. 1149.1 also specifies an optional TAP signal; TRST – Test ReSeT –
which is not provided.
When the JTAGEN fuse is unprogrammed, these four TAP pins are normal port pins
and the TAP controller is in reset. When programmed and the JTD bit in MCUCSR is
cleared, the TAP pins are internally pulled high and the JTAG is enabled for Boundaryscan and programming. The device is shipped with this fuse programmed.
For the On-chip Debug system, in addition to the JTAG interface pins, the RESET pin is
monitored by the debugger to be able to detect external reset sources. The debugger
can also pull the RESET pin low to reset the whole system, assuming only open collectors on the reset line are used in the application.
Figure 98. Block Diagram
I/O PORT 0
DEVICE BOUNDARY
BOUNDARY SCAN CHAIN
TDI
TDO
TCK
TMS
JTAG PROGRAMMING
INTERFACE
TAP
CONTROLLER
AVR CPU
INSTRUCTION
REGISTER
ID
REGISTER
M
U
X
FLASH
MEMORY
Address
Data
BREAKPOINT
UNIT
BYPASS
REGISTER
INTERNAL
SCAN
CHAIN
PC
Instruction
FLOW CONTROL
UNIT
DIGITAL
PERIPHERAL
UNITS
ANALOG
PERIPHERIAL
UNITS
Analog inputs
BREAKPOINT
SCAN CHAIN
ADDRESS
DECODER
JTAG / AVR CORE
COMMUNICATION
INTERFACE
OCD STATUS
AND CONTROL
Control & Clock lines
I/O PORT n
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Figure 99. TAP Controller State Diagram
1
Test-Logic-Reset
0
0
Run-Test/Idle
1
Select-DR Scan
1
Select-IR Scan
0
1
0
1
Capture-DR
Capture-IR
0
0
0
Shift-DR
1
1
Exit1-DR
0
0
Pause-DR
0
Pause-IR
1
1
0
Exit2-DR
Exit2-IR
1
1
Update-DR
TAP Controller
1
Exit1-IR
0
1
0
Shift-IR
1
0
1
Update-IR
0
1
0
The TAP controller is a 16-state finite state machine that controls the operation of the
Boundary-scan circuitry, JTAG programming circuitry, or On-chip Debug system. The
state transitions depicted in Figure 99 depend on the signal present on TMS (shown
adjacent to each state transition) at the time of the rising edge at TCK. The initial state
after a Power-on Reset is Test-Logic-Reset.
As a definition in this document, the LSB is shifted in and out first for all Shift Registers.
Assuming Run-Test/Idle is the present state, a typical scenario for using the JTAG interface is:
216
•
At the TMS input, apply the sequence 1, 1, 0, 0 at the rising edges of TCK to enter
the Shift Instruction Register – Shift-IR state. While in this state, shift the four bits of
the JTAG instructions into the JTAG Instruction Register from the TDI input at the
rising edge of TCK. The TMS input must be held low during input of the 3 LSBs in
order to remain in the Shift-IR state. The MSB of the instruction is shifted in when
this state is left by setting TMS high. While the instruction is shifted in from the TDI
pin, the captured IR-state 0x01 is shifted out on the TDO pin. The JTAG Instruction
selects a particular Data Register as path between TDI and TDO and controls the
circuitry surrounding the selected Data Register.
•
Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. The instruction
is latched onto the parallel output from the Shift Register path in the Update-IR
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state. The Exit-IR, Pause-IR, and Exit2-IR states are only used for navigating the
state machine.
•
At the TMS input, apply the sequence 1, 0, 0 at the rising edges of TCK to enter the
Shift Data Register – Shift-DR state. While in this state, upload the selected Data
Register (selected by the present JTAG instruction in the JTAG Instruction Register)
from the TDI input at the rising edge of TCK. In order to remain in the Shift-DR state,
the TMS input must be held low during input of all bits except the MSB. The MSB of
the data is shifted in when this state is left by setting TMS high. While the Data
Register is shifted in from the TDI pin, the parallel inputs to the Data Register
captured in the Capture-DR state is shifted out on the TDO pin.
•
Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. If the selected
Data Register has a latched parallel-output, the latching takes place in the UpdateDR state. The Exit-DR, Pause-DR, and Exit2-DR states are only used for navigating
the state machine.
As shown in the state diagram, the Run-Test/Idle state need not be entered between
selecting JTAG instruction and using Data Registers, and some JTAG instructions may
select certain functions to be performed in the Run-Test/Idle, making it unsuitable as an
Idle state.
Note:
Independent of the initial state of the TAP Controller, the Test-Logic-Reset state can
always be entered by holding TMS high for five TCK clock periods.
For detailed information on the JTAG specification, refer to the literature listed in “Bibliography” on page 219.
Using the Boundaryscan Chain
A complete description of the Boundary-scan capabilities are given in the section “IEEE
1149.1 (JTAG) Boundary-scan” on page 220.
Using the On-chip Debug As shown in Figure 98, the hardware support for On-chip Debugging consists mainly of
System
• A scan chain on the interface between the internal AVR CPU and the internal
peripheral units.
•
Break Point unit.
•
Communication interface between the CPU and JTAG system.
All read or modify/write operations needed for implementing the Debugger are done by
applying AVR instructions via the internal AVR CPU Scan Chain. The CPU sends the
result to an I/O memory mapped location which is part of the communication interface
between the CPU and the JTAG system.
The Break Point Unit implements Break on Change of Program Flow, Single Step
Break, two Program Memory Break Points, and two combined Break Points. Together,
the four Break Points can be configured as either:
•
4 single Program Memory Break Points.
•
3 Single Program Memory Break Point + 1 single Data Memory Break Point.
•
2 single Program Memory Break Points + 2 single Data Memory Break Points.
•
2 single Program Memory Break Points + 1 Program Memory Break Point with mask
(“range Break Point”).
•
2 single Program Memory Break Points + 1 Data Memory Break Point with mask
(“range Break Point”).
A debugger, like the AVR Studio, may however use one or more of these resources for
its internal purpose, leaving less flexibility to the end-user.
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A list of the On-chip Debug specific JTAG instructions is given in “On-chip Debug Specific JTAG Instructions” on page 218.
The JTAGEN Fuse must be programmed to enable the JTAG Test Access Port. In addition, the OCDEN Fuse must be programmed and no Lock bits must be set for the Onchip debug system to work. As a security feature, the On-chip debug system is disabled
when either of the LB1 or LB2 Lock bits are set. Otherwise, the On-chip debug system
would have provided a back-door into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR
device with On-chip Debug capability, AVR In-Circuit Emulator, or the built-in AVR
Instruction Set Simulator. AVR Studio® supports source level execution of Assembly
programs assembled with Atmel Corporation’s AVR Assembler and C programs compiled with third party vendors’ compilers.
AVR Studio runs under Microsoft® Windows® 95/98/2000, Windows NT® and Windows
XP®.
For a full description of the AVR Studio, please refer to the AVR Studio User Guide.
Only highlights are presented in this document.
All necessary execution commands are available in AVR Studio, both on source level
and on disassembly level. The user can execute the program, single step through the
code either by tracing into or stepping over functions, step out of functions, place the
cursor on a statement and execute until the statement is reached, stop the execution,
and reset the execution target. In addition, the user can have an unlimited number of
code Break Points (using the BREAK instruction) and up to two data memory Break
Points, alternatively combined as a mask (range) Break Point.
On-chip Debug Specific
JTAG Instructions
The On-chip debug support is considered being private JTAG instructions, and distributed within ATMEL and to selected third party vendors only. Instruction opcodes are
listed for reference.
PRIVATE0; 0x8
Private JTAG instruction for accessing On-chip debug system.
PRIVATE1; 0x9
Private JTAG instruction for accessing On-chip debug system.
PRIVATE2; 0xA
Private JTAG instruction for accessing On-chip debug system.
PRIVATE3; 0xB
Private JTAG instruction for accessing On-chip debug system.
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On-chip Debug Related
Register in I/O Memory
OCDR – On-chip Debug
Register
Bit
7
6
5
4
3
2
1
0
0x31 (0x51)
MSB/IDRD
LSB
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
OCDR
The OCDR Register provides a communication channel from the running program in the
microcontroller to the debugger. The CPU can transfer a byte to the debugger by writing
to this location. At the same time, an internal flag; I/O Debug Register Dirty – IDRD – is
set to indicate to the debugger that the register has been written. When the CPU reads
the OCDR Register the 7 LSB will be from the OCDR Register, while the MSB is the
IDRD bit. The debugger clears the IDRD bit when it has read the information.
In some AVR devices, this register is shared with a standard I/O location. In this case,
the OCDR Register can only be accessed if the OCDEN Fuse is programmed, and the
debugger enables access to the OCDR Register. In all other cases, the standard I/O
location is accessed.
Refer to the debugger documentation for further information on how to use this register.
Using the JTAG
Programming
Capabilities
Programming of AVR parts via JTAG is performed via the 4-pin JTAG port, TCK, TMS,
TDI, and TDO. These are the only pins that need to be controlled/observed to perform
JTAG programming (in addition to power pins). It is not required to apply 12V externally.
The JTAGEN Fuse must be programmed and the JTD bit in the MCUCR Register must
be cleared to enable the JTAG Test Access Port.
The JTAG programming capability supports:
•
Flash programming and verifying.
•
EEPROM programming and verifying.
•
Fuse programming and verifying.
•
Lock bit programming and verifying.
The Lock bit security is exactly as in parallel programming mode. If the Lock bits LB1 or
LB2 are programmed, the OCDEN Fuse cannot be programmed unless first doing a
chip erase. This is a security feature that ensures no back-door exists for reading out the
content of a secured device.
The details on programming through the JTAG interface and programming specific
JTAG instructions are given in the section “Programming via the JTAG Interface” on
page 279.
Bibliography
For more information about general Boundary-scan, the following literature can be
consulted:
•
IEEE: IEEE Std. 1149.1-1990. IEEE Standard Test Access Port and Boundary-scan
Architecture, IEEE, 1993.
Colin Maunder: The Board Designers Guide to Testable Logic Circuits, Addison-Wesley,
1992.
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IEEE 1149.1 (JTAG)
Boundary-scan
Features
•
•
•
•
•
System Overview
The Boundary-scan chain has the capability of driving and observing the logic levels on
the digital I/O pins, as well as the boundary between digital and analog logic for analog
circuitry having off-chip connections. At system level, all ICs having JTAG capabilities
are connected serially by the TDI/TDO signals to form a long Shift Register. An external
controller sets up the devices to drive values at their output pins, and observe the input
values received from other devices. The controller compares the received data with the
expected result. In this way, Boundary-scan provides a mechanism for testing interconnections and integrity of components on Printed Circuits Boards by using the four TAP
signals only.
JTAG (IEEE std. 1149.1 compliant) Interface
Boundary-scan Capabilities According to the JTAG Standard
Full Scan of all Port Functions as well as Analog Circuitry having Off-chip Connections
Supports the Optional IDCODE Instruction
Additional Public AVR_RESET Instruction to Reset the AVR
The four IEEE 1149.1 defined mandatory JTAG instructions IDCODE, BYPASS, SAMPLE/PRELOAD, and EXTEST, as well as the AVR specific public JTAG instruction
AVR_RESET can be used for testing the Printed Circuit Board. Initial scanning of the
Data Register path will show the ID-Code of the device, since IDCODE is the default
JTAG instruction. It may be desirable to have the AVR device in reset during test mode.
If not reset, inputs to the device may be determined by the scan operations, and the
internal software may be in an undetermined state when exiting the test mode. Entering
reset, the outputs of any port pin will instantly enter the high impedance state, making
the HIGHZ instruction redundant. If needed, the BYPASS instruction can be issued to
make the shortest possible scan chain through the device. The device can be set in the
reset state either by pulling the external RESET pin low, or issuing the AVR_RESET
instruction with appropriate setting of the Reset Data Register.
The EXTEST instruction is used for sampling external pins and loading output pins with
data. The data from the output latch will be driven out on the pins as soon as the
EXTEST instruction is loaded into the JTAG IR-Register. Therefore, the SAMPLE/PRELOAD should also be used for setting initial values to the scan ring, to avoid damaging
the board when issuing the EXTEST instruction for the first time. SAMPLE/PRELOAD
can also be used for taking a snapshot of the external pins during normal operation of
the part.
The JTAGEN Fuse must be programmed and the JTD bit in the I/O Register MCUCR
must be cleared to enable the JTAG Test Access Port.
When using the JTAG interface for Boundary-scan, using a JTAG TCK clock frequency
higher than the internal chip frequency is possible. The chip clock is not required to run.
Data Registers
The Data Registers relevant for Boundary-scan operations are:
•
220
Bypass Register
•
Device Identification Register
•
Reset Register
•
Boundary-scan Chain
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Bypass Register
The Bypass Register consists of a single Shift Register stage. When the Bypass Register is selected as path between TDI and TDO, the register is reset to 0 when leaving the
Capture-DR controller state. The Bypass Register can be used to shorten the scan
chain on a system when the other devices are to be tested.
Device Identification Register
Figure 100 shows the structure of the Device Identification Register.
Figure 100. The Format of the Device Identification Register
LSB
MSB
Bit
31
Device ID
28
27
12
11
1
0
Version
Part Number
Manufacturer ID
1
4 bits
16 bits
11 bits
1-bit
Version
Version is a 4-bit number identifying the revision of the component. The JTAG version
number follows the revision of the device. Revision A is 0x0, revision B is 0x1 and so on.
Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number for
ATmega325/3250/645/6450 is listed in Table 91.
Table 91. AVR JTAG Part Number
Part Number
Manufacturer ID
JTAG Part Number (Hex)
ATmega325
0x9505
ATmega3250
0x9506
ATmega645
0x9605
ATmega6450
0x9606
The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID for ATMEL is listed in Table 92.
Table 92. Manufacturer ID
Manufacturer
ATMEL
Reset Register
JTAG Manufacturer ID (Hex)
0x01F
The Reset Register is a test Data Register used to reset the part. Since the AVR tristates Port Pins when reset, the Reset Register can also replace the function of the
unimplemented optional JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The
part is reset as long as there is a high value present in the Reset Register. Depending
on the fuse settings for the clock options, the part will remain reset for a reset time-out
period (refer to “Clock Sources” on page 26) after releasing the Reset Register. The output from this Data Register is not latched, so the reset will take place immediately, as
shown in Figure 101.
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Figure 101. Reset Register
To
TDO
From Other Internal and
External Reset Sources
From
TDI
D
Q
Internal reset
ClockDR · AVR_RESET
Boundary-scan Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on
the digital I/O pins, as well as the boundary between digital and analog logic for analog
circuitry having off-chip connections.
See “Boundary-scan Chain” on page 224 for a complete description.
Boundary-scan Specific
JTAG Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. Listed below are
the JTAG instructions useful for Boundary-scan operation. Note that the optional HIGHZ
instruction is not implemented, but all outputs with tri-state capability can be set in highimpedant state by using the AVR_RESET instruction, since the initial state for all port
pins is tri-state.
As a definition in this data sheet, the LSB is shifted in and out first for all Shift Registers.
The OPCODE for each instruction is shown behind the instruction name in hex format.
The text describes which Data Register is selected as path between TDI and TDO for
each instruction.
EXTEST; 0x0
Mandatory JTAG instruction for selecting the Boundary-scan Chain as Data Register for
testing circuitry external to the AVR package. For port-pins, Pull-up Disable, Output
Control, Output Data, and Input Data are all accessible in the scan chain. For Analog circuits having off-chip connections, the interface between the analog and the digital logic
is in the scan chain. The contents of the latched outputs of the Boundary-scan chain is
driven out as soon as the JTAG IR-Register is loaded with the EXTEST instruction.
The active states are:
IDCODE; 0x1
•
Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
•
Shift-DR: The Internal Scan Chain is shifted by the TCK input.
•
Update-DR: Data from the scan chain is applied to output pins.
Optional JTAG instruction selecting the 32 bit ID-Register as Data Register. The IDRegister consists of a version number, a device number and the manufacturer code
chosen by JEDEC. This is the default instruction after power-up.
The active states are:
222
•
Capture-DR: Data in the IDCODE Register is sampled into the Boundary-scan
Chain.
•
Shift-DR: The IDCODE scan chain is shifted by the TCK input.
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SAMPLE_PRELOAD; 0x2
Mandatory JTAG instruction for pre-loading the output latches and taking a snap-shot of
the input/output pins without affecting the system operation. However, the output latches
are not connected to the pins. The Boundary-scan Chain is selected as Data Register.
The active states are:
AVR_RESET; 0xC
•
Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
•
Shift-DR: The Boundary-scan Chain is shifted by the TCK input.
•
Update-DR: Data from the Boundary-scan chain is applied to the output latches.
However, the output latches are not connected to the pins.
The AVR specific public JTAG instruction for forcing the AVR device into the Reset
mode or releasing the JTAG reset source. The TAP controller is not reset by this instruction. The one bit Reset Register is selected as Data Register. Note that the reset will be
active as long as there is a logic “one” in the Reset Chain. The output from this chain is
not latched.
The active states are:
•
BYPASS; 0xF
Shift-DR: The Reset Register is shifted by the TCK input.
Mandatory JTAG instruction selecting the Bypass Register for Data Register.
The active states are:
•
Capture-DR: Loads a logic “0” into the Bypass Register.
•
Shift-DR: The Bypass Register cell between TDI and TDO is shifted.
Boundary-scan Related
Register in I/O Memory
MCUCR – MCU Control
Register
The MCU Control Register contains control bits for general MCU functions.
Bit
7
6
5
4
3
2
1
0
0x35 (0x55)
JTD
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 7 – JTD: JTAG Interface Disable
When this bit is zero, the JTAG interface is enabled if the JTAGEN Fuse is programmed.
If this bit is one, the JTAG interface is disabled. In order to avoid unintentional disabling
or enabling of the JTAG interface, a timed sequence must be followed when changing
this bit: The application software must write this bit to the desired value twice within four
cycles to change its value. Note that this bit must not be altered when using the On-chip
Debug system.
If the JTAG interface is left unconnected to other JTAG circuitry, the JTD bit should be
set to one. The reason for this is to avoid static current at the TDO pin in the JTAG
interface.
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MCUSR – MCU Status
Register
The MCU Status Register provides information on which reset source caused an MCU
reset.
Bit
7
6
5
4
3
2
1
0
0x34 (0x54)
–
–
–
JTRF
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
MCUSR
See Bit Description
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register
selected by the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or
by writing a logic zero to the flag.
Boundary-scan Chain
The Boundary-scan chain has the capability of driving and observing the logic levels on
the digital I/O pins, as well as the boundary between digital and analog logic for analog
circuitry having off-chip connection.
Scanning the Digital Port Pins
Figure 102 shows the Boundary-scan Cell for a bi-directional port pin with pull-up function. The cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn
– function, and a bi-directional pin cell that combines the three signals Output Control –
OCxn, Output Data – ODxn, and Input Data – IDxn, into only a two-stage Shift Register.
The port and pin indexes are not used in the following description
The Boundary-scan logic is not included in the figures in the Data Sheet. Figure 103
shows a simple digital port pin as described in the section “I/O-Ports” on page 58. The
Boundary-scan details from Figure 102 replaces the dashed box in Figure 103.
When no alternate port function is present, the Input Data – ID – corresponds to the
PINxn Register value (but ID has no synchronizer), Output Data corresponds to the
PORT Register, Output Control corresponds to the Data Direction – DD Register, and
the Pull-up Enable – PUExn – corresponds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 103 to
make the scan chain read the actual pin value. For Analog function, there is a direct
connection from the external pin to the analog circuit, and a scan chain is inserted on
the interface between the digital logic and the analog circuitry.
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ATmega325/3250/645/6450
Figure 102. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function.
ShiftDR
To Next Cell
EXTEST
Pullup Enable (PUE)
Vcc
0
FF2
LD2
1
0
D
Q
D
Q
1
G
Output Control (OC)
FF1
LD1
0
D
Q
D
Q
0
1
1
G
FF0
0
1
LD0
0
D
Q
D
1
Q
0
1
Port Pin (PXn)
Output Data (OD)
G
Input Data (ID)
From Last Cell
ClockDR
UpdateDR
225
2570J–AVR–11/06
Figure 103. General Port Pin Schematic Diagram
See Boundary-scan
Description for Details!
PUExn
PUD
Q
D
DDxn
Q CLR
WDx
RESET
OCxn
DATA BUS
RDx
Pxn
1
Q
ODxn
IDxn
D
0
PORTxn
Q CLR
RESET
SLEEP
WPx
RRx
SYNCHRONIZER
D
Q
L
Q
D
WRx
RPx
Q
PINxn
Q
CLK I/O
PUD:
PUExn:
OCxn:
ODxn:
IDxn:
SLEEP:
Scanning the RESET Pin
PULLUP DISABLE
PULLUP ENABLE for pin Pxn
OUTPUT CONTROL for pin Pxn
OUTPUT DATA to pin Pxn
INPUT DATA from pin Pxn
SLEEP CONTROL
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
CLK I/O :
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
I/O CLOCK
The RESET pin accepts 5V active low logic for standard reset operation, and 12V active
high logic for High Voltage Parallel programming. An observe-only cell as shown in Figure 104 is inserted both for the 5V reset signal; RSTT, and the 12V reset signal;
RSTHV.
Figure 104. Observe-only Cell
To
Next
Cell
ShiftDR
From System Pin
To System Logic
FF1
0
D
Q
1
From
Previous
Cell
226
ClockDR
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Scanning the Clock Pins
The AVR devices have many clock options selectable by fuses. These are: Internal RC
Oscillator, External Clock, (High Frequency) Crystal Oscillator, Low-frequency Crystal
Oscillator, and Ceramic Resonator.
Figure 105 shows how each Oscillator with external connection is supported in the scan
chain. The Enable signal is supported with a general Boundary-scan cell, while the
Oscillator/clock output is attached to an observe-only cell. In addition to the main clock,
the timer Oscillator is scanned in the same way. The output from the internal RC Oscillator is not scanned, as this Oscillator does not have external connections.
Figure 105. Boundary-scan Cells for Oscillators and Clock Options
XTAL1/TOSC1
To
Next
Cell
ShiftDR
EXTEST
From Digital Logic
XTAL2/TOSC2
Oscillator
To
Next
Cell
ShiftDR
0
ENABLE
To System Logic
OUTPUT
1
FF1
0
D
Q
D
Q
0
1
D
G
From
Previous
Cell
ClockDR
Q
1
UpdateDR
From
Previous
Cell
ClockDR
Table 93 summaries the scan registers for the external clock pin XTAL1, oscillators with
XTAL1/XTAL2 connections as well as 32kHz Timer Oscillator.
Table 93. Scan Signals for the Oscillator(1)(2)(3)
Enable Signal
Scanned Clock Line
Clock Option
Scanned Clock
Line when not
Used
EXTCLKEN
EXTCLK (XTAL1)
External Clock
0
OSCON
OSCCK
External Crystal
External Ceramic Resonator
1
OSC32EN
OSC32CK
Low Freq. External Crystal
1
Notes:
1. Do not enable more than one clock source as main clock at a time.
2. Scanning an Oscillator output gives unpredictable results as there is a frequency drift
between the internal Oscillator and the JTAG TCK clock. If possible, scanning an
external clock is preferred.
3. The clock configuration is programmed by fuses. As a fuse is not changed run-time,
the clock configuration is considered fixed for a given application. The user is advised
to scan the same clock option as to be used in the final system. The enable signals
are supported in the scan chain because the system logic can disable clock options
in sleep modes, thereby disconnecting the Oscillator pins from the scan path if not
provided.
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2570J–AVR–11/06
Scanning the Analog
Comparator
The relevant Comparator signals regarding Boundary-scan are shown in Figure 106.
The Boundary-scan cell from Figure 107 is attached to each of these signals. The signals are described in Table 94.
The Comparator need not be used for pure connectivity testing, since all analog inputs
are shared with a digital port pin as well.
Figure 106. Analog Comparator
BANDGAP
REFERENCE
ACBG
ACD
ACO
AC_IDLE
ACME
ADCEN
ADC MULTIPLEXER
OUTPUT
Figure 107. General Boundary-scan cell Used for Signals for Comparator and ADC
To
Next
Cell
ShiftDR
EXTEST
From Digital Logic/
From Analog Ciruitry
0
1
To Analog Circuitry/
To Digital Logic
0
D
Q
D
Q
1
G
From
Previous
Cell
228
ClockDR
UpdateDR
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 94. Boundary-scan Signals for the Analog Comparator
Direction as
Seen from the
Comparator
Signal
Name
AC_IDLE
Output Values when
Recommended
Inputs are Used
1
Depends upon µC
code being executed
Turns off Analog
Comparator when
true
input
output
Analog
Comparator Output
Will become
input to µC code
being executed
0
ACME
input
Uses output signal
from ADC mux
when true
0
Depends upon µC
code being executed
ACBG
input
Bandgap
Reference enable
0
Depends upon µC
code being executed
ACO
Scanning the ADC
Description
Recommended
Input when Not
in Use
Figure 108 shows a block diagram of the ADC with all relevant control and observe signals. The Boundary-scan cell from Figure 104 is attached to each of these signals. The
ADC need not be used for pure connectivity testing, since all analog inputs are shared
with a digital port pin as well.
Figure 108. Analog to Digital Converter
VCCREN
AREF
IREFEN
1.11V
ref
To Comparator
PASSEN
MUXEN_7
ADC_7
MUXEN_6
ADC_6
MUXEN_5
ADC_5
MUXEN_4
ADC_4
ADCBGEN
SCTEST
1.22V
ref
EXTCH
MUXEN_3
ADC_3
MUXEN_2
ADC_2
MUXEN_1
ADC_1
MUXEN_0
ADC_0
PRECH
PRECH
AREF
AREF
DACOUT
DAC_9..0
10-bit DAC
+
COMP
COMP
-
ADCEN
ACTEN
+
1x
NEGSEL_2
GNDEN
ADC_1
NEGSEL_0
ADC_0
HOLD
-
ADC_2
NEGSEL_1
ST
ACLK
AMPEN
The signals are described briefly in Table 95.
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2570J–AVR–11/06
Table 95. Boundary-scan Signals for the ADC(1)
Recommended
Input when not
in use
Output Values when
recommended inputs are used,
and CPU is not using the ADC
Signal Name
Direction as seen
from the ADC
Description
COMP
Output
Comparator Output
0
0
ACLK
Input
Clock signal to differential amplifier
implemented as Switch-cap filters
0
0
ACTEN
Input
Enable path from differential amplifier to
the comparator
0
0
ADCBGEN
Input
Enable Band-gap reference as negative
input to comparator
0
0
ADCEN
Input
Power-on signal to the ADC
0
0
AMPEN
Input
Power-on signal to the differential amplifier
0
0
DAC_9
Input
Bit 9 of digital value to DAC
1
1
DAC_8
Input
Bit 8 of digital value to DAC
0
0
DAC_7
Input
Bit 7 of digital value to DAC
0
0
DAC_6
Input
Bit 6 of digital value to DAC
0
0
DAC_5
Input
Bit 5 of digital value to DAC
0
0
DAC_4
Input
Bit 4 of digital value to DAC
0
0
DAC_3
Input
Bit 3 of digital value to DAC
0
0
DAC_2
Input
Bit 2 of digital value to DAC
0
0
DAC_1
Input
Bit 1 of digital value to DAC
0
0
DAC_0
Input
Bit 0 of digital value to DAC
0
0
EXTCH
Input
Connect ADC channels 0 - 3 to by-pass
path around differential amplifier
1
1
GNDEN
Input
Ground the negative input to comparator
when true
0
0
HOLD
Input
Sample & Hold signal. Sample analog
signal when low. Hold signal when high. If
differential amplifier are used, this signal
must go active when ACLK is high.
1
1
IREFEN
Input
Enables Band-gap reference as AREF
signal to DAC
0
0
MUXEN_7
Input
Input Mux bit 7
0
0
MUXEN_6
Input
Input Mux bit 6
0
0
MUXEN_5
Input
Input Mux bit 5
0
0
MUXEN_4
Input
Input Mux bit 4
0
0
MUXEN_3
Input
Input Mux bit 3
0
0
MUXEN_2
Input
Input Mux bit 2
0
0
MUXEN_1
Input
Input Mux bit 1
0
0
MUXEN_0
Input
Input Mux bit 0
1
1
230
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 95. Boundary-scan Signals for the ADC(1) (Continued)
Recommended
Input when not
in use
Output Values when
recommended inputs are used,
and CPU is not using the ADC
Signal Name
Direction as seen
from the ADC
NEGSEL_2
Input
Input Mux for negative input for differential
signal, bit 2
0
0
NEGSEL_1
Input
Input Mux for negative input for differential
signal, bit 1
0
0
NEGSEL_0
Input
Input Mux for negative input for differential
signal, bit 0
0
0
PASSEN
Input
Enable pass-gate of differential amplifier.
1
1
PRECH
Input
Precharge output latch of comparator.
(Active low)
1
1
SCTEST
Input
Switch-cap TEST enable. Output from
differential amplifier send out to Port Pin
having ADC_4
0
0
ST
Input
Output of differential amplifier will settle
faster if this signal is high first two ACLK
periods after AMPEN goes high.
0
0
VCCREN
Input
Selects Vcc as the ACC reference voltage.
0
0
Note:
Description
1. Incorrect setting of the switches in Figure 108 will make signal contention and may damage the part. There are several input
choices to the S&H circuitry on the negative input of the output comparator in Figure 108. Make sure only one path is
selected from either one ADC pin, Bandgap reference source, or Ground.
If the ADC is not to be used during scan, the recommended input values from Table 95
should be used. The user is recommended not to use the differential amplifier during
scan. Switch-Cap based differential amplifier require fast operation and accurate timing
which is difficult to obtain when used in a scan chain. Details concerning operations of
the differential amplifier is therefore not provided.
The AVR ADC is based on the analog circuitry shown in Figure 108 with a successive
approximation algorithm implemented in the digital logic. When used in Boundary-scan,
the problem is usually to ensure that an applied analog voltage is measured within some
limits. This can easily be done without running a successive approximation algorithm:
apply the lower limit on the digital DAC[9:0] lines, make sure the output from the comparator is low, then apply the upper limit on the digital DAC[9:0] lines, and verify the
output from the comparator to be high.
The ADC need not be used for pure connectivity testing, since all analog inputs are
shared with a digital port pin as well.
When using the ADC, remember the following
•
The port pin for the ADC channel in use must be configured to be an input with pullup disabled to avoid signal contention.
•
In Normal mode, a dummy conversion (consisting of 10 comparisons) is performed
when enabling the ADC. The user is advised to wait at least 200ns after enabling the
ADC before controlling/observing any ADC signal, or perform a dummy conversion
before using the first result.
•
The DAC values must be stable at the midpoint value 0x200 when having the HOLD
signal low (Sample mode).
231
2570J–AVR–11/06
As an example, consider the task of verifying a 1.5V ± 5% input signal at ADC channel 3
when the power supply is 5.0V and AREF is externally connected to VCC.
1024 ⋅ 1,5V ⋅ 0,95 ⁄ 5V = 291 = 0x123
1024 ⋅ 1,5V ⋅ 1,05 ⁄ 5V = 323 = 0x143
The lower limit is:
The upper limit is:
The recommended values from Table 95 are used unless other values are given in the
algorithm in Table 96. Only the DAC and port pin values of the Scan Chain are shown.
The column “Actions” describes what JTAG instruction to be used before filling the
Boundary-scan Register with the succeeding columns. The verification should be done
on the data scanned out when scanning in the data on the same row in the table.
Table 96. Algorithm for Using the ADC
MUXEN
HOLD
PRECH
PA3.
Data
PA3.
Control
PA3.
Pullup_
Enable
0x200
0x08
1
1
0
0
0
1
0x200
0x08
0
1
0
0
0
3
1
0x200
0x08
1
1
0
0
0
4
1
0x123
0x08
1
1
0
0
0
5
1
0x123
0x08
1
0
0
0
0
1
0x200
0x08
1
1
0
0
0
7
1
0x200
0x08
0
1
0
0
0
8
1
0x200
0x08
1
1
0
0
0
9
1
0x143
0x08
1
1
0
0
0
10
1
0x143
0x08
1
0
0
0
0
1
0x200
0x08
1
1
0
0
0
Step
Actions
1
SAMPLE_
PRELOAD
1
2
EXTEST
6
11
Verify the
COMP bit
scanned
out to be 0
Verify the
COMP bit
scanned
out to be 1
ADCEN
DAC
Using this algorithm, the timing constraint on the HOLD signal constrains the TCK clock
frequency. As the algorithm keeps HOLD high for five steps, the TCK clock frequency
has to be at least five times the number of scan bits divided by the maximum hold time,
thold,max
232
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Boundary-scan Order
Table 97 and Table 98 shows the Scan order between TDI and TDO when the Boundary-scan chain is selected as data path. Bit 0 is the LSB; the first bit scanned in, and the
first bit scanned out. The scan order follows the pin-out order as far as possible. Therefore, the bits of Port A is scanned in the opposite bit order of the other ports. Exceptions
from the rules are the Scan chains for the analog circuits, which constitute the most significant bits of the scan chain regardless of which physical pin they are connected to. In
Figure 102, PXn. Data corresponds to FF0, PXn. Control corresponds to FF1, and PXn.
Pull-up_enable corresponds to FF2. Bit 4, 5, 6 and 7 of Port F is not in the scan chain,
since these pins constitute the TAP pins when the JTAG is enabled.
Table 97. ATmega325/645 Boundary-scan Order, 64-pin
Bit Number
Signal Name
Module
197
AC_IDLE
Comparator
196
ACO
195
ACME
194
AINBG
193
COMP
192
ACLK
191
ACTEN
190
PRIVATE_SIGNAL1(1)
189
ADCBGEN
188
ADCEN
187
AMPEN
186
DAC_9
185
DAC_8
184
DAC_7
183
DAC_6
182
DAC_5
181
DAC_4
180
DAC_3
179
DAC_2
178
DAC_1
177
DAC_0
176
EXTCH
175
GNDEN
174
HOLD
173
IREFEN
172
MUXEN_7
171
MUXEN_6
170
MUXEN_5
ADC
233
2570J–AVR–11/06
Table 97. ATmega325/645 Boundary-scan Order, 64-pin (Continued)
234
Bit Number
Signal Name
169
MUXEN_4
168
MUXEN_3
167
MUXEN_2
166
MUXEN_1
165
MUXEN_0
164
NEGSEL_2
163
NEGSEL_1
162
NEGSEL_0
161
PASSEN
160
PRECH
159
ST
158
VCCREN
157
PE0.Data
156
PE0.Control
155
PE0.Pull-up_Enable
154
PE1.Data
153
PE1.Control
152
PE1.Pull-up_Enable
151
PE2.Data
150
PE2.Control
149
PE2.Pull-up_Enable
148
PE3.Data
147
PE3.Control
146
PE3.Pull-up_Enable
145
PE4.Data
144
PE4.Control
143
PE4.Pull-up_Enable
142
PE5.Data
141
PE5.Control
140
PE5.Pull-up_Enable
139
PE6.Data
138
PE6.Control
137
PE6.Pull-up_Enable
136
PE7.Data
135
PE7.Control
134
PE7.Pull-up_Enable
Module
Port E
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 97. ATmega325/645 Boundary-scan Order, 64-pin (Continued)
Bit Number
Signal Name
Module
133
PB0.Data
Port B
132
PB0.Control
131
PB0.Pull-up_Enable
130
PB1.Data
129
PB1.Control
128
PB1.Pull-up_Enable
127
PB2.Data
126
PB2.Control
125
PB2.Pull-up_Enable
124
PB3.Data
123
PB3.Control
122
PB3.Pull-up_Enable
121
PB4.Data
120
PB4.Control
119
PB4.Pull-up_Enable
118
PB5.Data
117
PB5.Control
116
PB5.Pull-up_Enable
115
PB6.Data
114
PB6.Control
113
PB6.Pull-up_Enable
112
PB7.Data
111
PB7.Control
110
PB7.Pull-up_Enable
109
PG3.Data
108
PG3.Control
107
PG3.Pull-up_Enable
106
PG4.Data
105
PG4.Control
104
PG4.Pull-up_Enable
103
PG5
(Observe Only)
102
RSTT
101
RSTHV
Reset Logic
(Observe-only)
Port G
235
2570J–AVR–11/06
Table 97. ATmega325/645 Boundary-scan Order, 64-pin (Continued)
236
Bit Number
Signal Name
Module
100
EXTCLKEN
Enable signals for main Clock/Oscillators
99
OSCON
98
RCOSCEN
97
OSC32EN
96
EXTCLK (XTAL1)
95
OSCCK
94
RCCK
93
OSC32CK
92
PD0.Data
91
PD0.Control
90
PD0.Pull-up_Enable
89
PD1.Data
88
PD1.Control
87
PD1.Pull-up_Enable
86
PD2.Data
85
PD2.Control
84
PD2.Pull-up_Enable
83
PD3.Data
82
PD3.Control
81
PD3.Pull-up_Enable
80
PD4.Data
79
PD4.Control
78
PD4.Pull-up_Enable
77
PD5.Data
76
PD5.Control
75
PD5.Pull-up_Enable
74
PD6.Data
73
PD6.Control
72
PD6.Pull-up_Enable
71
PD7.Data
70
PD7.Control
69
PD7.Pull-up_Enable
68
PG0.Data
67
PG0.Control
66
PG0.Pull-up_Enable
65
PG1.Data
Clock input and Oscillators for the main
clock
(Observe-only)
Port D
Port G
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 97. ATmega325/645 Boundary-scan Order, 64-pin (Continued)
Bit Number
Signal Name
64
PG1.Control
63
PG1.Pull-up_Enable
62
PC0.Data
61
PC0.Control
60
PC0.Pull-up_Enable
59
PC1.Data
58
PC1.Control
57
PC1.Pull-up_Enable
56
PC2.Data
55
PC2.Control
54
PC2.Pull-up_Enable
53
PC3.Data
52
PC3.Control
51
PC3.Pull-up_Enable
50
PC4.Data
49
PC4.Control
48
PC4.Pull-up_Enable
47
PC5.Data
46
PC5.Control
45
PC5.Pull-up_Enable
44
PC6.Data
43
PC6.Control
42
PC6.Pull-up_Enable
41
PC7.Data
40
PC7.Control
39
PC7.Pull-up_Enable
38
PG2.Data
37
PG2.Control
36
PG2.Pull-up_Enable
35
PA7.Data
34
PA7.Control
33
PA7.Pull-up_Enable
32
PA6.Data
31
PA6.Control
30
PA6.Pull-up_Enable
29
PA5.Data
Module
Port C
Port G
Port A
237
2570J–AVR–11/06
Table 97. ATmega325/645 Boundary-scan Order, 64-pin (Continued)
Bit Number
Signal Name
28
PA5.Control
27
PA5.Pull-up_Enable
26
PA4.Data
25
PA4.Control
24
PA4.Pull-up_Enable
23
PA3.Data
22
PA3.Control
21
PA3.Pull-up_Enable
20
PA2.Data
19
PA2.Control
18
PA2.Pull-up_Enable
17
PA1.Data
16
PA1.Control
15
PA1.Pull-up_Enable
14
PA0.Data
13
PA0.Control
12
PA0.Pull-up_Enable
11
PF3.Data
10
PF3.Control
9
PF3.Pull-up_Enable
8
PF2.Data
7
PF2.Control
6
PF2.Pull-up_Enable
5
PF1.Data
4
PF1.Control
3
PF1.Pull-up_Enable
2
PF0.Data
1
PF0.Control
0
PF0.Pull-up_Enable
Note:
238
Module
Port F
1. PRIVATE_SIGNAL1 should always be scanned in as zero.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin
Bit Number
Signal Name
Module
242
AC_IDLE
Comparator
241
ACO
240
ACME
239
AINBG
238
COMP
237
ACLK
236
ACTEN
235
PRIVATE_SIGNAL1(1)
234
ADCBGEN
233
ADCEN
232
AMPEN
231
DAC_9
230
DAC_8
229
DAC_7
228
DAC_6
227
DAC_5
226
DAC_4
225
DAC_3
224
DAC_2
223
DAC_1
222
DAC_0
221
EXTCH
220
GNDEN
219
HOLD
218
IREFEN
217
MUXEN_7
216
MUXEN_6
215
MUXEN_5
214
MUXEN_4
213
MUXEN_3
212
MUXEN_2
211
MUXEN_1
210
MUXEN_0
209
NEGSEL_2
208
NEGSEL_1
ADC
239
2570J–AVR–11/06
Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
240
Bit Number
Signal Name
207
NEGSEL_0
206
PASSEN
205
PRECH
204
ST
203
VCCREN
202
PE0.Data
201
PE0.Control
200
PE0.Pull-up_Enable
199
PE1.Data
198
PE1.Control
197
PE1.Pull-up_Enable
196
PE2.Data
195
PE2.Control
194
PE2.Pull-up_Enable
193
PE3.Data
192
PE3.Control
191
PE3.Pull-up_Enable
190
PE4.Data
189
PE4.Control
188
PE4.Pull-up_Enable
187
PE5.Data
186
PE5.Control
185
PE5.Pull-up_Enable
184
PE6.Data
183
PE6.Control
182
PE6.Pull-up_Enable
181
PE7.Data
180
PE7.Control
179
PE7.Pull-up_Enable
178
PJ0.Data
177
PJ0.Control
176
PJ0.Pull-up_Enable
175
PJ1.Data
174
PJ1.Control
173
PJ1.Pull-up_Enable
172
PB0.Data
Module
Port E
Port J
Port B
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
Bit Number
Signal Name
Module
171
PB0.Control
170
PB0.Pull-up_Enable
169
PB1.Data
168
PB1.Control
167
PB1.Pull-up_Enable
166
PB2.Data
165
PB2.Control
164
PB2.Pull-up_Enable
163
PB3.Data
162
PB3.Control
161
PB3.Pull-up_Enable
160
PB4.Data
159
PB4.Control
158
PB4.Pull-up_Enable
157
PB5.Data
156
PB5.Control
155
PB5.Pull-up_Enable
154
PB6.Data
153
PB6.Control
152
PB6.Pull-up_Enable
151
PB7.Data
150
PB7.Control
149
PB7.Pull-up_Enable
148
PG3.Data
147
PG3.Control
146
PG3.Pull-up_Enable
145
PG4.Data
144
PG4.Control
143
PG4.Pull-up_Enable
142
PG5
(Observe Only)
141
RSTT
140
RSTHV
Reset Logic
(Observe-only)
139
EXTCLKEN
138
OSCON
137
RCOSCEN
136
OSC32EN
Port G
Enable signals for main Clock/Oscillators
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Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
242
Bit Number
Signal Name
Module
135
EXTCLK (XTAL1)
134
OSCCK
Clock input and Oscillators for the main
clock
(Observe-only)
133
RCCK
132
OSC32CK
131
PJ2.Data
130
PJ2.Control
129
PJ2.Pull-up_Enable
128
PJ3.Data
127
PJ3.Control
126
PJ3.Pull-up_Enable
125
PJ4.Data
124
PJ4.Control
123
PJ4.Pull-up_Enable
122
PJ5.Data
121
PJ5.Control
120
PJ5.Pull-up_Enable
119
PJ6.Data
118
PJ6.Control
117
PJ6.Pull-up_Enable
116
PD0.Data
115
PD0.Control
114
PD0.Pull-up_Enable
113
PD1.Data
112
PD1.Control
111
PD1.Pull-up_Enable
110
PD2.Data
109
PD2.Control
108
PD2.Pull-up_Enable
107
PD3.Data
106
PD3.Control
105
PD3.Pull-up_Enable
104
PD4.Data
103
PD4.Control
102
PD4.Pull-up_Enable
101
PD5.Data
100
PD5.Control
Port J
Port D
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
Bit Number
Signal Name
99
PD5.Pull-up_Enable
98
PD6.Data
97
PD6.Control
96
PD6.Pull-up_Enable
95
PD7.Data
94
PD7.Control
93
PD7.Pull-up_Enable
92
PG0.Data
91
PG0.Control
90
PG0.Pull-up_Enable
89
PG1.Data
88
PG1.Control
87
PG1.Pull-up_Enable
86
PC0.Data
85
PC0.Control
84
PC0.Pull-up_Enable
83
PC1.Data
82
PC1.Control
81
PC1.Pull-up_Enable
80
PC2.Data
79
PC2.Control
78
PC2.Pull-up_Enable
77
PC3.Data
76
PC3.Control
75
PC3.Pull-up_Enable
74
PC4.Data
73
PC4.Control
72
PC4.Pull-up_Enable
71
PC5.Data
70
PC5.Control
69
PC5.Pull-up_Enable
68
PH0.Data
67
PH0.Control
66
PH0.Pull-up_Enable
65
PH1.Data
64
PH1.Control
Module
Port G
Port C
Port H
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Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
244
Bit Number
Signal Name
63
PH1.Pull-up_Enable
62
PH2.Data
61
PH2.Control
60
PH2.Pull-up_Enable
59
PH3.Data
58
PH3.Control
57
PH3.Pull-up_Enable
56
PC6.Data
55
PC6.Control
54
PC6.Pull-up_Enable
53
PC7.Data
52
PC7.Control
51
PC7.Pull-up_Enable
50
PG2.Data
49
PG2.Control
48
PG2.Pull-up_Enable
47
PA7.Data
46
PA7.Control
45
PA7.Pull-up_Enable
44
PA6.Data
43
PA6.Control
42
PA6.Pull-up_Enable
41
PA5.Data
40
PA5.Control
39
PA5.Pull-up_Enable
38
PA4.Data
37
PA4.Control
36
PA4.Pull-up_Enable
35
PA3.Data
34
PA3.Control
33
PA3.Pull-up_Enable
32
PA2.Data
31
PA2.Control
30
PA2.Pull-up_Enable
29
PA1.Data
28
PA1.Control
Module
Port C
Port G
Port A
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ATmega325/3250/645/6450
Table 98. ATmega3250/6450 Boundary-scan Order, 100-pin (Continued)
Bit Number
Signal Name
27
PA1.Pull-up_Enable
26
PA0.Data
25
PA0.Control
24
PA0.Pull-up_Enable
23
PH4.Data
22
PH4.Control
21
PH4.Pull-up_Enable
20
PH5.Data
19
PH5.Control
18
PH5.Pull-up_Enable
17
PH6.Data
16
PH6.Control
15
PH6.Pull-up_Enable
14
PH7.Data
13
PH7.Control
12
PH7.Pull-up_Enable
11
PF3.Data
10
PF3.Control
9
PF3.Pull-up_Enable
8
PF2.Data
7
PF2.Control
6
PF2.Pull-up_Enable
5
PF1.Data
4
PF1.Control
3
PF1.Pull-up_Enable
2
PF0.Data
1
PF0.Control
0
PF0.Pull-up_Enable
Note:
Boundary-scan
Description Language
Files
Module
Port H
Port F
1. PRIVATE_SIGNAL1 should always be scanned in as zero.
Boundary-scan Description Language (BSDL) files describe Boundary-scan capable
devices in a standard format used by automated test-generation software. The order
and function of bits in the Boundary-scan Data Register are included in this description.
A BSDL file for ATmega325/3250/645/6450 is available.
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2570J–AVR–11/06
Boot Loader Support
– Read-While-Write
Self-Programming
The Boot Loader Support provides a real Read-While-Write Self-Programming mechanism for downloading and uploading program code by the MCU itself. This feature
allows flexible application software updates controlled by the MCU using a Flash-resident Boot Loader program. The Boot Loader program can use any available data
interface and associated protocol to read code and write (program) that code into the
Flash memory, or read the code from the program memory. The program code within
the Boot Loader section has the capability to write into the entire Flash, including the
Boot Loader memory. The Boot Loader can thus even modify itself, and it can also
erase itself from the code if the feature is not needed anymore. The size of the Boot
Loader memory is configurable with fuses and the Boot Loader has two separate sets of
Boot Lock bits which can be set independently. This gives the user a unique flexibility to
select different levels of protection.
Boot Loader Features
•
•
•
•
•
•
•
Read-While-Write Self-Programming
Flexible Boot Memory Size
High Security (Separate Boot Lock Bits for a Flexible Protection)
Separate Fuse to Select Reset Vector
Optimized Page(1) Size
Code Efficient Algorithm
Efficient Read-Modify-Write Support
Note:
1. A page is a section in the Flash consisting of several bytes (see Table 116 on page
264) used during programming. The page organization does not affect normal
operation.
Application and Boot
Loader Flash Sections
The Flash memory is organized in two main sections, the Application section and the
Boot Loader section (see Figure 110). The size of the different sections is configured by
the BOOTSZ Fuses as shown in Table 104 on page 258 and Figure 110. These two
sections can have different level of protection since they have different sets of Lock bits.
Application Section
The Application section is the section of the Flash that is used for storing the application
code. The protection level for the Application section can be selected by the application
Boot Lock bits (Boot Lock bits 0), see Table 100 on page 249. The Application section
can never store any Boot Loader code since the SPM instruction is disabled when executed from the Application section.
BLS – Boot Loader Section
While the Application section is used for storing the application code, the The Boot
Loader software must be located in the BLS since the SPM instruction can initiate a programming when executing from the BLS only. The SPM instruction can access the
entire Flash, including the BLS itself. The protection level for the Boot Loader section
can be selected by the Boot Loader Lock bits (Boot Lock bits 1), see Table 101 on page
249.
Read-While-Write and No Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot
Loader software update is dependent on which address that is being programmed. In
Read-While-Write Flash
addition to the two sections that are configurable by the BOOTSZ Fuses as described
Sections
above, the Flash is also divided into two fixed sections, the Read-While-Write (RWW)
section and the No Read-While-Write (NRWW) section. The limit between the RWWand NRWW sections is given in Table 105 on page 258 and Figure 110 on page 248.
The main difference between the two sections is:
246
•
When erasing or writing a page located inside the RWW section, the NRWW section
can be read during the operation.
•
When erasing or writing a page located inside the NRWW section, the CPU is halted
during the entire operation.
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Note that the user software can never read any code that is located inside the RWW
section during a Boot Loader software operation. The syntax “Read-While-Write section” refers to which section that is being programmed (erased or written), not which
section that actually is being read during a Boot Loader software update.
RWW – Read-While-Write
Section
If a Boot Loader software update is programming a page inside the RWW section, it is
possible to read code from the Flash, but only code that is located in the NRWW section. During an on-going programming, the software must ensure that the RWW section
never is being read. If the user software is trying to read code that is located inside the
RWW section (i.e., by a call/jmp/lpm or an interrupt) during programming, the software
might end up in an unknown state. To avoid this, the interrupts should either be disabled
or moved to the Boot Loader section. The Boot Loader section is always located in the
NRWW section. The RWW Section Busy bit (RWWSB) in the Store Program Memory
Control and Status Register (SPMCSR) will be read as logical one as long as the RWW
section is blocked for reading. After a programming is completed, the RWWSB must be
cleared by software before reading code located in the RWW section. See “Store Program Memory Control and Status Register – SPMCSR” on page 250. for details on how
to clear RWWSB.
NRWW – No Read-While-Write
Section
The code located in the NRWW section can be read when the Boot Loader software is
updating a page in the RWW section. When the Boot Loader code updates the NRWW
section, the CPU is halted during the entire Page Erase or Page Write operation.
Table 99. Read-While-Write Features
Which Section does the Zpointer Address During the
Programming?
Which Section Can
be Read During
Programming?
Is the CPU
Halted?
Read-While-Write
Supported?
RWW Section
NRWW Section
No
Yes
NRWW Section
None
Yes
No
Figure 109. Read-While-Write vs. No Read-While-Write
Read-While-Write
(RWW) Section
Z-pointer
Addresses RWW
Section
Z-pointer
Addresses NRWW
Section
No Read-While-Write
(NRWW) Section
CPU is Halted
During the Operation
Code Located in
NRWW Section
Can be Read During
the Operation
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2570J–AVR–11/06
Figure 110. Memory Sections
Program Memory
BOOTSZ = '10'
Program Memory
BOOTSZ = '11'
0x0000
No Read-While-Write Section
Read-While-Write Section
Application Flash Section
End RWW
Start NRWW
Application Flash Section
Boot Loader Flash Section
End Application
Start Boot Loader
Flashend
No Read-While-Write Section
Read-While-Write Section
0x0000
Program Memory
BOOTSZ = '01'
Application Flash Section
End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '00'
No Read-While-Write Section
Boot Loader Lock Bits
Read-While-Write Section
Application Flash Section
End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
Note:
0x0000
No Read-While-Write Section
Read-While-Write Section
0x0000
Application Flash Section
End RWW, End Application
Start NRWW, Start Boot Loader
Boot Loader Flash Section
Flashend
1. The parameters in the figure above are given in Table 104 on page 258.
If no Boot Loader capability is needed, the entire Flash is available for application code.
The Boot Loader has two separate sets of Boot Lock bits which can be set independently. This gives the user a unique flexibility to select different levels of protection.
The user can select:
•
To protect the entire Flash from a software update by the MCU.
•
To protect only the Boot Loader Flash section from a software update by the MCU.
•
To protect only the Application Flash section from a software update by the MCU.
•
Allow software update in the entire Flash.
See Table 100 and Table 101 for further details. The Boot Lock bits and general Lock
bits can be set in software and in Serial or Parallel Programming mode, but they can be
cleared by a Chip Erase command only. The general Write Lock (Lock Bit mode 2) does
not control the programming of the Flash memory by SPM instruction. Similarly, the general Read/Write Lock (Lock Bit mode 1) does not control reading nor writing by
LPM/SPM, if it is attempted.
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Table 100. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0 Mode
BLB02
BLB01
1
1
1
No restrictions for SPM or LPM accessing the Application
section.
2
1
0
SPM is not allowed to write to the Application section.
3
0
0
SPM is not allowed to write to the Application section, and
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
4
0
1
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
Note:
Protection
1. “1” means unprogrammed, “0” means programmed
Table 101. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1 Mode
BLB12
BLB11
1
1
1
No restrictions for SPM or LPM accessing the Boot Loader
section.
2
1
0
SPM is not allowed to write to the Boot Loader section.
3
0
0
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
4
0
1
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
Note:
Protection
1. “1” means unprogrammed, “0” means programmed
Entering the Boot Loader Entering the Boot Loader takes place by a jump or call from the application program.
This may be initiated by a trigger such as a command received via USART, or SPI interProgram
face. Alternatively, the Boot Reset Fuse can be programmed so that the Reset Vector is
pointing to the Boot Flash start address after a reset. In this case, the Boot Loader is
started after a reset. After the application code is loaded, the program can start executing the application code. Note that the fuses cannot be changed by the MCU itself. This
means that once the Boot Reset Fuse is programmed, the Reset Vector will always
point to the Boot Loader Reset and the fuse can only be changed through the serial or
parallel programming interface.
Table 102. Boot Reset Fuse(1)
BOOTRST
Note:
Reset Address
1
Reset Vector = Application Reset (address 0x0000)
0
Reset Vector = Boot Loader Reset (see Table 104 on page 258)
1. “1” means unprogrammed, “0” means programmed
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2570J–AVR–11/06
Store Program Memory
Control and Status Register –
SPMCSR
The Store Program Memory Control and Status Register contains the control bits
needed to control the Boot Loader operations.
Bit
7
6
5
4
3
2
1
0
SPMIE
RWWSB
–
RWWSRE
BLBSET
PGWRT
PGERS
SPMEN
Read/Write
R/W
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPMCSR
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the
SPM ready interrupt will be enabled. The SPM ready Interrupt will be executed as long
as the SPMEN bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is
initiated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the
RWW section cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit
is written to one after a Self-Programming operation is completed. Alternatively the
RWWSB bit will automatically be cleared if a page load operation is initiated.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the ATmega325/3250/645/6450 and always read as zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section
is blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW
section, the user software must wait until the programming is completed (SPMEN will be
cleared). Then, if the RWWSRE bit is written to one at the same time as SPMEN, the
next SPM instruction within four clock cycles re-enables the RWW section. The RWW
section cannot be re-enabled while the Flash is busy with a Page Erase or a Page Write
(SPMEN is set). If the RWWSRE bit is written while the Flash is being loaded, the Flash
load operation will abort and the data loaded will be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles sets Boot Lock bits and general Lock bits, according to the data in R0.
The data in R1 and the address in the Z-pointer are ignored. The BLBSET bit will automatically be cleared upon completion of the Lock bit set, or if no SPM instruction is
executed within four clock cycles.
An LPM instruction within three cycles after BLBSET and SPMEN are set in the
SPMCSR Register, will read either the Lock bits or the Fuse bits (depending on Z0 in
the Z-pointer) into the destination register. See “Reading the Fuse and Lock Bits from
Software” on page 254 for details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles executes Page Write, with the data stored in the temporary buffer. The
page address is taken from the high part of the Z-pointer. The data in R1 and R0 are
ignored. The PGWRT bit will auto-clear upon completion of a Page Write, or if no SPM
instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation if the NRWW section is addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles executes Page Erase. The page address is taken from the high part of
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the Z-pointer. The data in R1 and R0 are ignored. The PGERS bit will auto-clear upon
completion of a Page Erase, or if no SPM instruction is executed within four clock
cycles. The CPU is halted during the entire Page Write operation if the NRWW section is
addressed.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one
together with either RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM
instruction will have a special meaning, see description above. If only SPMEN is written,
the following SPM instruction will store the value in R1:R0 in the temporary page buffer
addressed by the Z-pointer. The LSB of the Z-pointer is ignored. The SPMEN bit will
auto-clear upon completion of an SPM instruction, or if no SPM instruction is executed
within four clock cycles. During Page Erase and Page Write, the SPMEN bit remains
high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the
lower five bits will have no effect.
Addressing the Flash
During SelfProgramming
The Z-pointer is used to address the SPM commands.
Bit
15
14
13
12
11
10
9
8
ZH (R31)
Z15
Z14
Z13
Z12
Z11
Z10
Z9
Z8
ZL (R30)
Z7
Z6
Z5
Z4
Z3
Z2
Z1
Z0
7
6
5
4
3
2
1
0
Since the Flash is organized in pages (see Table 116 on page 264), the Program
Counter can be treated as having two different sections. One section, consisting of the
least significant bits, is addressing the words within a page, while the most significant
bits are addressing the pages. This is shown in Figure 111. Note that the Page Erase
and Page Write operations are addressed independently. Therefore it is of major importance that the Boot Loader software addresses the same page in both the Page Erase
and Page Write operation. Once a programming operation is initiated, the address is
latched and the Z-pointer can be used for other operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock
bits. The content of the Z-pointer is ignored and will have no effect on the operation. The
LPM instruction does also use the Z-pointer to store the address. Since this instruction
addresses the Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
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Figure 111. Addressing the Flash During SPM(1)
BIT
15
ZPCMSB
ZPAGEMSB
Z - REGISTER
1 0
0
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
1. The different variables used in Figure 111 are listed in Table 106 on page 258.
2. PCPAGE and PCWORD are listed in Table 116 on page 264.
Self-Programming the
Flash
The program memory is updated in a page by page fashion. Before programming a
page with the data stored in the temporary page buffer, the page must be erased. The
temporary page buffer is filled one word at a time using SPM and the buffer can be filled
either before the Page Erase command or between a Page Erase and a Page Write
operation:
Alternative 1, fill the buffer before a Page Erase
•
Fill temporary page buffer
•
Perform a Page Erase
•
Perform a Page Write
Alternative 2, fill the buffer after Page Erase
•
Perform a Page Erase
•
Fill temporary page buffer
•
Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for
example in the temporary page buffer) before the erase, and then be rewritten. When
using alternative 1, the Boot Loader provides an effective Read-Modify-Write feature
which allows the user software to first read the page, do the necessary changes, and
then write back the modified data. If alternative 2 is used, it is not possible to read the
old data while loading since the page is already erased. The temporary page buffer can
be accessed in a random sequence. It is essential that the page address used in both
the Page Erase and Page Write operation is addressing the same page. See “Simple
Assembly Code Example for a Boot Loader” on page 256 for an assembly code
example.
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Performing Page Erase by
SPM
Filling the Temporary Buffer
(Page Loading)
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to
SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in
R1 and R0 is ignored. The page address must be written to PCPAGE in the Z-register.
Other bits in the Z-pointer will be ignored during this operation.
•
Page Erase to the RWW section: The NRWW section can be read during the Page
Erase.
•
Page Erase to the NRWW section: The CPU is halted during the operation.
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing
SPMCSR. The content of PCWORD in the Z-register is used to address the data in the
temporary buffer. The temporary buffer will auto-erase after a Page Write operation or
by writing the RWWSRE bit in SPMCSR. It is also erased after a system reset. Note that
it is not possible to write more than one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded
will be lost.
Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “X0000101” to
SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in
R1 and R0 is ignored. The page address must be written to PCPAGE. Other bits in the
Z-pointer must be written to zero during this operation.
•
Page Write to the RWW section: The NRWW section can be read during the Page
Write.
•
Page Write to the NRWW section: The CPU is halted during the operation.
Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt
when the SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used
instead of polling the SPMCSR Register in software. When using the SPM interrupt, the
Interrupt Vectors should be moved to the BLS section to avoid that an interrupt is
accessing the RWW section when it is blocked for reading. How to move the interrupts
is described in “Interrupts” on page 48.
Consideration While Updating
BLS
Special care must be taken if the user allows the Boot Loader section to be updated by
leaving Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can
corrupt the entire Boot Loader, and further software updates might be impossible. If it is
not necessary to change the Boot Loader software itself, it is recommended to program
the Boot Lock bit11 to protect the Boot Loader software from any internal software
changes.
Prevent Reading the RWW
Section During SelfProgramming
During Self-Programming (either Page Erase or Page Write), the RWW section is
always blocked for reading. The user software itself must prevent that this section is
addressed during the self programming operation. The RWWSB in the SPMCSR will be
set as long as the RWW section is busy. During Self-Programming the Interrupt Vector
table should be moved to the BLS as described in “Interrupts” on page 48, or the interrupts must be disabled. Before addressing the RWW section after the programming is
completed, the user software must clear the RWWSB by writing the RWWSRE. See
“Simple Assembly Code Example for a Boot Loader” on page 256 for an example.
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2570J–AVR–11/06
Setting the Boot Loader Lock
Bits by SPM
To set the Boot Loader Lock bits and general Lock bits, write the desired data to R0,
write “X0001001” to SPMCSR and execute SPM within four clock cycles after writing
SPMCSR.
Bit
7
6
5
4
3
2
1
0
R0
1
1
BLB12
BLB11
BLB02
BLB01
LB2
LB1
See Table 100 and Table 101 for how the different settings of the Boot Loader bits affect
the Flash access.
If bits 5..0 in R0 are cleared (zero), the corresponding Lock bit will be programmed if an
SPM instruction is executed within four cycles after BLBSET and SPMEN are set in
SPMCSR. The Z-pointer is don’t care during this operation, but for future compatibility it
is recommended to load the Z-pointer with 0x0001 (same as used for reading the Lock
bits). For future compatibility it is also recommended to set bits 7, and 6 in R0 to “1”
when writing the Lock bits. When programming the Lock bits the entire Flash can be
read during the operation.
EEPROM Write Prevents
Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash.
Reading the Fuses and Lock bits from software will also be prevented during the
EEPROM write operation. It is recommended that the user checks the status bit (EEWE)
in the EECR Register and verifies that the bit is cleared before writing to the SPMCSR
Register.
Reading the Fuse and Lock
Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits,
load the Z-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCSR.
When an LPM instruction is executed within three CPU cycles after the BLBSET and
SPMEN bits are set in SPMCSR, the value of the Lock bits will be loaded in the destination register. The BLBSET and SPMEN bits will auto-clear upon completion of reading
the Lock bits or if no LPM instruction is executed within three CPU cycles or no SPM
instruction is executed within four CPU cycles. When BLBSET and SPMEN are cleared,
LPM will work as described in the Instruction set Manual.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
BLB12
BLB11
BLB02
BLB01
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for
reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and
set the BLBSET and SPMEN bits in SPMCSR. When an LPM instruction is executed
within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the value
of the Fuse Low byte (FLB) will be loaded in the destination register as shown below.
Refer to Table 111 on page 261 for a detailed description and mapping of the Fuse Low
byte.
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM
instruction is executed within three cycles after the BLBSET and SPMEN bits are set in
the SPMCSR, the value of the Fuse High byte (FHB) will be loaded in the destination
register as shown below. Refer to Table 110 on page 261 for detailed description and
mapping of the Fuse High byte.
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an LPM
instruction is executed within three cycles after the BLBSET and SPMEN bits are set in
254
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the SPMCSR, the value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown below. Refer to Table 109 on page 260 for detailed description
and mapping of the Extended Fuse byte.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
–
–
EFB2
EFB1
EFB0
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that
are unprogrammed, will be read as one.
Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is too low for the CPU and the Flash to operate properly. These issues are the same
as for board level systems using the Flash, and the same design solutions should be
applied.
A Flash program corruption can be caused by two situations when the voltage is too low.
First, a regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage
for executing instructions is too low.
Flash corruption can easily be avoided by following these design recommendations (one
is sufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot
Loader Lock bits to prevent any Boot Loader software updates.
2. Keep the AVR RESET active (low) during periods of insufficient power supply
voltage. This can be done by enabling the internal Brown-out Detector (BOD) if
the operating voltage matches the detection level. If not, an external low VCC
reset protection circuit can be used. If a reset occurs while a write operation is in
progress, the write operation will be completed provided that the power supply
voltage is sufficient.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This
will prevent the CPU from attempting to decode and execute instructions, effectively protecting the SPMCSR Register and thus the Flash from unintentional
writes.
Programming Time for Flash
when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 103 shows the typical programming time for Flash accesses from the CPU.
Table 103. SPM Programming Time
Symbol
Min Programming Time
Max Programming Time
Flash write (Page Erase, Page Write,
and write Lock bits by SPM)
3.7 ms
4.5 ms
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Simple Assembly Code
Example for a Boot Loader
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section
can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
;-It is assumed that either the interrupt table is moved to the
Boot
; loader section or that the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2
;PAGESIZEB is page size in BYTES, not
words
.org SMALLBOOTSTART
Write_page:
; Page Erase
ldi spmcrval, (1<<PGERS) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB)
;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:
ld
r0, Y+
ld
r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2
;use subi for PAGESIZEB<=256
brne Wrloop
; execute Page Write
subi ZL, low(PAGESIZEB)
;restore pointer
sbci ZH, high(PAGESIZEB)
;not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; read back and check, optional
ldi looplo, low(PAGESIZEB)
;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB)
;restore pointer
sbci YH, high(PAGESIZEB)
Rdloop:
lpm r0, Z+
ld
r1, Y+
cpse r0, r1
jmp Error
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ATmega325/3250/645/6450
sbiw loophi:looplo, 1
brne Rdloop
;use subi for PAGESIZEB<=256
; return to RWW section
; verify that RWW section is safe to read
Return:
in
temp1, SPMCSR
sbrs temp1, RWWSB
; If RWWSB is set, the RWW section is not
ready yet
ret
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
rjmp Return
Do_spm:
; check for previous SPM complete
Wait_spm:
in
temp1, SPMCSR
sbrc temp1, SPMEN
rjmp Wait_spm
; input: spmcrval determines SPM action
; disable interrupts if enabled, store status
in
temp2, SREG
cli
; check that no EEPROM write access is present
Wait_ee:
sbic EECR, EEWE
rjmp Wait_ee
; SPM timed sequence
out SPMCSR, spmcrval
spm
; restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret
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ATmega325/3250/645/6450
Boot Loader Parameters
In Table 104 through Table 106, the parameters used in the description of the Self-Programming are given.
Table 104. Boot Size Configuration(1)
Pages
Boot Loader
Flash Section
End
Application
Section
BOOTSZ1
BOOTSZ0
1
1
256/512 words
4
0x0000-0x3EFF/
0x0000-0x7DFF
0x3F00-0x3FFF/
0x7E00-0x7FFF
0x3EFF/
0x7DFF
0x3F00/
0x7E00
1
0
512/1024 words
8
0x0000-0x3DFF/
0x0000-0x7BFF/
0x3E00-0x3FFF/
0x7C00-0x7FFF
0x3DFF/
0x7BFF
0x3E00/
0x7C00
0
1
1024/2048 words
16
0x0000-0x3BFF/
0x0000-0x77FF
0x3C00-0x3FFF/
0x7800-0x7FFF
0x3BFF/
0x77FF
0x3C00/
0x7800
0
0
2048/4096 words
32
0x0000-0x37FF/
0x0000-0x6FFF
0x3800-0x3FFF/
0x7000-0x7FFF
0x37FF/
0x6FFF
0x3800/
0x7000
Note:
Boot Size
Application
Flash Section
Boot Reset
Address
(Start
Boot Loader
Section)
1. The different BOOTSZ Fuse configurations are shown in Figure 110
Table 105. Read-While-Write Limit(1)
Section
Pages
Read-While-Write section (RWW)
No Read-While-Write section (NRWW)
Note:
Address
224/224
0x0000 - x37FF/ 0x0000 - 0x6FFF
32/32
0x3800 - 0x3FFF/ 0x7000-0x7FFF
1. For details about these two section, see “NRWW – No Read-While-Write Section” on page 247 and “RWW – Read-WhileWrite Section” on page 247.
Table 106. Explanation of different variables used in Figure 111 and the mapping to the Z-pointer(1)
Corresponding
Z-value
Variable
PCMSB
Most significant bit in the Program Counter. (Program Counter is 14/15 bits
PC[13/14:0])
13/14
PAGEMSB
Most significant bit which is used to address the words within one page
(64/128 words in a page requires six/seven bits PC [5/6:0]).
5/6
ZPCMSB
ZPAGEMSB
Description
Z14/15
Bit in Z-register that is mapped to PCMSB. Because Z0 is not used, the
ZPCMSB equals PCMSB + 1.
Z6/7
Bit in Z-register that is mapped to PCMSB. Because Z0 is not used, the
ZPAGEMSB equals PAGEMSB + 1.
PCPAGE
PC[13/14:6/7]
Z14/15:Z7/8
Program Counter page address: Page select, for Page Erase and Page
Write
PCWORD
PC[5/6:0]
Z6/7:Z1
Program Counter word address: Word select, for filling temporary buffer
(must be zero during Page Write operation)
Note:
258
1. Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See “Addressing the Flash During Self-Programming” on page 251 for details about the use of Z-pointer during SelfProgramming.
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Memory
Programming
Program And Data
Memory Lock Bits
The ATmega325/3250/645/6450 provides six Lock bits which can be left unprogrammed
(“1”) or can be programmed (“0”) to obtain the additional features listed in Table 108.
The Lock bits can only be erased to “1” with the Chip Erase command.
Table 107. Lock Bit Byte(1)
Lock Bit Byte
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
BLB12
5
Boot Lock bit
1 (unprogrammed)
BLB11
4
Boot Lock bit
1 (unprogrammed)
BLB02
3
Boot Lock bit
1 (unprogrammed)
BLB01
2
Boot Lock bit
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
Note:
Bit No
1. “1” means unprogrammed, “0” means programmed
Table 108. Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
LB2
LB1
1
1
1
No memory lock features enabled.
0
Further programming of the Flash and EEPROM is
disabled in Parallel and Serial Programming mode. The
Fuse bits are locked in both Serial and Parallel
Programming mode.(1)
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming
mode. The Boot Lock bits and Fuse bits are locked in both
Serial and Parallel Programming mode.(1)
2
1
3
0
0
BLB0 Mode
BLB02
BLB01
1
1
1
No restrictions for SPM or LPM accessing the Application
section.
2
1
0
SPM is not allowed to write to the Application section.
0
SPM is not allowed to write to the Application section, and
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
1
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
3
4
0
0
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Table 108. Lock Bit Protection Modes(1)(2) (Continued)
Memory Lock Bits
BLB1 Mode
BLB12
BLB11
1
1
1
No restrictions for SPM or LPM accessing the Boot Loader
section.
2
1
0
SPM is not allowed to write to the Boot Loader section.
0
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
1
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
3
0
4
Notes:
Fuse Bits
Protection Type
0
1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
The ATmega325/3250/645/6450 has three Fuse bytes. Table 109 - Table 111 describe
briefly the functionality of all the fuses and how they are mapped into the Fuse bytes.
Note that the fuses are read as logical zero, “0”, if they are programmed.
Table 109. Extended Fuse Byte
Extended Fuse Byte
Bit No
Description
Default Value
–
7
–
1
–
6
–
1
–
5
–
1
–
4
–
1
–
5
–
1
(1)
BODLEVEL1
2
Brown-out Detector trigger level
1 (unprogrammed)
BODLEVEL0(1)
1
Brown-out Detector trigger level
1 (unprogrammed)
0
External Reset Disable
1 (unprogrammed)
RSTDISBL
Notes:
260
(2)
1. See Table 17 on page 42 for BODLEVEL Fuse decoding.
2. Port G, PG5 is input only. Pull-up is always on. See “Alternate Functions of Port G” on
page 74.
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Table 110. Fuse High Byte
Fuse High Byte
Bit No
Description
Default Value
OCDEN(4)
7
Enable OCD
1 (unprogrammed,
OCD disabled)
JTAGEN(5)
6
Enable JTAG
0 (programmed, JTAG
enabled)
SPIEN(1)
5
Enable Serial Program and Data
Downloading
0 (programmed, SPI
prog. enabled)
WDTON(3)
4
Watchdog Timer always on
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not
preserved)
BOOTSZ1
2
Select Boot Size (see Table 112
for details)
0 (programmed)(2)
BOOTSZ0
1
Select Boot Size (see Table 112
for details)
0 (programmed)(2)
BOOTRST
0
Select Reset Vector
1 (unprogrammed)
Note:
1. The SPIEN Fuse is not accessible in serial programming mode.
2. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 104 on
page 258 for details.
3. See “WDTCR – Watchdog Timer Control Register” on page 45 for details.
4. Never ship a product with the OCDEN Fuse programmed regardless of the setting of
Lock bits and JTAGEN Fuse. A programmed OCDEN Fuse enables some parts of the
clock system to be running in all sleep modes. This may increase the power
consumption.
5. If the JTAG interface is left unconnected, the JTAGEN fuse should if possible be disabled. This to avoid static current at the TDO pin in the JTAG interface.
Table 111. Fuse Low Byte
Fuse Low Byte
Bit No
Description
Default Value
(4)
7
Divide clock by 8
0 (programmed)
(3)
6
Clock output
1 (unprogrammed)
SUT1
5
Select start-up time
1 (unprogrammed)(1)
SUT0
4
Select start-up time
0 (programmed)(1)
CKSEL3
3
Select Clock source
0 (programmed)(2)
CKSEL2
2
Select Clock source
0 (programmed)(2)
CKSEL1
1
Select Clock source
1 (unprogrammed)(2)
CKSEL0
0
Select Clock source
0 (programmed)(2)
CKDIV8
CKOUT
Note:
1. The default value of SUT1..0 results in maximum start-up time for the default clock
source. See Table 16 on page 40 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See
Table 7 on page 28 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Output Buffer” on page 30 for details.
4. See “System Clock Prescaler” on page 31 for details.
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2570J–AVR–11/06
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are
locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the
Lock bits.
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of
the fuse values will have no effect until the part leaves Programming mode. This does
not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses
are also latched on Power-up in Normal mode.
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device.
This code can be read in both serial and parallel mode, also when the device is locked.
The three bytes reside in a separate address space.
For the ATmega325/3250/645/6450 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x95/0x96 (indicates Flash memory,refer to “Part Number” on page 221).
3. 0x002: 0x05/0x06 (indicates device, refer to “Part Number” on page 221).
Calibration Byte
The ATmega325/3250/645/6450 has a byte calibration value for the internal RC Oscillator. This byte resides in the high byte of address 0x000 in the signature address space.
During reset, this byte is automatically written into the OSCCAL Register to ensure correct frequency of the calibrated RC Oscillator.
Parallel Programming
Parameters, Pin
Mapping, and
Commands
This section describes how to parallel program and verify Flash Program memory,
EEPROM Data memory, Memory Lock bits, and Fuse bits in the
ATmega325/3250/645/6450. Pulses are assumed to be at least 250ns unless otherwise
noted.
Signal Names
In this section, some pins of the ATmega325/3250/645/6450 are referenced by signal
names describing their functionality during parallel programming, see Figure 112 and
Table 112. Pins not described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in Table 114.
When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 115.
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ATmega325/3250/645/6450
Figure 112. Parallel Programming
+5V
RDY/BSY
PD1
OE
PD2
WR
PD3
BS1
PD4
XA0
PD5
XA1
PD6
PAGEL
PD7
+12 V
BS2
VCC
+5V
AVCC
PB7 - PB0
DATA
RESET
PA0
XTAL1
GND
Table 112. Pin Name Mapping
Signal Name in
Programming Mode
Pin Name
I/O
Function
RDY/BSY
PD1
O
0: Device is busy programming, 1: Device is ready
for new command.
OE
PD2
I
Output Enable (Active low).
WR
PD3
I
Write Pulse (Active low).
BS1
PD4
I
Byte Select 1 (“0” selects low byte, “1” selects high
byte).
XA0
PD5
I
XTAL Action Bit 0
XA1
PD6
I
XTAL Action Bit 1
PAGEL
PD7
I
Program Memory and EEPROM data Page Load.
BS2
PA0
I
Byte Select 2 (“0” selects low byte, “1” selects 2’nd
high byte).
DATA
PB7-0
I/O
Bi-directional Data bus (Output when OE is low).
Table 113. Pin Values Used to Enter Programming Mode
Pin
Symbol
Value
PAGEL
Prog_enable[3]
0
XA1
Prog_enable[2]
0
XA0
Prog_enable[1]
0
BS1
Prog_enable[0]
0
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Table 114. XA1 and XA0 Coding
XA1
XA0
Action when XTAL1 is Pulsed
0
0
Load Flash or EEPROM Address (High or low address byte
determined by BS1).
0
1
Load Data (High or Low data byte for Flash determined by BS1).
1
0
Load Command
1
1
No Action, Idle
Table 115. Command Byte Bit Coding
Command Byte
Command Executed
1000 0000
Chip Erase
0100 0000
Write Fuse bits
0010 0000
Write Lock bits
0001 0000
Write Flash
0001 0001
Write EEPROM
0000 1000
Read Signature Bytes and Calibration byte
0000 0100
Read Fuse and Lock bits
0000 0010
Read Flash
0000 0011
Read EEPROM
Table 116. No. of Words in a Page and No. of Pages in the Flash
Flash Size
Page Size
PCWORD
No. of Pages
PCPAGE
PCMSB
16/32K words
(32/64K bytes)
64/128
words
PC[5/6:0]
256
PC
[13/14:6/7]
13/14
Table 117. No. of Words in a Page and No. of Pages in the EEPROM
264
EEPROM Size
Page Size
PCWORD
No. of Pages
PCPAGE
EEAMSB
1K/2K bytes
4/8 bytes
EEA[1/2:0]
256
EEA
[13/14:2/3]
13/14
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Parallel Programming
Enter Programming Mode
The following algorithm puts the device in Parallel (High-voltage) Programming mode:
1. Set Prog_enable pins listed in Table 113 on page 263 to “0000”, RESET pin and
VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Ensure that VCC reaches at least 1.8V within the next 20 µs.
4. Wait 20 - 60 µs, and apply 11.5 - 12.5V to RESET.
5. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage
has been applied to ensure the Prog_enable Signature has been latched.
6. Wait at least 300 µs before giving any parallel programming commands.
7. Exit Programming mode by power the device down or by bringing RESET pin to
0V.
If the rise time of the VCC is unable to fulfill the requirements listed above, the following
alternative algorithm can be used.
1. Set Prog_enable pins listed in Table 113 on page 263 to “0000”, RESET pin to
0V and VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Monitor VCC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V to
RESET.
4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage
has been applied to ensure the Prog_enable Signature has been latched.
5. Wait until VCC actually reaches 4.5 -5.5V before giving any parallel programming
commands.
6. Exit Programming mode by power the device down or by bringing RESET pin to
0V.
Considerations for Efficient
Programming
Chip Erase
The loaded command and address are retained in the device during programming. For
efficient programming, the following should be considered.
•
The command needs only be loaded once when writing or reading multiple memory
locations.
•
Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless
the EESAVE Fuse is programmed) and Flash after a Chip Erase.
•
Address high byte needs only be loaded before programming or reading a new 256
word window in Flash or 256 byte EEPROM. This consideration also applies to
Signature bytes reading.
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock
bits are not reset until the program memory has been completely erased. The Fuse bits
are not changed. A Chip Erase must be performed before the Flash and/or EEPROM
are reprogrammed.
Note:
1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is
programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
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4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
Programming the Flash
The Flash is organized in pages, see Table 116 on page 264. When programming the
Flash, the program data is latched into a page buffer. This allows one page of program
data to be programmed simultaneously. The following procedure describes how to program the entire Flash memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 114 for
signal waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is
loaded.
While the lower bits in the address are mapped to words within the page, the higher bits
address the pages within the FLASH. This is illustrated in Figure 113 on page 267. Note
that if less than eight bits are required to address words in the page (pagesize < 256),
the most significant bit(s) in the address low byte are used to address the page when
performing a Page Write.
G. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
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H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of data.
RDY/BSY goes low.
2. Wait until RDY/BSY goes high (See Figure 114 for signal waveforms).
I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.
Figure 113. Addressing the Flash Which is Organized in Pages(1)
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
1. PCPAGE and PCWORD are listed in Table 116 on page 264.
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Figure 114. Programming the Flash Waveforms(1)
F
DATA
A
B
0x10
ADDR. LOW
C
DATA LOW
D
E
DATA HIGH
XX
B
ADDR. LOW
C
D
DATA LOW
DATA HIGH
E
XX
G
ADDR. HIGH
H
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
Note:
Programming the EEPROM
1. “XX” is don’t care. The letters refer to the programming description above.
The EEPROM is organized in pages, see Table 117 on page 264. When programming
the EEPROM, the program data is latched into a page buffer. This allows one page of
data to be programmed simultaneously. The programming algorithm for the EEPROM
data memory is as follows (refer to “Programming the Flash” on page 266 for details on
Command, Address and Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page.
RDY/BSY goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure
115 for signal waveforms).
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Figure 115. Programming the EEPROM Waveforms
K
DATA
A
G
0x11
ADDR. HIGH
B
ADDR. LOW
C
DATA
E
XX
B
ADDR. LOW
C
DATA
E
L
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the
Flash” on page 266 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS1 to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the
Flash” on page 266 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at
DATA.
5. Set OE to “1”.
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Programming the Fuse Low
Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming
the Flash” on page 266 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
Programming the Fuse High
Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming
the Flash” on page 266 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
Programming the Extended
Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the Flash” on page 266 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse
bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 116. Programming the FUSES Waveforms
Write Fuse Low byte
DATA
A
C
0x40
DATA
XX
Write Fuse high byte
A
C
0x40
DATA
XX
Write Extended Fuse byte
A
C
0x40
DATA
XX
XA1
XA0
BS1
BS2
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” on page 266 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed (LB1 and LB2 is programmed), it is not possible to program the Boot
Lock bits by any External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
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Reading the Fuse and Lock
Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming
the Flash” on page 266 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can
now be read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can
now be read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the Extended Fuse bits
can now be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be
read at DATA (“0” means programmed).
6. Set OE to “1”.
Figure 117. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
Fuse Low Byte
0
Extended Fuse Byte
1
0
DATA
BS2
0
Lock Bits
1
Fuse High Byte
1
BS1
BS2
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the
Flash” on page 266 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS1 to “0”. The selected Signature byte can now be read at
DATA.
4. Set OE to “1”.
Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the
Flash” on page 266 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
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Parallel Programming
Characteristics
Figure 118. Parallel Programming Timing, Including some General Timing
Requirements
tXLWL
tXHXL
XTAL1
tDVXH
tXLDX
Data & Contol
(DATA, XA0/1, BS1, BS2)
tPLBX t BVWL
tBVPH
PAGEL
tWLBX
tPHPL
tWLWH
WR
tPLWL
WLRL
RDY/BSY
tWLRH
Figure 119. Parallel Programming Timing, Loading Sequence with Timing
Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA LOAD DATA
(HIGH BYTE)
LOAD DATA
(LOW BYTE)
t XLXH
tXLPH
LOAD ADDRESS
(LOW BYTE)
tPLXH
XTAL1
BS1
PAGEL
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
272
1. The timing requirements shown in Figure 118 (i.e., tDVXH, tXHXL, and tXLDX) also apply
to loading operation.
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Figure 120. Parallel Programming Timing, Reading Sequence (within the Same Page)
with Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
tXLOL
XTAL1
tBVDV
BS1
tOLDV
OE
tOHDZ
DATA
ADDR0 (Low Byte)
ADDR1 (Low Byte)
DATA (High Byte)
DATA (Low Byte)
XA0
XA1
Note:
1. The timing requirements shown in Figure 118 (i.e., tDVXH, tXHXL, and tXLDX) also apply
to reading operation.
Table 118. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol
Parameter
Min
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXLXH
XTAL1 Low to XTAL1 High
200
ns
tXHXL
XTAL1 Pulse Width High
150
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
0
ns
tXLPH
XTAL1 Low to PAGEL high
0
ns
tPLXH
PAGEL low to XTAL1 high
150
ns
tBVPH
BS1 Valid before PAGEL High
67
ns
tPHPL
PAGEL Pulse Width High
150
ns
tPLBX
BS1 Hold after PAGEL Low
67
ns
tWLBX
BS2/1 Hold after WR Low
67
ns
tPLWL
PAGEL Low to WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tWLWH
WR Pulse Width Low
150
ns
tWLRL
WR Low to RDY/BSY Low
tWLRH
WR Low to RDY/BSY High(1)
(2)
tWLRH_CE
WR Low to RDY/BSY High for Chip Erase
tXLOL
XTAL1 Low to OE Low
Typ
Max
Units
12.5
V
250
μA
0
1
μs
3.7
4.5
ms
7.5
9
ms
0
ns
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Table 118. Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
Symbol
Parameter
tBVDV
BS1 Valid to DATA valid
tOLDV
tOHDZ
Notes:
Serial Downloading
Serial Programming Pin
Mapping
Min
Max
Units
250
ns
OE Low to DATA Valid
250
ns
OE High to DATA Tri-stated
250
ns
0
Typ
1.
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock
bits commands.
2. tWLRH_CE is valid for the Chip Erase command.
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI
bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI
(input) and MISO (output). After RESET is set low, the Programming Enable instruction
needs to be executed first before program/erase operations can be executed. NOTE, in
Table 119 on page 274, the pin mapping for SPI programming is listed. Not all parts use
the SPI pins dedicated for the internal SPI interface.
Table 119. Pin Mapping Serial Programming
Symbol
Pins
I/O
Description
MOSI
PB2
I
Serial Data in
MISO
PB3
O
Serial Data out
SCK
PB1
I
Serial Clock
Figure 121. Serial Programming and Verify(1)
+1.8 - 5.5V
VCC
+1.8 - 5.5V(2)
MOSI
AVCC
MISO
SCK
XTAL1
RESET
GND
Notes:
1. If the device is clocked by the internal Oscillator, it is no need to connect a clock
source to the XTAL1 pin.
2. VCC - 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8 - 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the Serial mode ONLY) and there is no need to first execute the
Chip Erase instruction. The Chip Erase operation turns the content of every memory
location in both the Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high
periods for the serial clock (SCK) input are defined as follows:
Low:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
High:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
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Serial Programming
Algorithm
When writing serial data to the ATmega325/3250/645/6450, data is clocked on the rising
edge of SCK.
When reading data from the ATmega325/3250/645/6450, data is clocked on the falling
edge of SCK. See Figure 122 for timing details.
To program and verify the ATmega325/3250/645/6450 in the serial programming mode,
the following sequence is recommended (See four byte instruction formats in Table
121):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In
some systems, the programmer can not guarantee that SCK is held low during
power-up. In this case, RESET must be given a positive pulse of at least two
CPU clock cycles duration after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of
synchronization. When in sync. the second byte (0x53), will echo back when
issuing the third byte of the Programming Enable instruction. Whether the echo
is correct or not, all four bytes of the instruction must be transmitted. If the 0x53
did not echo back, give RESET a positive pulse and issue a new Programming
Enable command.
4. The Flash is programmed one page at a time. The page size is found in Table
116 on page 264. The memory page is loaded one byte at a time by supplying
the 6 LSB of the address and data together with the Load Program Memory
Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program
Memory Page is stored by loading the Write Program Memory Page instruction
with the 8 MSB of the address. If polling is not used, the user must wait at least
tWD_FLASH before issuing the next page. (See Table 120.) Accessing the serial
programming interface before the Flash write operation completes can result in
incorrect programming.
5. A: The EEPROM array is programmed one byte at a time by supplying the
address and data together with the appropriate Write instruction. An EEPROM
memory location is first automatically erased before new data is written. If polling
(RDY/BSY) is not used, the user must wait at least tWD_EEPROM before issuing the
next byte (See Table 120.) In a chip erased device, no 0xFFs in the data file(s)
need to be programmed.
B: The EEPROM array is programmed one page at a time. The Memory page is
loaded one byte at a time by supplying the 2 LSB of the address and data
together with the Load EEPROM Memory Page instruction. The EEPROM Memory Page is stored by loading the Write EEPROM Memory Page Instruction with
the 4 MSB of the address. When using EEPROM page access only byte locations loaded with the Load EEPROM Memory Page instruction is altered. The
remaining locations remain unchanged. If polling (RDY/BSY) is not used, the
used must wait at least tWD_EEPROM before issuing the next page (See Table 117).
In a chip erased device, no 0xFF in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns
the content at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence
normal operation.
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8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
Table 120. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol
Minimum Wait Delay
tWD_FUSE
4.5 ms
tWD_FLASH
4.5 ms
tWD_EEPROM
9.0 ms
tWD_ERASE
9.0 ms
Figure 122. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
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Serial Programming
Instruction set
Table 121 and Figure 123 on page 278 describes the Instruction set.
Table 121. Serial Programming Instruction Set
Instruction Format
Instruction/Operation
Byte 1
Byte 2
Byte 3
Byte4
Programming Enable
$AC
$53
$00
$00
Chip Erase (Program Memory/EEPROM)
$AC
$80
$00
$00
Poll RDY/BSY
$F0
$00
$00
data byte out
Load Extended Address byte(1)
$4D
$00
Extended adr
$00
Load Program Memory Page, High byte
$48
$00
adr LSB
high data byte in
Load Program Memory Page, Low byte
$40
$00
adr LSB
low data byte in
Load EEPROM Memory Page (page access)
$C1
$00
0000 00aa
/
0000 0aaa
data byte in
Read Program Memory, High byte
$28
adr MSB
adr LSB
high data byte out
Read Program Memory, Low byte
$20
adr MSB
adr LSB
low data byte out
Read EEPROM Memory
$A0
0000 00aa
/
0000 0aaa
aaaa aaaa
data byte out
Read Lock bits
$58
$00
$00
data byte out
Read Signature Byte
$30
$00
0000 000aa
data byte out
Read Fuse bits
$50
$00
$00
data byte out
Read Fuse High bits
$58
$08
$00
data byte out
Read Extended Fuse Bits
$50
$08
$00
data byte out
Read Calibration Byte
$38
$00
$00
data byte out
Write Program Memory Page
$4C
adr MSB
adr LSB
$00
Write EEPROM Memory
$C0
0000 00aa
/
0000 0aaa
aaaa aaaa
data byte in
Write EEPROM Memory Page (page access)
$C2
0000 00aa
/
0000 0aaa
aaaa aa00
/
aaaa a000
$00
Write Lock bits
$AC
$E0
$00
data byte in
Write Fuse bits
$AC
$A0
$00
data byte in
Write Fuse High bits
$AC
$A8
$00
data byte in
Write Extended Fuse Bits
$AC
$A4
$00
data byte in
Load Instructions
Read Instructions
Write Instructions
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Notes:
1.
2.
3.
4.
Not all instructions are applicable for all parts
a = address
Bits are programmed ‘0’, unprogrammed ‘1’.
To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed
(‘1’) .
5. Refer to the correspondig section for Fuse and Lock bits, Calibration and Signature
bytes and Page size.
6. See htt://www.atmel.com/avr for Application Notes regarding programming and
programmers.
If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending.
Wait until this bit returns ‘0’ before the next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 123.
Figure 123. Serial Programming Instruction example
Serial Programming Instruction
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Byte 1
Byte 2
Adr MSB
A
Bit 15 B
Byte 3
Write Program Memory Page/
Write EEPROM Memory Page
Byte 1
Byte 4
Byte 2
Adr LSB
Adr MSB
Bit 15 B
0
Byte 3
Byte 4
Adrr LSB
B
0
Page Buffer
Page Offset
Page 0
Page 1
Page 2
Page Number
Page N-1
Program Memory/
EEPROM Memory
SPI Serial Programming
Characteristics
278
For characteristics of the SPI module see “SPI Timing Characteristics” on page 294.
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Programming via the
JTAG Interface
Programming through the JTAG interface requires control of the four JTAG specific
pins: TCK, TMS, TDI, and TDO. Control of the reset and clock pins is not required.
To be able to use the JTAG interface, the JTAGEN Fuse must be programmed. The
device is default shipped with the fuse programmed. In addition, the JTD bit in MCUCSR
must be cleared. Alternatively, if the JTD bit is set, the external reset can be forced low.
Then, the JTD bit will be cleared after two chip clocks, and the JTAG pins are available
for programming. This provides a means of using the JTAG pins as normal port pins in
Running mode while still allowing In-System Programming via the JTAG interface. Note
that this technique can not be used when using the JTAG pins for Boundary-scan or Onchip Debug. In these cases the JTAG pins must be dedicated for this purpose.
During programming the clock frequency of the TCK Input must be less than the maximum frequency of the chip. The System Clock Prescaler can not be used to divide the
TCK Clock Input into a sufficiently low frequency.
As a definition in this data sheet, the LSB is shifted in and out first of all Shift Registers.
Programming Specific JTAG
Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. The JTAG
instructions useful for programming are listed below.
The OPCODE for each instruction is shown behind the instruction name in hex format.
The text describes which Data Register is selected as path between TDI and TDO for
each instruction.
The Run-Test/Idle state of the TAP controller is used to generate internal clocks. It can
also be used as an idle state between JTAG sequences. The state machine sequence
for changing the instruction word is shown in Figure 124.
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Figure 124. State Machine Sequence for Changing the Instruction Word
1
Test-Logic-Reset
0
0
Run-Test/Idle
1
Select-DR Scan
1
Select-IR Scan
0
1
0
1
Capture-DR
Capture-IR
0
0
0
Shift-DR
1
1
Exit1-DR
0
0
Pause-DR
0
Pause-IR
1
1
0
Exit2-DR
Exit2-IR
1
1
Update-DR
AVR_RESET (0xC)
1
Exit1-IR
0
1
0
Shift-IR
1
0
1
Update-IR
0
1
0
The AVR specific public JTAG instruction for setting the AVR device in the Reset mode
or taking the device out from the Reset mode. The TAP controller is not reset by this
instruction. The one bit Reset Register is selected as Data Register. Note that the reset
will be active as long as there is a logic “one” in the Reset Chain. The output from this
chain is not latched.
The active states are:
•
PROG_ENABLE (0x4)
280
Shift-DR: The Reset Register is shifted by the TCK input.
The AVR specific public JTAG instruction for enabling programming via the JTAG port.
The 16-bit Programming Enable Register is selected as Data Register. The active states
are the following:
•
Shift-DR: The programming enable signature is shifted into the Data Register.
•
Update-DR: The programming enable signature is compared to the correct value,
and Programming mode is entered if the signature is valid.
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PROG_COMMANDS (0x5)
PROG_PAGELOAD (0x6)
PROG_PAGEREAD (0x7)
Data Registers
The AVR specific public JTAG instruction for entering programming commands via the
JTAG port. The 15-bit Programming Command Register is selected as Data Register.
The active states are the following:
•
Capture-DR: The result of the previous command is loaded into the Data Register.
•
Shift-DR: The Data Register is shifted by the TCK input, shifting out the result of the
previous command and shifting in the new command.
•
Update-DR: The programming command is applied to the Flash inputs
•
Run-Test/Idle: One clock cycle is generated, executing the applied command (not
always required, see Table 122 below).
The AVR specific public JTAG instruction to directly load the Flash data page via the
JTAG port. An 8-bit Flash Data Byte Register is selected as the Data Register. This is
physically the 8 LSBs of the Programming Command Register. The active states are the
following:
•
Shift-DR: The Flash Data Byte Register is shifted by the TCK input.
•
Update-DR: The content of the Flash Data Byte Register is copied into a temporary
register. A write sequence is initiated that within 11 TCK cycles loads the content of
the temporary register into the Flash page buffer. The AVR automatically alternates
between writing the low and the high byte for each new Update-DR state, starting
with the low byte for the first Update-DR encountered after entering the
PROG_PAGELOAD command. The Program Counter is pre-incremented before
writing the low byte, except for the first written byte. This ensures that the first data is
written to the address set up by PROG_COMMANDS, and loading the last location
in the page buffer does not make the program counter increment into the next page.
The AVR specific public JTAG instruction to directly capture the Flash content via the
JTAG port. An 8-bit Flash Data Byte Register is selected as the Data Register. This is
physically the 8 LSBs of the Programming Command Register. The active states are the
following:
•
Capture-DR: The content of the selected Flash byte is captured into the Flash Data
Byte Register. The AVR automatically alternates between reading the low and the
high byte for each new Capture-DR state, starting with the low byte for the first
Capture-DR encountered after entering the PROG_PAGEREAD command. The
Program Counter is post-incremented after reading each high byte, including the
first read byte. This ensures that the first data is captured from the first address set
up by PROG_COMMANDS, and reading the last location in the page makes the
program counter increment into the next page.
•
Shift-DR: The Flash Data Byte Register is shifted by the TCK input.
The Data Registers are selected by the JTAG instruction registers described in section
“Programming Specific JTAG Instructions” on page 279. The Data Registers relevant for
programming operations are:
•
Reset Register
•
Programming Enable Register
•
Programming Command Register
•
Flash Data Byte Register
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Reset Register
The Reset Register is a Test Data Register used to reset the part during programming. It
is required to reset the part before entering Programming mode.
A high value in the Reset Register corresponds to pulling the external reset low. The
part is reset as long as there is a high value present in the Reset Register. Depending
on the Fuse settings for the clock options, the part will remain reset for a Reset Time-out
period (refer to “Clock Sources” on page 26) after releasing the Reset Register. The output from this Data Register is not latched, so the reset will take place immediately, as
shown in Figure 101 on page 222.
Programming Enable Register
The Programming Enable Register is a 16-bit register. The contents of this register is
compared to the programming enable signature, binary code
0b1010_0011_0111_0000. When the contents of the register is equal to the programming enable signature, programming via the JTAG port is enabled. The register is reset
to 0 on Power-on Reset, and should always be reset when leaving Programming mode.
Figure 125. Programming Enable Register
TDI
D
A
T
A
0xA370
=
D
Q
Programming Enable
ClockDR & PROG_ENABLE
TDO
Programming Command
Register
The Programming Command Register is a 15-bit register. This register is used to serially shift in programming commands, and to serially shift out the result of the previous
command, if any. The JTAG Programming Instruction Set is shown in Table 122. The
state sequence when shifting in the programming commands is illustrated in Figure 127.
Figure 126. Programming Command Register
TDI
S
T
R
O
B
E
S
A
D
D
R
E
S
S
/
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
TDO
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Table 122. JTAG Programming Instruction Set
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
TDO Sequence
Notes
1a. Chip Erase
0100011_10000000
0110001_10000000
0110011_10000000
0110011_10000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
1b. Poll for Chip Erase Complete
0110011_10000000
xxxxxox_xxxxxxxx
2a. Enter Flash Write
0100011_00010000
xxxxxxx_xxxxxxxx
2b. Load Address High Byte
0000111_aaaaaaaa
xxxxxxx_xxxxxxxx
2c. Load Address Low Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
2d. Load Data Low Byte
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
2e. Load Data High Byte
0010111_iiiiiiii
xxxxxxx_xxxxxxxx
2f. Latch Data
0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2g. Write Flash Page
0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2h. Poll for Page Write Complete
0110111_00000000
xxxxxox_xxxxxxxx
(2)
3a. Enter Flash Read
0100011_00000010
xxxxxxx_xxxxxxxx
3b. Load Address High Byte
0000111_aaaaaaaa
xxxxxxx_xxxxxxxx
3c. Load Address Low Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
3d. Read Data Low and High Byte
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
4a. Enter EEPROM Write
0100011_00010001
xxxxxxx_xxxxxxxx
4b. Load Address High Byte
0000111_aaaaaaaa
xxxxxxx_xxxxxxxx
4c. Load Address Low Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
4d. Load Data Byte
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
4e. Latch Data
0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4f. Write EEPROM Page
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4g. Poll for Page Write Complete
0110011_00000000
xxxxxox_xxxxxxxx
(2)
5a. Enter EEPROM Read
0100011_00000011
xxxxxxx_xxxxxxxx
5b. Load Address High Byte
0000111_aaaaaaaa
xxxxxxx_xxxxxxxx
(2)
(9)
(9)
Low byte
High byte
(9)
(9)
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Table 122. JTAG Programming Instruction Set (Continued)
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
TDO Sequence
5c. Load Address Low Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
5d. Read Data Byte
0110011_bbbbbbbb
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
0100011_01000000
xxxxxxx_xxxxxxxx
6b. Load Data Low Byte
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
(3)
6c. Write Fuse Extended Byte
0111011_00000000
0111001_00000000
0111011_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6d. Poll for Fuse Write Complete
0110111_00000000
xxxxxox_xxxxxxxx
(2)
6e. Load Data Low Byte(7)
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
(3)
6f. Write Fuse High Byte
0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6g. Poll for Fuse Write Complete
0110111_00000000
xxxxxox_xxxxxxxx
(2)
6h. Load Data Low Byte
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
(3)
6i. Write Fuse Low Byte
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6j. Poll for Fuse Write Complete
0110011_00000000
xxxxxox_xxxxxxxx
(2)
7a. Enter Lock Bit Write
0100011_00100000
xxxxxxx_xxxxxxxx
7b. Load Data Byte
0010011_11iiiiii
xxxxxxx_xxxxxxxx
(4)
7c. Write Lock Bits
0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
7d. Poll for Lock Bit Write complete
0110011_00000000
xxxxxox_xxxxxxxx
(2)
8a. Enter Fuse/Lock Bit Read
0100011_00000100
xxxxxxx_xxxxxxxx
8b. Read Extended Fuse Byte(6)
0111010_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8c. Read Fuse High Byte(7)
0111110_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8d. Read Fuse Low Byte(8)
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8e. Read Lock Bits(9)
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxoooooo
6a. Enter Fuse Write
(6)
(7)
(9)
284
Notes
(5)
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Table 122. JTAG Programming Instruction Set (Continued)
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction
TDI Sequence
TDO Sequence
Notes
8f. Read Fuses and Lock Bits
0111010_00000000
0111110_00000000
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
(5)
Fuse Ext. byte
Fuse High byte
Fuse Low byte
Lock bits
9a. Enter Signature Byte Read
0100011_00001000
xxxxxxx_xxxxxxxx
9b. Load Address Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
9c. Read Signature Byte
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
10a. Enter Calibration Byte Read
0100011_00001000
xxxxxxx_xxxxxxxx
10b. Load Address Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
10c. Read Calibration Byte
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
11a. Load No Operation Command
0100011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
Notes:
1. This command sequence is not required if the seven MSB are correctly set by the previous command sequence (which is
normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the Fuse.
4. Set bits to “0” to program the corresponding Lock bit, “1” to leave the Lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for Fuses Extended byte is listed in Table 109 on page 260
7. The bit mapping for Fuses High byte is listed in Table 110 on page 261
8. The bit mapping for Fuses Low byte is listed in Table 111 on page 261
9. The bit mapping for Lock bits byte is listed in Table 107 on page 259
10. Address bits exceeding PCMSB and EEAMSB (Table 116 and Table 117) are don’t care
11. All TDI and TDO sequences are represented by binary digits (0b...).
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Figure 127. State Machine Sequence for Changing/Reading the Data Word
1
Test-Logic-Reset
0
0
Run-Test/Idle
1
Select-DR Scan
1
Select-IR Scan
0
1
0
1
Capture-DR
Capture-IR
0
0
Shift-DR
Shift-IR
0
1
Exit1-DR
0
Pause-DR
0
0
Pause-IR
1
1
0
Exit2-DR
Exit2-IR
1
1
Update-DR
Flash Data Byte Register
1
Exit1-IR
0
1
0
1
1
0
1
Update-IR
0
1
0
The Flash Data Byte Register provides an efficient way to load the entire Flash page
buffer before executing Page Write, or to read out/verify the content of the Flash. A state
machine sets up the control signals to the Flash and senses the strobe signals from the
Flash, thus only the data words need to be shifted in/out.
The Flash Data Byte Register actually consists of the 8-bit scan chain and a 8-bit temporary register. During page load, the Update-DR state copies the content of the scan
chain over to the temporary register and initiates a write sequence that within 11 TCK
cycles loads the content of the temporary register into the Flash page buffer. The AVR
automatically alternates between writing the low and the high byte for each new UpdateDR state, starting with the low byte for the first Update-DR encountered after entering
the PROG_PAGELOAD command. The Program Counter is pre-incremented before
writing the low byte, except for the first written byte. This ensures that the first data is
written to the address set up by PROG_COMMANDS, and loading the last location in
the page buffer does not make the Program Counter increment into the next page.
During Page Read, the content of the selected Flash byte is captured into the Flash
Data Byte Register during the Capture-DR state. The AVR automatically alternates
between reading the low and the high byte for each new Capture-DR state, starting with
the low byte for the first Capture-DR encountered after entering the PROG_PAGEREAD
command. The Program Counter is post-incremented after reading each high byte,
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including the first read byte. This ensures that the first data is captured from the first
address set up by PROG_COMMANDS, and reading the last location in the page
makes the program counter increment into the next page.
Figure 128. Flash Data Byte Register
STROBES
TDI
State
Machine
ADDRESS
Flash
EEPROM
Fuses
Lock Bits
D
A
T
A
TDO
The state machine controlling the Flash Data Byte Register is clocked by TCK. During
normal operation in which eight bits are shifted for each Flash byte, the clock cycles
needed to navigate through the TAP controller automatically feeds the state machine for
the Flash Data Byte Register with sufficient number of clock pulses to complete its operation transparently for the user. However, if too few bits are shifted between each
Update-DR state during page load, the TAP controller should stay in the Run-Test/Idle
state for some TCK cycles to ensure that there are at least 11 TCK cycles between each
Update-DR state.
Programming Algorithm
All references below of type “1a”, “1b”, and so on, refer to Table 122.
Entering Programming Mode
1. Enter JTAG instruction AVR_RESET and shift 1 in the Reset Register.
2. Enter instruction PROG_ENABLE and shift 0b1010_0011_0111_0000 in the
Programming Enable Register.
Leaving Programming Mode
1. Enter JTAG instruction PROG_COMMANDS.
2. Disable all programming instructions by using no operation instruction 11a.
3. Enter instruction PROG_ENABLE and shift 0b0000_0000_0000_0000 in the
programming Enable Register.
4. Enter JTAG instruction AVR_RESET and shift 0 in the Reset Register.
Performing Chip Erase
1. Enter JTAG instruction PROG_COMMANDS.
2. Start Chip Erase using programming instruction 1a.
3. Poll for Chip Erase complete using programming instruction 1b, or wait for
tWLRH_CE (refer to Table 118 on page 273).
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Programming the Flash
Before programming the Flash a Chip Erase must be performed, see “Performing Chip
Erase” on page 287.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load address High byte using programming instruction 2b.
4. Load address Low byte using programming instruction 2c.
5. Load data using programming instructions 2d, 2e and 2f.
6. Repeat steps 4 and 5 for all instruction words in the page.
7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH
(refer to Table 118 on page 273).
9. Repeat steps 3 to 7 until all data have been programmed.
A more efficient data transfer can be achieved using the PROG_PAGELOAD
instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load the page address using programming instructions 2b and 2c. PCWORD
(refer to Table 116 on page 264) is used to address within one page and must be
written as 0.
4. Enter JTAG instruction PROG_PAGELOAD.
5. Load the entire page by shifting in all instruction words in the page byte-by-byte,
starting with the LSB of the first instruction in the page and ending with the MSB
of the last instruction in the page. Use Update-DR to copy the contents of the
Flash Data Byte Register into the Flash page location and to auto-increment the
Program Counter before each new word.
6. Enter JTAG instruction PROG_COMMANDS.
7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH
(refer to Table 118 on page 273).
9. Repeat steps 3 to 8 until all data have been programmed.
Reading the Flash
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
3. Load address using programming instructions 3b and 3c.
4. Read data using programming instruction 3d.
5. Repeat steps 3 and 4 until all data have been read.
A more efficient data transfer can be achieved using the PROG_PAGEREAD
instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
3. Load the page address using programming instructions 3b and 3c. PCWORD
(refer to Table 116 on page 264) is used to address within one page and must be
written as 0.
4. Enter JTAG instruction PROG_PAGEREAD.
5. Read the entire page (or Flash) by shifting out all instruction words in the page
(or Flash), starting with the LSB of the first instruction in the page (Flash) and
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ending with the MSB of the last instruction in the page (Flash). The Capture-DR
state both captures the data from the Flash, and also auto-increments the program counter after each word is read. Note that Capture-DR comes before the
shift-DR state. Hence, the first byte which is shifted out contains valid data.
6. Enter JTAG instruction PROG_COMMANDS.
7. Repeat steps 3 to 6 until all data have been read.
Programming the EEPROM
Before programming the EEPROM a Chip Erase must be performed, see “Performing
Chip Erase” on page 287.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM write using programming instruction 4a.
3. Load address High byte using programming instruction 4b.
4. Load address Low byte using programming instruction 4c.
5. Load data using programming instructions 4d and 4e.
6. Repeat steps 4 and 5 for all data bytes in the page.
7. Write the data using programming instruction 4f.
8. Poll for EEPROM write complete using programming instruction 4g, or wait for
tWLRH (refer to Table 118 on page 273).
9. Repeat steps 3 to 8 until all data have been programmed.
Note that the PROG_PAGELOAD instruction can not be used when programming the
EEPROM.
Reading the EEPROM
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM read using programming instruction 5a.
3. Load address using programming instructions 5b and 5c.
4. Read data using programming instruction 5d.
5. Repeat steps 3 and 4 until all data have been read.
Note that the PROG_PAGEREAD instruction can not be used when reading the
EEPROM.
Programming the Fuses
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse write using programming instruction 6a.
3. Load data high byte using programming instructions 6b. A bit value of “0” will program the corresponding fuse, a “1” will unprogram the fuse.
4. Write Fuse High byte using programming instruction 6c.
5. Poll for Fuse write complete using programming instruction 6d, or wait for tWLRH
(refer to Table 118 on page 273).
6. Load data low byte using programming instructions 6e. A “0” will program the
fuse, a “1” will unprogram the fuse.
7. Write Fuse low byte using programming instruction 6f.
8. Poll for Fuse write complete using programming instruction 6g, or wait for tWLRH
(refer to Table 118 on page 273).
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Programming the Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Lock bit write using programming instruction 7a.
3. Load data using programming instructions 7b. A bit value of “0” will program the
corresponding lock bit, a “1” will leave the lock bit unchanged.
4. Write Lock bits using programming instruction 7c.
5. Poll for Lock bit write complete using programming instruction 7d, or wait for
tWLRH (refer to Table 118 on page 273).
Reading the Fuses and Lock
Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse/Lock bit read using programming instruction 8a.
3. To read all Fuses and Lock bits, use programming instruction 8e.
To only read Fuse High byte, use programming instruction 8b.
To only read Fuse Low byte, use programming instruction 8c.
To only read Lock bits, use programming instruction 8d.
Reading the Signature Bytes
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Signature byte read using programming instruction 9a.
3. Load address 0x00 using programming instruction 9b.
4. Read first signature byte using programming instruction 9c.
5. Repeat steps 3 and 4 with address 0x01 and address 0x02 to read the second
and third signature bytes, respectively.
Reading the Calibration Byte
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Calibration byte read using programming instruction 10a.
3. Load address 0x00 using programming instruction 10b.
Read the calibration byte using programming instruction 10c.
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Electrical Characteristics
Absolute Maximum Ratings*
Operating Temperature.................................. -55°C to +125°C
*NOTICE:
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA
DC Characteristics
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
(1)
VIL
Input Low Voltage, Except
XTAL1 pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
-0.5
0.2VCC
0.3VCC(1)
V
VIL1
Input Low Voltage, XTAL1
pin
VCC = 1.8V - 5.5V
-0.5
0.1VCC(1)
V
VIH
Input High Voltage,
Except XTAL1 and
RESET pins
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC + 0.5
VCC + 0.5
V
VIH1
Input High Voltage,
XTAL1 pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.8VCC(2)
0.7VCC(2)
VCC + 0.5
VCC + 0.5
V
VIH2
Input High Voltage,
RESET pin
VCC = 1.8V - 5.5V
0.85VCC(2)
VCC + 0.5
V
VOL
Output Low Voltage(3),
Port A, C, D, E, F, G, H, J
IOL = 10mA, VCC = 5V
IOL = 5mA, VCC = 3V
0.7
0.5
V
VOL1
Output Low Voltage(3),
Port B
IOL = 20mA, VCC = 5V
IOL = 10mA, VCC = 3V
0.7
0.5
V
VOH
Output High Voltage(4),
Port A, C, D, E, F, G, H, J
IOH = -10mA, VCC = 5V
IOH = -5mA, VCC = 3V
4.2
2.3
V
VOH1
Output High Voltage(4),
Port B
IOH = -20mA, VCC = 5V
IOH = -10mA, VCC = 3V
4.2
2.3
V
IIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value)
1
µA
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value)
1
µA
RRST
Reset Pull-up Resistor
20
100
kΩ
RPU
I/O Pin Pull-up Resistor
20
100
kΩ
291
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TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted) (Continued)
Symbol
Parameter
Power Supply Current
ICC
Power-down mode(5)
Condition
Max.
Units
Active 1MHz, VCC = 2V
0.55
mA
Active 4MHz, VCC = 3V
2.5
mA
Active 8MHz, VCC = 5V
9
mA
Idle 1MHz, VCC = 2V
0.2
mA
Idle 4MHz, VCC = 3V
0.85
mA
Idle 8MHz, VCC = 5V
3
mA
Typ.
WDT enabled, VCC = 3V
7
15
µA
WDT disabled, VCC = 3V
0.25
5
µA
<10
40
mV
50
nA
VACIO
Analog Comparator
Input Offset Voltage
VCC = 5V
Vin = VCC/2
IACLK
Analog Comparator
Input Leakage Current
VCC = 5V
Vin = VCC/2
tACID
Analog Comparator
Propagation Delay
VCC = 2.7V
VCC = 4.0V
Note:
Min.
-50
750
500
ns
1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V for Port B and 10 mA
at VCC = 5V, 5 mA at VCC = 3V for all other ports) under steady state conditions (non-transient), the following must be
observed:
TQFP and QFN/MLF Package:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for ports A0 - A7, C4 - C7, G2 should not exceed 100 mA.
3] The sum of all IOL, for ports B0 - B7, E0 - E7, G3 - G5 should not exceed 100 mA.
4] The sum of all IOL, for ports D0 - D7, C0 - C3, G0 - G1 should not exceed 100 mA.
5] The sum of all IOL, for ports F0 - F7, should not exceed 100 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
4. Although each I/O port can source more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V for Port B and 10mA
at VCC = 5V, 5 mA at VCC = 3V for all other ports) under steady state conditions (non-transient), the following must be
observed:
TQFP and QFN/MLF Package:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for ports A0 - A7, C4 - C7, G2 should not exceed 100 mA.
3] The sum of all IOL, for ports B0 - B7, E0 - E7, G3 - G5 should not exceed 100 mA.
4] The sum of all IOL, for ports D0 - D7, C0 - C3, G0 - G1 should not exceed 100 mA.
5] The sum of all IOL, for ports F0 - F7, should not exceed 100 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
5. Typical values at 25°C.
292
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External Clock Drive
Waveforms
Figure 129. External Clock Drive Waveforms
V IH1
V IL1
External Clock Drive
Table 123. External Clock Drive
Speed vs. VCC
VCC=1.8-5.5V
VCC=2.7-5.5V
VCC=4.5-5.5V
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Max.
Units
1/tCLCL
Oscillator
Frequency
0
1
0
8
0
16
MHz
tCLCL
Clock Period
1000
125
62.5
ns
tCHCX
High Time
400
50
25
ns
tCLCX
Low Time
400
50
25
ns
tCLCH
Rise Time
2.0
1.6
0.5
μs
tCHCL
Fall Time
2.0
1.6
0.5
μs
ΔtCLCL
Change in period
from one clock
cycle to the next
2
2
2
%
Figure 130. Maximum Frequency vs. VCC (4 - 8 MHz).
8 MHz
4 MHz
Safe Operating Area
1.8V
2.7V
5.5V
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Figure 131. Maximum Frequency vs. VCC (8 - 16 MHz).
16 MHz
8 MHz
Safe Operating Area
2.7V
SPI Timing
Characteristics
5.5V
See Figure 132 and Figure 133 for details.
Table 124. SPI Timing Parameters
Description
Mode
1
SCK period
Master
See Table 67
2
SCK high/low
Master
50% duty cycle
3
Rise/Fall time
Master
3.6
4
Setup
Master
10
5
Hold
Master
10
6
Out to SCK
Master
0.5 • tsck
7
SCK to out
Master
10
8
SCK to out high
Master
10
9
SS low to out
Slave
15
10
SCK period
Slave
4 • tck
Slave
2 • tck
11
(1)
SCK high/low
Min
12
Rise/Fall time
Slave
13
Setup
Slave
10
14
Hold
Slave
tck
15
SCK to out
Slave
16
SCK to SS high
Slave
17
SS high to tri-state
Slave
18
SS low to SCK
Slave
Note:
294
4.5V
Typ
1.6
15
Max
ns
µs
ns
20
10
20 • tck
1. In SPI Programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12 MHz
- 3 tCLCL for fCK > 12 MHz
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 132. SPI Interface Timing Requirements (Master Mode)
SS
6
1
SCK
(CPOL = 0)
2
2
SCK
(CPOL = 1)
4
MISO
(Data Input)
5
3
MSB
...
LSB
8
7
MOSI
(Data Output)
MSB
...
LSB
Figure 133. SPI Interface Timing Requirements (Slave Mode)
SS
10
9
16
SCK
(CPOL = 0)
11
11
SCK
(CPOL = 1)
13
MOSI
(Data Input)
14
12
MSB
...
LSB
15
MISO
(Data Output)
MSB
17
...
LSB
X
295
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ADC Characteristics – Preliminary Data
Table 125. ADC Characteristics
Symbol
Parameter
Condition
Min
Typ
Max
Units
Single Ended Conversion
10
Bits
Differential Conversion
8
Bits
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
4.5
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
Noise Reduction Mode
2
LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1 MHz
Noise Reduction Mode
4.5
LSB
Integral Non-Linearity (INL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
0.5
LSB
Differential Non-Linearity (DNL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
0.25
LSB
Gain Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2
LSB
Offset Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200 kHz
2
LSB
Conversion Time
Free Running Conversion
13
260
µs
Clock Frequency
Single Ended Conversion
50
1000
kHz
VCC - 0.3
VCC + 0.3
V
Single Ended Conversion
1.0
AVCC
V
Differential Conversion
1.0
AVCC - 0.5
V
Single Ended Channels
GND
VREF
V
Differential Channels
GND
AVCC
V
Single Ended Channels
GND
VREF
V
-0.85VREF
VREF
V
Resolution
Absolute accuracy (Including
INL, DNL, quantization error,
gain and offset error)
AVCC
Analog Supply Voltage
VREF
Reference Voltage
Pin Input Voltage
VIN
Input Range
Differential Channels
(1)
Single Ended Channels
2.5
LSB
38,5
kHz
4
kHz
Input Bandwidth
Differential Channels
296
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Table 125. ADC Characteristics
Symbol
Parameter
Condition
Min
Typ
Max
Units
1.0
1.1
1.2
V
VINT
Internal Voltage Reference
RREF
Reference Input Resistance
32
kΩ
RAIN
Analog Input Resistance
100
MΩ
Note:
1. Voltage difference between channels
Calibrated Internal RC Oscillator Accuracy
Table 126. Calibration Accuracy of Internal RC Oscillator
Frequency
VCC
Temperature
Calibration Accuracy
Factory
Calibration
8.0 MHz
3V
25°C
±10%
User
Calibration
7.3 - 8.1 MHz
1.8V - 5.5V(1)
2.7V - 5.5V(2)
-40°C - 85°C
±1%
Notes:
1. Voltage range for ATmega325V/3250V/645V/6450V.
2. Voltage range for ATmega325/3250/645/6450.
297
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Typical Characteristics – Preliminary Data
The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins
configured as inputs and with internal pull-ups enabled. A sine wave generator with railto-rail output is used as clock source.
All Active- and Idle current consumption measurements are done with all bits in the PRR
register set and thus, the corresponding I/O modules are turned off. Also the Analog
Comparator is disabled during these measurements. See “Power Reduction Register”
on page 35 for details.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage,
operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and
ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as
CL*VCC*f where CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog
Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.
Active Supply Current
Figure 134. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
I CC (m A)
1.6
1.4
5.5 V
1.2
5.0 V
1
4.5 V
4.0 V
0.8
3.3 V
0.6
2.7 V
0.4
1.8 V
0.2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
298
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 135. Active Supply Current vs. Frequency (1 - 16 MHz))
ACTIVE SUPPLY CURRENT vs. FREQUENCY
1 - 16 MHz
16
5.5 V
14
5.0 V
12
4.5 V
ICC (mA)
10
8
6
4.0 V
3.3 V
2.7 V
4
2
1.8 V
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
Figure 136. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
14
85°C
25°C
-40°C
12
ICC (mA)
10
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
299
2570J–AVR–11/06
Figure 137. Active Supply Current vs. V CC (Internal RC Oscillator, CKDIV8 Programmed, 1 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, CKDIV8 PROGRAMMED, 1 MHz
2.5
85°C
2
25°C
-40°C
ICC (mA)
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 138. Active Supply Current vs. VCC (32 kHz External Oscillator)
ACTIVE SUPPLY CURRENT vs. VCC
32kHz EXTERNAL OSCILLATOR
70
85 ˚C
60
25 ˚C
-40 ˚C
I CC (u A)
50
40
30
20
10
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
300
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Idle Supply Current
Figure 139. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
0.4
5.5 V
0.35
5.0 V
0.3
4.5 V
ICC (mA)
0.25
4.0 V
0.2
3.3 V
0.15
2.7 V
0.1
1.8 V
0.05
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
Figure 140. Idle Supply Current vs. Frequency (1 - 16 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
1 - 16 MHz
6
5.5 V
5
5.0 V
4.5 V
ICC (mA)
4
3
2
4.0 V
3.3 V
1
2.7 V
1.8 V
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
301
2570J–AVR–11/06
Figure 141. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
7
6
85°C
5
-40°C
ICC (mA)
25°C
4
3
2
1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 142. Idle Supply Current vs. VCC (Internal RC Oscillator, CKDIV8 Programmed,
1 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, CKDIV8 PROGRAMMED, 1 MHz
1
0.9
85°C
0.8
25°C
0.7
-40°C
ICC (mA)
0.6
0.5
0.4
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
302
ATmega325/3250/645/6450
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ATmega325/3250/645/6450
Figure 143. Idle Supply Current vs. VCC (32 kHz External Oscillator)
IDLE SUPPLY CURRENT vs. V CC
32kHz EXTERNAL OSCILLATOR
35
85 ˚C
30
25 ˚C
-40 ˚C
ICC (uA)
25
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Supply Current of I/O modules The tables and formulas below can be used to calculate the additional current consumption for the different I/O modules in Active and Idle mode. The enabling or disabling of
the I/O modules are controlled by the Power Reduction Register. See “PRR – Power
Reduction Register” on page 37 for details.
Table 127.
Additional Current Consumption for the different I/O modules (absolute values)
PRR bit
Typical numbers
VCC = 2V, F = 1MHz
VCC = 3V, F = 4MHz
VCC = 5V, F = 8MHz
PRADC
17 µA
116 µA
562 µA
PRUSART0
9 µA
59 µA
248 µA
PRSPI
10 µA
62 µA
257 µA
PRTIM1
5 µA
33 µA
135 µA
Table 128.
Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external
clock
(see Figure 134 and Figure 135)
Additional Current consumption
compared to Idle with external
clock
(see Figure 139 and Figure 140)
PRADC
5.4%
16.8%
PRUSART0
2.7%
8.5%
PRSPI
2.9%
9.0%
PRTIM1
1.5%
4.8%
It is possible to calculate the typical current consumption based on the numbers from
Table 128 for other VCC and frequency settings than listed in Table 127.
303
2570J–AVR–11/06
Example
Calculate the expected current consumption in idle mode with USART0, TIMER1, and
SPI enabled at VCC = 3.0V and F = 1MHz. Table 128 shows that we need to add 8.5%
for the USART0, 9% for the SPI, and 4.8% for the TIMER1 module. From Figure 139,
we find that the idle current consumption is ~0.16mA at VCC = 3.0V and F = 1MHz. The
total current consumption in idle mode with USART0, TIMER1, and SPI enabled, gives:
I CC total ≈ 0,16mA • ( 1 + 0,085 + 0,09 + 0,048 ) ≈ 0,20mA
Power-down Supply Current
Figure 144. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER DISABLED
4
85 ˚C
3.5
3
ICC (uA)
2.5
2
1.5
1
25 ˚C
-40 ˚C
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 145. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER ENABLED
20
85 ˚C
18
25 ˚C
16
-40 ˚C
14
ICC (uA)
12
10
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
304
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ATmega325/3250/645/6450
Power-save Supply Current
Figure 146. Power-save Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-SAVE SUPPLY CURRENT vs. V CC
WATCHDOG TIMER DISABLED
30
25
85°C
25°C
ICC (uA)
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Standby Supply Current
Figure 147. Standby Supply Current vs. VCC (Low Power Crystal Oscillator)
STANDBY SUPPLY CURRENT vs. VCC
Low Power Crystal Oscillator
180
6 MHz Xtal
6 MHz Res.
160
140
4 MHz Res.
4 MHz Xtal
ICC (uA)
120
100
80
2 MHz Xtal
2 MHz Res.
60
455kHz Res.
1 MHz Res.
40
20
32 kHz Xtal
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
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Pin Pull-up
Figure 148. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5V
160
85°C
140
25°C
120
-40°C
IIO (uA)
100
80
60
40
20
0
0
1
2
3
4
5
VIO (V)
Figure 149. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7V
90
80
25°C
85°C
70
-40°C
IIO (uA)
60
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VIO (V)
306
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ATmega325/3250/645/6450
Figure 150. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 1.8V
60
50
85°C
25°C
IOP (uA)
40
-40°C
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOP (V)
Figure 151. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 5V
120
-40°C
25°C
100
85°C
IRESET (uA)
80
60
40
20
0
0
1
2
3
4
5
VRESET (V)
307
2570J–AVR–11/06
Figure 152. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 2.7V
70
60
-40°C
25°C
IRESET (uA)
50
85°C
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
VRESET (V)
Figure 153. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 1.8V
40
-40°C
35
25°C
30
IRESET (uA)
85°C
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VRESET (V)
308
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ATmega325/3250/645/6450
Pin Driver Strength
Figure 154. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 5V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 5V
70
IOH (mA)
60
-40°C
50
25°C
40
85°C
30
20
10
0
0
1
2
3
4
5
6
VOH (V)
Figure 155. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 2.7V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 2.7V
25
-40°C
20
25°C
IOH (mA)
85°C
15
10
5
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
309
2570J–AVR–11/06
Figure 156. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 1.8V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 1.8V
8
-40°C
7
25°C
6
85°C
IOH (mA)
5
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOH (V)
Figure 157. I/O Pin Source Current vs. Output Voltage, Port B (VCC= 5V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 5V
80
70
-40°C
60
25°C
85°C
IOH (mA)
50
40
30
20
10
0
0
1
2
3
4
VOH (V)
310
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 158. I/O Pin Source Current vs. Output Voltage, Port B (VCC = 2.7V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 2.7V
35
30
-40°C
25°C
25
IOH (mA)
85°C
20
15
10
5
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
Figure 159. I/O Pin Source Current vs. Output Voltage, Port B (VCC = 1.8V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 1.8V
10
-40°C
9
25°C
8
85°C
IOH (mA)
7
6
5
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOH (V)
311
2570J–AVR–11/06
Figure 160. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 5V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 5V
50
-40°C
45
40
25°C
IOL (mA)
35
85°C
30
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
Figure 161. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 2.7V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 2.7V
20
-40°C
18
16
25°C
IOL (mA)
14
85°C
12
10
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
312
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 162. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 1.8V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORTS A, C, D, E, F, G, H, J
Vcc = 1.8V
7
-40°C
6
25°C
IOL (mA)
5
85°C
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
Figure 163. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 5V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 5V
90
80
-40°C
70
25°C
IOL (mA)
60
85°C
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
313
2570J–AVR–11/06
Figure 164. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 2.7V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 2.7V
35
-40°C
30
25°C
25
IOL (mA)
85°C
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
Figure 165. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 1.8V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE, PORT B
Vcc = 1.8V
12
-40°C
10
25°C
85°C
IOL (mA)
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
VOL (V)
314
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Pin Thresholds and hysteresis Figure 166. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as “1”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIH, I/O PIN READ AS '1'
3
85°C
25°C
-40°C
2.5
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 167. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as “0”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. VCC
VIL, I/O PIN READ AS '0'
3
85°C
25°C
-40°C
2.5
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
315
2570J–AVR–11/06
Figure 168. I/O Pin Input Hysteresis vs. VCC
I/O PIN INPUT HYSTERESIS vs. VCC
0.6
-40°C
0.5
Input Hysteresis (V)
25°C
0.4
85°C
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 169. Reset Input Threshold Voltage vs. VCC (VIH,Reset Pin Read as “1”)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIH, RESET PIN READ AS '1'
2.5
Threshold (V)
2
1.5
-40°C
25°C
1
85°C
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
316
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 170. Reset Input Threshold Voltage vs. VCC (VIL,Reset Pin Read as “0”)
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIL, RESET PIN READ AS '0'
2.5
85°C
25°C
-40°C
Threshold (V)
2
1.5
1
0.5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
5
5.5
VCC (V)
Figure 171. Reset Input Pin Hysteresis vs. VCC
RESET INPUT PIN HYSTERESIS vs. VCC
0.7
0.6
-40°C
Input Hysteresis (V)
0.5
25°C
0.4
0.3
85°C
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
VCC (V)
317
2570J–AVR–11/06
BOD Thresholds and Analog
Comparator Offset
Figure 172. BOD Thresholds vs. Temperature (BOD Level is 4.3V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 4.3V
4.6
4.5
Rising VCC
Threshold (V)
4.4
4.3
Falling VCC
4.2
4.1
4
-60
-40
-20
0
20
40
60
80
100
80
100
Temperature (C)
Figure 173. BOD Thresholds vs. Temperature (BOD Level is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 2.7V
3
2.9
Rising VCC
Threshol d ( V)
2.8
2.7
Falling VCC
2.6
2.5
2.4
-60
-40
-20
0
20
40
60
Temperature (C)
318
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 174. BOD Thresholds vs. Temperature (BOD Level is 1.8V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 1.8V
1.95
Threshold (V)
1.9
Rising VCC
1.85
1.8
Falling VCC
1.75
1.7
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
Figure 175. Bandgap Voltage vs. VCC
BANDGAP VOLTAGE vs. VCC
1.076
1.075
Bandgap Voltage (V)
1.074
25˚C
1.073
1.072
85˚C
1.071
1.07
1.069
-40˚C
1.068
1.5
2
2.5
3
3.5
4
4.5
5
VCC (V)
319
2570J–AVR–11/06
Figure 176. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC = 5V)
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
VCC = 5 V
0.007
85˚C
Comparator Offset Voltage (V)
0.006
0.005
25˚C
0.004
0.003
-40˚C
0.002
0.001
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Common Mode Voltage (V)
Figure 177. Analog Comparator Offset Voltage vs. Common Mode Voltage
(VCC = 2.7V)
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
VCC = 2.7 V
0.0035
Comparator Offset Voltage (V)
0.003
0.0025
85˚C
0.002
0.0015
25˚C
0.001
0.0005
-40˚C
0
0
0.5
1
1.5
2
2.5
3
Common Mode Voltage (V)
320
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Internal Oscillator Speed
Figure 178. Watchdog Oscillator Frequency vs. VCC
WATCHDOG OSCILLATOR FREQUENCY vs.VCC
1300
1250
-40 ˚C
25 ˚C
85 ˚C
F RC (kHz)
1200
1150
1100
1050
1000
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 179. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
8.6
8.4
5.5 V
4.5 V
3.3 V
2.7 V
1.8 V
F RC (M Hz)
8.2
8
7.8
7.6
7.4
7.2
-60
-40
-20
0
20
40
60
80
100
Temperature (C)
321
2570J–AVR–11/06
Figure 180. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. VCC
8.6
8.4
85 ˚C
8.2
F RC (MHz)
25 ˚C
8
-40 ˚C
7.8
7.6
7.4
7.2
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 181. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
16
85 ˚C
25 ˚C
-40 ˚C
14
F RC (M Hz)
12
10
8
6
4
0
16
32
48
64
80
96
112 128 144 160 176 192 208 224 240 256
OSCCAL VALUE
322
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Current Consumption of
Peripheral Units
Figure 182. Brownout Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs. VCC
40
-40 ˚C
25 ˚C
85 ˚C
35
30
I CC (u A)
25
20
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 183. ADC Current vs. VCC (AREF = AVCC)
ADC CURRENT vs. VCC
AREF = AVCC
350
-40°C
25°C
85°C
300
ICC (uA)
250
200
150
100
50
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
323
2570J–AVR–11/06
Figure 184. AREF External Reference Current vs. VCC
AREF EXTERNAL REFERENCE CURRENT vs. V CC
85°C
25°C
-40°C
160
140
120
IAREF (uA)
100
80
60
40
20
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 185. 32 kHZ TOSC Current vs. VCC (Watchdog Timer Disabled)
32kHz TOSC CURRENT vs. VCC
WATCHDOG TIMER DISABLED
25
85°C
25°C
20
ICC (uA)
15
10
5
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
324
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 186. Watchdog Timer Current vs. VCC
WATCHDOG TIMER CURRENT vs. VCC
16
85°C
25°C
-40°C
14
12
ICC (uA)
10
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 187. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. VCC
120
100
-40°C
80
25°C
ICC (uA)
85°C
60
40
20
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
325
2570J–AVR–11/06
Figure 188. Programming Current vs. VCC
PROGRAMMING CURRENT vs. Vcc
20
-40 ˚C
18
ICC (mA)
16
14
25 ˚C
12
85 ˚C
10
8
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Current Consumption in
Reset and Reset Pulsewidth
Figure 189. Reset Supply Current vs. VCC (0.1 - 1.0 MHz, Excluding Current Through
The Reset Pull-up)
RESET SUPPLY CURRENT vs. VCC
0.1 - 1.0 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
0.2
0.18
5.5 V
0.16
5.0 V
0.14
4.5 V
ICC (mA)
0.12
4.0 V
0.1
3.3 V
0.08
0.06
2.7 V
0.04
1.8 V
0.02
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (MHz)
326
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Figure 190. Reset Supply Current vs. VCC (1 - 16 MHz, Excluding Current Through The
Reset Pull-up)
RESET SUPPLY CURRENT vs. V CC
1 - 16 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
3
5.5 V
2.5
5.0 V
ICC (mA)
2
4.5 V
1.5
1
4.0 V
3.3 V
0.5
2.7 V
1.8 V
0
0
2
4
6
8
10
12
14
16
Frequency (MHz)
Figure 191. Reset Pulse Width vs. VCC
RESET PULSE WIDTH vs. VCC
2500
Pulsewidth (ns)
2000
1500
1000
500
85°C
25°C
-40°C
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
327
2570J–AVR–11/06
Register Summary
Note:
Registers with bold type only available in ATmega3250/6450.
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(0xFF)
Reserved
-
-
-
-
-
-
-
-
Page
(0xFE)
Reserved
-
-
-
-
-
-
-
-
(0xFD)
Reserved
-
-
-
-
-
-
-
-
(0xFC)
Reserved
-
-
-
-
-
-
-
-
(0xFB)
Reserved
-
-
-
-
-
-
-
-
(0xFA)
Reserved
-
-
-
-
-
-
-
-
(0xF9)
Reserved
-
-
-
-
-
-
-
-
(0xF8)
Reserved
-
-
-
-
-
-
-
-
(0xF7)
Reserved
-
-
-
-
-
-
-
-
(0xF6)
Reserved
-
-
-
-
-
-
-
-
(0xF5)
Reserved
-
-
-
-
-
-
-
-
(0xF4)
Reserved
-
-
-
-
-
-
-
-
(0xF3)
Reserved
-
-
-
-
-
-
-
-
(0xF2)
Reserved
-
-
-
-
-
-
-
-
(0xF1)
Reserved
-
-
-
-
-
-
-
-
(0xF0)
Reserved
-
-
-
-
-
-
-
-
(0xEF)
Reserved
-
-
-
-
-
-
-
-
(0xEE)
Reserved
-
-
-
-
-
-
-
-
(0xED)
Reserved
-
-
-
-
-
-
-
-
(0xEC)
Reserved
-
-
-
-
-
-
-
-
(0xEB)
Reserved
-
-
-
-
-
-
-
-
(0xEA)
Reserved
-
-
-
-
-
-
-
-
(0xE9)
Reserved
-
-
-
-
-
-
-
-
(0xE8)
Reserved
-
-
-
-
-
-
-
-
(0xE7)
Reserved
-
-
-
-
-
-
-
-
(0xE6)
Reserved
-
-
-
-
-
-
-
-
(0xE5)
Reserved
-
-
-
-
-
-
-
-
(0xE4)
Reserved
-
-
-
-
-
-
-
-
(0xE3)
Reserved
-
-
-
-
-
-
-
-
(0xE2)
Reserved
-
-
-
-
-
-
-
-
(0xE1)
Reserved
-
-
-
-
-
-
-
-
(0xE0)
Reserved
-
-
-
-
-
-
-
-
(0xDF)
Reserved
-
-
-
-
-
-
-
-
(0xDE)
Reserved
-
-
-
-
-
-
-
-
(0xDD)
PORTJ
-
PORTJ6
PORTJ5
PORTJ4
PORTJ3
PORTJ2
PORTJ1
PORTJ0
82
(0xDC)
DDRJ
-
DDJ6
DDJ5
DDJ4
DDJ3
DDJ2
DDJ1
DDJ0
82
(0xDB)
PINJ
-
PINJ6
PINJ5
PINJ4
PINJ3
PINJ2
PINJ1
PINJ0
82
(0xDA)
PORTH
PORTH7
PORTH6
PORTH5
PORTH4
PORTH3
PORTH2
PORTH1
PORTH0
82
(0xD9)
DDRH
DDH7
DDH6
DDH5
DDH4
DDH3
DDH2
DDH1
DDH0
82
(0xD8)
PINH
PINH7
PINH6
PINH5
PINH4
PINH3
PINH2
PINH1
PINH0
82
(0xD7)
Reserved
-
-
-
-
-
-
-
-
(0xD6)
Reserved
-
-
-
-
-
-
-
-
(0xD5)
Reserved
-
-
-
-
-
-
-
-
(0xD4)
Reserved
-
-
-
-
-
-
-
-
(0xD3)
Reserved
-
-
-
-
-
-
-
-
(0xD2)
Reserved
-
-
-
-
-
-
-
-
(0xD1)
Reserved
-
-
-
-
-
-
-
-
(0xD0)
Reserved
-
-
-
-
-
-
-
-
(0xCF)
Reserved
-
-
-
-
-
-
-
-
(0xCE)
Reserved
-
-
-
-
-
-
-
-
(0xCD)
Reserved
-
-
-
-
-
-
-
-
(0xCC)
Reserved
-
-
-
-
-
-
-
-
(0xCB)
Reserved
-
-
-
-
-
-
-
-
(0xCA)
Reserved
-
-
-
-
-
-
-
-
(0xC9)
Reserved
-
-
-
-
-
-
-
-
(0xC8)
Reserved
-
-
-
-
-
-
-
-
(0xC7)
Reserved
-
-
-
-
-
-
-
-
(0xC6)
UDR0
(0xC5)
UBRR0H
(0xC4)
UBRR0L
(0xC3)
Reserved
328
USART0 Data Register
173
USART0 Baud Rate Register High
176
USART0 Baud Rate Register Low
-
-
-
-
-
176
-
-
-
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0xC2)
UCSR0C
-
UMSEL0
UPM01
UPM00
USBS0
UCSZ01
UCSZ00
UCPOL0
175
(0xC1)
UCSR0B
RXCIE0
TXCIE0
UDRIE0
RXEN0
TXEN0
UCSZ02
RXB80
TXB80
174
(0xC0)
UCSR0A
RXC0
TXC0
UDRE0
FE0
DOR0
UPE0
U2X0
MPCM0
173
(0xBF)
Reserved
-
-
-
-
-
-
-
-
(0xBE)
Reserved
-
-
-
-
-
-
-
-
(0xBD)
Reserved
-
-
-
-
-
-
-
-
(0xBC)
Reserved
-
-
-
-
-
-
-
-
(0xBB)
Reserved
-
-
-
-
-
-
-
-
(0xBA)
USIDR
(0xB9)
USISR
USISIF
USIOIF
USIPF
USIDC
USICNT3
USICNT2
USICNT1
USICNT0
189
(0xB8)
USICR
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
191
USI Data Register
188
(0xB7)
Reserved
-
-
-
-
-
-
-
-
(0xB6)
ASSR
-
-
-
EXCLK
AS2
TCN2UB
OCR2UB
TCR2UB
(0xB5)
Reserved
-
-
-
-
-
-
-
-
(0xB4)
Reserved
-
-
-
-
-
-
-
-
(0xB3)
OCR2A
Timer/Counter 2 Output Compare Register A
140
(0xB2)
TCNT2
Timer/Counter2
140
(0xB1)
Reserved
-
-
-
-
-
-
-
-
(0xB0)
TCCR2A
FOC2A
WGM20
COM2A1
COM2A0
WGM21
CS22
CS21
CS20
(0xAF)
Reserved
-
-
-
-
-
-
-
-
141
138
(0xAE)
Reserved
-
-
-
-
-
-
-
-
(0xAD)
Reserved
-
-
-
-
-
-
-
-
(0xAC)
Reserved
-
-
-
-
-
-
-
-
(0xAB)
Reserved
-
-
-
-
-
-
-
-
(0xAA)
Reserved
-
-
-
-
-
-
-
-
(0xA9)
Reserved
-
-
-
-
-
-
-
-
(0xA8)
Reserved
-
-
-
-
-
-
-
-
(0xA7)
Reserved
-
-
-
-
-
-
-
-
(0xA6)
Reserved
-
-
-
-
-
-
-
-
(0xA5)
Reserved
-
-
-
-
-
-
-
-
(0xA4)
Reserved
-
-
-
-
-
-
-
-
(0xA3)
Reserved
-
-
-
-
-
-
-
-
(0xA2)
Reserved
-
-
-
-
-
-
-
-
(0xA1)
Reserved
-
-
-
-
-
-
-
-
(0xA0)
Reserved
-
-
-
-
-
-
-
-
(0x9F)
Reserved
-
-
-
-
-
-
-
-
(0x9E)
Reserved
-
-
-
-
-
-
-
-
(0x9D)
Reserved
-
-
-
-
-
-
-
-
(0x9C)
Reserved
-
-
-
-
-
-
-
-
(0x9B)
Reserved
-
-
-
-
-
-
-
-
(0x9A)
Reserved
-
-
-
-
-
-
-
-
(0x99)
Reserved
-
-
-
-
-
-
-
-
(0x98)
Reserved
-
-
-
-
-
-
-
-
(0x97)
Reserved
-
-
-
-
-
-
-
-
(0x96)
Reserved
-
-
-
-
-
-
-
-
(0x95)
Reserved
-
-
-
-
-
-
-
-
(0x94)
Reserved
-
-
-
-
-
-
-
-
(0x93)
Reserved
-
-
-
-
-
-
-
-
(0x92)
Reserved
-
-
-
-
-
-
-
-
(0x91)
Reserved
-
-
-
-
-
-
-
-
(0x90)
Reserved
-
-
-
-
-
-
-
-
(0x8F)
Reserved
-
-
-
-
-
-
-
-
(0x8E)
Reserved
-
-
-
-
-
-
-
-
(0x8D)
Reserved
-
-
-
-
-
-
-
-
(0x8C)
Reserved
-
-
-
-
-
-
-
-
(0x8B)
OCR1BH
Timer/Counter1 Output Compare Register B High
(0x8A)
OCR1BL
Timer/Counter1 Output Compare Register B Low
124
(0x89)
OCR1AH
Timer/Counter1 Output Compare Register A High
124
(0x88)
OCR1AL
Timer/Counter1 Output Compare Register A Low
124
(0x87)
ICR1H
Timer/Counter1 Input Capture Register High
124
(0x86)
ICR1L
Timer/Counter1 Input Capture Register Low
124
(0x85)
TCNT1H
Timer/Counter1 High
124
(0x84)
TCNT1L
Timer/Counter1 Low
124
124
329
2570J–AVR–11/06
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(0x83)
Reserved
-
-
-
-
-
-
-
-
Page
(0x82)
TCCR1C
FOC1A
FOC1B
-
-
-
-
-
-
123
(0x81)
TCCR1B
ICNC1
ICES1
-
WGM13
WGM12
CS12
CS11
CS10
122
120
(0x80)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1B0
-
-
WGM11
WGM10
(0x7F)
DIDR1
-
-
-
-
-
-
AIN1D
AIN0D
196
(0x7E)
DIDR0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ADC2D
ADC1D
ADC0D
213
(0x7D)
Reserved
-
-
-
-
-
-
-
-
(0x7C)
ADMUX
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
209
(0x7B)
ADCSRB
-
ACME
-
-
-
ADTS2
ADTS1
ADTS0
194/212
(0x7A)
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
(0x79)
ADCH
ADC Data Register High
211
212
(0x78)
ADCL
(0x77)
Reserved
-
-
-
ADC Data Register Low
-
-
-
-
-
212
(0x76)
Reserved
-
-
-
-
-
-
-
-
(0x75)
Reserved
-
-
-
-
-
-
-
-
(0x74)
Reserved
-
-
-
-
-
-
-
-
(0x73)
PCMSK3
-
PCINT30
PCINT29
PCINT28
PCINT27
PCINT26
PCINT25
PCINT24
(0x72)
Reserved
-
-
-
-
-
-
-
-
(0x71)
Reserved
-
-
-
-
-
-
-
-
(0x70)
TIMSK2
-
-
-
-
-
-
OCIE2A
TOIE2
143
(0x6F)
TIMSK1
-
-
ICIE1
-
-
OCIE1B
OCIE1A
TOIE1
125
(0x6E)
TIMSK0
-
-
-
-
-
-
OCIE0A
TOIE0
96
(0x6D)
PCMSK2
PCINT23
PCINT22
PCINT21
PCINT20
PCINT19
PCINT18
PCINT17
PCINT16
57
(0x6C)
PCMSK1
PCINT15
PCINT14
PCINT13
PCINT12
PCINT11
PCINT10
PCINT9
PCINT8
57
(0x6B)
PCMSK0
PCINT7
PCINT6
PCINT5
PCINT4
PCINT3
PCINT2
PCINT1
PCINT0
57
(0x6A)
Reserved
-
-
-
-
-
-
-
-
(0x69)
EICRA
-
-
-
-
-
-
ISC01
ISC00
(0x68)
Reserved
-
-
-
-
-
-
-
-
(0x67)
Reserved
-
-
-
-
-
-
-
-
(0x66)
OSCCAL
(0x65)
Reserved
-
-
-
-
-
-
-
-
Oscillator Calibration Register [CAL7..0]
56
54
29
(0x64)
PRR
-
-
-
-
PRTIM1
PRSPI
PSUSART0
PRADC
(0x63)
Reserved
-
-
-
-
-
-
-
-
(0x62)
Reserved
-
-
-
-
-
-
-
-
(0x61)
CLKPR
CLKPCE
-
-
-
CLKPS3
CLKPS2
CLKPS1
CLKPS0
31
(0x60)
WDTCR
-
-
-
WDCE
WDE
WDP2
WDP1
WDP0
45
I
T
H
S
V
N
Z
C
11
37
0x3F (0x5F)
SREG
0x3E (0x5E)
SPH
Stack Pointer High
0x3D (0x5D)
SPL
Stack Pointer Low
0x3C (0x5C)
Reserved
-
-
-
-
-
-
-
-
0x3B (0x5B)
Reserved
-
-
-
-
-
-
-
-
0x3A (0x5A)
Reserved
-
-
-
-
-
-
-
-
0x39 (0x59)
Reserved
-
-
-
-
-
-
-
-
0x38 (0x58)
Reserved
-
-
-
-
-
-
-
-
0x37 (0x57)
SPMCSR
SPMIE
RWWSB
-
RWWSRE
BLBSET
PGWRT
PGERS
SPMEN
250
0x36 (0x56)
Reserved
51/66/223
13
13
0x35 (0x55)
MCUCR
JTD
-
-
PUD
-
-
IVSEL
IVCE
0x34 (0x54)
MCUSR
-
-
-
JTRF
WDRF
BORF
EXTRF
PORF
43
0x33 (0x53)
SMCR
-
-
-
-
SM2
SM1
SM0
SE
34
0x32 (0x52)
Reserved
-
-
-
-
-
-
-
-
0x31 (0x51)
OCDR
IDRD/OCDR7
OCDR6
OCDR5
OCDR4
OCDR3
OCDR2
OCDR1
OCDR0
219
0x30 (0x50)
ACSR
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
194
0x2F (0x4F)
Reserved
-
-
-
-
-
-
-
-
0x2E (0x4E)
SPDR
0x2D (0x4D)
SPSR
SPIF
WCOL
-
-
-
-
-
SPI2X
153
0x2C (0x4C)
SPCR
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
151
0x2B (0x4B)
GPIOR2
General Purpose I/O Register
0x2A (0x4A)
GPIOR1
General Purpose I/O Register
0x29 (0x49)
Reserved
-
-
-
0x28 (0x48)
Reserved
-
-
-
0x27 (0x47)
OCR0A
Timer/Counter0 Output Compare A
96
0x26 (0x46)
TCNT0
Timer/Counter0
95
0x25 (0x45)
Reserved
330
SPI Data Register
-
-
-
153
24
24
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x24 (0x44)
TCCR0A
FOC0A
WGM00
COM0A1
COM0A0
WGM01
CS02
CS01
CS00
93
0x23 (0x43)
GTCCR
TSM
-
-
-
-
-
PSR2
PSR10
98/145
0x22 (0x42)
EEARH
-
-
-
-
-
0x21 (0x41)
EEARL
EEPROM Address Register Low
0x20 (0x40)
EEDR
EEPROM Data Register
0x1F (0x3F)
EECR
-
-
-
-
EERIE
EEPROM Address Register High
Page
20
20
20
EEMWE
EEWE
EERE
General Purpose I/O Register
20
0x1E (0x3E)
GPIOR0
0x1D (0x3D)
EIMSK
PCIE3
PCIE2
PCIE1
PCIE0
-
-
-
INT0
24
55
0x1C (0x3C)
EIFR
PCIF3
PCIF2
PCIF1
PCIF0
-
-
-
INTF0
56
0x1B (0x3B)
Reserved
-
-
-
-
-
-
-
-
0x1A (0x3A)
Reserved
-
-
-
-
-
-
-
-
0x19 (0x39)
Reserved
-
-
-
-
-
-
-
-
0x18 (0x38)
Reserved
-
-
-
-
-
-
-
-
0x17 (0x37)
TIFR2
-
-
-
-
-
-
OCF2A
TOV2
143
0x16 (0x36)
TIFR1
-
-
ICF1
-
-
OCF1B
OCF1A
TOV1
125
0x15 (0x35)
TIFR0
-
-
-
-
-
-
OCF0A
TOV0
96
0x14 (0x34)
PORTG
-
-
-
PORTG4
PORTG3
PORTG2
PORTG1
PORTG0
82
0x13 (0x33)
DDRG
-
-
-
DDG4
DDG3
DDG2
DDG1
DDG0
82
0x12 (0x32)
PING
-
-
PING5
PING4
PING3
PING2
PING1
PING0
82
0x11 (0x31)
PORTF
PORTF7
PORTF6
PORTF5
PORTF4
PORTF3
PORTF2
PORTF1
PORTF0
81
0x10 (0x30)
DDRF
DDF7
DDF6
DDF5
DDF4
DDF3
DDF2
DDF1
DDF0
81
0x0F (0x2F)
PINF
PINF7
PINF6
PINF5
PINF4
PINF3
PINF2
PINF1
PINF0
81
0x0E (0x2E)
PORTE
PORTE7
PORTE6
PORTE5
PORTE4
PORTE3
PORTE2
PORTE1
PORTE0
81
0x0D (0x2D)
DDRE
DDE7
DDE6
DDE5
DDE4
DDE3
DDE2
DDE1
DDE0
81
0x0C (0x2C)
PINE
PINE7
PINE6
PINE5
PINE4
PINE3
PINE2
PINE1
PINE0
81
0x0B (0x2B)
PORTD
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
81
0x0A (0x2A)
DDRD
DDD7
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
81
81
0x09 (0x29)
PIND
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
0x08 (0x28)
PORTC
PORTC7
PORTC6
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
80
0x07 (0x27)
DDRC
DDC7
DDC6
DDC5
DDC4
DDC3
DDC2
DDC1
DDC0
80
0x06 (0x26)
PINC
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
80
0x05 (0x25)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
80
0x04 (0x24)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
80
0x03 (0x23)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
80
0x02 (0x22)
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
80
0x01 (0x21)
DDRA
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
80
0x00 (0x20)
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
80
Note:
1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operate on the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O
Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The
ATmega325/3250/645/6450 is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only
the ST/STS/STD and LD/LDS/LDD instructions can be used.
331
2570J–AVR–11/06
Instruction Set Summary
Mnemonics
Operands
Description
Operation
Flags
#Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD
Rd, Rr
Add two Registers
Rd ← Rd + Rr
Z,C,N,V,H
ADC
Rd, Rr
Add with Carry two Registers
Rd ← Rd + Rr + C
Z,C,N,V,H
1
ADIW
Rdl,K
Add Immediate to Word
Rdh:Rdl ← Rdh:Rdl + K
Z,C,N,V,S
2
SUB
Rd, Rr
Subtract two Registers
Rd ← Rd - Rr
Z,C,N,V,H
1
SUBI
Rd, K
Subtract Constant from Register
Rd ← Rd - K
Z,C,N,V,H
1
SBC
Rd, Rr
Subtract with Carry two Registers
Rd ← Rd - Rr - C
Z,C,N,V,H
1
SBCI
Rd, K
Subtract with Carry Constant from Reg.
Rd ← Rd - K - C
Z,C,N,V,H
1
SBIW
Rdl,K
Subtract Immediate from Word
Rdh:Rdl ← Rdh:Rdl - K
Z,C,N,V,S
2
AND
Rd, Rr
Logical AND Registers
Rd ← Rd • Rr
Z,N,V
1
ANDI
Rd, K
Logical AND Register and Constant
Rd ← Rd • K
Z,N,V
1
OR
Rd, Rr
Logical OR Registers
Rd ← Rd v Rr
Z,N,V
1
ORI
Rd, K
Logical OR Register and Constant
Rd ← Rd v K
Z,N,V
1
EOR
Rd, Rr
Exclusive OR Registers
Rd ← Rd ⊕ Rr
Z,N,V
1
1
COM
Rd
One’s Complement
Rd ← 0xFF − Rd
Z,C,N,V
1
NEG
Rd
Two’s Complement
Rd ← 0x00 − Rd
Z,C,N,V,H
1
SBR
Rd,K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
1
CBR
Rd,K
Clear Bit(s) in Register
Rd ← Rd • (0xFF - K)
Z,N,V
1
INC
Rd
Increment
Rd ← Rd + 1
Z,N,V
1
DEC
Rd
Decrement
Rd ← Rd − 1
Z,N,V
1
TST
Rd
Test for Zero or Minus
Rd ← Rd • Rd
Z,N,V
1
CLR
Rd
Clear Register
Rd ← Rd ⊕ Rd
Z,N,V
1
SER
Rd
Set Register
Rd ← 0xFF
None
1
MUL
Rd, Rr
Multiply Unsigned
R1:R0 ← Rd x Rr
Z,C
2
MULS
Rd, Rr
Multiply Signed
R1:R0 ← Rd x Rr
Z,C
2
MULSU
Rd, Rr
Multiply Signed with Unsigned
R1:R0 ← Rd x Rr
Z,C
2
FMUL
Rd, Rr
Fractional Multiply Unsigned
R1:R0 ← (Rd x Rr) <<
1
R1:R0 ← (Rd x Rr) << 1
R1:R0 ← (Rd x Rr) << 1
Z,C
2
Z,C
2
Z,C
2
2
FMULS
Rd, Rr
Fractional Multiply Signed
FMULSU
Rd, Rr
Fractional Multiply Signed with Unsigned
BRANCH INSTRUCTIONS
RJMP
k
IJMP
Relative Jump
PC ← PC + k + 1
None
Indirect Jump to (Z)
PC ← Z
None
2
JMP
k
Direct Jump
PC ← k
None
3
RCALL
k
Relative Subroutine Call
PC ← PC + k + 1
None
3
Indirect Call to (Z)
PC ← Z
None
3
Direct Subroutine Call
PC ← k
None
4
RET
Subroutine Return
PC ← STACK
None
4
RETI
Interrupt Return
PC ← STACK
I
4
ICALL
CALL
k
CPSE
Rd,Rr
Compare, Skip if Equal
if (Rd = Rr) PC ← PC + 2 or 3
None
CP
Rd,Rr
Compare
Rd − Rr
Z, N,V,C,H
1
CPC
Rd,Rr
Compare with Carry
Rd − Rr − C
Z, N,V,C,H
1
CPI
Rd,K
Compare Register with Immediate
Rd − K
Z, N,V,C,H
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ← PC + 2 or 3
None
1/2/3
1/2/3
1
SBRS
Rr, b
Skip if Bit in Register is Set
if (Rr(b)=1) PC ← PC + 2 or 3
None
1/2/3
SBIC
P, b
Skip if Bit in I/O Register Cleared
if (P(b)=0) PC ← PC + 2 or 3
None
1/2/3
SBIS
P, b
Skip if Bit in I/O Register is Set
if (P(b)=1) PC ← PC + 2 or 3
None
1/2/3
BRBS
s, k
Branch if Status Flag Set
if (SREG(s) = 1) then PC←PC+k + 1
None
1/2
BRBC
s, k
Branch if Status Flag Cleared
if (SREG(s) = 0) then PC←PC+k + 1
None
1/2
BREQ
k
Branch if Equal
if (Z = 1) then PC ← PC + k + 1
None
1/2
BRNE
k
Branch if Not Equal
if (Z = 0) then PC ← PC + k + 1
None
1/2
BRCS
k
Branch if Carry Set
if (C = 1) then PC ← PC + k + 1
None
1/2
BRCC
k
Branch if Carry Cleared
if (C = 0) then PC ← PC + k + 1
None
1/2
BRSH
k
Branch if Same or Higher
if (C = 0) then PC ← PC + k + 1
None
1/2
BRLO
k
Branch if Lower
if (C = 1) then PC ← PC + k + 1
None
1/2
BRMI
k
Branch if Minus
if (N = 1) then PC ← PC + k + 1
None
1/2
BRPL
k
Branch if Plus
if (N = 0) then PC ← PC + k + 1
None
1/2
BRGE
k
Branch if Greater or Equal, Signed
if (N ⊕ V= 0) then PC ← PC + k + 1
None
1/2
BRLT
k
Branch if Less Than Zero, Signed
if (N ⊕ V= 1) then PC ← PC + k + 1
None
1/2
BRHS
k
Branch if Half Carry Flag Set
if (H = 1) then PC ← PC + k + 1
None
1/2
BRHC
k
Branch if Half Carry Flag Cleared
if (H = 0) then PC ← PC + k + 1
None
1/2
BRTS
k
Branch if T Flag Set
if (T = 1) then PC ← PC + k + 1
None
1/2
BRTC
k
Branch if T Flag Cleared
if (T = 0) then PC ← PC + k + 1
None
1/2
BRVS
k
Branch if Overflow Flag is Set
if (V = 1) then PC ← PC + k + 1
None
1/2
BRVC
k
Branch if Overflow Flag is Cleared
if (V = 0) then PC ← PC + k + 1
None
1/2
332
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Mnemonics
Operands
Description
Operation
Flags
#Clocks
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ← PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ← PC + k + 1
None
1/2
BIT AND BIT-TEST INSTRUCTIONS
SBI
P,b
Set Bit in I/O Register
I/O(P,b) ← 1
None
2
CBI
P,b
Clear Bit in I/O Register
I/O(P,b) ← 0
None
2
LSL
Rd
Logical Shift Left
Rd(n+1) ← Rd(n), Rd(0) ← 0
Z,C,N,V
1
LSR
Rd
Logical Shift Right
Rd(n) ← Rd(n+1), Rd(7) ← 0
Z,C,N,V
1
ROL
Rd
Rotate Left Through Carry
Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7)
Z,C,N,V
1
ROR
Rd
Rotate Right Through Carry
Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0)
Z,C,N,V
1
ASR
Rd
Arithmetic Shift Right
Rd(n) ← Rd(n+1), n=0..6
Z,C,N,V
1
SWAP
Rd
Swap Nibbles
Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0)
None
1
BSET
s
Flag Set
SREG(s) ← 1
SREG(s)
1
BCLR
s
Flag Clear
SREG(s) ← 0
SREG(s)
1
BST
Rr, b
Bit Store from Register to T
T ← Rr(b)
T
1
BLD
Rd, b
Bit load from T to Register
Rd(b) ← T
None
1
SEC
Set Carry
C←1
C
1
CLC
Clear Carry
C←0
C
1
SEN
Set Negative Flag
N←1
N
1
CLN
Clear Negative Flag
N←0
N
1
SEZ
Set Zero Flag
Z←1
Z
1
CLZ
Clear Zero Flag
Z←0
Z
1
SEI
Global Interrupt Enable
I←1
I
1
CLI
Global Interrupt Disable
I←0
I
1
SES
Set Signed Test Flag
S←1
S
1
CLS
Clear Signed Test Flag
S←0
S
1
SEV
Set Twos Complement Overflow.
V←1
V
1
CLV
Clear Twos Complement Overflow
V←0
V
1
SET
Set T in SREG
T←1
T
1
CLT
Clear T in SREG
T←0
T
1
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
H←1
H←0
H
H
1
1
Rd ← Rr
Rd+1:Rd ← Rr+1:Rr
None
1
None
1
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
MOVW
Rd, Rr
Copy Register Word
LDI
Rd, K
Load Immediate
Rd ← K
None
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ← X - 1, Rd ← (X)
None
LD
Rd, Y
Load Indirect
Rd ← (Y)
None
2
LD
Rd, Y+
Load Indirect and Post-Inc.
Rd ← (Y), Y ← Y + 1
None
2
LD
Rd, - Y
Load Indirect and Pre-Dec.
Y ← Y - 1, Rd ← (Y)
None
2
LDD
Rd,Y+q
Load Indirect with Displacement
Rd ← (Y + q)
None
2
LD
Rd, Z
Load Indirect
Rd ← (Z)
None
2
LD
Rd, Z+
Load Indirect and Post-Inc.
Rd ← (Z), Z ← Z+1
None
2
LD
Rd, -Z
Load Indirect and Pre-Dec.
Z ← Z - 1, Rd ← (Z)
None
2
LDD
Rd, Z+q
Load Indirect with Displacement
Rd ← (Z + q)
None
2
LDS
Rd, k
Load Direct from SRAM
Rd ← (k)
None
2
ST
X, Rr
Store Indirect
(X) ← Rr
None
2
ST
X+, Rr
Store Indirect and Post-Inc.
(X) ← Rr, X ← X + 1
None
2
ST
- X, Rr
Store Indirect and Pre-Dec.
X ← X - 1, (X) ← Rr
None
2
ST
Y, Rr
Store Indirect
(Y) ← Rr
None
2
ST
Y+, Rr
Store Indirect and Post-Inc.
(Y) ← Rr, Y ← Y + 1
None
2
ST
- Y, Rr
Store Indirect and Pre-Dec.
Y ← Y - 1, (Y) ← Rr
None
2
STD
Y+q,Rr
Store Indirect with Displacement
(Y + q) ← Rr
None
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
2
ST
Z+, Rr
Store Indirect and Post-Inc.
(Z) ← Rr, Z ← Z + 1
None
2
ST
-Z, Rr
Store Indirect and Pre-Dec.
Z ← Z - 1, (Z) ← Rr
None
2
STD
Z+q,Rr
Store Indirect with Displacement
(Z + q) ← Rr
None
2
STS
k, Rr
Store Direct to SRAM
(k) ← Rr
None
2
Load Program Memory
R0 ← (Z)
None
3
LPM
LPM
Rd, Z
Load Program Memory
Rd ← (Z)
None
3
LPM
Rd, Z+
Load Program Memory and Post-Inc
Rd ← (Z), Z ← Z+1
None
3
Store Program Memory
(Z) ← R1:R0
None
-
IN
Rd, P
In Port
Rd ← P
None
1
OUT
P, Rr
Out Port
P ← Rr
None
1
PUSH
Rr
Push Register on Stack
STACK ← Rr
None
2
SPM
333
2570J–AVR–11/06
Mnemonics
POP
Operands
Rd
Description
Pop Register from Stack
Operation
Rd ← STACK
Flags
#Clocks
None
2
MCU CONTROL INSTRUCTIONS
NOP
No Operation
None
1
SLEEP
Sleep
(see specific descr. for Sleep function)
None
1
WDR
BREAK
Watchdog Reset
Break
(see specific descr. for WDR/timer)
For On-chip Debug Only
None
None
1
N/A
334
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Ordering Information
ATmega325
Speed (MHz)(3)
8
16
Notes:
Ordering Code
Package Type(1)
1.8 - 5.5V
ATmega325V-8AI
ATmega325V-8AU(2)
ATmega325V-8MI
ATmega325V-8MU(2)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATmega325-16AI
ATmega325-16AU(2)
ATmega325-16MI
ATmega325-16MU(2)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
Power Supply
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 130 on page 293 and Figure 131 on page 294.
Package Type
64A
64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1
64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A
100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
335
2570J–AVR–11/06
ATmega3250
Speed (MHz)(3)
Power Supply
8
16
Notes:
Ordering Code
Package Type(1)
1.8 - 5.5V
ATmega3250V-8AI
ATmega3250V-8AU(2)
100A
100A
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATmega3250-16AI
ATmega3250-16AU(2)
100A
100A
Industrial
(-40°C to 85°C)
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 130 on page 293 and Figure 131 on page 294.
Package Type
64A
64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1
64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A
100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
336
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
ATmega645
Speed (MHz)(3)
8
16
Notes:
Ordering Code
Package Type(1)
1.8 - 5.5V
ATmega645V-8AI
ATmega645V-8AU(2)
ATmega645V-8MI
ATmega645V-8MU(2)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATmega645-16AI
ATmega645-16AU(2)
ATmega645-16MI
ATmega645-16MU(2)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
Power Supply
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 130 on page 293 and Figure 131 on page 294.
Package Type
64A
64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1
64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A
100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
337
2570J–AVR–11/06
ATmega6450
Speed (MHz)(3)
Power Supply
8
16
Notes:
Ordering Code
Package Type(1)
1.8 - 5.5V
ATmega6450V-8AI
ATmega6450V-8AU(2)
100A
100A
Industrial
(-40°C to 85°C)
2.7 - 5.5V
ATmega6450-16AI
ATmega6450-16AU(2)
100A
100A
Industrial
(-40°C to 85°C)
Operational Range
1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 130 on page 293 and Figure 131 on page 294.
Package Type
64A
64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1
64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A
100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
338
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Packaging Information
64A
PIN 1
B
PIN 1 IDENTIFIER
E1
e
E
D1
D
C
0˚~7˚
A1
A2
A
L
COMMON DIMENSIONS
(Unit of Measure = mm)
Notes:
1. This package conforms to JEDEC reference MS-026, Variation AEB.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10 mm maximum.
SYMBOL
MIN
NOM
MAX
A
–
–
1.20
A1
0.05
–
0.15
A2
0.95
1.00
1.05
D
15.75
16.00
16.25
D1
13.90
14.00
14.10
E
15.75
16.00
16.25
E1
13.90
14.00
14.10
B
0.30
–
0.45
C
0.09
–
0.20
L
0.45
–
0.75
e
NOTE
Note 2
Note 2
0.80 TYP
10/5/2001
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
64A, 64-lead, 14 x 14 mm Body Size, 1.0 mm Body Thickness,
0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
DRAWING NO.
REV.
64A
B
339
2570J–AVR–11/06
64M1
D
Marked Pin# 1 ID
E
C
SEATING PLANE
A1
TOP VIEW
A
K
0.08 C
L
Pin #1 Corner
D2
1
2
3
Option A
SIDE VIEW
Pin #1
Triangle
COMMON DIMENSIONS
(Unit of Measure = mm)
E2
Option B
Pin #1
Chamfer
(C 0.30)
SYMBOL
MIN
NOM
MAX
A
0.80
0.90
1.00
–
0.02
0.05
0.18
0.25
0.30
A1
b
K
Option C
b
e
Pin #1
Notch
(0.20 R)
BOTTOM VIEW
Note: 1. JEDEC Standard MO-220, (SAW Singulation) Fig. 1, VMMD.
2. Dimension and tolerance conform to ASMEY14.5M-1994.
D
8.90
9.00
9.10
D2
5.20
5.40
5.60
E
8.90
9.00
9.10
E2
5.20
5.40
5.60
e
NOTE
0.50 BSC
L
0.35
0.40
0.45
K
1.25
1.40
1.55
5/25/06
R
340
2325 Orchard Parkway
San Jose, CA 95131
TITLE
64M1, 64-pad, 9 x 9 x 1.0 mm Body, Lead Pitch 0.50 mm,
5.40 mm Exposed Pad, Micro Lead Frame Package (MLF)
DRAWING NO.
64M1
REV.
G
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
100A
PIN 1
B
PIN 1 IDENTIFIER
E1
e
E
D1
D
C
0˚~7˚
A1
A2
A
L
COMMON DIMENSIONS
(Unit of Measure = mm)
Notes:
1. This package conforms to JEDEC reference MS-026, Variation AED.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.08 mm maximum.
SYMBOL
MIN
NOM
MAX
A
–
–
1.20
A1
0.05
–
0.15
A2
0.95
1.00
1.05
D
15.75
16.00
16.25
D1
13.90
14.00
14.10
E
15.75
16.00
16.25
E1
13.90
14.00
14.10
B
0.17
–
0.27
C
0.09
–
0.20
L
0.45
–
0.75
e
NOTE
Note 2
Note 2
0.50 TYP
10/5/2001
R
2325 Orchard Parkway
San Jose, CA 95131
TITLE
100A, 100-lead, 14 x 14 mm Body Size, 1.0 mm Body Thickness,
0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
DRAWING NO.
100A
REV.
C
341
2570J–AVR–11/06
Errata
ATmega325 Rev. C
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
ATmega325 Rev. B
Not sampled.
ATmega325 Rev. A
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
ATmega3250 Rev. C
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
ATmega3250 Rev. B
Not sampled.
342
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
ATmega3250 Rev. A
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
ATmega645 Rev. A
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
ATmega6450 Rev. A
• Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/ Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2.
343
2570J–AVR–11/06
Datasheet Revision
History
Please note that the referring page numbers in this section are referring to this document. The referring revision in this section are referring to the document revision.
Rev. 2570J – 11/06
1.
2.
Updated Table 125 on page 296.
Updated note in Table 125 on page 296.
1.
2.
3.
4.
5.
6.
Updated Table 33 on page 89.
Updated Table 47 on page 94, Table 49 on page 94, Table 54 on page 121,
Table 56 on page 122, Table 59 on page 138 and Table 61 on page 139.
Updated “Fast PWM Mode” on page 112.
Updated Features in “USI – Universal Serial Interface” on page 181.
Added “Clock speed considerations.” on page 188.
Updated “Errata” on page 342.
1.
2.
3.
Updated “Calibrated Internal RC Oscillator” on page 28.
Updated “OSCCAL – Oscillator Calibration Register” on page 29.
Added Table 126 on page 297.
1.
Updated “Calibrated Internal RC Oscillator” on page 28.
1.
Updated “Errata” on page 342.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Added Addresses in Register Descriptions.
Updated number of Genearl Purpose I/O pins.
Correction of Bitnames in “Register Summary” on page 328.
Added “Resources” on page 8.
Updated “Power Management and Sleep Modes” on page 33.
Updated “Bit 0 – IVCE: Interrupt Vector Change Enable” on page 51.
Updated Introduction in “I/O-Ports” on page 58.
Updated “SPI – Serial Peripheral Interface” on page 146.
Updated “Bit 6 – ACBG: Analog Comparator Bandgap Select” on page
195.
Updated Features in “Analog to Digital Converter” on page 197.
Updated “Prescaling and Conversion Timing” on page 200.
Updated “ATmega325/3250/645/6450 Boot Loader Parameters” on page
258.
Updated “DC Characteristics” on page 291.
Rev. 2570I – 07/06
Rev. 2570H – 06/06
Rev. 2570G – 04/06
Rev. 2570F – 03/06
Rev. 2570E – 03/06
10
11.
12.
13.
344
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2570J–AVR–11/06
ATmega325/3250/645/6450
Rev. 2570D – 05/05
1.
2.
3.
4.
5.
6.
7.
8.
9.
MLF-package alternative changed to “Quad Flat No-Lead/Micro Lead
Frame Package QFN/MLF”.
Added “Pin Change Interrupt Timing” on page 53.
Updated “Signature Bytes” on page 262.
Updated Table 121 on page 277.
Added Figure 123 on page 278.
Updated Figure 92 on page 205 and Figure 116 on page 270.
Updated algorithm “Enter Programming Mode” on page 265.
Added “Supply Current of I/O modules” on page 303.
Updated “Ordering Information” on page 335.
Rev. 2570C – 11/04
1.
2.
3.
5.
6.
7.
8.
“Features (Continued)” on page 2 updated.
Table 10 on page 29 updated.
COM01:0 renamed COM0A1:0 in “8-bit Timer/Counter0 with PWM” on
page 83.
PRR-bit descripton added to “16-bit Timer/Counter1” on page 99, “SPI –
Serial Peripheral Interface” on page 146, and “USART0” on page 155.
“Part Number” on page 221 updated.
“Typical Characteristics – Preliminary Data” on page 298 updated.
“DC Characteristics” on page 291 updated.
“Alternate Functions of Port G” on page 74 updated.
1.
Updated “Ordering Information” on page 335.
1.
Initial revision.
4.
Rev. 2570B – 09/04
Rev. 2570A – 09/04
345
2570J–AVR–11/06
346
ATmega325/3250/645/6450
2570J–AVR–11/06
ATmega325/3250/645/6450
Table of Contents
Features................................................................................................ 1
Features (Continued)........................................................................... 2
Pin Configurations............................................................................... 2
Disclaimer ............................................................................................................. 3
Overview............................................................................................... 4
Block Diagram ...................................................................................................... 4
Comparison between ATmega325, ATmega3250, ATmega645 and ATmega6450
6
Pin Descriptions.................................................................................................... 6
Resources ............................................................................................ 8
About Code Examples......................................................................... 8
AVR CPU Core ..................................................................................... 9
Introduction ........................................................................................................... 9
Architectural Overview.......................................................................................... 9
ALU – Arithmetic Logic Unit................................................................................ 10
AVR Status Register........................................................................................... 11
General Purpose Register File ........................................................................... 12
Stack Pointer ...................................................................................................... 13
Instruction Execution Timing............................................................................... 14
Reset and Interrupt Handling.............................................................................. 14
AVR Memories ................................................................................... 17
In-System Reprogrammable Flash Program Memory ........................................
SRAM Data Memory...........................................................................................
EEPROM Data Memory......................................................................................
I/O Memory .........................................................................................................
17
18
19
24
System Clock and Clock Options .................................................... 25
Clock Systems and their Distribution ..................................................................
Clock Sources.....................................................................................................
Default Clock Source ..........................................................................................
Crystal Oscillator.................................................................................................
Low-frequency Crystal Oscillator ........................................................................
Calibrated Internal RC Oscillator ........................................................................
External Clock.....................................................................................................
Clock Output Buffer ............................................................................................
Timer/Counter Oscillator.....................................................................................
System Clock Prescaler......................................................................................
25
26
26
26
28
28
30
30
31
31
Power Management and Sleep Modes............................................. 33
i
2570J–AVR–11/06
Idle Mode ............................................................................................................
ADC Noise Reduction Mode...............................................................................
Power-down Mode..............................................................................................
Power-save Mode...............................................................................................
Standby Mode.....................................................................................................
Power Reduction Register ..................................................................................
Minimizing Power Consumption .........................................................................
Register Description ...........................................................................................
34
34
34
34
35
35
35
37
System Control and Reset ................................................................ 39
Internal Voltage Reference ................................................................................. 44
Watchdog Timer ................................................................................................. 44
Timed Sequences for Changing the Configuration of the Watchdog Timer ....... 47
Interrupts ............................................................................................ 48
Interrupt Vectors in ATmega325/3250/645/6450................................................ 48
External Interrupts............................................................................. 53
Pin Change Interrupt Timing............................................................................... 53
I/O-Ports.............................................................................................. 58
Introduction .........................................................................................................
Ports as General Digital I/O ................................................................................
Alternate Port Functions .....................................................................................
Register Description for I/O-Ports.......................................................................
58
59
64
80
8-bit Timer/Counter0 with PWM........................................................ 83
Overview.............................................................................................................
Timer/Counter Clock Sources.............................................................................
Counter Unit........................................................................................................
Output Compare Unit..........................................................................................
Compare Match Output Unit ...............................................................................
Modes of Operation ............................................................................................
Timer/Counter Timing Diagrams.........................................................................
8-bit Timer/Counter Register Description ...........................................................
83
84
84
85
86
88
92
93
Timer/Counter0 and Timer/Counter1 Prescalers ............................ 97
16-bit Timer/Counter1........................................................................ 99
Overview............................................................................................................. 99
Accessing 16-bit Registers ............................................................................... 102
Timer/Counter Clock Sources........................................................................... 105
Counter Unit...................................................................................................... 105
Input Capture Unit............................................................................................. 106
Output Compare Units ...................................................................................... 108
Compare Match Output Unit ............................................................................. 110
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ATmega325/3250/645/6450
Modes of Operation .......................................................................................... 111
Timer/Counter Timing Diagrams....................................................................... 118
16-bit Timer/Counter Register Description ....................................................... 120
8-bit Timer/Counter2 with PWM and Asynchronous Operation .. 127
Overview...........................................................................................................
Timer/Counter Clock Sources...........................................................................
Counter Unit......................................................................................................
Output Compare Unit........................................................................................
Compare Match Output Unit .............................................................................
Modes of Operation ..........................................................................................
Timer/Counter Timing Diagrams.......................................................................
8-bit Timer/Counter Register Description .........................................................
Asynchronous operation of the Timer/Counter .................................................
Timer/Counter Prescaler...................................................................................
127
128
128
129
131
132
136
138
141
144
SPI – Serial Peripheral Interface..................................................... 146
Overview........................................................................................................... 146
SS Pin Functionality.......................................................................................... 151
Data Modes ...................................................................................................... 154
USART0 ............................................................................................ 155
Overview...........................................................................................................
Clock Generation ..............................................................................................
Frame Formats .................................................................................................
USART Initialization..........................................................................................
Data Transmission – The USART Transmitter .................................................
Data Reception – The USART Receiver ..........................................................
Asynchronous Data Reception .........................................................................
Multi-processor Communication Mode .............................................................
USART Register Description ............................................................................
Examples of Baud Rate Setting........................................................................
155
156
159
160
162
165
168
172
173
177
USI – Universal Serial Interface...................................................... 181
Overview...........................................................................................................
Functional Descriptions ....................................................................................
Alternative USI Usage ......................................................................................
USI Register Descriptions.................................................................................
181
182
188
188
Analog Comparator ......................................................................... 194
Analog Comparator Multiplexed Input .............................................................. 196
Analog to Digital Converter ............................................................ 197
Features............................................................................................................ 197
Operation .......................................................................................................... 198
Starting a Conversion ....................................................................................... 199
iii
2570J–AVR–11/06
Prescaling and Conversion Timing ...................................................................
Changing Channel or Reference Selection ......................................................
ADC Noise Canceler.........................................................................................
ADC Conversion Result....................................................................................
200
202
203
207
JTAG Interface and On-chip Debug System ................................. 214
Overview...........................................................................................................
TAP – Test Access Port....................................................................................
TAP Controller ..................................................................................................
Using the Boundary-scan Chain .......................................................................
Using the On-chip Debug System ....................................................................
On-chip Debug Specific JTAG Instructions ......................................................
On-chip Debug Related Register in I/O Memory ..............................................
Using the JTAG Programming Capabilities ......................................................
Bibliography ......................................................................................................
214
214
216
217
217
218
219
219
219
IEEE 1149.1 (JTAG) Boundary-scan .............................................. 220
Features............................................................................................................
System Overview..............................................................................................
Data Registers ..................................................................................................
Boundary-scan Specific JTAG Instructions ......................................................
Boundary-scan Related Register in I/O Memory ..............................................
Boundary-scan Chain .......................................................................................
Boundary-scan Order .......................................................................................
Boundary-scan Description Language Files .....................................................
220
220
220
222
223
224
233
245
Boot Loader Support – Read-While-Write Self-Programming ..... 246
Boot Loader Features .......................................................................................
Application and Boot Loader Flash Sections ....................................................
Read-While-Write and No Read-While-Write Flash Sections...........................
Boot Loader Lock Bits.......................................................................................
Entering the Boot Loader Program ...................................................................
Addressing the Flash During Self-Programming ..............................................
Self-Programming the Flash .............................................................................
246
246
246
248
249
251
252
Memory Programming..................................................................... 259
Program And Data Memory Lock Bits ..............................................................
Fuse Bits...........................................................................................................
Signature Bytes ................................................................................................
Calibration Byte ................................................................................................
Parallel Programming Parameters, Pin Mapping, and Commands ..................
Parallel Programming .......................................................................................
Serial Downloading...........................................................................................
Programming via the JTAG Interface ...............................................................
259
260
262
262
262
265
274
279
Electrical Characteristics................................................................ 291
iv
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ATmega325/3250/645/6450
Absolute Maximum Ratings*............................................................................. 291
DC Characteristics............................................................................................ 291
External Clock Drive Waveforms ...................................................................... 293
External Clock Drive ......................................................................................... 293
Speed vs. VCC ................................................................................................................................................ 293
SPI Timing Characteristics ............................................................................... 294
ADC Characteristics – Preliminary Data........................................................... 296
Calibrated Internal RC Oscillator Accuracy ...................................................... 297
Typical Characteristics – Preliminary Data .................................. 298
Register Summary ........................................................................... 328
Instruction Set Summary ................................................................ 332
Ordering Information....................................................................... 335
ATmega325 ......................................................................................................
ATmega3250 ....................................................................................................
ATmega645 ......................................................................................................
ATmega6450 ....................................................................................................
335
336
337
338
Packaging Information .................................................................... 339
64A ................................................................................................................... 339
64M1................................................................................................................. 340
100A ................................................................................................................. 341
Errata ................................................................................................ 342
ATmega325 Rev. C ..........................................................................................
ATmega325 Rev. B ..........................................................................................
ATmega325 Rev. A ..........................................................................................
ATmega3250 Rev. C ........................................................................................
ATmega3250 Rev. B ........................................................................................
ATmega3250 Rev. A ........................................................................................
ATmega645 Rev. A ..........................................................................................
ATmega6450 Rev. A ........................................................................................
342
342
342
342
342
343
343
343
Datasheet Revision History ............................................................ 344
Rev. 2570J – 11/06...........................................................................................
Rev. 2570I – 07/06 ...........................................................................................
Rev. 2570H – 06/06..........................................................................................
Rev. 2570G – 04/06..........................................................................................
Rev. 2570F – 03/06 ..........................................................................................
Rev. 2570E – 03/06 ..........................................................................................
Rev. 2570D – 05/05..........................................................................................
Rev. 2570C – 11/04..........................................................................................
Rev. 2570B – 09/04 ..........................................................................................
344
344
344
344
344
344
345
345
345
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2570J–AVR–11/06
Rev. 2570A – 09/04 .......................................................................................... 345
Table of Contents ................................................................................. i
vi
ATmega325/3250/645/6450
2570J–AVR–11/06
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2570J–AVR–11/06