ATmega323(L) - Mature

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 8 MIPS Throughput at 8 MHz
– On-chip 2-cycle Multiplier
Non-volatile Program and Data Memories
– 32K Bytes of In-System Self-programmable Flash
Endurance: 1,000 Write/Erase Cycles
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
– 1K Byte EEPROM
Endurance: 100,000 Write/Erase Cycles
– 2K Bytes Internal SRAM
– Programming Lock for Software Security
JTAG (IEEE Std. 1149.1 Compliant) Interface
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
– Boundary-Scan Capabilities According to the JTAG Standard
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
– Byte-oriented Two-wire Serial Interface
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby
and Extended Standby
I/O and Packages
– 32 Programmable I/O Lines
– 40-pin PDIP and 44-lead TQFP
Operating Voltages
– 2.7 - 5.5V (ATmega323L)
– 4.0 - 5.5V (ATmega323)
Speed Grades
– 0 - 4 MHz (ATmega323L)
– 0 - 8 MHz (ATmega323)
8-bit
Microcontroller
with 32K Bytes
of In-System
Programmable
Flash
ATmega323
ATmega323L
Not recommended
for new designs.
Use ATmega32.
1457G–AVR–09/03
Pin Configurations
PDIP
(XCK/T0) PB0
(T1) PB1
(INT2/AIN0) PB2
(OC0/AIN1) PB3
(SS) PB4
(MOSI) PB5
(MISO) PB6
(SCK) PB7
RESET
VCC
GND
XTAL2
XTAL1
(RXD) PD0
(TXD) PD1
(INT0) PD2
(INT1) PD3
(OC1B) PD4
(OC1A) PD5
(ICP) PD6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
PA0 (ADC0)
PA1 (ADC1)
PA2 (ADC2)
PA3 (ADC3)
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AGND
AVCC
PC7 (TOSC2)
PC6 (TOSC1)
PC5 (TDI)
PC4 (TDO)
PC3 (TMS)
PC2 (TCK)
PC1 (SDA)
PC0 (SCL)
PD7 (OC2)
44
43
42
41
40
39
38
37
36
35
34
PB4 (SS)
PB3 (AIN1/OC0)
PB2 ((AIN0/INT2)
PB1 (T1)
PB0 (XCK/T0)
GND
VCC
PA0 (ADC0)
PA1 (ADC1)
PA2 (ADC2)
PA3 (ADC3)
TQFP
33
32
31
30
29
28
27
26
25
24
23
1
2
3
4
5
6
7
8
9
10
11
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AGND
AVCC
PC7 (TOSC2)
PC6 (TOSC1)
PC5 (TDI)
PC4 (TDO)
(INT1) PD3
(OC1B) PD4
(OC1A) PD5
(ICP) PD6
(OC2) PD7
VCC
GND
(SCL) PC0
(SDA) PC1
(TCK) PC2
(TMS) PC3
12
13
14
15
16
17
18
19
20
21
22
(MOSI) PB5
(MISO) PB6
(SCK) PB7
RESET
VCC
GND
XTAL2
XTAL1
(RXD) PD0
(TXD) PD1
(INT0) PD2
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Overview
The ATmega323 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 ATmega323 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.
Block Diagram
Figure 1. Block Diagram
PA0 - PA7
PC0 - PC7
PORTA DRIVERS
PORTC DRIVERS
VCC
GND
DATA DIR.
REG. PORTA
DATA REGISTER
PORTA
DATA REGISTER
PORTC
DATA DIR.
REG. PORTC
8-BIT DATA BUS
AVCC
ANALOG MUX
JTAG
INTERFACE
ADC
AGND
AREF
INTERNAL
REFERENCE
2-WIRE SERIAL
INTERFACE
OSCILLATOR
INTERNAL
OSCILLATOR
OSCILLATOR
TIMING AND
CONTROL
PROGRAM
COUNTER
STACK
POINTER
WATCHDOG
TIMER
PROGRAM
FLASH
SRAM
MCU CONTROL
REGISTER
INSTRUCTION
REGISTER
GENERAL
PURPOSE
REGISTERS
TIMER/
COUNTERS
X
Y
Z
INTERRUPT
UNIT
ALU
EEPROM
STATUS
REGISTER
INTERNAL
CALIBRATED
OSCILLATOR
SPI
USART
INSTRUCTION
DECODER
CONTROL
LINES
ANALOG
COMPARATOR
+
-
PROGRAMMING
LOGIC
DATA REGISTER
PORTB
DATA DIR.
REG. PORTB
DATA REGISTER
PORTD
XTAL1
XTAL2
RESET
DATA DIR.
REG. PORTD
PORTB DRIVERS
PORTD DRIVERS
PB0 - PB7
PD0 - PD7
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1457G–AVR–09/03
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 ATmega323 provides the following features: 32K bytes of In-System Programmable
Flash, 1K bytes EEPROM, 2K bytes SRAM, 32 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, a byte oriented Two-wire Serial
Interface, an 8-channel, 10-bit ADC, a programmable Watchdog Timer with internal
Oscillator, an SPI serial port, and six 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 continues 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. In Extended Standby mode,
both the main Oscillator and the asynchronous timer continue to run.
The device is manufactured using Atmel’s high-density non-volatile memory technology.
The On-chip ISP Flash allows the Program memory to be re-programmed 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. By combining an 8-bit RISC CPU with In-System Programmable Flash on a monolithic chip, the
Atmel ATmega323 is a powerful microcontroller that provides a highly flexible and cost
effective solution to many embedded control applications.
The ATmega323 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.
Pin Descriptions
VCC
Digital supply voltage.
GND
Digital ground.
Port A (PA7..PA0)
Port A serves as the analog inputs to the A/D Converter.
Port A 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 A output
buffers can sink 20 mA and can drive LED displays directly. When pins PA0 to PA7 are
used as inputs and are externally pulled low, they will source current if the internal pullup resistors are activated. The Port A pins are tri-stated when a reset condition
becomes active, even if the clock is not running.
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
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 can sink 20 mA. 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 also serves the functions of various special features of the ATmega323 as listed
on page 139.
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 can sink 20 mA. 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 C also serves the functions of the JTAG interface and other special features of the
ATmega323 as listed on page 146. If the JTAG interface is enabled, the pull-up resistors
on pins PC5 (TDI), PC3 (TMS) and PC2 (TCK) will be activated even if a Reset occurs.
Port D (PD7..PD0)
Port D is an 8-bit bidirectional I/O port with internal pull-up resistors (selected for each
bit). The Port D output buffers can sink 20 mA. 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 ATmega323 as listed
on page 151.
RESET
Reset input. A low level on this pin for more than 500 ns will generate a Reset, even if
the clock is not running. 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 A 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. See page 127 for details on operation of the
ADC.
AREF
AREF is the analog reference pin for the A/D Converter. For ADC operations, a voltage
in the range 2.56V to AVCC can be applied to this pin.
AGND
Analog ground. If the board has a separate analog ground plane, this pin should be connected to this ground plane. Otherwise, connect to GND.
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1457G–AVR–09/03
Clock Options
The device has the following clock source options, selectable by Flash Fuse bits as
shown:
Table 1. Device Clocking Options Select(1)
Device Clocking Option
CKSEL3..0
External Crystal/Ceramic Resonator
1111 - 1010
External Low-frequency Crystal
1001 - 1000
External RC Oscillator
0111 - 0101
Internal RC Oscillator
0100 - 0010
External Clock
0001 - 0000
Note:
1. “1” means unprogrammed, “0” means programmed.
The various choices for each clocking option give different start-up times as shown in
Table 6 on page 27.
Internal RC Oscillator
The internal RC Oscillator option is an On-chip Oscillator running at a fixed frequency of
nominally 1 MHz. If selected, the device can operate with no external components. See
“Calibrated Internal RC Oscillator” on page 41 for information on calibrating this
Oscillator.
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 2. Either a quartz
crystal or a ceramic resonator may be used.
Figure 2. Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in
Figure 3.
Figure 3. External Clock Drive Configuration
External RC Oscillator
For timing insensitive applications, the external RC configuration shown in Figure 4 can
be used. For details on how to choose R and C, see Table 73 on page 215.
Figure 4. External RC Configuration
VCC
R
NC
XTAL2
XTAL1
C
GND
Timer Oscillator
For the Timer Oscillator pins, PC6(TOSC1) and PC7(TOSC2), the crystal is connected
directly between the pins. No external capacitors are needed. The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external clock source to
PC6(TOSC1) is not recommended.
7
1457G–AVR–09/03
Architectural
Overview
The fast-access Register File concept contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This means that during one single clock
cycle, one Arithmetic Logic Unit (ALU) operation is executed. Two operands are output
from the Register File, 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-bits indirect address register pointers for
Data Space addressing – enabling efficient address calculations. One of the three
address pointers is also used as the address pointer for look up tables in Flash Program
memory. These added function registers are the 16-bits X-, Y-, and Z-register.
The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations are also executed in the ALU. Figure 5
shows the ATmega323 AVR Enhanced RISC microcontroller architecture.
In addition to the register operation, the conventional memory addressing modes can be
used on the Register File as well. This is enabled by the fact that the Register File is
assigned the 32 lowest Data Space addresses ($00 - $1F), allowing them to be
accessed as though they were ordinary memory locations.
The I/O Memory space contains 64 addresses for CPU peripheral functions as Control
Registers, Timer/Counters, A/D Converters, 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, $20 - $5F.
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 5. The ATmega323 AVR Enhanced RISC Architecture
Data Bus 8-bit
Interrupt
Unit
16K X 16
Program
Memory
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
Control Lines
Direct Addressing
Instruction
Decoder
Indirect Addressing
Instruction
Register
ALU
SPI
Unit
Serial
USART
Serial
TWI Bus
8-bit
Timer/Counter
with PWM
16-bit
Timer/Counter
with PWM
2K x 8
Data
SRAM
1K x 8
EEPROM
32
I/O Lines
8-bit
Timer/Counter
with PWM
Watchdog
Timer
A/D Converter
MUX and Gain
Analog
Comparator
The AVR uses a Harvard architecture concept – with separate memories and buses for
Program and Data. The Program memory is 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 In-System Reprogrammable Flash memory.
With the jump and call instructions, the whole 16K address space is directly accessed.
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 (512
to 4K bytes, see page 177) 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 is allowed only 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 12-bit Stack Pointer SP is read/write accessible in the
I/O space.
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1457G–AVR–09/03
The 2K bytes data SRAM can be easily 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.
Figure 6. Memory Maps
Program Memory
$0000
Application Flash Section
Boot Flash Section
$3FFF
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The General Purpose
Register File
Figure 7 shows the structure of the 32 general purpose working registers in the CPU.
Figure 7. AVR CPU General Purpose Working Registers
7
0
Addr.
R0
$00
R1
$01
R2
$02
…
R13
$0D
General
R14
$0E
Purpose
R15
$0F
Working
R16
$10
Registers
R17
$11
…
R26
$1A
X-register Low Byte
R27
$1B
X-register High Byte
R28
$1C
Y-register Low Byte
R29
$1D
Y-register High Byte
R30
$1E
Z-register Low Byte
R31
$1F
Z-register High Byte
Most register operating instructions in the instruction set have direct access to all registers, and most of them are single cycle instructions.
As shown in Figure 7, 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-registers can be set to index any
register in the file.
The X-register, Y-register, and
Z-register
The registers R26..R31 have some added functions to their general purpose usage.
These registers are address pointers for indirect addressing of the Data Space. The
three indirect address registers X, Y, and Z are defined as:
Figure 8. The X-, Y-, and Z-registers
15
X - register
XH
70
XL
0
R27 ($1B)
15
Y - register
YH
70
15
70
R31 ($1F)
7
0
R26 ($1A)
YL
0
R29 ($1D)
Z - register
0
0
7
0
R28 ($1C)
ZH
ZL
0
7
0
0
R30 ($1E)
In the different addressing modes these address registers have functions as fixed displacement, automatic increment and decrement (see the descriptions for the different
instructions).
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1457G–AVR–09/03
The ALU – Arithmetic
Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general
purpose working registers. Within a single clock cycle, ALU operations between registers in the Register File are executed. The ALU operations are divided into three main
categories – arithmetic, logical, and bit-functions. ATmega323 also provides a powerful
multiplier supporting both signed/unsigned multiplication and fractional format. See the
“Instruction Set” section for a detailed description.
The In-System
Reprogrammable Flash
Program Memory
The ATmega323 contains 32K bytes On-chip In-System Reprogrammable Flash memory for program storage. Since all instructions are 16- or 32-bit words, the Flash is
organized as 16K x 16. The Flash Program memory space is divided in two sections,
Boot Program section and Application Program section.
The Flash memory has an endurance of at least 1,000 write/erase cycles. The
ATmega323 Program Counter (PC) is 14 bits wide, thus addressing the 16K Program
memory locations. The operation of Boot Program section and associated Boot Lock
bits for software protection are described in detail on page 177. See page 197 for a
detailed description on Flash data serial downloading using the SPI pins. See page 202
for details on serial downloading using the JTAG Interface.
Constant tables can be allocated within the entire Program memory address space (see
the LPM – Load Program memory instruction description).
See also page 13 for the different Program memory addressing modes.
The SRAM Data Memory
Figure 9 shows how the ATmega323 SRAM Memory is organized.
The lower 2,144 Data memory locations address the Register File, the I/O Memory, and
the internal data SRAM. The first 96 locations address the Register File + I/O Memory,
and the next 2,048 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 features a 63 address locations reach 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 and incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 2,048 bytes of
internal data SRAM in the ATmega323 are all accessible through all these addressing
modes.
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 9. SRAM Organization
Register File
Data Address Space
R0
R1
R2
...
$0000
$0001
$0002
...
R29
R30
R31
I/O Registers
$00
$01
$02
...
$001D
$001E
$001F
$3D
$3E
$3F
$005D
$005E
$005F
Internal SRAM
$0060
$0061
...
$0020
$0021
$0022
...
$085E
$085F
The Program and Data
Addressing Modes
The ATmega323 AVR Enhanced RISC microcontroller supports powerful and efficient
addressing modes for access to the Program memory (Flash) and Data memory
(SRAM, Register File, and I/O Memory). This section describes the different addressing
modes supported by the AVR architecture. In the figures, OP means the operation code
part of the instruction word. To simplify, not all figures show the exact location of the
addressing bits.
Register Direct, Single
Register Rd
Figure 10. Direct Single Register Addressing
The operand is contained in register d (Rd).
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1457G–AVR–09/03
Register Direct, Two Registers
Rd and Rr
Figure 11. Direct Register Addressing, Two Registers
Operands are contained in register r (Rr) and d (Rd). The result is stored in register d
(Rd).
I/O Direct
Figure 12. I/O Direct Addressing
Operand address is contained in 6-bits of the instruction word. n is the destination or
source register address.
Data Direct
Figure 13. Direct Data Addressing
Data Space
20 19
31
OP
16
$0000
Rr/Rd
16 LSBs
15
0
$085F
A 16-bit Data Address is contained in the 16 LSBs of a two-word instruction. Rd/Rr
specify the destination or source register.
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Data Indirect with
Displacement
Figure 14. Data Indirect with Displacement
Data Space
$0000
15
0
Y OR Z - REGISTER
15
10
OP
6 5
n
0
a
$085F
Operand address is the result of the Y- or Z-register contents added to the address contained in 6 bits of the instruction word.
Data Indirect
Figure 15. Data Indirect Addressing
Data Space
$0000
15
0
X, Y OR Z - REGISTER
$085F
Operand address is the contents of the X-, Y-, or the Z-register.
Data Indirect with Pre-decrement
Figure 16. Data Indirect Addressing With Pre-decrement
Data Space
$0000
15
0
X, Y OR Z - REGISTER
-1
$085F
The X-, Y-, or the Z-register is decremented before the operation. Operand address is
the decremented contents of the X-, Y-, or the Z-register.
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1457G–AVR–09/03
Data Indirect with Postincrement
Figure 17. Data Indirect Addressing With Post-increment
Data Space
$0000
15
0
X, Y OR Z - REGISTER
1
$085F
The X-, Y-, or the Z-register is incremented after the operation. Operand address is the
content of the X-, Y-, or the Z-register prior to incrementing.
Constant Addressing Using
Figure 18. Code Memory Constant Addressing
the LPM and SPM Instructions
$3FFF
Constant byte address is specified by the Z-register contents. The 15 MSBs select word
address (0 - 16K). For LPM, the LSB selects Low Byte if cleared (LSB = 0) or High Byte
if set (LSB = 1). For SPM, the LSB should be cleared.
Indirect Program Addressing,
IJMP and ICALL
Figure 19. Indirect Program Memory Addressing
$3FFF
Program execution continues at address contained by the Z-register (i.e., the PC is
loaded with the contents of the Z-register).
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ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Relative Program Addressing,
RJMP and RCALL
Figure 20. Relative Program Memory Addressing
1
$3FFF
Program execution continues at address PC + k + 1. The relative address k is from –
2048 to 2047.
The EEPROM Data
Memory
The ATmega323 contains 1K 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 on page 66 specifying the EEPROM Address Registers, the
EEPROM Data Register, and the EEPROM Control Register.
For SPI data downloading of the EEPROM, see page 197 for a detailed description.
Memory Access Times
and Instruction
Execution Timing
This section describes the general access timing concepts for instruction execution and
internal memory access.
The AVR CPU is driven by the System Clock Ø, directly generated from the selected
clock source for the chip. No internal clock division is used.
Figure 21 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 21. The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
System Clock Ø
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 22 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.
17
1457G–AVR–09/03
Figure 22. Single Cycle ALU Operation
T1
T2
T3
T4
System Clock Ø
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
The internal data SRAM access is performed in two System Clock cycles as described
in Figure 23.
Figure 23. On-chip Data SRAM Access Cycles
T1
T2
T3
T4
System Clock Ø
Address
Prev. Address
Address
Write
Data
WR
Read
Data
RD
I/O Memory
The I/O space definition of the ATmega323 is shown in Table 2.
Table 2. ATmega323 I/O Space
18
I/O Address (SRAM
Address)
Name
Function
$3F ($5F)
SREG
Status Register
$3E ($5E)
SPH
Stack Pointer High
$3D ($5D)
SPL
Stack Pointer Low
$3C ($3C)
OCR0
Timer/Counter0 Output Compare Register
$3B ($5B)
GICR
General Interrupt Control Register
$3A ($5A)
GIFR
General Interrupt Flag Register
$39 ($59)
TIMSK
Timer/Counter Interrupt Mask Register
$38 ($58)
TIFR
Timer/Counter Interrupt Flag Register
$37 ($57)
SPMCR
SPM Control Register
$36 ($56)
TWCR
Two-wire Serial Interface Control Register
$35 ($55)
MCUCR
MCU general Control Register
$34 ($54)
MCUCSR
MCU general Control and Status Register
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 2. ATmega323 I/O Space (Continued)
I/O Address (SRAM
Address)
Name
Function
$33 ($53)
TCCR0
Timer/Counter0 Control Register
$32 ($52)
TCNT0
Timer/Counter0 (8-bit)
OSCCAL
Oscillator Calibration Register
OCDR
On-chip Debug Register
$30 ($50)
SFIOR
Special Function I/O Register
$2F ($4F)
TCCR1A
Timer/Counter1 Control Register A
$2E ($4E)
TCCR1B
Timer/Counter1 Control Register B
$2D ($4D)
TCNT1H
Timer/Counter1 High Byte
$2C ($4C)
TCNT1L
Timer/Counter1 Low Byte
$2B ($4B)
OCR1AH
Timer/Counter1 Output Compare Register A High Byte
$2A ($4A)
OCR1AL
Timer/Counter1 Output Compare Register A Low Byte
$29 ($49)
OCR1BH
Timer/Counter1 Output Compare Register B High Byte
$28 ($48)
OCR1BL
Timer/Counter1 Output Compare Register B Low Byte
$27 ($47)
ICR1H
T/C 1 Input Capture Register High Byte
$26 ($46)
ICR1L
T/C 1 Input Capture Register Low Byte
$25 ($45)
TCCR2
Timer/Counter2 Control Register
$24 ($44)
TCNT2
Timer/Counter2 (8-bit)
$23 ($43)
OCR2
Timer/Counter2 Output Compare Register
$22 ($42)
ASSR
Asynchronous Mode Status Register
$21 ($41)
WDTCR
Watchdog Timer Control Register
UBRRH
USART Baud Rate Register High Byte
UCSRC
USART Control and Status Register C
$1F ($3F)
EEARH
EEPROM Address Register High Byte
$1E ($3E)
EEARL
EEPROM Address Register Low Byte
$1D ($3D)
EEDR
EEPROM Data Register
$1C ($3C)
EECR
EEPROM Control Register
$1B ($3B)
PORTA
Data Register, Port A
$1A ($3A)
DDRA
Data Direction Register, Port A
$19 ($39)
PINA
Input Pins, Port A
$18 ($38)
PORTB
Data Register, Port B
$17 ($37)
DDRB
Data Direction Register, Port B
$16 ($36)
PINB
Input Pins, Port B
$15 ($35)
PORTC
Data Register, Port C
$14 ($34)
DDRC
Data Direction Register, Port C
$13 ($33)
PINC
Input Pins, Port C
$31 ($51)(1)
$20 ($40)(2)
19
1457G–AVR–09/03
Table 2. ATmega323 I/O Space (Continued)
I/O Address (SRAM
Address)
Name
Function
$12 ($32)
PORTD
Data Register, Port D
$11 ($31)
DDRD
Data Direction Register, Port D
$10 ($30)
PIND
Input Pins, Port D
$0F ($2F)
SPDR
SPI I/O Data Register
$0E ($2E)
SPSR
SPI Status Register
$0D ($2D)
SPCR
SPI Control Register
$0C ($2C)
UDR
USART I/O Data Register
$0B ($2B)
UCSRA
USART Control and Status Register A
$0A ($2A)
UCSRB
USART Control and Status Register B
$09 ($29)
UBRRL
USART Baud Rate Register Low Byte
$08 ($28)
ACSR
Analog Comparator Control and Status Register
$07 ($27)
ADMUX
ADC Multiplexer Select Register
$06 ($26)
ADCSR
ADC Control and Status Register
$05 ($25)
ADCH
ADC Data Register High
$04 ($24)
ADCL
ADC Data Register Low
$03 ($23)
TWDR
Two-wire Serial Interface Data Register
$02 ($22)
TWAR
Two-wire Serial Interface (Slave) Address Register
$01 ($21)
TWSR
Two-wire Serial Interface Status Register
$00 ($20)
TWBR
Two-wire Serial Interface Bit Rate Register
Notes:
1. When the OCDEN Fuse is unprogrammed, the OSCCAL Register is always
accessed on this address. Refer to the debugger specific documentation for details
on how to use the OCDR Register.
2. Refer to the USART description for details on how to access UBRRH and UCSRC.
All ATmega323 I/Os and peripherals are placed in the I/O space. The I/O locations are
accessed by the IN and OUT instructions, transferring data between the 32 general purpose working registers and the I/O space. I/O Registers within the address range $00 $1F 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 chapter for more details. When using the I/O specific commands IN
and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O Registers as
SRAM, $20 must be added to these addresses. All I/O Register addresses throughout
this document are shown with the SRAM address in parentheses.
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 the CBI
and SBI instructions will operate on all bits in the I/O Register, writing a one back into
any flag read as set, thus clearing the flag. The CBI and SBI instructions work with registers $00 to $1F only.
The I/O and Peripherals Control Registers are explained in the following sections.
20
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The Status Register – SREG
The AVR Status Register – SREG – at I/O space location $3F ($5F) is defined as:
Bit
7
6
5
4
3
2
1
0
$3F ($5F)
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 (one) 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 (zero), 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.
• Bit 6 – T: Bit Copy Storage
The Bit Copy Instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source
and 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. 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.
Note that the Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt routine. This must be handled by
software.
21
1457G–AVR–09/03
The Stack Pointer – SP
The ATmega323 Stack Pointer is implemented as two 8-bit registers in the I/O space
locations $3E ($5E) and $3D ($5D). As the ATmega323 Data memory has $860 locations, 12 bits are used.
Bit
15
14
13
12
11
10
9
8
$3E ($5E)
–
–
–
–
SP11
SP10
SP9
SP8
SPH
$3D ($5D)
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
7
6
5
4
3
2
1
0
Read/Write
Initial Value
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
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 $60. 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 and 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.
Reset and Interrupt
Handling
The ATmega323 provides nineteen 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 set (one)
together with the I-bit in the Status Register in order to enable the interrupt. Depending
on the Program Counter value, interrupts may be disabled when Boot Lock bits BLB02
or BLB12 are set. See the section “Boot Loader Support” on page 177 for details
The lowest addresses in the Program memory space are automatically defined as the
Reset and Interrupt Vectors. The complete list of vectors is shown in Table 3. 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, etc. The Interrupt Vectors can be moved to the start of the boot
Flash section by setting the IVSEL bit in the General Interrupt Control Register (GICR).
See the GICR description on page 33 for details..
Table 3. Reset and Interrupt Vectors
22
Vector No.
Program Address(2)
Source
Interrupt Definition
1
$000(1)
RESET
External Pin, Power-on Reset,
Brown-out Reset and Watchdog
Reset
2
$002
INT0
External Interrupt Request 0
3
$004
INT1
External Interrupt Request 1
4
$006
INT2
External Interrupt Request 2
5
$008
TIMER2 COMP
Timer/Counter2 Compare Match
6
$00A
TIMER2 OVF
Timer/Counter2 Overflow
7
$00C
TIMER1 CAPT
Timer/Counter1 Capture Event
8
$00E
TIMER1 COMPA
Timer/Counter1 Compare Match A
9
$010
TIMER1 COMPB
Timer/Counter1 Compare Match B
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 3. Reset and Interrupt Vectors (Continued)
Vector No.
Program Address(2)
10
Source
Interrupt Definition
$012
TIMER1 OVF
Timer/Counter1 Overflow
11
$014
TIMER0 COMP
Timer/Counter0 Compare Match
12
$016
TIMER0 OVF
Timer/Counter0 Overflow
13
$018
SPI, STC
Serial Transfer Complete
14
$01A
USART, RXC
USART, Rx Complete
15
$01C
USART, UDRE
USART Data Register Empty
16
$01E
USART, TXC
USART, Tx Complete
17
$020
ADC
ADC Conversion Complete
18
$022
EE_RDY
EEPROM Ready
19
$024
ANA_COMP
Analog Comparator
20
$026
TWSI
Two-wire Serial Interface
Notes:
1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader
address at reset, see “Boot Loader Support” on page 177.
2. When the IVSEL bit in GICR is set, Interrupt Vectors will be moved to the start of the
boot Flash section. The address of each Interrupt Vector will then be address in this
table plus the start address of the boot Flash section.
Table 4 shows Reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings.
Table 4. Reset and Interrupt Vectors Placement
BOOTRST
IVSEL
0
Note:
Reset address
Interrupt Vectors Start Address
0
$0000
$0002
0
1
$0000
Boot Reset Address + $0002
1
0
Boot Reset Address
$0002
1
1
Boot Reset Address
Boot Reset Address + $0002
The Boot Reset Address is shown in Table 59 on page 177.
The most typical and general program setup for the Reset and Interrupt Vector
Addresses in ATmega323 is:
Address
Labels Code
Comments
$000
jmp
RESET
; Reset Handler
$002
jmp
EXT_INT0
; IRQ0 Handler
$004
jmp
EXT_INT1
; IRQ1 Handler
$006
jmp
EXT_INT2
; IRQ2 Handler
$008
jmp
TIM2_COMP
; Timer2 Compare Handler
$00a
jmp
TIM2_OVF
; Timer2 Overflow Handler
$00c
jmp
TIM1_CAPT
; Timer1 Capture Handler
$00e
jmp
TIM1_COMPA ; Timer1 CompareA Handler
$010
jmp
TIM1_COMPB ; Timer1 CompareB Handler
$012
jmp
TIM1_OVF
; Timer1 Overflow Handler
$014
jmp
TIM0_COMP
; Timer0 Compare Handler
$016
jmp
TIM0_OVF
; Timer0 Overflow Handler
23
1457G–AVR–09/03
$018
jmp
SPI_STC;
; SPI Transfer Complete Handler
$01a
jmp
USART_RXC
; USART RX Complete Handler
$01c
jmp
USART_UDRE ; UDR Empty Handler
$01e
jmp
USART_TXC
$020
jmp
ADC
; ADC Conversion Complete Interrupt Handler
$022
jmp
EE_RDY
; EEPROM Ready Handler
$024
jmp
ANA_COMP
; Analog Comparator Handler
$026
Handler
jmp
TWSI
; Two-wire Serial Interface Interrupt
; USART TX Complete Handler
;
$028
MAIN: ldi
$029
out
SPH,r16
$02a
ldi
r16,low(RAMEND)
$02b
out
SPL,r16
$02c
r16,high(RAMEND); Main program start
<instr>
...
...
; Set Stack Pointer to top of RAM
xxx
...
When the BOOTRST Fuse is unprogrammed, the boot section size set to 4K bytes and
the IVSEL bit in the GICR Register is set before any interrupts are enabled, the most
typical and general program setup for the Reset and Interrupt Vector Addresses are:
Address
Labels Code
$000
;
Comments
jmp
RESET
ldi
r16,high(RAMEND); Main program start
$003
out
SPH,r16
$004
ldi
r16,low(RAMEND)
$005
out
SPL,r16
$006
<instr>
$002
MAIN:
; Reset handler
; Set Stack Pointer to top of RAM
xxx
;
.org $3802
$3802
jmp
EXT_INT0
; IRQ0 Handler
$3804
jmp
EXT_INT1
; IRQ1 Handler
...
...
...
;
$3826
Handler
jmp
TWSI
; Two-wire Serial Interface Interrupt
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
are:
Address
Labels Code
Comments
.org $002
$002
jmp
EXT_INT0
; IRQ0 Handler
$004
jmp
EXT_INT1
; IRQ1 Handler
...
...
...
;
$026
Handler
jmp
TWSI
; Two-wire Serial Interface Interrupt
ldi
r16,high(RAMEND); Main program start
out
SPH,r16
;
$028
$029
24
MAIN:
; Set Stack Pointer to top of RAM
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
$02a
ldi
r16,low(RAMEND)
$02b
out
SPL,r16
$02c
<instr>
xxx
;
.org $3800
$3800
…
…
jmp
…
RESET
…
; Reset handler
When the BOOTRST Fuse is programmed, the boot section size set to 4K bytes and the
IVSEL bit in the GICR Register is set before any interrupts are enabled, the most typical
and general program setup for the Reset and Interrupt Vector Addresses are:
Address Labels Code
$000
MAIN:
Comments
ldi
r16,high(RAMEND); Main program start
$001
out
SPH,r16
$002
ldi
r16,low(RAMEND)
$003
out
SPL,r16
$004
<instr>
; Set Stack Pointer to top of RAM
xxx
;
Reset Sources
.org $3800
$3800
$3802
jmp
jmp
RESET
; Reset handler
EXT_INT0 ; IRQ0 Handler
$3804
jmp
EXT_INT1 ; IRQ1 Handler
...
...
...
;
$3826
jmp
TWSI
; Two-wire Serial Interface Interrupt Handler
The ATmega323 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
more than 500 ns.
•
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).
•
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.
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 24 shows the Reset Logic. Table 5 and Table 6 define the timing and
electrical parameters of the reset circuitry.
25
1457G–AVR–09/03
Figure 24. Reset Logic
DATA BUS
PORF
BORF
EXTRF
WDRF
JTRF
MCU Control and Status
Register (MCUCSR)
Power-on
Reset Circuit
VCC
Brown-out
Reset Circuit
BODEN
BODLEVEL
SPIKE
FILTER
Reset Circuit
JTAG Reset
Register
Watchdog
Timer
Counter Reset
RESET
Internal Reset
100-500kΩ
On-chip RC
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
Table 5. Reset Characteristics(1)
Symbol
VPOT
Min
Typ
Max
Units
Power-on Reset
Threshold Voltage (rising)
1.0
1.4
1.8
V
Power-on Reset
Threshold Voltage
(falling)(2)
0.4
0.6
0.8
V
0.1VCC
–
0.9VCC
V
(BODLEVEL = 1)
2.4
2.7
3.2
(BODLEVEL = 0)
3.5
4.0
4.5
VRST
RESET Pin Threshold
Voltage
VBOT
Brown-out Reset
Threshold Voltage
Notes:
26
Parameter
Condition
V
1. Values are guidelines only. Actual values are TBD.
2. The Power-on Reset will not work unless the supply voltage has been below VPOT
(falling)
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 6. Reset Delay Selections(1)
CKSEL(2)
0000
0001
0010
Start-up Time, VCC =
2.7V, BODLEVEL
Unprogrammed
Start-up Time, VCC =
4.0V, BODLEVEL
Programmed
4.2 ms + 6 CK
5.8 ms + 6 CK
Ext. Clock, Fast Rising
Power
30 µs + 6 CK(4)
10 µs + 6 CK(5)
Ext. Clock, BOD Enabled
67 ms + 6 CK
92 ms + 6 CK
Int. RC Oscillator, Slowly
Rising Power
4.2 ms + 6 CK
5.8 ms + 6 CK
Int. RC Oscillator, Fast
Rising Power
30 µs + 6 CK(4)
10 µs + 6 CK(5)
Int. RC Oscillator, BOD
Enabled
67 ms + 6 CK
92 ms + 6 CK
Ext. RC Oscillator, Slowly
Rising Power
4.2 ms + 6 CK
5.8 ms + 6 CK
Ext. RC Oscillator, Fast
Rising Power
30 µs + 6 CK(4)
10 µs + 6 CK(5)
Ext. RC Oscillator, BOD
Enabled
67 ms + 32K CK
92 ms + 32K CK
Ext. Low-frequency
Crystal
67 ms + 1K CK
92 ms + 1K CK
Ext. Low-frequency
Crystal
67 ms + 16K CK
92 ms + 16K CK
Crystal Oscillator, Slowly
Rising Power
4.2 ms + 16K CK
5.8 ms + 16K CK
Crystal Oscillator, Fast
Rising Power
30 µs + 16K CK(4)
10 µs + 16K CK(5)
Crystal Oscillator, BOD
Enabled
67 ms 1K CK
92 ms + 1K CK
Ceramic Resonator/Ext.
Clock, Slowly Rising
Power
4.2 ms + 1K CK
5.8 ms + 1K CK
Ceramic Resonator, Fast
Rising Power
30 µs + 1K CK(4)
10 µs + 1K CK(5)
Ceramic Resonator, BOD
Enabled
(6)
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Notes:
1.
2.
3.
4.
5.
6.
Recommended Usage(3)
On Power-up, the start-up time is increased with Typ 0.6 ms.
“1” means unprogrammed, “0” means programmed.
For possible clock selections, see “Clock Options” on page 6.
When BODEN is programmed, add 100 µs.
When BODEN is programmed, add 25 µs.
Default value.
27
1457G–AVR–09/03
Table 6 shows the start-up times from Reset. When the CPU wakes up from Powerdown or Power-save, only the clock counting part of the start-up time is used. The
Watchdog Oscillator is used for timing the Real Time part of the start-up time. The number WDT Oscillator cycles used for each time-out is shown in Table 7.
The frequency of the Watchdog Oscillator is voltage dependent as shown in the Electrical Characteristics section. The device is shipped with CKSEL = “0010” (Internal RC
Oscillator, slowly rising power).
Table 7. Number of Watchdog Oscillator Cycles
BODLEVEL(1)
VCC Condition
Time-out
Number of Cycles
Unprogrammed
2.7V
30 µs
8
Unprogrammed
2.7V
130 µs
32
Unprogrammed
2.7V
4.2 ms
1K
Unprogrammed
2.7V
67 ms
16K
Programmed
4.0V
10 µs
8
Programmed
4.0V
35 µs
32
Programmed
4.0V
5.8 ms
4K
Programmed
4.0V
92 ms
64K
Note:
Power-on Reset
1. The BODLEVEL Fuse can be used to select start-up times even if the Brown-out
Detection is disabled (BODEN Fuse unprogrammed).
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level is defined in Table 5. 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 a delay counter, which determines
the delay, for which the device is kept in RESET after VCC rise. The time-out period of
the delay counter can be defined by the user through the CKSEL Fuses. The different
selections for the delay period are presented in Table 6. The RESET signal is activated
again, without any delay, when the VCC decreases below detection level.
Figure 25. MCU Start-up, RESET Tied to VCC
VCC
RESET
TIME-OUT
VPOT
VRST
tTOUT
INTERNAL
RESET
28
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 26. 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 500 ns 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 timer starts the MCU after the Time-out
Period tTOUT has expired.
Figure 27. External Reset During Operation
Brown-out Detection
ATmega323 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC
level during the operation. The BOD circuit can be enabled/disabled by the fuse
BODEN. When the BOD is enabled (BODEN programmed), and VCC decreases to a
value below the trigger level, the Brown-out Reset is immediately activated. When VCC
increases above the trigger level, the Brown-out Reset is deactivated after a delay. The
delay is defined by the user in the same way as the delay of POR signal, in Table 6. The
trigger level for the BOD can be selected by the fuse BODLEVEL to be 2.7V
(BODLEVEL unprogrammed), or 4.0V (BODLEVEL programmed). The trigger level has
a hysteresis of 50 mV to ensure spike free Brown-out Detection.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level
for longer than 9 µs for trigger level 4.0V, 21 µs for trigger level 2.7V (typical values).
29
1457G–AVR–09/03
Figure 28. Brown-out Reset During Operation
VCC
VBOT+
VBOT-
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
The hysteresis on VBOT: VBOT+ = VBOT + 25 mV, VBOT- = VBOT - 25 mV
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of 1 CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out Period
tTOUT. Refer to page 64 for details on operation of the Watchdog Timer.
Figure 29. Watchdog Reset During Operation
CK
MCU Control and Status
Register – MCUCSR
The MCU Control and Status Register contains control bits for general MCU functions,
and provides information on which reset source caused an MCU Reset.
Bit
7
6
5
4
3
2
1
0
$34 ($54)
JTD
ISC2
–
JTRF
WDRF
BORF
EXTRF
PORF
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
MCUCSR
See Bit Description
• Bit 7 – JTD: JTAG Interface Disable
When this bit is cleared (zero), the JTAG interface is enabled if the JTAGEN Fuse is
programmed. If this bit is set (one), the JTAG interface is disabled. To avoid unintentional disabling of the JTAG interface, the user software must write this bit as one twice
within four cycles to set the bit.
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.
30
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
• Bit 6 – ISC2: Interrupt Sense Control 2
The asynchronous external interrupt 2 is activated by the external pin INT2 if the SREG
I-flag and the corresponding interrupt mask in the GICR are set. If ISC2 is cleared
(zero), a falling edge on INT2 activates the interrupt. If ISC2 is set (one) a rising edge on
INT2 activates the interrupt. Edges on INT2 are registered asynchronously. Pulses on
INT2 wider than 50 ns will generate an interrupt. Shorter pulses are not guaranteed to
generate an interrupt. When changing the ISC2 bit, an interrupt can occur. Therefore, it
is recommended to first disable INT2 by clearing its Interrupt Enable bit in the GICR
Register. Then, the ISC2 bit can be changed. Finally, the INT2 Interrupt Flag should be
cleared by writing a logical one to its Interrupt Flag bit in the GIFR Register before the
interrupt is re-enabled.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the ATmega323 and always reads as zero.
• 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 MCUCSR 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.
Internal Voltage Reference
ATmega323 features an internal bandgap reference with a nominal voltage of 1.22V.
This reference is used for Brown-out Detection, and it can be used as an input to the
Analog Comparator or the ADC. The 2.56V reference to the ADC is generated from the
internal bandgap reference.
31
1457G–AVR–09/03
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 maximum start-up time is TBD. 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 BODEN 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, the user must always
allow the reference to start up before the output from the Analog Comparator is used.
The bandgap reference uses typically 10 µA, and 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.
Interrupt Handling
The ATmega323 has two 8-bit Interrupt Mask Control Registers: GICR – General Interrupt Control Register and TIMSK – Timer/Counter Interrupt Mask Register.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared (zero) and all interrupts are disabled. The user software can set (one) the I-bit to enable nested interrupts.
The I-bit is set (one) when a Return from Interrupt instruction – RETI – is executed.
When the Program Counter is vectored to the actual Interrupt Vector in order to execute
the interrupt handling routine, hardware clears the corresponding flag that generated the
interrupt. Some of the 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
(zero), the Interrupt Flag will be set and remembered until the interrupt is enabled, or the
flag is cleared by software.
If one or more interrupt conditions occur while the Global Interrupt Enable bit is cleared
(zero), the corresponding Interrupt Flag(s) will be set and remembered until the Global
Interrupt Enable bit is set (one), and will be executed by order of priority.
Note that external level interrupt does not have a flag, and will only be remembered for
as long as the interrupt condition is present.
Note that the Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt routine. This must be handled by
software.
Interrupt Response Time
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
(14 bits) 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 multicycle 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.
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-flag in SREG is set. When AVR exits from an
interrupt, it will always return to the main program and execute one more instruction
before any pending interrupt is served.
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ATmega323(L)
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ATmega323(L)
The General Interrupt Control
Register – GICR
l
Bit
7
6
5
4
3
2
1
0
$3B ($5B)
INT1
INT0
INT2
–
–
–
IVSEL
IVCE
Read/Write
R/W
R/W
R/W
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
GICR
• Bit 7 – INT1: External Interrupt Request 1 Enable
When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
the external pin interrupt is activated. The Interrupt Sense Control1 bits 1/0 (ISC11 and
ISC10) in the MCU general Control Register (MCUCR) define whether the external
interrupt is activated on rising and/or falling edge of the INT1 pin or level sensed. Activity
on the pin will cause an interrupt request even if INT1 is configured as an output. The
corresponding interrupt of External Interrupt Request 1 is executed from the INT1 Interrupt Vector. See also “External Interrupts” on page 37.
• Bit 6 – 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 activated. The Interrupt Sense Control0 bits 1/0 (ISC01 and
ISC00) in the MCU general Control Register (MCUCR) define whether the external
interrupt is activated on rising 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. See also “External Interrupts” on page 37.
• Bit 5 – INT2: External Interrupt Request 2 Enable
When the INT2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
the external pin interrupt is activated. The Interrupt Sense Control2 bit (ISC02) in the
MCU Control and Status Register (MCUCSR) defines whether the external interrupt is
activated on rising or falling edge of the INT2 pin. Activity on the pin will cause an interrupt request even if INT2 is configured as an output. The corresponding interrupt of
External Interrupt Request 2 is executed from the INT2 Interrupt Vector. See also
“External Interrupts” on page 37.
• Bits 4..2 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and always read as zero.
• 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 to the start of the Boot
Flash section is determined by the BOOTSZ Fuses. Refer to the section “Boot Loader
Support” on page 177 for details. To avoid unintentional changes of Interrupt Vector
tables, a special write procedure must be followed to change the IVSEL bit:
1. Set the Interrupt Vector Change Enable (IVCE) bit.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will be automatically 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 in four
cycles. The I-flag in the Status Register is unaffected by the automatic disabling.
33
1457G–AVR–09/03
Note: If Boot Lock bits BLB02 or BLB12 are set, changing the Interrupt Vector table will
change from what part of the Program memory interrupts are allowed. Refer to the section “Boot Loader Support” on page 177 for details on Boot Lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be set 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.
The General Interrupt Flag
Register – GIFR
Bit
7
6
5
4
3
2
1
$3A ($5A)
INTF1
INTF0
INTF2
–
–
–
–
0
–
Read/Write
R/W
R/W
R/W
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
GIFR
• Bit 7 – INTF1: External Interrupt Flag1
When an event on the INT1 pin triggers an interrupt request, INTF1 becomes set (one).
If the I-bit in SREG and the INT1 bit in GICR 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 INT1 is configured as a level interrupt.
• Bit 6 – INTF0: External Interrupt Flag0
When an event on the INT0 pin triggers an interrupt request, INTF0 becomes set (one).
If the I-bit in SREG and the INT0 bit in GICR 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.
• Bit 5 – INTF2: External Interrupt Flag2
When an event on the INT2 pin triggers an interrupt request, INTF2 becomes set (one).
If the I-bit in SREG and the INT2 bit in GICR 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.
• Bits 4..0 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and always read as zero.
The Timer/Counter Interrupt
Mask Register – TIMSK
Bit
7
6
5
4
3
2
1
0
OCIE2
TOIE2
TICIE1
OCIE1A
OCIE1B
TOIE1
OCIE0
TOIE0
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
$39 ($59)
TIMSK
• Bit 7 – OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable
When the OCIE2 bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt is
executed if a compare match in Timer/Counter2 occurs, i.e. when the OCF2 bit is set in
the Timer/Counter Interrupt Flag Register – TIFR.
34
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
• Bit 6 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is set (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 ov erflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the
Timer/Counter Interrupt Flag Register – TIFR.
• Bit 5 – TICIE1: Timer/Counter1 Input Capture Interrupt Enable
When the TICIE1 bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Input Capture Event Interrupt is enabled. The corresponding interrupt is
executed if a capture triggering event occurs on PD6 (ICP), i.e., when the ICF1 bit is set
in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 4 – OCIE1A: Timer/Counter1 Output Compare A Match Interrupt Enable
When the OCIE1A bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare A Match interrupt is enabled. The corresponding interrupt is
executed if a Compare A Match in Timer/Counter1 occurs, i.e., when the OCF1A bit is
set in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 3 – OCIE1B: Timer/Counter1 Output Compare B Match Interrupt Enable
When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Compare B Match interrupt is enabled. The corresponding interrupt is
executed if a Compare B Match in Timer/Counter1 occurs, i.e., when the OCF1B bit is
set in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 2 – TOIE1: Timer/Counter1 Overflow Interrupt Enable
When the TOIE1 bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter1 Overflow interrupt is enabled. The corresponding interrupt is executed if
an ov erflow in Timer/Counter1 occurs, i.e., when the TOV1 bit is set in the
Timer/Counter Interrupt Flag Register – TIFR.
• Bit 1 – OCIE0: Timer/Counter0 Output Compare Match Interrupt Enable
When the OCIE0 bit is set (one) and the I-bit in the Status Register is set (one), the
Timer/Counter0 Compare Match interrupt is enabled. The corresponding interrupt is
executed if a Compare0 Match in Timer/Counter0 occurs, i.e., when the OCF0 bit is set
in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is set (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
Interrupt Flag Register – TIFR.
35
1457G–AVR–09/03
The Timer/Counter Interrupt
Flag Register – TIFR
Bit
7
6
5
4
3
2
1
0
OCF2
TOV2
ICF1
OCF1A
OCF1B
TOV1
OCF0
TOV0
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
$38 ($58)
TIFR
• Bit 7 – OCF2: Output Compare Flag 2
The OCF2 bit is set (one) when a Compare Match occurs between the Timer/Counter2
and the data in OCR2 – Output Compare Register2. OCF2 is cleared by hardware when
executing the corresponding interrupt handling vector. Alternatively, OCF2 is cleared by
writing a logic one to the flag. When the I-bit in SREG, and OCIE2 (Timer/Counter2
Compare match Interrupt Enable), and the OCF2 are set (one), the Timer/Counter2
Compare match Interrupt is executed.
• Bit 6 – 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, and TOIE2
(Tim er /Counter2 Overf low Interrupt Enabl e), and TO V2 are set (one), the
Timer/Counter2 Overflow interrupt is executed. In PWM mode, this bit is set when
Timer/Counter2 changes counting direction at $00.
• Bit 5 – ICF1: Input Capture Flag 1
The ICF1 bit is set (one) to flag an Input Capture event, indicating that the
Timer/Counter1 value has been transferred to the Input Capture Register – ICR1. ICF1
is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, ICF1 is cleared by writing a logic one to the flag. When the I-bit in SREG,
and TICIE1 (Timer/Counter1 Input Capture Interrupt Enable), and the ICF1 are set
(one), the Timer/Counter1 Capture Interrupt is executed.
• Bit 4 – OCF1A: Output Compare Flag 1A
The OCF1A bit is set (one) when a Compare Match occurs between the Timer/Counter1
and the data in OCR1A – Output Compare Register 1A. OCF1A is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, OCF1A is
cleared by writing a logic one to the flag. When the I-bit in SREG, and OCIE1A
(Timer/Counter1 Compare Match Interrupt A Enable), and the OCF1A are set (one), the
Timer/Counter1 Compare Match A Interrupt is executed.
• Bit 3 – OCF1B: Output Compare Flag 1B
The OCF1B bit is set (one) when a Compare Match occurs between the Timer/Counter1
and the data in OCR1B – Output Compare Register 1B. OCF1B is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, OCF1B is
cleared by writing a logic one to the flag. When the I-bit in SREG, and OCIE1B
(Timer/Counter1 Compare Match Interrupt B Enable), and the OCF1B are set (one), the
Timer/Counter1 Compare Match B Interrupt is executed.
36
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
• Bit 2 – TOV1: Timer/Counter1 Overflow Flag
The TOV1 is set (one) when an overflow occurs in Timer/Counter1. TOV1 is cleared by
hardware when executing the corresponding interrupt handling vector. Alternatively,
TOV1 is cleared by writing a logic one to the flag. When the I-bit in SREG, and TOIE1
(Tim er /Counter1 Overf low Interrupt Enabl e), and TO V1 are set (one), the
Timer/Counter1 Overflow Interrupt is executed. In PWM mode, this bit is set when
Timer/Counter1 changes counting direction at $0000.
• Bit 1– OCF0: Output Compare Flag 0
The OCF0 bit is set (one) when a Compare Match occurs between the Timer/Counter0
and the data in OCR0 – Output Compare Register 0. OCF0 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, OCF0 is
cleared by writing a logic one to the flag. When the I-bit in SREG, and OCIE0
(Timer/Counter0 Compare Match Interrupt Enable), and the OCF0 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, and TOIE0
(Tim er /Counter0 Overf low Interrupt Enabl e), and TO V0 are set (one), the
Timer/Counter0 Overflow interrupt is executed. In PWM mode, this bit is set when
Timer/Counter0 changes counting direction at $00.
External Interrupts
The External Interrupts are triggered by the INT0, INT1, and INT2 pins. Observe that, if
enabled, the interrupts will trigger even if the INT0..2 pins are configured as outputs.
This feature provides a way of generating a software interrupt. The External Interrupts
can be triggered by a falling or rising edge or a low level (INT2 is only an edge triggered
interrupt). This is set up as indicated in the specification for the MCU Control Register –
MCUCR and MCU Control and Status Register – MCUCSR. When the External Interrupt
is enabled and is configured as level triggered (only INT0/INT1), the interrupt will trigger
as long as the pin is held low.
MCU Control Register –
MCUCR
The MCU Control Register contains control bits for general MCU functions.
Bit
7
6
5
4
3
2
1
0
SE
SM2
SM1
SM0
ISC11
ISC10
ISC01
ISC00
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
$37 ($57)
MCUCR
• Bit 7 – SE: Sleep Enable
The SE bit must be set (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 programmers purpose, it is recommended to set the Sleep Enable (SE) bit just before the
execution of the SLEEP instruction.
37
1457G–AVR–09/03
• Bits 6..4 – SM2..0: Sleep Mode Select Bits 2, 1 and 0
These bits select between the six available sleep modes as shown in Table 8.
Table 8. 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
Extended Standby(1)
Note:
Sleep Mode
1. Standby mode and Extended Standby mode are only available with external crystals
or resonators.
• Bits 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The External Interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the
corresponding interrupt mask in the GICR are set. The level and edges on the external
INT1 pin that activate the interrupt are defined in Table 9. The value on the INT1 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 9. Interrupt 1 Sense Control
ISC11
ISC10
Description
0
0
The low level of INT1 generates an interrupt request.
0
1
Any logical change on INT1 generates an interrupt request.
1
0
The falling edge of INT1 generates an interrupt request.
1
1
The rising edge of INT1 generates an interrupt request.
• 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 10. 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.
38
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 10. Interrupt 0 Sense Control
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.
Sleep Modes
To enter any of the six sleep modes, the SE bit in MCUCR must be set (one) and a
SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the MCUCR Register select which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save,
Standby or Extended Standby) will be activated by the SLEEP instruction. See Table 8
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, executes the interrupt routine,
and resumes execution from the instruction following SLEEP. The contents of the Register File, SRAM, and I/O Memory 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.
Idle Mode
When the SM2..0 bits are set to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing SPI, USART, Analog Comparator, ADC, Two-wire
Serial Interface, Timer/Counters, Watchdog, and the interrupt system to continue operating. This 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 set to 001, the SLEEP instruction makes the MCU enter ADC
Noise Reduction mode, stopping the MCU but allowing the ADC, the external interrupts,
the Two-wire Serial Interface address watch, Timer/Counter2 and the Watchdog to continue operating (if enabled). 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 Two-wire Serial Interface address match interrupt, or an external level interrupt on INT0 or INT1, or an
external edge interrupt on INT2, can wake up the MCU from ADC Noise Reduction
mode. A Timer/Counter2 Output Compare or overflow event will wake up the MCU, but
will not generate an interrupt unless Timer/Counter2 is clocked asynchronously.
In future devices this is subject to change. It is recommended for future code compatibility to disable Timer/Counter2 interrupts during ADC Noise Reduction mode if the
Timer/Counter2 is clocked synchronously.
39
1457G–AVR–09/03
Power-down Mode
When the SM2..0 bits are 010, the SLEEP instruction makes the MCU enter Powerdown mode. In this mode, the external Oscillator is stopped, while the external interrupts, the Two-wire Serial Interface address watch, and the Watchdog continue
operating (if enabled). Only an External Reset, a Watchdog Reset, an Two-wire Serial
Interface address match interrupt, an external level interrupt on INT0 or INT1, or an
external edge interrupt on INT2 can wake up the MCU.
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. This makes the MCU
less sensitive to noise. The changed level is sampled twice by the Watchdog Oscillator
clock, and if the input has the required level during this time, the MCU will wake up. The
period of the Watchdog Oscillator is 1 µs (nominal) at 5.0V and 25°C. The frequency of
the Watchdog Oscillator is voltage dependent as shown in the Electrical Characteristics
section.
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 seen in Table 6 on page 27.
Power-save Mode
When the SM2..0 bits are 011, the SLEEP instruction forces the MCU into the Powersave mode. This mode is identical to Power-down, with one exception:
If Timer/Counter2 is clocked asynchronously, i.e., the AS2 bit in ASSR is set,
Timer/Counter2 will run during sleep. The device can wake up from either Timer Overf lo w o r Ou tp ut Co mp are e v ent f r om Ti m er/ Cou nt er2 i f t he correspo ndi ng
Timer/Counter2 interrupt enable bits are set in TIMSK, and the Global Interrupt Enable
bit in SREG is set.
If the asynchronous timer is NOT clocked asynchronously, Power-down mode is recommended instead of Power-save mode because the contents of the registers in the
asynchronous timer should be considered undefined after wake-up in Power-save mode
if AS2 is 0.
Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected,
the SLEEP instruction forces the MCU into the 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 only six clock cycles.
Extended Standby Mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected,
the SLEEP instruction forces the MCU into the Extended Standby mode. This mode is
identical to Power-save mode with the exception that the Oscillator is kept running.
From Extended Standby mode, the device wakes up in only six clock cycles.
40
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Calibrated Internal
RC Oscillator
Oscillator Calibration Register
– OSCCAL
The calibrated internal Oscillator provides a fixed 1.0 MHz (nominal) clock at 5V and
25°C. This clock may be used as the system clock. See the section “Clock Options” on
page 6 for information on how to select this clock as the system clock. This Oscillator
can be calibrated by writing the calibration byte to the OSCCAL Register. 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 details on how to use the pre-programmed calibration value, see the section “Calibration Byte” on page 188.
Bit
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
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
$31 ($51)
OSCCAL
• Bits 7..0 – CAL7..0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the internal Oscillator to remove process variations from the Oscillator frequency. When OSCCAL is zero, the lowest
available frequency is chosen. Writing non-zero values to this register will increase the
frequency of the internal Oscillator. Writing $FF to the register gives the highest available frequency. The calibrated Oscillator is used to time EEPROM and Flash access. If
EEPROM or Flash is written, do not calibrate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash write may fail. Note that the Oscillator is
intended for calibration to 1.0 MHz, thus tuning to other values is not guaranteed.
Table 11. Internal RC Oscillator Frequency Range
Special Function IO Register –
SFIOR
OSCCAL Value
Min Frequency (MHz)
Max Frequency (MHz)
$00
0.5
1.0
$7F
0.7
1.5
$FF
1.0
2.0
Bit
7
6
5
4
3
2
1
0
$30 ($50)
–
–
–
–
ACME
PUD
PSR2
PSR10
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SFIOR
• Bit 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and always read as zero.
• Bit 3 – ACME: Analog Comparator Multiplexer Enable
When this bit is set (one) and the ADC is switched off (ADEN in ADCSR is zero), the
ADC multiplexer selects the negative input to the Analog Comparator. When this bit is
cleared (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 126.
• Bit 2 – PUD: Pull-up Disable
When this bit is set (one), all pull-ups on all ports are disabled. If the bit is cleared (zero),
the pull-ups can be individually enabled as described in the chapter “I/O Ports” on page
137.
41
1457G–AVR–09/03
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is set (one) the Timer/Counter2 prescaler will be reset. The bit will be
cleared by hardware after the operation is performed. Writing a zero to this bit will have
no effect. This bit will always be read as zero if Timer/Counter2 is clocked by the internal
CPU clock. If this bit is written when Timer/Counter2 is operating in asynchronous
mode, the bit will remain one until the prescaler has been reset. See “Asynchronous
Operation of Timer/Counter2” on page 53 for a detailed description of asynchronous
operation.
• Bit 0 – PSR10: Prescaler Reset Timer/Counter1 and Timer/Counter0
When this bit is set (one) the Timer/Counter1 and Timer/Counter0 prescaler will be
reset. The bit will be cleared by hardware after the operation is performed. Writing a
zero to this bit will have no effect. Note that Timer/Counter1 and Timer/Counter0 share
the same prescaler and a reset of this prescaler will affect both timers. This bit will
always be read as zero.
42
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Timer/Counters
The ATmega323 provides three general purpose Timer/Counters – two 8-bit T/Cs and
one 16-bit T/C. Timer/Counter2 can optionally be asynchronously clocked from an external Oscillator. This Oscillator is optimized for use with a 32.768 kHz watch crystal,
enabling use of Timer/Counter2 as a Real Time Counter (RTC). Timer/Counters 0 and 1
have individual prescaling selection from the same 10-bit prescaler. Timer/Counter2 has
its own prescaler. Both these prescalers can be reset by setting the corresponding control bits in the Special Functions IO Register (SFIOR). These Timer/Counters can either
be used as a timer with an internal clock time-base or as a counter with an external pin
connection which triggers the counting.
Timer/Counter
Prescalers
Figure 30. Prescaler for Timer/Counter0 and Timer/Counter1
Clear
PSR10
TCK1
TCK0
For Timer/Counters 0 and 1, the four different prescaled selections are: CK/8, CK/64,
CK/256, and CK/1024, where CK is the Oscillator clock. For the two Timer/Counters0
and 1, CK, external source, and stop can also be selected as clock sources. Setting the
PSR10 bit in SFIOR Resets the prescaler. This allows the user to operate with a predictable prescaler. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler
and a Prescaler Reset will affect both Timer/Counters.
43
1457G–AVR–09/03
Figure 31. Prescaler for Timer/Counter2
PSR2
PCK2/1024
PCK2/256
PCK2/128
AS2
PCK2/64
10-BIT T/C PRESCALER
Clear
PCK2/32
XTAL1
PCK2
PCK2/8
CK
0
CS20
CS21
CS22
TIMER/COUNTER2 CLOCK SOURCE
TCK2
The clock source for Timer/Counter2 is named PCK2. PCK2 is by default connected to
the main system clock CK. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously clocked from the PC6(TOSC1) pin. This enables use of Timer/Counter2 as a
Real Time Counter (RTC). When AS2 is set, pins PC6(TOSC1) and PC7(TOSC2) are
disconnected from Port C. A crystal can then be connected between the PC6(TOSC1)
and PC7(TOSC2) pins to serve as an independent clock source for Timer/Counter2.
The Oscillator is optimized for use with a 32.768 kHz crystal. Applying an external clock
source to TOSC1 is not recommended. Setting the PSR2 bit in SFIOR resets the prescaler. This allows the user to operate with a predictable prescaler.
44
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
8-bit Timers/Counters
Timer/Counter0 and
Timer/Counter2
Figure 32 shows the block diagram for Timer/Counter0. Figure 33 shows the block diagram for Timer/Counter2.
Figure 32. Timer/Counter0 Block Diagram
7
0
TIMER/COUNTER0
(TCNT0)
7
PSR2
PSR10
SPECIAL FUNCTIONS
IO REGISTER (SFIOR)
CS00
CS01
CS02
CTC0
COM00
COM01
FOC0
T/C0 CONTROL
REGISTER (TCCR0)
TOV0
TOV1
OCF0
OCF1B
ICF1
OCF1A
TOV2
OCF2
TIMER INT. FLAG
REGISTER (TIFR)
PWM0
TIMER INT. MASK
REGISTER (TIMSK)
TOV0
OCF0
TOIE0
TOIE1
OCIE0
OCIE1A
OCIE1B
TICIE1
OCIE2
8-BIT DATA BUS
TOIE2
T/C0 COMPARE T/C0 OVERFLOW IRQ
MATCH IRQ
T/C CLEAR
T/C CLK SOURCE
UP/DOWN
CONTROL
LOGIC
CK
T0
0
8-BIT COMPARATOR
7
0
OUTPUT COMPARE
REGISTER0 (OCR0)
45
1457G–AVR–09/03
Figure 33. Timer/Counter2 Block Diagram
T/C2 OVER- T/C2 COMPARE
FLOW IRQ
MATCH IRQ
8-BIT DATA BUS
7
0
TIMER/COUNTER2
(TCNT2)
PSR2
CS20
CS21
CS22
CTC2
COM20
FOC2
PWM2
COM21
PSR10
SPECIAL FUNCTIONS
IO REGISTER (SFIOR)
T/C2 CONTROL
REGISTER (TCCR2)
T/C CLEAR
T/C CLK SOURCE
UP/DOWN
7
TOV0
TOV1
OCF0
OCF1B
OCF1A
ICF1
TOV2
TIMER INT. FLAG
REGISTER (TIFR)
OCF2
TIMER INT. MASK
REGISTER (TIMSK)
TOV2
OCF2
TOIE0
TOIE1
OCIE0
OCIE1A
OCIE1B
TICIE1
TOIE2
OCIE2
8-BIT ASYNCH T/C2 DATA BUS
CK
CONTROL
LOGIC
TOSC1
0
8-BIT COMPARATOR
0
OUTPUT COMPARE
REGISTER2 (OCR2)
CK
PCK2
ICR2UB
OCR2UB
AS2
ASYNCH. STATUS
REGISTER (ASSR)
TC2UB
7
SYNCH UNIT
The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK, or an external
pin.
The 8-bit Timer/Counter2 can select clock source from CK, prescaled CK, external
TOSC1 or prescaled external TOSC1.
Both Timers/Counters can be stopped as described in section “Timer/Counter0 Control
Register – TCCR0” on page 47 and “Bit 7 – FOC0/FOC2: Force Output Compare” on
page 47.
The various Status Flags (Overflow and Compare Matc h) are f ound in the
Timer/Counter Interrupt Flag Register – TIFR (see page 36). Control signals are found in
the Timer/Counter Control Register – TCCR0 and TCCR2. The interrupt enable/disable
settings are found in the Timer/Counter Interrupt Mask Register – TIMSK (see page 34).
When Timer/Counter0 is externally clocked, the external signal is synchronized with the
Oscillator frequency of the CPU. To assure proper sampling of the external clock, the
minimum time between two external clock transitions must be at least one internal CPU
clock period. The external clock signal is sampled on the rising edge of the internal CPU
clock.
The 8-bit Timer/Counters feature both a high-resolution and a high-accuracy usage with
the lower prescaling opportunities. Similarly, the high-prescaling opportunities make the
Timer/Counter0 useful for lower speed functions or exact timing functions with infrequent actions.
46
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Timer/Counter0 and 2 can also be used as 8-bit Pulse Width Modulators. In this mode,
the Timer/Counter and the Output Compare Register serve as a glitch-free, stand-alone
PWM with centered pulses. Refer to page 49 for a detailed description on this function.
Timer/Counter0 Control
Register – TCCR0
Bit
7
6
5
4
3
2
1
0
FOC0
PWM0
COM01
COM00
CTC0
CS02
CS01
CS00
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
$33 ($53)
Timer/Counter2 Control
Register – TCCR2
Bit
7
6
5
4
3
2
1
0
FOC2
PWM2
COM21
COM20
CTC2
CS22
CS21
CS20
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
$25 ($45)
TCCR0
TCCR2
• Bit 7 – FOC0/FOC2: Force Output Compare
Writing a logical one to this bit, forces a change in the Compare Match output pin PB3
(Timer/Counter0) and PD7 (Timer/Counter2) according to the values already set in
COMn1 and COMn0. If the COMn1 and COMn0 bits are written in the same cycle as
FOC0/FOC2, the new settings will not take effect until next Compare Match or Forced
Output Compare Match occurs. The Force Output Compare bit can be used to change
the output pin without waiting for a Compare Match in the timer. The automatic action
programmed in COMn1 and COMn0 happens as if a Compare Match had occurred, but
no interrupt is generated and the Timer/Counters will not be cleared even if CTC0/CTC2
is set. The corresponding I/O pin must be set as an output pin for the FOC0/FOC2 bit to
have effect on the pin. The FOC0/FOC2 bits will always be read as zero. Setting the
FOC0/FOC2 bits has no effect in PWM mode.
• Bit 6 – PWM0/PWM2: Pulse Width Modulator Enable
When set (one) this bit enables PWM mode for Timer/Counter0 or Timer/Counter2. This
mode is described on page 49.
• Bits 5, 4 – COM01, COM00/COM21, COM20: Compare Output Mode, Bits 1 and 0
The COMn1 and COMn0 control bits determine any output pin action following a compare match in Timer/Counter0 or Timer/Counter2. Output pin actions affect pins
PB3(OC0) or PD7(OC2). This is an alternative function to an I/O port, and the corresponding direction control bit must be set (one) to control an output pin. The control
configuration is shown in Table 12.
Table 12. Compare Mode Select(1)
COMn1(2)
COMn0
0
0
Timer/Counter Disconnected from Output Pin OCn
0
1
Toggle the OCn Output Line.
1
0
Clear the OCn Output Line (to Zero).
1
1
Set the OCn Output Line (to One).
Notes:
Description
1. In PWM mode, these bits have a different function. Refer to Table 15 for a
description.
2. n = 0 or 2
47
1457G–AVR–09/03
• Bit 3 – CTC0/CTC2: Clear Timer/Counter on Compare Match
When the CTC0 or CTC2 control bit is set (one), Timer/Counter0 or Timer/Counter2 is
reset to $00 in the CPU clock cycle following a Compare Match. If the control bit is
cleared, the Timer/Counter continues counting and is unaffected by a Compare Match.
When a prescaling of 1 is used, and the Compare Register is set to C, the timer will
count as follows if CTC0/CTC2 is set:
... | C-1 | C | 0 | 1 | ...
When the prescaler is set to divide by 8, the timer will count like this:
... | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, C, C, C, C, C, C, C | 0, 0, 0, 0, 0, 0, 0, 0 |
1, 1, 1, ...
In PWM mode, this bit has a different function. If the CTC0 or CTC2 bit is cleared in
PWM mode, the Timer/Counter acts as an up/down counter. If the CTC0 or CTC2 bit is
set (one), the Timer/Counter wraps when it reaches $FF. Refer to page 49 for a detailed
description.
• Bits 2, 1, 0 – CS02, CS01, CS00/ CS22, CS21, CS20: Clock Select bits 2, 1, and 0
The Clock Select bits 2, 1, and 0 define the prescaling source of Timer/Counter0 and
Timer/Counter2.
Table 13. Clock 0 Prescale Select
CS02
CS01
CS00
Description
0
0
0
Stop, the Timer/Counter0 is Stopped
0
0
1
CK
0
1
0
CK/8
0
1
1
CK/64
1
0
0
CK/256
1
0
1
CK/1024
1
1
0
External Pin PB0(T0), Falling Edge
1
1
1
External Pin PB0(T0), Rising Edge
Table 14. Clock 2 Prescale Select
48
CS22
CS21
CS20
Description
0
0
0
Stop, the Timer/Counter2 is Stopped
0
0
1
PCK2
0
1
0
PCK2/8
0
1
1
PCK2 /32
1
0
0
PCK2/64
1
0
1
PCK2/128
1
1
0
PCK2/256
1
1
1
PCK2/1024
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The Stop condition provides a Timer Enable/Disable function. The prescaled modes are
scaled directly from the CK Oscillator clock for Timer/Counter0 and PCK2 for
Timer/Counter2. If the external pin modes are used for Timer/Counter0, transitions on
PB0(T0) will clock the counter even if the pin is configured as an output. This feature
can give the user SW control of the counting.
Timer Counter0 – TCNT0
Bit
7
6
5
4
3
2
1
0
$32 ($52)
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
7
6
5
4
3
2
1
TCNT0
Timer/Counter2 – TCNT2
Bit
0
$24 ($44)
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
TCNT2
These 8-bit registers contain the value of the Timer/Counters.
Both Timer/Counters is realized as up or up/down (in PWM mode) counters with read
and write access. If the Timer/Counter is written to and a clock source is selected, it continues counting in the timer clock cycle following the write operation.
Timer/Counter0 Output
Compare Register – OCR0
Timer/Counter2 Output
Compare Register – OCR2
Bit
7
6
5
4
3
2
1
0
$3C ($5C)
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
OCR0
0
$23 ($43)
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
OCR2
The Output Compare Registers are 8-bit read/write registers. The Timer/Counter Output
Compare Registers contains the data to be continuously compared with the
Timer/Counter. Actions on compare matches are specified in TCCR0 and TCCR2. A
software write to the Timer/Counter Register blocks compare matches in the next
Timer/Counter clock cycle. This prevents immediate interrupts when initializing the
Timer/Counter.
A Compare Match will set the Compare Interrupt Flag in the CPU clock cycle following
the compare event.
Timer/Counter 0 and 2 in PWM
Mode
When PWM mode is selected, the Timer/Counter either wraps (overflows) when it
reaches $FF or it acts as an up/down counter.
If the up/down mode is selected, the Timer/Counter and the Output Compare Registers
– OCR0 or OCR2 form an 8-bit, free running, glitch-free and phase correct PWM with
outputs on the PB3(OC0/PWM0) or PD7(OC2/PWM2) pin.
If the overflow mode is selected, the Timer/Counter and the Output Compare Registers
– OCR0 or OCR2 form an 8-bit, free running and glitch-free PWM, operating with twice
the speed of the up/down counting mode.
49
1457G–AVR–09/03
PWM Modes (Up/Down and
Overflow)
The two different PWM modes are selected by the CTC0 or CTC2 bit in the
Timer/Counter Control Registers –TCCR0 or TCCR2 respectively.
If CTC0/CTC2 is cleared and PWM mode is selected, the Timer/Counter acts as an
up/down counter, counting up from $00 to $FF, where it turns and counts down again to
zero before the cycle is repeated. When the counter value matches the contents of the
Output Compare Register, the PB3(OC0/PWM0) or PD7(OC2/PWM2) pin is set or
cleared according to the settings of the COMn1/COMn0 bits in the Timer/Counter Control Registers TCCR0 or TCCR2.
If CTC0/CTC2 is set and PWM mode is selected, the Timer/Counters will wrap and start
counting from $00 after reaching $FF. The PB3(OC0/PWM0) or PD7(OC2/PWM2) pin
will be set or cleared according to the settings of COMn1/COMn0 on a Timer/Counter
overflow or when the counter value matches the contents of the Output Compare Register. Refer to Table 15 for details.
Table 15. Compare Mode Select in PWM Mode(1)
CTCn
COMn1
COMn0
0
0
0
Not connected
0
0
1
Not connected
0
1
0
Cleared on Compare Match, up-counting. Set on
Compare Match, down-counting (non-inverted
PWM)
fTCK0/2/510
0
1
1
Cleared on Compare Match, down-counting. Set
on Compare Match, up-counting (inverted PWM)
fTCK0/2/510
1
0
0
Not connected
1
0
1
Not connected
1
1
0
Cleared on Compare Match, set on overflow
fTCK0/2/256
1
1
1
Set on Compare Match, cleared on overflow
fTCK0/2/256
Note:
Effect on Compare Pin
Frequency
1. n = 0 or 2
Note that in PWM mode, the value to be written to the Output Compare Register is first
transferred to a temporary location, and then latched into the OCR when the
Timer/Counter reaches $FF. This prevents the occurrence of odd-length PWM pulses
(glitches) in the event of an unsynchronized OCR0 or OCR2 write. See Figure 34 and
Figure 35 for examples.
50
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 34. Effects of Unsynchronized OCR Latching in Up/Down Mode
Compare Value changes
Counter Value
Compare Value
PWM Output OCn
Synchronized OCn Latch
Compare Value changes
Counter Value
Compare Value
PWM Output OCn
Unsynchronized OCn Latch
Glitch
Figure 35. Effects of Unsynchronized OCR Latching in Overflow Mode
Compare Value changes
Counter Value
Compare Value
PWM Output OCn
Synchronized OCn Latch
Compare Value changes
Counter Value
Compare Value
PWM Output OCn
Unsynchronized OCn Latch
Note:
Glitch
n = 0 or 2 (Figure 34 and Figure 35).
During the time between the write and the latch operation, a read from the Output Compare Registers will read the contents of the temporary location. This means that the
most recently written value always will read out of OCR0 and OCR2.
When the Output Compare Register contains $00 or $FF, and the up/down PWM mode
is selected, the output PB3(OC0/PWM0)/PD7(OC2/PWM2) is updated to low or high on
the next compare match according to the settings of COMn1/COMn0. This is shown in
Table 16. In overflow PWM mode, the output PB3(OC0/PWM0)/PD7(OC2/PWM2) is
held low or high only when the Output Compare Register contains $FF.
51
1457G–AVR–09/03
Table 16. PWM Outputs OCRn = $00 or $FF(1)
COMn1
COMn0
OCRn
Output PWMn
1
0
$00
L
1
0
$FF
H
1
1
$00
H
1
1
$FF
L
Note:
1. n = 0 or 2
In overflow PWM mode, the table above is only valid for OCRn = $FF.
In up/down PWM mode, the Timer Overflow Flag, TOV0 or TOV2, is set when the
counter advances from $00. In overflow PWM mode, the Timer Overflow Flag is set as
in normal Timer/Counter mode. Timer Overflow Interrupt0 and 2 operate exactly as in
normal Timer/Counter mode, i.e., they are executed when TOV0 or TOV2 are set provided that Timer Overflow Interrupt and Global Interrupts are enabled. This does also
apply to the Timer Output Compare Flag and interrupt.
Asynchronous Status
Register – ASSR
Bit
7
6
5
4
3
2
1
0
$22 ($22)
–
–
–
–
AS2
TCN2UB
OCR2UB
TCR2UB
Read/Write
R
R
R
R
R/W
R
R
R
Initial Value
0
0
0
0
0
0
0
0
ASSR
• Bit 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and always read as zero.
• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is cleared (zero), Timer/Counter2 is clocked from the internal system clock,
CK. When AS2 is set (one), Timer/Counter2 is clocked from the TOSC1 pin. Pins PC6
and PC7 are connected to a crystal Oscillator and cannot be used as general I/O pins.
When the value of this bit is changed, the contents of TCNT2, OCR2, and TCCR2 might
be corrupted.
• Bit 2 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes
set (one). When TCNT2 has been updated from the temporary storage register, this bit
is cleared (zero) 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 OCR2 is written, this bit becomes
set (one). When OCR2 has been updated from the temporary storage register, this bit is
cleared (zero) by hardware. A logical zero in this bit indicates that OCR2 is ready to be
updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes
set (one). When TCCR2 has been updated from the temporary storage register, this bit
is cleared (zero) by hardware. A logical zero in this bit indicates that TCCR2 is ready to
be updated with a new value.
52
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
If a write is performed to any of the three Timer/Counter2 Registers while its Update
Busy Flag is set (one), the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2, and TCCR2 are different. When reading
TCNT2, the actual timer value is read. When reading OCR2 or TCCR2, the value in the
temporary storage register is read.
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, OCR2, and TCCR2 might be corrupted. A
safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2 and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2, and TCCR2.
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 Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external
clock to the TOSC1 pin may result in incorrect Timer/Counter2 operation. The CPU
main clock frequency must be more than four times the Oscillator frequency.
When writing to one of the registers TCNT2, OCR2, or TCCR2, 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 OCR2
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 Extended Standby mode after having written to TCNT2,
OCR2, or TCCR2, 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 OCR2 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 Extended Standby
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 reentering 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 Extended Standby mode is sufficient, the following algorithm can be
used to ensure that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2, TCNT2 or OCR2.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or Extended Standby mode.
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
53
1457G–AVR–09/03
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 Powerup 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 Power-down 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.
Description of wake up from Power-save or Extended Standby 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.
During asynchronous operation, the synchronization of the Interrupt Flags for the asynchronous timer takes three 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.
16-bit Timer/Counter1
Figure 36 shows the block diagram for Timer/Counter1.
Figure 36. Timer/Counter1 Block Diagram
TOV0
8 7
CS11
CS10
CS12
CTC1
ICNC1
ICES1
FOC1B
PWM11
T/C1 CONTROL
REGISTER B (TCCR1B)
PWM10
FOC1A
COM1B1
COM1B0
COM1A1
TOV1
OCF1A
OCF1B
ICF1
T/C1 CONTROL
REGISTER A (TCCR1A)
COM1A0
OCF0
OCF1A
TOV1
ICF1
T/C1 COMPARE T/C1 INPUT
MATCH B IRQ CAPTURE IRQ
TIMER INT. FLAG
REGISTER (TIFR)
TIMER INT. MASK
REGISTER (TIMSK)
15
OCF1B
OCF2
TOIE0
TOIE1
OCIE0
OCIE1A
OCIE1B
TICIE1
TOIE2
OCIE2
8-BIT DATA BUS
TOV2
T/C1 COMPARE
MATCH A IRQ
T/C1 OVERFLOW IRQ
0
T/C1 INPUT CAPTURE REGISTER (ICR1)
PSR10
CK
T1
CONTROL
LOGIC
CAPTURE
TRIGGER
15
8 7
0
15
8
7
T/C CLEAR
T/C CLOCK SOURCE
TIMER/COUNTER1 (TCNT1)
UP/DOWN
0
15
15
8
7
8
7
0
16 BIT COMPARATOR
16 BIT COMPARATOR
0
TIMER/COUNTER1 OUTPUT COMPARE REGISTER A
15
8
7
0
TIMER/COUNTER1 OUTPUT COMPARE REGISTER B
The 16-bit Timer/Counter1 can select clock source from CK, prescaled CK, or an external pin. In addition it can be stopped as described in section “Timer/Counter1 Control
54
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Register B – TCCR1B” on page 57. The different Status Flags (Overflow, Compare
Match, and Capture Event) are found in the Timer/Counter Interrupt Flag Register –
TIFR. Control signals are found in the Timer/Counter1 Control Registers – TCCR1A and
TCCR1B. The interrupt enable/disable settings for Timer/Counter1 are found in the
Timer/Counter Interrupt Mask Register – TIMSK.
When Timer/Counter1 is externally clocked, the external signal is synchronized with the
Oscillator frequency of the CPU. To assure proper sampling of the external clock, the
minimum time between two external clock transitions must be at least one internal CPU
clock period. The external clock signal is sampled on the rising edge of the internal CPU
clock.
The 16-bit Timer/Counter1 features both a high-resolution and a high-accuracy usage
with the lower prescaling opportunities. Similarly, the high-prescaling opportunities
makes the Timer/Counter1 useful for lower speed functions or exact timing functions
with infrequent actions.
The Timer/Counter1 supports two Output Compare functions using the Output Compare
Register 1 A and B (OCR1A and OCR1B) as the data sources to be compared to the
Timer/Counter1 contents. The Output Compare functions include optional clearing of
the counter on compareA match, and actions on the Output Compare Pins on both compare matches.
Timer/Counter1 can also be used as an 8-, 9-, or 10-bit Pulse Width Modulator. In this
mode the counter and the OCR1A/OCR1B Registers serve as a dual glitch-free standalone PWM with centered pulses. Alternatively, the Timer/Counter1 can be configured
to operate at twice the speed in PWM mode, but without centered pulses. Refer to page
60 for a detailed description of this function.
The Input Capture function of Timer/Counter1 provides a capture of the Timer/Counter1
contents to the Input Capture Register – ICR1, triggered by an external event on the
Input Capture Pin – ICP. The actual capture event settings are defined by the
Timer/Counter1 Control Register – TCCR1B. In addition, the Analog Comparator can be
set to trigger the Input Capture. Refer to the section, “The Analog Comparator”, for
details on this. The ICP pin logic is shown in Figure 37.
Figure 37. ICP Pin Schematic Diagram
If the noise canceler function is enabled, the actual trigger condition for the capture
event is monitored over four samples, and all four must be equal to activate the Capture
Flag.
55
1457G–AVR–09/03
Timer/Counter1 Control
Register A – TCCR1A
Bit
7
6
5
4
3
2
1
0
COM1A1
COM1A0
COM1B1
COM1B0
FOC1A
FOC1B
PWM11
PWM10
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
$2F ($4F)
TCCR1A
• Bits 7, 6 – COM1A1, COM1A0: Compare Output Mode1A, Bits 1 and 0
The COM1A1 and COM1A0 control bits determine any output pin action following a
Compare Match in Timer/Counter1. Any output pin actions affect pin OC1A – Output
Compare A. This is an alternative function to an I/O port, and the corresponding direction control bit must be set (one) to control an output pin. The control configuration is
shown in Table 10.
• Bits 5, 4 – COM1B1, COM1B0: Compare Output Mode1B, Bits 1 and 0
The COM1B1 and COM1B0 control bits determine any output pin action following a
Compare Match in Timer/Counter1. Any output pin actions affect pin OC1B – Output
Compare B. This is an alternative function to an I/O port, and the corresponding direction control bit must be set (one) to control an output pin. The control configuration is
shown in Table 10.
Table 17. Compare 1 Mode Select(1)
Note:
COM1X1
COM1X0
Description
0
0
Timer/Counter1 Disconnected from Output Pin OC1X
0
1
Toggle the OC1X Output Line.
1
0
Clear the OC1X Output Line (to Zero).
1
1
Set the OC1X Output Line (to One).
1. X = A or B.
In PWM mode, these bits have a different function. Refer to Table 22 for a description.
• Bit 3 – FOC1A: Force Output Compare 1A
Writing a logical one to this bit, forces a change in the Compare Match output pin PD5
according to the values already set in COM1A1 and COM1A0. If the COM1A1 and
COM1A0 bits are written in the same cycle as FOC1A, the new settings will not take
effect until next Compare Match or Forced Compare Match occurs. The Force Output
Compare bit can be used to change the output pin without waiting for a Compare Match
in the timer. The automatic action programmed in COM1A1 and COM1A0 happens as if
a Compare Match had occurred, but no interrupt is generated and it will not clear the
timer even if CTC1 in TCCR1B is set. The corresponding I/O pin must be set as an output pin for the FOC1A bit to have effect on the pin. The FOC1A bit will always be read as
zero. The setting of the FOC1A bit has no effect in PWM mode.
• Bit 2 – FOC1B: Force Output Compare 1B
Writing a logical one to this bit, forces a change in the Compare Match output pin PD4
according to the values already set in COM1B1 and COM1B0. If the COM1B1 and
COM1B0 bits are written in the same cycle as FOC1B, the new settings will not take
effect until next Compare Match or Forced Compare Match occurs. The Force Output
Compare bit can be used to change the output pin without waiting for a Compare Match
in the timer. The automatic action programmed in COM1B1 and COM1B0 happens as if
56
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
a Compare Match had occurred, but no interrupt is generated. The corresponding I/O
pin must be set as an output pin for the FOC1B bit to have effect on the pin. The FOC1B
bit will always be read as zero. The setting of the FOC1B bit has no effect in PWM
mode.
• Bits 1..0 – PWM11, PWM10: Pulse Width Modulator Select Bits
These bits select PWM operation of Timer/Counter1 as specified in Table 11. This mode
is described on page 60.
Table 18. PWM Mode Select
Timer/Counter1 Control
Register B – TCCR1B
PWM11
PWM10
0
0
PWM Operation of Timer/Counter1 is Disabled
0
1
Timer/Counter1 is an 8-bit PWM
1
0
Timer/Counter1 is a 9-bit PWM
1
1
Timer/Counter1 is a 10-bit PWM
Bit
Description
7
6
5
4
3
2
1
0
$2E ($4E)
ICNC1
ICES1
–
–
CTC1
CS12
CS11
CS10
Read/Write
R/W
R/W
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR1B
• Bit 7 – ICNC1: Input Capture1 Noise Canceler (Four CKs)
When the ICNC1 bit is cleared (zero), the Input Capture trigger Noise Canceler function
is disabled. The Input Capture is triggered at the first rising/falling edge sampled on the
ICP – Input Capture Pin – as specified. When the ICNC1 bit is set (one), four successive
samples are measures on the ICP – Input Capture Pin, and all samples must be
high/low according to the Input Capture trigger specification in the ICES1 bit. The actual
sampling frequency is XTAL clock frequency.
• Bit 6 – ICES1: Input Capture1 Edge Select
While the ICES1 bit is cleared (zero), the Timer/Counter1 contents are transferred to the
Input Capture Register – ICR1 – on the falling edge of the Input Capture Pin – ICP.
While the ICES1 bit is set (one), the Timer/Counter1 contents are transferred to the
Input Capture Register – ICR1 – on the rising edge of the Input Capture Pin – ICP.
• Bits 5, 4 – Res: Reserved bits
These bits are reserved bits in the ATmega323 and always read as zero.
• Bit 3 – CTC1: Clear Timer/Counter1 on Compare Match
When the CTC1 control bit is set (one), the Timer/Counter1 is reset to $0000 in the clock
cycle after a Compare A Match. If the CTC1 control bit is cleared, Timer/Counter1 continues counting and is unaffected by a compare match. When a prescaling of one is
used, and the Compare A Register is set to C, the timer will count as follows if CTC1 is
set:
... | C-1 | C | 0 | 1 |...
57
1457G–AVR–09/03
When the prescaler is set to divide by 8, the timer will count like this:
... | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, C, C, C, C, C, C, C | 0, 0, 0, 0, 0, 0, 0, 0
|1,1,1,1,1,1,1,1|...
In PWM mode, this bit has a different function. If the CTC1 bit is cleared in PWM mode,
the Timer/Counter1 acts as an up/down counter. If the CTC1 bit is set (one), the
Timer/Counter wraps when it reaches the TOP value. Refer to page 60 for a detailed
description.
• Bits 2..0 – CS12, CS11, CS10: Clock Select1, Bit 2, 1, and 0
The Clock Select1 bits 2, 1, and 0 define the prescaling source of Timer/Counter1.
Table 19. Clock 1 Prescale Select
CS12
CS11
CS10
Description
0
0
0
Stop, the Timer/Counter1 is Stopped.
0
0
1
CK
0
1
0
CK/8
0
1
1
CK/64
1
0
0
CK/256
1
0
1
CK/1024
1
1
0
External Pin T1, Falling Edge
1
1
1
External Pin T1, Rising Edge
The Stop condition provides a Timer Enable/Disable function. The prescaled modes are
scaled directly from the CK Oscillator clock. If the external pin modes are used for
Timer/Counter1, transitions on PB1/(T1) will clock the counter even if the pin is configured as an output. This feature can give the user SW control of the counting.
Timer/Counter1 – TCNT1H
and TCNT1L
Bit
$2D ($4D)
15
14
13
12
11
10
9
TCNT1H
$2C ($4C)
Read/Write
Initial Value
8
MSB
LSB
7
6
5
4
3
2
1
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
TCNT1L
0
This 16-bit register contains the prescaled value of the 16-bit Timer/Counter1. 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 register (TEMP). This temporary register is also used when accessing OCR1A, OCR1B, and
ICR1. If the main program and also interrupt routines perform access to registers using
TEMP, interrupts must be disabled during access from the main program and interrupt
routines.
58
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
TCNT1 Timer/Counter1 Write
When the CPU writes to the High Byte TCNT1H, the written data is placed in the TEMP
Register. Next, when the CPU writes the Low Byte TCNT1L, this byte of data is combined with the byte data in the TEMP Register, and all 16-bits are written to the TCNT1
Timer/Counter1 Register simultaneously. Consequently, the High Byte TCNT1H must
be accessed first for a full 16-bit register write operation.
TCNT1 Timer/Counter1 Read
When the CPU reads the Low Byte TCNT1L, the data of the Low Byte TCNT1L is sent
to the CPU and the data of the High Byte TCNT1H is placed in the TEMP Register.
When the CPU reads the data in the High Byte TCNT1H, the CPU receives the data in
the TEMP Register. Consequently, the Low Byte TCNT1L must be accessed first for a
full 16-bit register read operation.
The Timer/Counter1 is realized as an up or up/down (in PWM mode) counter with read
and write access. If Timer/Counter1 is written to and a clock source is selected, the
Timer/Counter1 continues counting in the timer clock cycle after it is preset with the written value.
Timer/Counter1 Output
Compare Register – OCR1AH
and OCR1AL
Bit
$2B ($4B)
15
14
13
12
11
10
9
OCR1AH
$2A ($4A)
Read/Write
Initial Value
Timer/Counter1 Output
Compare Register – OCR1BH
and OCR1BL
Bit
$29 ($49)
LSB
7
6
5
4
3
R/W
R/W
R/W
R/W
0
0
15
2
1
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
14
13
12
11
10
9
8
Initial Value
OCR1AL
0
MSB
OCR1BH
$28 ($48)
Read/Write
8
MSB
LSB
7
6
5
4
3
2
1
0
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
OCR1BL
The Output Compare Registers are 16-bit read/write registers.
The Timer/Counter1 Output Compare Registers contain the data to be continuously
compared with Timer/Counter1. Actions on compare matches are specified in the
Timer/Counter1 Control and Status Register. A software write to the Timer/Counter
Register blocks compare matches in the next Timer/Counter clock cycle. This prevents
immediate interrupts when initializing the Timer/Counter.
A Compare Match will set the Compare Interrupt Flag in the CPU clock cycle following
the compare event.
Since the Output Compare Registers – OCR1A and OCR1B – are 16-bit registers, a
temporary register TEMP is used when OCR1A/B are written to ensure that both bytes
are updated simultaneously. When the CPU writes the High Byte, OCR1AH or
OCR1BH, the data is temporarily stored in the TEMP Register. When the CPU writes
the Low Byte, OCR1AL or OCR1BL, the TEMP Register is simultaneously written to
OCR1AH or OCR1BH. Consequently, the High Byte OCR1AH or OCR1BH must be
written first for a full 16-bit register write operation.
59
1457G–AVR–09/03
The TEMP Register is also used when accessing TCNT1 and ICR1. If the main program
and also interrupt routines perform access to registers using TEMP, interrupts must be
disabled during access from the main program and interrupt routines.
Timer/Counter1 Input Capture
Register – ICR1H and ICR1L
Bit
$27 ($47)
15
14
13
12
11
10
9
ICR1H
$26 ($46)
Read/Write
Initial Value
8
MSB
LSB
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
ICR1L
The Input Capture Register is a 16-bit read-only register.
When the rising or falling edge (according to the Input Capture Edge setting – ICES1) of
the signal at the Input Capture Pin – ICP – is detected, the current value of the
Timer/Counter1 Register – TCNT1 – is transferred to the Input Capture Register – ICR1.
At the same time, the Input Capture Flag – ICF1 – is set (one).
Since the Input Capture Register – ICR1 – is a 16-bit register, a temporary register
TEMP is used when ICR1 is read to ensure that both bytes are read simultaneously.
When the CPU reads the Low Byte ICR1L, the data is sent to the CPU and the data of
the High Byte ICR1H is placed in the TEMP Register. When the CPU reads the data in
the High Byte ICR1H, the CPU receives the data in the TEMP Register. Consequently,
the Low Byte ICR1L must be accessed first for a full 16-bit register read operation.
The TEMP Register is also used when accessing TCNT1, OCR1A, and OCR1B. If the
main program and also interrupt routines accesses registers using TEMP, interrupts
must be disabled during access from the main program and interrupt routines.
Timer/Counter1 In PWM Mode
When the PWM mode is selected, Timer/Counter1 and the Output Compare Register1A
– OCR1A and the Output Compare Register1B – OCR1B, form a dual 8-, 9-, or 10-bit,
Free Running, Glitch-free, and phase correct PWM with outputs on the PD5(OC1A) and
PD4(OC1B) pins. In this mode, the Timer/Counter1 acts as an up/down counter, counting up from $0000 to TOP (see Table 21), where it turns and counts down again to zero
before the cycle is repeated. When the counter value matches the contents of the 8, 9,
or 10 least significant bits (depending on resolution) of OCR1A or OCR1B, the
PD5(OC1A)/PD4(OC1B) pins are set or cleared according to the settings of the
COM1A1/COM1A0 or COM1B1/COM1B0 bits in the Timer/Counter1 Control Register
TCCR1A. Refer to Table 17 on page 56 for details.
Alternatively, the Timer/Counter1 can be configured to a PWM that operates at twice the
speed as in the mode described above. Then the Timer/Counter1 and the Output Compare Register1A – OCR1A and the Output Compare Register1B – OCR1B, form a dual
8-, 9-, or 10-bit, free running and glitch-free PWM with outputs on the PD5(OC1A) and
PD4(OC1B) pins..
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ATmega323(L)
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ATmega323(L)
Table 20. Timer TOP Values and PWM Frequency
CTC1
PWM11
PWM10
PWM Resolution
Timer TOP Value
Frequency
0
0
1
8-bit
$00FF (255)
fTCK1/510
0
1
0
9-bit
$01FF (511)
fTCK1/1022
0
1
1
10-bit
$03FF(1023)
fTCK1/2046
1
0
1
8-bit
$00FF (255)
fTCK1/256
1
1
0
9-bit
$01FF (511)
fTCK1/512
1
1
1
10-bit
$03FF(1023)
fTCK1/1024
As shown in Table 20, the PWM operates at either 8, 9, or 10 bits resolution. Note the
unused bits in OCR1A, OCR1B, and TCNT1 will automatically be written to zero by
hardware. I.e., bit 9 to 15 will be set to zero in OCR1A, OCR1B, and TCNT1 if the 9-bit
PWM resolution is selected. This makes it possible for the user to perform Read-ModifyWrite operations in any of the three resolution modes and the unused bits will be treated
as don’t care.
Table 21. Timer TOP Values and PWM Frequency
PWM Resolution
Timer TOP Value
Frequency
8-bit
$00FF (255)
fTC1/510
9-bit
$01FF (511)
fTC1/1022
10-bit
$03FF(1023)
fTC1/2046
Table 22. Compare1 Mode Select in PWM Mode(1)
CTC1
COM1X1
COM1X0
0
0
0
Not connected
0
0
1
Reserved
0
1
0
Cleared on Compare Match, up-counting. Set on
Compare Match, down-counting (non-inverted PWM).
0
1
1
Cleared on Compare Match, down-counting. Set on
Compare Match, up-counting (inverted PWM).
1
0
0
Not connected
1
0
1
Reserved
1
1
0
Cleared on Compare Match, set on overflow.
1
1
1
Set on Compare Match, cleared on overflow.
Note:
Effect on OCX1
1. X = A or B
Note that in the PWM mode, the 8, 9, or 10 least significant OCR1A/OCR1B bits
(depending on resolution), when written, are transferred to a temporary location. They
are latched when Timer/Counter1 reaches the value TOP. This prevents the occurrence
of odd-length PWM pulses (glitches) in the event of an unsynchronized OCR1A/OCR1B
write. See Figure 38 and Figure 39 for an example in each mode.
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Figure 38. Effects of Unsynchronized OCR1 Latching.
PWM Output OC1x
Synchronized OC1x Latch
PWM Output OC1x
Unsynchronized OC1x Latch
Note: x = A or B
Figure 39. Effects of Unsynchronized OCR1 Latching in Overflow Mode
PWM Output OC1x
Synchronized OC1x Latch
PWM Output OC1x
Unsynchronized OC1x Latch
Note: X = A or B
During the time between the write and the latch operation, a read from OCR1A or
OCR1B will read the contents of the temporary location. This means that the most
recently written value always will read out of OCR1A/B.
When the OCR1X contains $0000 or TOP, and the up/down PWM mode is selected, the
output OC1A/OC1B is updated to low or high on the next compare match according to
the settings of COM1A1/COM1A0 or COM1B1/COM1B0. This is shown in Table 23. In
overflow PWM mode, the output OC1A/OC1B is held low or high only when the Output
Compare Register contains TOP.
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Table 23. PWM Outputs OCR1X = $0000 or TOP
COM1X1
COM1X0
OCR1X
Output OC1X
1
0
$0000
L
1
0
TOP
H
1
1
$0000
H
1
1
TOP
L
In overflow PWM mode, the table above is only valid for OCR1X = TOP.
In PWM mode, the Timer Overflow Flag1, TOV1, is set when the counter advances from
$0000. In overflow PWM mode, the Timer Overflow Flag is set as in normal
Timer/Counter mode. Timer Overflow Interrupt1 operates exactly as in normal
Timer/Counter mode, i.e., it is executed when TOV1 is set provided that Timer Overflow
Interrupt1 and global interrupts are enabled. This also applies to the Timer Output
Compare1 Flags and interrupts.
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Watchdog Timer
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 24 on page 65. The WDR – Watchdog Reset –
instruction resets the Watchdog Timer. Eight different clock cycle periods can be
selected to determine the reset period. If the reset period expires without another
Watchdog Reset, the ATmega323 resets and executes from the Reset Vector. For timing details on the Watchdog Reset, refer to page 30.
To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be
followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer
Control Register for details.
Figure 40. Watchdog Timer
OSCILLATOR
1 MHz at VCC = 5V
The Watchdog Timer Control
Register – WDTCR
Bit
7
6
5
4
3
2
1
0
$21 ($41)
–
–
–
WDTOE
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 ATmega323 and will always read as zero.
• Bit 4 – WDTOE: Watchdog Turn-off Enable
This bit must be set (one) when the WDE bit is cleared. Otherwise, the Watchdog will
not be disabled. Once set, hardware will clear this bit to zero after four clock cycles.
Refer to the description of the WDE bit for a Watchdog disable procedure.
• Bit 3 – WDE: Watchdog Enable
When the WDE is set (one) the Watchdog Timer is enabled, and if the WDE is cleared
(zero) the Watchdog Timer function is disabled. WDE can only be cleared if the WDTOE
bit is set(one). To disable an enabled Watchdog timer, the following procedure must be
followed:
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1. In the same operation, write a logical one to WDTOE and WDE. A logical 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 logical 0 to WDE. This disables the
Watchdog.
• 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
Timeout Periods are shown in Table 24.
Table 24. 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
47 ms
15 ms
0
0
1
32K cycles
94 ms
30 ms
0
1
0
64K cycles
0.19 s
60 ms
0
1
1
128K cycles
0.38 s
0.12 s
1
0
0
256K cycles
0.75 s
0.24 s
1
0
1
512K cycles
1.5 s
0.49 s
1
1
0
1,024K cycles
3.0 s
0.97 s
1
1
1
2,048K cycles
6.0 s
1.9 s
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EEPROM Read/Write
Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time is in the range of 1.9 - 3.8 ms, depending on the frequency of the
calibrated RC Oscillator. See Table 25 for details. A self-timing function, however, lets
the user software detect when the next byte can be written. If the user code contains
code that writes 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. CPU operation under these conditions is likely to cause the
Program Counter to perform unintentional jumps and possibly execute the EEPROM
write code. To secure EEPROM integrity, the user is advised to use an external undervoltage reset circuit or the internal Brown-out Detector in this case.
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.
The EEPROM Address
Register – EEARH and EEARL
Bit
15
14
13
12
11
10
9
8
$1F ($3F)
–
–
–
–
–
–
EEAR9
EEAR8
EEARH
$1E ($3E)
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
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
X
X
X
X
X
X
X
X
X
X
• Bits 15..10 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and will always read as zero.
• Bits 9..0 – EEAR9..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address
in the 1K bytes EEPROM space. The EEPROM data bytes are addressed linearly
between 0 and 1,023. The initial value of EEAR is undefined. A proper value must be
written before the EEPROM may be accessed.
The EEPROM Data Register –
EEDR
Bit
7
6
5
4
3
2
1
0
$1D ($3D)
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.
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ATmega323(L)
The EEPROM Control Register
– EECR
Bit
7
6
5
4
3
2
1
0
$1C ($3C)
–
–
–
–
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 ATmega323 and will always read as zero.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
When the I bit in SREG and EERIE are set (one), the EEPROM Ready Interrupt is
enabled. When cleared (zero), the interrupt is disabled. The EEPROM Ready interrupt
generates a constant interrupt when EEWE is cleared (zero).
• 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(one) setting EEWE will write data to the EEPROM at the
selected address If EEMWE is zero, setting EEWE will have no effect. When EEMWE
has been set (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
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 set to write the value into
the EEPROM. The EEMWE bit must be set when the 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 2 and 3 is not essential):
1. Wait until EEWE becomes zero.
2. Write new EEPROM address to EEAR (optional).
3. Write new EEPROM data to EEDR (optional).
4. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.
5. Within four clock cycles after setting EEMWE, write a logical one to EEWE.
Caution: An interrupt between step 4 and step 5 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 the 4 last steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared (zero) 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 set. When the
EERE bit is cleared (zero) by hardware, requested data is found in the EEDR Register.
The EEPROM read access takes one instruction, and there is no need to poll the EERE
bit. When EERE has been set, the CPU is halted for four cycles before the next instruction is executed.
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The user should poll the EEWE bit before starting the read operation. If a write operation
is in progress, it is not possible to set the EERE bit, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 25 lists the typical programming time for EEPROM access from the CPU.
Table 25. EEPROM Programming Time.
Symbol
EEPROM write (from
CPU)
Preventing EEPROM
Corruption
Number of Calibrated
RC Oscillator Cycles
Min Programming
Time
Max Programming
Time
2048
1.9 ms
3.8 ms
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 the 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 for executing instructions is too low.
EEPROM data corruption can easily be avoided by following these design recommendations (one is sufficient):
1. 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 is voltage is sufficient.
2. 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 EEPROM Registers from unintentional writes.
3. Store constants in Flash memory if the ability to change memory contents
from software is not required. Flash memory can not be updated by the CPU
unless the Boot Loader software supports writing to the Flash and the Boot
Lock bits are configured so that writing to the Flash memory from CPU is
allowed. See “Boot Loader Support” on page 177 for details.
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ATmega323(L)
Serial Peripheral
Interface – SPI
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer
between the ATmega323 and peripheral devices or between several AVR devices. The
ATmega323 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
Figure 41. SPI Block Diagram
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128
The interconnection between Master and Slave CPUs with SPI is shown in Figure 42.
The PB7(SCK) pin is the clock output in the Master mode and the clock input in the
Slave mode. Writing to the SPI Data Register of the Master CPU starts the SPI clock
generator, and the data written shifts out of the PB5(MOSI) pin and into the PB5(MOSI)
pin of the Slave CPU. 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 Slave Select input, PB4(SS), is set low to
select an individual Slave SPI device. The two Shift Registers in the Master and the
Slave can be considered as one distributed 16-bit circular Shift Register. This is shown
in Figure 42. When data is shifted from the Master to the Slave, data is also shifted in
the opposite direction, simultaneously. During one shift cycle, data in the Master and the
Slave is interchanged.
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Figure 42. SPI Master-Slave Interconnection
MSB
MASTER
LSB
MISO
MISO
8 BIT SHIFT REGISTER
SPI
CLOCK GENERATOR
MSB
SLAVE
LSB
8 BIT SHIFT REGISTER
MOSI
MOSI
SCK
SCK
SS
VCC
SS
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.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is
overridden according to Table 26.
Table 26. SPI Pin Overrides(1)
Pin
Note:
SS Pin Functionality
Direction, Master SPI
Direction, Slave SPI
MOSI
User Defined
Input
MISO
Input
User Defined
SCK
User Defined
Input
SS
User Defined
Input
1. See “Alternate Functions of Port B” on page 140 for a detailed description of how to
define the direction of the user defined SPI pins.
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. 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.
When the SPI is configured as a Slave, the 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
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once the SS pin is driven high. If the SS pin is driven high during a transmission, the SPI
will stop sending and receiving immediately and both data received and data sent must
be considered as lost.
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 43 and Figure 44.
Figure 43. SPI Transfer Format with CPHA = 0 and DORD = 0(1)
Note:
1. * Not defined but normally MSB of character just received.
Figure 44. SPI Transfer Format with CPHA = 1 and DORD = 0(1)
Note:
1. * Not defined but normally LSB of previously transmitted character.
SPI Control Register – SPCR
Bit
7
6
5
4
3
2
1
0
$0D ($2D)
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 set (one), the SPI is enabled. This bit must be set to enable any SPI
operations.
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• Bit 5 – DORD: Data Order
When the DORD bit is set (one), the LSB of the data word is transmitted first.
When the DORD bit is cleared (zero), the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when set (one), and Slave SPI mode when cleared
(zero). If SS is configured as an input and is driven low while MSTR is set, MSTR will be
cleared, and SPIF in SPSR will become set. The user will then have to set MSTR to reenable SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is set (one), SCK is high when idle. When CPOL is cleared (zero), SCK is
low when idle. Refer to Figure 43 and Figure 44 for additional information.
• Bit 2 – CPHA: Clock Phase
Refer to Figure 43 and Figure 44 for the functionality of this bit.
• 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 fck is shown in Table 27.
Table 27. Relationship Between SCK and the Oscillator Frequency
The SPI Status Register –
SPSR
SPI2X
SPR1
SPR0
SCK Frequency
0
0
0
fck/4
0
0
1
fck/16
0
1
0
fck/64
0
1
1
fck/128
1
0
0
fck/2
1
0
1
fck/8
1
1
0
fck/32
1
1
1
fck /64
Bit
7
6
5
4
3
2
1
0
$0E ($2E)
SPIF
WCOL
–
–
–
–
–
SPI2X
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF bit is set (one) and an interrupt is generated if SPIE in SPCR is set (one) 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
(one), then accessing the SPI Data Register (SPDR).
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ATmega323(L)
• 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 (zero) by first reading the SPI Status Register with WCOL set (one), and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the ATmega323 and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is set (one) the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see Table 27). This means that the minimum SCK period will be 2
CPU clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to
work at fck/4 or lower.
The SPI interface on the ATmega323 is also used for Program memory and EEPROM
downloading or uploading. See page 197 for Serial Programming and verification.
The SPI Data Register – SPDR
Bit
7
6
5
4
3
2
1
0
$0F ($2F)
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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USART
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 45. CPU accessible I/O Registers and I/O pins are shown in bold.
Figure 45. USART Block Diagram
Clock Generator
UBRR[H:L]
OSC
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCK
Transmitter
TX
CONTROL
UDR (Transmit)
DATABUS
PARITY
GENERATOR
PIN
CONTROL
TRANSMIT SHIFT REGISTER
TxD
Receiver
UCSRA
CLOCK
RECOVERY
RX
CONTROL
RECEIVE SHIFT REGISTER
DATA
RECOVERY
PIN
CONTROL
UDR (Receive)
PARITY
CHECKER
UCSRB
RxD
UCSRC
The dashed boxes in the block diagram separates the three main parts of the USART
(listed from the top): Clock Generation, 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
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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
(UDR). The Receiver supports the same frame formats as the Transmitter, and can
detect Frame Error, Data OverRun and Parity Errors.
ATmega323 USART Pin
Specification
Table 28 shows the ATmega323 specific USART pin placement.
Table 28. ATmega323 Specific USART Pin Placement
USART Pin Name
Corresponding ATmega323 Pin
RxD
PD0
TxD
PD1
XCK
PB0
As XCK is placed on PB0, DDR_XCK in the following refers to DDB0.
About Code Examples
This USART documentation contains simple code examples that briefly show how to
use the USART. 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 that interrupt handling in C is compiler dependent. Please
confirm with the C compiler documentation.
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 operates as a
circular FIFO buffer. Therefore the UDR must only be read once for each incoming
data. More important is the fact that the Error Flags (FE and DOR) and the ninth
data bit (RXB8) are buffered with the data in the receive buffer. Therefore the status
bits must always be read before the UDR 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 45) if the
Buffer Registers are full, until a new start bit is detected. The USART is therefore
more resistant to Data OverRun (DOR) error conditions.
The following control bits have changed name, but have same functionality and register
location:
•
CHR9 is changed to UCSZ2
•
OR is changed to DOR
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Clock Generation
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 UMSEL
bit in USART Control and Status Register C (UCSRC) selects between asynchronous
and synchronous operation. Double Speed (asynchronous mode only) is controlled by
the U2X found in the UCSRA Register. When using synchronous mode (UMSEL = 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 46 shows a block diagram of the clock generation logic.
Figure 46. 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 46.
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
count er re aches zero. Thi s clock is t he b aud rate generat or clock o utput
(= 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 UMSEL,
U2X and DDR_XCK bits.
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Table 29 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.
Table 29. Equations for Calculating Baud Rate Register Setting
Equation for Calculating
Baud Rate(1)
Equation for Calculating
UBRR Value
Asynchronous Normal Mode
(U2X = 0)
f OSC
BAUD = --------------------------------------16 ( UBRR + 1 )
f OSC
UBRR = -----------------------–1
16BAUD
Asynchronous Double Speed
Mode (U2X = 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:
Double Speed Operation
(U2X)
1. The baud rate is defined to be the transfer rate in bit per second (bps).
BAUD
Baud rate (in bits per second, bps)
System Oscillator clock frequency
fOSC
UBRR
Contents of the UBRRH and UBRRL Registers, (0 - 4095)
Some examples of UBRR values for some system clock frequency are found in Table
36 (see page 99).
The transfer rate can be doubled by setting the U2X bit in UCSRA. 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 46 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.
Synchronous Clock Operation When synchronous mode is used (UMSEL = 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.
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Figure 47. Synchronous Mode XCK Timing
UCPOL = 0
XCK
RxD / TxD
Sample
UCPOL = 1
XCK
RxD / TxD
Sample
The UCPOL bit UCRSC selects which XCK clock edge is used for data sampling and
which is used for data change. As Figure 47 shows, when UCPOL is zero the data will
be changed at falling XCK edge and sampled at rising XCK edge. If UCPOL is set, the
data will be changed at rising XCK edge and sampled at falling 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 accept 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 a idle (high) state. Figure 48 illustrates the possible
combinations of the frame formats. Bits inside brackets are optional.
Figure 48. Frame Formats
FRAME
(IDLE)
78
St
0
1
2
3
4
[5]
[6]
[7]
[8]
[P]
Sp1 [Sp2]
St
Start bit, always low.
(n)
Data bits (0 to 8).
P
Parity bit. Can be odd or even.
Sp
Stop bit, always high.
IDLE
No transfers on the communication line (RxD or TxD).
An IDLE line must be high.
(St / IDLE)
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The frame format used by the USART is set by the UCSZ2:0, UPM1:0 and USBS bits in
UCSRB and UCSRC. The Receiver and Transmitter uses 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 (UCSZ2:0) bits select the number of data bits in the frame.
The USART Parity Mode (UPM1:0) 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 (USBS) bit. The
Receiver ignores the second stop bit. An FE (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 ev en = 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
TXC Flag can be used to check that the Transmitter has completed all transfers, and the
RXC Flag can be used to check that there are no unread data in the Receive Buffer.
Note that the TXC Flag must be cleared before each transmission (before UDR is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one
C function that is equal in functionality. The examples assume asynchronous operation
using polling (no interrupts enabled) and a fixed frame format. The baud rate is given as
a function parameter. For the assembly code, the baud rate parameter is assumed to be
stored in the r17:r16 Registers. When the function writes to the UCSRC Register, the
URSEL bit (MSB) must be set due to the sharing of I/O location by UBRRH and
UCSRC.
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Assembly Code Example(1)
USART_Init:
; Set baud rate
out UBRRH, r17
out UBRRL, r16
; Enable Receiver and Transmitter
ldi r16, (1<<RXEN)|(1<<TXEN)
out UCSRB,r16
; Set frame format: 8data, 2stop bit
ldi r16, (1<<URSEL)|(1<<USBS)|(3<<UCSZ0)
out UCSRC,r16
ret
C Code Example(1)
void USART_Init( unsigned int baud )
{
/* Set baud rate */
UBRRH = (unsigned char)(baud>>8);
UBRRL = (unsigned char)baud;
/* Enable Receiver and Transmitter */
UCSRB = (1<<RXEN)|(1<<TXEN);
/* Set frame format: 8data, 2stop bit */
UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);
}
Note:
1. The example code assumes that the part specific header file is included.
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 (TXEN) bit in the
UCSRB 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 UDR 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, U2X 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 (UDRE) Flag. When using frames with less than eight bit,
the most significant bits written to the UDR 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 UCSRA,UDRE
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out
UDR,r16
ret
C Code Example
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE)) ) {};
/* Put data into buffer, sends the data */
UDR = data;
}
Note:
1. The example code assumes that the part specific header file is included.
The function simply waits for the Transmit Buffer to be empty by checking the UDRE
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 TXB8 bit in
UCSRB before the Low Byte of the character written to UDR. 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)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy ninth bit from r17 to TXB8
cbi
UCSRB,TXB8
sbrc r17,0
sbi
UCSRB,TXB8
; Put LSB data (r16) into buffer, sends the data
out
UDR,r16
ret
C Code Example
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) ) {};
/* Copy ninth bit to TXB8 */
UCSRB &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSRB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDR = data;
}
Note:
1. These transmit functions are written to be general functions. They can be optimized if
the contents of the UCSRB is static. I.e., only the TXB8 bit of the UCSRB Register is
used after initialization.
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.
Transmitter Flags and
Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register
Empty (UDRE) and Transmit Complete (TXC). Both flags can be used for generating
interrupts.
The Data Register Empty (UDRE) 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 set this bit to zero when writing
the UCSRA Register.
When the Data Register Empty Interrupt Enable (UDRIE) bit in UCSRB is set, the
USART Data Register Empty Interrupt will be executed as long as UDRE is set (provided that global interrupts are enabled). UDRE is cleared by writing UDR. When
interrupt-driven data transmission is used, the Data Register empty Interrupt routine
must either write new data to UDR in order to clear UDRE or disable the Data Register
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Empty Interrupt, otherwise a new interrupt will occur once the interrupt routine
terminates.
The Transmit Complete (TXC) 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 TXC 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 TXC
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 (TXCIE) bit in UCSRB is set, the USART
Transmit Complete Interrupt will be executed when the TXC 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 TXC 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 (UPM1 = 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 TXEN to zero) will not become effective
until ongoing and pending transmissions are completed, i.e., when the Transmit Shift
Register and Transmit Buffer Register does 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 setting the Receive Enable (RXEN) bit in the
UCSRB Register. 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 UDR I/O
location.
The following code example shows a simple USART Receive function based on polling
of the Receive Complete (RXC) Flag. When using frames with less than eight bits the
most significant bits of the data read from the UDR 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 UCSRA, RXC
rjmp USART_Receive
; Get and return received data from buffer
in
r16, UDR
ret
C Code Example
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSRA & (1<<RXC)) ) {};
/* Get and return received data from buffer */
return UDR;
}
Note:
1. The example code assumes that the part specific header file is included.
The function simply waits for data to be present in the receive buffer by checking the
RXC Flag, before reading the buffer and returning the value.
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Receiving Frames with 9 Data
Bits
If 9-bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8 bit in
UCSRB before reading the low bits from the UDR. This rule applies to the FE, DOR,
and PE Status Flags as well. Read status from UCSRA, then data from UDR. Reading
the UDR I/O location will change the state of the receive buffer FIFO and consequently
the TXB8, FE, DOR and PE bits, which all are stored in the FIFO, will change.
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 UCSRA, RXC
rjmp USART_Receive
; Get status and ninth bit, then data from buffer
in
r18, UCSRA
in
r17, UCSRB
in
r16, UDR
; If error, return -1
andi r18,(1<<FE)|(1<<DOR)|(1<<PE)
breq USART_ReceiveNoError
ldi
r17, HIGH(-1)
ldi
r16, LOW(-1)
USART_ReceiveNoError:
; Filter the ninth 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 ( !(UCSRA & (1<<RXC)) ) {};
/* Get status and ninth bit, then data */
/* from buffer */
status = UCSRA;
resh = UCSRB;
resl = UDR;
/* If error, return -1 */
if ( status & (1<<FE)|(1<<DOR)|(1<<PE) )
return -1;
/* Filter the ninth bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
Note:
1. The example code assumes that the part specific header file is included.
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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.
Receive Compete Flag and
Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) 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 (RXEN = 0), the receive buffer will be flushed and consequently the RXC bit
will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRB is set, the USART
Receive Complete Interrupt will be executed as long as the RXC 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 UDR in order to clear the
RXC Flag, otherwise a new interrupt will occur once the interrupt routine terminates.
Receiver Error Flags
The USART Receiver has three Error Flags: Frame Error (FE), Data OverRun (DOR)
and Parity Enable (PE). All can be accessed by reading UCSRA. 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 UCSRA must be
read before the receive buffer (UDR), since reading the UDR 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 UCSRA is written for upward compatibility of future USART implementations.
None of the Error Flags can generate interrupts.
The Frame Error (FE) Flag indicates the state of the first stop bit of the next readable
frame stored in the receive buffer. The FE Flag is zero when the stop bit was correctly
read (as one), and the FE 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 FE Flag is not affected by the setting of the USBS bit in UCSRC
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 UCSRA.
The Data OverRun (DOR) 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
DOR Flag is set there was one or more serial frame lost between the frame last read
from UDR, and the next frame read from UDR. For compatibility with future devices,
always set this bit to zero when writing to UCSRA. The DOR Flag is cleared when the
frame received was successfully moved from the Shift Register to the receive buffer.
The Parity Error (PE) Flag indicates that the next frame in the receive buffer did have an
parity error when received. If parity check is not enabled the PE bit will always be read
zero. For compatibility with future devices, always set this bit to zero when writing to
UCSRA. For more details see “Parity Bit Calculation” on page 79 and “Parity Checker”
on page 87.
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Parity Checker
The parity checker is active when the high USART Parity Mode (UPM1) bit is set. Type
of parity check to be performed (odd or even) is selected by the UPM0 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 (PE) Flag can then be read by software to check if the frame had a parity error.
The PE 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 (UPM1 = 1).
This bit is valid until the receive buffer (UDR) is read.
Disabling the Receiver
In contrast to the Transmitter, disabling the of the Receiver will be immediate. Data from
ongoing receptions will therefore be lost. When disabled (i.e. the RXEN 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 UDR I/O location until the RXC Flag is cleared. The following code example shows how to flush the
receive buffer.
Assembly Code Example(1)
USART_Flush:
sbis UCSRA, RXC
ret
in
r16, UDR
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSRA & (1<<RXC) ) dummy = UDR;
}
Note:
1. The example code assumes that the part specific header file is included.
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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 49 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 8 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
(U2X = 1) of operation. Samples denoted zero are samples done when the RxD line is
idle (i.e. no communication activity).
Figure 49. 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 8 states for each bit in Double Speed mode. Figure 50 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 50. 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)
88
1
2
3
4
5
6
7
8
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ATmega323(L)
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ATmega323(L)
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 act 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 51 shows the sampling of the stop bit and the earliest possible beginning of the
start bit of the next frame.
Figure 51. 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 (FE) 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 51. 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 of 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 exact 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.
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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 30 and Table 31 list the maximum Receiver baud rate error that can be tolerated.
Note that normal speed mode has higher toleration of baud rate variations.
Table 30. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode
(U2X = 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 31. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2X = 1)
D
# (Data+Parity
Bit)
Rslow (%)
5
Rfast (%)
Max Total
Error (%)
Recommended
Max Receiver
Error (%)
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 (MPCM) bit in UCSRA 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 MPCM 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 contain data or address information. If the Receiver is set up for
frames with 9 data bits, then the ninth bit (RXB8) 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 MPCM
For an MCU to act as a Master MCU, it can use a 9-bit character frame format (UCSZ =
7). The ninth bit (TXB8) must be set when an address frame (TXB8 = 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 (MPCM in UCSRA
is set).
2. The Master MCU sends an address frame, and all Slaves Receive and read this
frame. In the Slave MCUs, the RXC Flag in UCSRA will be set as normal.
3. Each Slave MCU reads the UDR Register and determines if it has been
selected. If so, it clears the MPCM bit in UCSRA, otherwise it waits for the next
address byte and keeps the MPCM 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 MPCM bit set, will ignore
the data frames.
5. When the last data frame is received by the addressed MCU, the addressed
MCU sets the MPCM 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 (USBS = 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 MPCM bit.
The MPCM bit shares the same I/O location as the TXC Flag and this might accidentally
be cleared when using SBI or CBI instructions.
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Accessing
UBRRH/UCSRC
Registers
The UBRRH Register shares the same I/O location as the UCSRC Register. Therefore
some special consideration must be taken when accessing this I/O location.
Write Access
When doing a write access of this I/O location, the high bit of the value written, the
USART Register Select (URSEL) bit, controls which one of the two registers that will be
written. If URSEL is zero during a write operation, the UBRRH value will be updated. If
URSEL is one, the UCSRC setting will be updated.
The following code examples show how to access the two registers.
Assembly Code Examples(1)
...
; Set UBRRH to 2
ldi r16,0x02
out UBRRH,r16
...
; Set the USBS and the UCSZ1 bit to one, and
; the remaining bits to zero.
ldi r16,(1<<URSEL)|(1<<USBS)|(1<<UCSZ1)
out UCSRC,r16
...
C Code Examples(1)
...
/* Set UBRRH to 2 */
UBRRH = 0x02;
...
/* Set the USBS and the UCSZ1 bit to one, and */
/* the remaining bits to zero. */
UCSRC = (1<<URSEL)|(1<<USBS)|(1<<UCSZ1)
...
Note:
1. The example code assumes that the part specific header file is included.
As the code examples illustrate, write accesses of the two registers are relatively unaffected of the sharing of I/O location.
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Read Access
Doing a read access to the UBRRH or the UCSRC Register is a more complex operation. However, in most applications, it is rarely necessary to read any of these registers.
The read access is controlled by a timed sequence. Reading the I/O location once
returns the UBRRH Register contents. If the register location was read in previous system clock cycle, reading the register in the current clock cycle will return the UCSRC
contents. Note that the timed sequence for reading the UCSRC is an atomic operation.
Interrupts must therefore be disabled during the read operation.
The following code example shows how to read the UCSRC Register contents.
Assembly Code Example(1)
USART_ReadUCSRC:
; Save Global Interrupt Flag
in
r17,SREG
; Disable interrupts
cli
; Read UCSRC
in
r16,UBRRH
in
r16,UCSRC
; Restore Global Interrupt Flag
out SREG,r17
ret
C Code Example(1)
unsigned char USART_ReadUCSRC( void )
{
unsigned char sreg, ucsrc;
/* Save Global Interrupt Flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read UCSRC */
ucsrc = UBRRH;
ucsrc = UCSRC;
/* Restore Global Interrupt Flag */
SREG = sreg;
return ucsrc;
}
Note:
1. The example code assumes that the part specific header file is included.
The assembly code example returns the UCSRC value in r16.
Reading the UBRRH contents is not an atomic operation and therefore it can be read as
an ordinary register, as long as the previous instruction did not access the register
location.
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USART Register
Description
USART I/O Data Register –
UDR
Bit
7
6
5
4
3
2
1
0
$0C ($2C) Read
RXB[7:0]
UDR (Read)
$0C ($2C) Write
TXB[7:0]
UDR (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 UDR. The Transmit
Data Buffer Register (TXB) will be the destination for data written to the UDR Register
location. Reading the UDR 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 UDRE Flag in the UCSRA Register is
set. Data written to UDR when the UDRE 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.
USART Control and Status
Register A – UCSRA
Bit
7
6
5
4
3
2
1
0
$0B ($2B)
RXC
TXC
UDRE
FE
DOR
PE
U2X
MPCM
Read/Write
R
R/W
R
R
R
R
R/W
R/W
Initial Value
0
0
1
0
0
0
0
0
UCSRA
• Bit 7 – RXC: USART Receive Complete
This flag bit is one when there are unread data 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, the receive buffer will be flushed and consequently the RXC bit will become zero.
The RXC Flag can be used to generate a Receive Complete interrupt (see description of
the RXCIE bit).
• Bit 6 – TXC: USART Transmit Complete
This 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 (UDR). The
TXC 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 TXC Flag can generate a Transmit Complete interrupt (see description of the TXCIE bit).
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• Bit 5 – UDRE: USART Data Register Empty
The UDRE Flag indicates if the transmit buffer (UDR) is ready to receive new data. If
UDRE is one the buffer is empty and therefore ready be written. The UDRE Flag can
generate a Data Register Empty interrupt (see description of the UDRIE bit).
UDRE is set (one) after a reset to indicate that the Transmitter is ready.
• Bit 4 – FE: 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 (UDR) is read. The FE bit is zero when the stop
bit of received data is one. Always set this bit to zero when writing to UCSRA.
• Bit 3 – DOR: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occur 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. Always set this bit to zero when writing to
UCSRA.
• Bit 2 – PE: 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 (UPM1 = 1). This bit is valid until the
Receive Buffer (UDR) is read. Always set this bit to zero when writing to UCSRA.
• Bit 1 – U2X: Double the USART Transmission Speed
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.
• Bit 0 – MPCM: Multi-processor Communication Mode
Setting this bit enables the Multi-processor Communication mode. When the MPCM bit
is set, all the incoming frames received by the USART Receiver that do not contain
address information will be ignored. The Transmitter is unaffected by the MPCM setting.
For more detailed information see “Multi-processor Communication Mode” on page 91.
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USART Control and Status
Register B – UCSRB
Bit
7
6
5
4
3
2
1
0
$0A ($2A)
RXCIE
TXCIE
UDRIE
RXEN
TXEN
UCSZ2
RXB8
TXB8
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
W
Initial Value
0
0
0
0
0
0
0
0
UCSRB
• Bit 7 – RXCIE: RX Complete Interrupt Enable
Setting this bit to one enables interrupt on the RXC Flag. A USART Receive Complete
interrupt will be generated only if the RXCIE bit is set, the Global Interrupt Flag in SREG
is set and the RXC bit in UCSRA is set.
• Bit 6 – TXCIE: TX Complete Interrupt Enable
Setting this bit to one enables interrupt on the TXC Flag. A USART Transmit Complete
interrupt will be generated only if the TXCIE bit is set, the Global Interrupt Flag in SREG
is set and the TXC bit in UCSRA is set.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Setting this bit to one enables interrupt on the UDRE Flag. A Data Register Empty Interrupt will be generated only if the UDRIE bit is set, the Global Interrupt Flag in SREG is
set and the UDRE bit in UCSRA is set.
• Bit 4 – RXEN: Receiver Enable
Setting 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 FE, DOR, and PE Flags.
• Bit 3 – TXEN: Transmitter Enable
Setting 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
(setting the TXEN to zero) will not become effective until ongoing and pending transmissions are completed, i.e. when the Transmit Shift Register and Transmit Buffer Register
does not contain data to be transmitted. When disabled the Transmitter will no longer
override the TxD port.
• Bit 2 – UCSZ2: Character Size
The UCSZ2 bits combined with the UCSZ1:0 bit in UCSRC sets the number of data bits
(character size) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8: Receive Data Bit 8
RXB8 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 UDR.
• Bit 0 – TXB8: Transmit Data Bit 8
TXB8 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 UDR.
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USART Control and Status
Register C – UCSRC
Bit
7
6
5
4
3
2
1
0
URSEL
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
1
0
0
0
0
1
1
0
$20 ($40)
UCSRC
The UCSRC Register shares the same I/O location as the UBRRH Register. See the
“Accessing UBRRH/UCSRC Registers” on page 92 section which describes how to
access this register.
• Bit 7 – URSEL: Register Select
This bit selects between accessing the UCSRC or the UBRRH Register. It is read as
one when reading UCSRC. The URSEL must be one when writing the UCSRC.
• Bit 6 – UMSEL: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
Table 32. USART Mode
UMSEL
Mode
0
Asynchronous Operation
1
Synchronous Operation
• Bit 5:4 – UPM1:0: Parity Mode
This bit 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 UPM0 setting. If a mismatch is detected, the PE Flag in UCSRA will be set.
Table 33. Parity Mode
UPM1
UPM0
Parity Mode
0
0
Disabled
0
1
(Reserved)
1
0
Enabled, Even Parity
1
1
Enabled, Odd Parity
• Bit 3 – USBS: Stop Bit Select
This bit selects number of stop bits to be inserted by the Transmitter. The Receiver
ignores this setting.
Table 34. Stop Bit Select
USBS
Stop Bit(s)
0
1-bit
1
2-bit
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• Bit 2:1 – UCSZ1:0: Character Size
The UCSZ1:0 bits combined with the UCSZ2 bit in UCSRB sets the number of data bits
(character size) in a frame the Receiver and Transmitter uses.
Table 35. Character Size
UCSZ2
UCSZ1
UCSZ0
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 – UCPOL: Clock Polarity
This bit is used for synchronous mode only. Set this bit to zero when asynchronous
mode is used. The UCPOL bit sets the relationship between data output change and
data input sample, and the synchronous clock (XCK).
Transmitted Data Changed (Output
of TxD Pin)
Received Data Sampled (Input on
RxD Pin)
0
Falling XCK Edge
Rising XCK Edge
1
Rising XCK Edge
Falling XCK Edge
UCPOL
USART Baud Rate Registers –
UBRRL and UBRRHs
Bit
$20 ($40)
15
14
13
12
URSEL
–
–
–
$09 ($29)
Initial Value
10
9
8
UBRR[11:8]
UBRRH
UBRR[7:0]
7
Read/Write
11
6
5
4
3
UBRRL
2
1
0
R/W
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
The UBRRH Register shares the same I/O location as the UCSRC Register. See the
“Accessing UBRRH/UCSRC Registers” on page 92 section which describes how to
access this register.
• Bit 15 – URSEL: Register Select
This bit selects between accessing the UBRRH or the UCSRC Register. It is read as
zero when reading UBRRH. The URSEL must be zero when writing the UBRRH.
• Bit 14:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit
must be set to zero when UBRRH is written.
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• 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 36.
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 89). The error values are calculated using the following equation:
BaudRateClosest Match
- – 1 • 100%
Error[%] =  ------------------------------------------------------BaudRate
Table 36. Examples of UBRR Settings for Commonly Used Oscillator Frequencies –
UBRR = 0, Error = 0.0%
fosc = 1.0000 MHz
fosc = 1.8432 MHz
Baud
Rate
(bps)
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
14.4K
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
19.2K
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
28.8K
1
8.5%
3
8.5%
3
0.0%
7
0.0%
38.4K
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
57.6K
0
8.5%
1
8.5%
1
0.0%
3
0.0%
76.8K
–
–
1
-18.6%
1
-25.0%
2
0.0%
115.2K
–
–
0
8.5%
0
0.0%
1
0.0%
230.4K
–
–
–
–
–
–
0
0.0%
250K
–
–
–
–
–
–
–
–
Max
U2X = 0
U2X = 1
62.5 Kbps
U2X = 0
125 Kbps
U2X = 1
115.2 Kbps
fosc = 2.0000 MHz
230.4 Kbps
fosc = 3.6864 MHz
Baud
Rate
(bps)
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
2400
51
0.2%
103
0.2%
95
0.0%
191
0.0%
4800
25
0.2%
51
0.2%
47
0.0%
95
0.0%
9600
12
0.2%
25
0.2%
23
0.0%
47
0.0%
U2X = 0
U2X = 1
U2X = 0
U2X = 1
99
1457G–AVR–09/03
Table 36. Examples of UBRR Settings for Commonly Used Oscillator Frequencies –
UBRR = 0, Error = 0.0% (Continued)
14.4K
8
-3.5%
16
2.1%
15
0.0%
31
0.0%
19.2K
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
28.8K
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
38.4K
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
57.6K
1
8.5%
3
8.5%
3
0.0%
7
0.0%
76.8K
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
115.2K
0
8.5%
1
8.5%
1
0.0%
3
0.0%
230.4K
–
–
–
–
0
0.0%
1
0.0%
250K
–
–
0
0.0%
0
-7.8%
1
-7.8%
–
–
0
-7.8%
1M
Max
125 Kbps
250 Kbps
230.4 Kbps
fosc = 4.0000 MHz
460.8 Kbps
fosc = 7.3728 MHz
Baud
Rate
(bps)
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
2400
103
0.2%
207
0.2%
191
0.0%
383
0.0%
4800
51
0.2%
103
0.2%
95
0.0%
191
0.0%
9600
25
0.2%
51
0.2%
47
0.0%
95
0.0%
14.4K
16
2.1%
34
-0.8%
31
0.0%
63
0.0%
19.2K
12
0.2%
25
0.2%
23
0.0%
47
0.0%
28.8K
8
-3.5%
16
2.1%
15
0.0%
31
0.0%
38.4K
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
57.6K
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
76.8K
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
115.2K
1
8.5%
3
8.5%
3
0.0%
7
0.0%
230.4K
0
8.5%
1
8.5%
1
0.0%
3
0.0%
250K
0
0.0%
1
0.0%
1
-7.8%
3
-7.8%
0.5M
–
–
0
0.0%
0
-7.8%
1
-7.8%
1M
–
–
–
–
–
–
0
-7.8%
Max
U2X = 0
U2X = 1
250 Kbps
U2X = 0
0.5 Mbps
U2X = 1
460.8 Kpbs
921.6 Kbps
fosc = 8.0000 MHz
100
Baud
Rate
(bps)
UBRR
Error
UBRR
Error
2400
207
0.2%
416
-0.1%
4800
103
0.2%
207
0.2%
9600
51
0.2%
103
0.2%
14.4K
34
-0.8%
68
0.6%
U2X = 0
U2X = 1
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 36. Examples of UBRR Settings for Commonly Used Oscillator Frequencies –
UBRR = 0, Error = 0.0% (Continued)
19.2K
25
0.2%
51
0.2%
28.8K
16
2.1%
34
-0.8%
38.4K
12
0.2%
25
0.2%
57.6K
8
-3.5%
16
2.1%
76.8K
6
-7.0%
12
0.2%
115.2K
3
8.5%
8
-3.5%
230.4K
1
8.5%
3
8.5%
250K
1
0.0%
3
0.0%
0.5M
0
0.0%
1
0.0%
1M
–
–
0
0.0%
Max
0.5 Mbps
1 Mbps
101
1457G–AVR–09/03
Two-wire Serial
Interface (Byte
Oriented)
The Two-wire Serial Interface supports bi-directional serial communication. It is
designed primarily for simple but efficient integrated circuit (IC) control. The system is
comprised of two lines, SCL (Serial Clock) and SDA (Serial Data) that carry information
between the ICs connected to them. Various communication configurations can be
designed using this bus. Figure 52 shows a typical Two-wire Serial Bus configuration.
Any device connected to the bus can be Master or Slave. Note that all AVR devices connected to the bus must be powered to allow any bus operation.
Figure 52. Two-wire Serial Bus Configuration
V
Device 1
Device 2
Device 3 ....... Device n
R1
CC
R2
SCL
SDA
The Two-wire Serial Interface supports Master/Slave and Transmitter/Receiver operation at up to 400 kHz bus clock rate. The Two-wire Serial Interface has hardware
support for 7-bit addressing. When the Two-wire Serial Interface is enabled (TWEN in
TWCR is set), a glitch filter is enabled for the input signals from the pins PC0 (SCL) and
PC1 (SDA), and the output from these pins is slew-rate controlled. The Two-wire Serial
Interface is byte oriented. The operation of the Two-wire Serial Bus is shown as a pulse
diagram in Figure 53, including the START and STOP conditions and generation of ACK
signal by the bus Receiver.
Figure 53. Two-wire Serial Bus Timing Diagram
ACKNOWLEDGE
FROM RECEIVER
SDA
MSB
1
SCL
START
CONDITION
STOP CONDITION
REPEATED START CONDIT
R/W
BIT
2
7
8
9
ACK
1
2
8
9
ACK
The block diagram of the Two-wire Serial Interface is shown in Figure 54.
102
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 54. Block diagram of the Two-wire Serial Interface
ADDRESS REGISTER
AND
COMPARATOR
TWAR
INPUT
SDA
OUTPUT
DATA SHIFT
REGISTER
ACK
INPUT
SCL
OUTPUT
START/STOP
AND SYNC
ARBITRATION
TIMING
AND
CONTROL
SERIAL CLOCK
GENERATOR
CONTROL
REGISTER
AVR 8-BIT DATA BUS
TWDR
TWCR
STATUS
STATE MACHINE
AND
STATUS DECODER
STATUS
REGISTER
TWSR
The CPU interfaces with the Two-wire Serial Interface via the following five I/O Registers: the Two-wire Serial Interface Bit Rate Register (TWBR), the Two-wire Serial
Interface Control Register (TWCR), the Two-wire Serial Interface Status Register
(TWSR), the Two-wire Serial Interface Data Register (TWDR), and the Two-wire Serial
Interface Address Register (TWAR, used in Slave mode).
103
1457G–AVR–09/03
The Two-wire Serial Interface
Bit Rate Register – TWBR
Bit
7
6
5
4
3
2
1
0
TWBR7
TWBR6
TWBR5
TWBR4
TWBR3
TWBR2
TWBR1
TWBR0
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
$00 ($20)
TWBR
• Bits 7..0 – Two-wire Serial Interface Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a
frequency divider which generates the SCL clock frequency in the Master modes
according to the following equation:
•
f CK
Bit Rate = ---------------------------------------------------------16 + 2(TWBR) + t A f CK
Bit Rate = SCL frequency
•
fCK
= CPU Clock frequency
•
TWBR
= Contents of the Two-wire Serial Interface Bit Rate Register
•
tA
= Bus alignment adjustment
Note:
Both the Receiver and the Transmitter can stretch the low period of the SCL line when
waiting for user response, thereby reducing the average bit rate.
TWBR should be set to a value higher than seven to ensure correct Two-wire Serial Bus
functionality. The bus alignment adjustment is automatically inserted by the Two-wire
Serial Interface, and ensures the validity of setup and hold times on the bus for any
TWBR value higher than 7. This adjustment may vary from 200 ns to 600 ns depending
on bus loads and drive capabilities of the devices connected to the bus.
The Two-wire Serial Interface
Control Register – TWCR
Bit
7
6
5
4
3
2
1
0
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
Read/Write
R/W
R/W
R/W
R/W
R
R/W
R
R/W
Initial Value
0
0
0
0
0
0
0
0
$36 ($56)
TWCR
• Bit 7 – TWINT: Two-wire Serial Interface Interrupt Flag
This bit is set by hardware when the Two-wire Serial Interface has finished its current
job and expects application software response. If the I-bit in the SREG and TWIE in the
TWCR Register are set (one), the MCU will jump to the Interrupt Vector at address
$026. While the TWINT Flag is set, the bus SCL clock line low period is stretched. The
TWINT Flag must be cleared by software by writing a logic one to it. Note that this flag is
not automatically cleared by hardware when executing the interrupt routine. Also note
that clearing this flag starts the operation of the Two-wire Serial Interface, so all
accesses to the Two-wire Serial Interface Address Register – TWAR, Two-wire Serial
Interface Status Register – TWSR, and Two-wire Serial Interface Data Register – TWDR
must be complete before clearing this flag.
• Bit 6 – TWEA: Two-wire Serial Interface Enable Acknowledge Flag
TWEA Flag controls the generation of the acknowledge pulse. If the TWEA bit is set, the
ACK pulse is generated on the Two-wire Serial Bus if the following conditions are met:
1. The device’s own slave address has been received.
2. A general call has been received, while the TWGCE bit in the TWAR is set.
3. A data byte has been received in Master Receiver or Slave Receiver mode.
104
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
By setting the TWEA bit low, the device can be virtually disconnected from the Two-wire
Serial Bus temporarily. Address recognition can then be resumed by setting the TWEA
bit again.
• Bit 5 – TWSTA: Two-wire Serial Bus START Condition Flag
The TWSTA Flag is set by the application when it desires to become a Master on the
Two-wire Serial Bus. The Two-wire Serial Interface hardware checks if the bus is available, and generates a START condition on the bus if it is free. However, if the bus is not
free, the Two-wire Serial Interface waits until a STOP condition is detected, and then
generates a new START condition to claim the bus Master status.
• Bit 4 – TWSTO: Two-wire Serial Bus STOP Condition Flag
TWSTO is a Stop Condition Flag. In Master mode setting the TWSTO bit in the Control
Register will generate a STOP condition on the Two-wire Serial Bus. When the STOP
condition is executed on the bus, the TWSTO bit is cleared automatically. In Slave mode
setting the TWSTO bit can be used to recover from an error condition. No stop condition
is generated on the bus then, but the Two-wire Serial Interface returns to a well-defined
unaddressed Slave mode and releases the SCL and SDA lines to a high impedance
state.
• Bit 3 – TWWC: Two-wire Serial Bus Write Collision Flag
The TWWC bit is set when attempting to write to the Two-wire Serial Interface Data
Register – TWDR when TWINT is low. This flag is cleared by writing the TWDR Register
when TWINT is high.
• Bit 2 – TWEN: Two-wire Serial Interface Enable Bit
The TWEN bit enables Two-wire Serial Interface operation. If this bit is cleared (zero),
the bus outputs SDA and SCL are set to high impedance state, and the input signals are
ignored. The interface is activated by setting this bit (one).
• Bit 1 – Res: Reserved Bit
This bit is a reserved bit in the ATmega323 and will always read as zero.
• Bit 0 – TWIE: Two-wire Serial Interface Interrupt Enable
When this bit is enabled, and the I-bit in SREG is set, the Two-wire Serial Interface interrupt will be activated for as long as the TWINT Flag is high.
The TWCR is used to control the operation of the Two-wire Serial Interface. It is used to
enable the Two-wire Serial Interface, to initiate a Master access by applying a START
condition to the bus, to generate a Receiver acknowledge, to generate a stop condition,
and to control halting of the bus while the data to be written to the bus are written to the
TWDR. It also indicates a write collision if data is attempted written to TWDR while the
register is inaccessible.
105
1457G–AVR–09/03
The Two-wire Serial Interface
Status Register – TWSR
Bit
7
6
5
4
3
2
1
0
TWS7
TWS6
TWS5
TWS4
TWS3
–
–
–
Read/Write
R
R
R
R
R
R
R
R
Initial Value
1
1
1
1
1
0
0
0
$01 ($21)
TWSR
• Bits 7..3 – TWS: Two-wire Serial Interface Status
These five bits reflect the status of the Two-wire Serial Interface logic and the Two-wire
Serial Bus.
• Bits 2..0 – Res: Reserved bits
These bits are reserved in ATmega323 and will always read as zero
The TWSR is read only. It contains a status code which reflects the status of the Twowire Serial Interface logic and the Two-wire Serial Bus. There are 26 possible status
codes. When TWSR contains $F8, no relevant state information is available and no
Two-wire Serial Interface interrupt is requested. A valid status code is available in
TWSR one CPU clock cycle after the Two-wire Serial Interface Interrupt Flag (TWINT) is
set by hardware and is valid until one CPU clock cycle after TWINT is cleared by software. Table 37 to Table 44 give the status information for the various modes.
The Two-wire Serial Interface
Data Register – TWDR
Bit
7
6
5
4
3
2
1
0
TWD7
TWD6
TWD5
TWD4
TWD3
TWD2
TWD1
TWD0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
1
1
1
1
1
1
1
1
$03 ($23)
TWDR
• Bits 7..0 – TWD: Two-wire Serial Interface Data Register
These eight bits constitute the next data byte to be transmitted, or the latest data byte
received on the Two-wire Serial Bus.
In Transmit mode, TWDR contains the next byte to be transmitted. In Receive mode, the
TWDR contains the last byte received. It is writable while the Two-wire Serial Interface
is not in the process of shifting a byte. This occurs when the Two-wire Serial Interface
Interrupt Flag (TWINT) is set by hardware. Note that the Data Register cannot be initialized by the user before the first interrupt occurs. The data in TWDR remain stable as
long as TWINT is set. While data is shifted out, data on the bus is simultaneously shifted
in. TWDR always contains the last byte present on the bus, except after a wake up from
ADC Noise Reduction mode, Power-down mode, or Power-save mode by the Two-wire
Serial Interface interrupt. For example, in the case of a lost bus arbitration, no data is
lost in the transition from Master to Slave. Handling of the ACK Flag is controlled automatically by the Two-wire Serial Interface logic, the CPU cannot access the ACK bit
directly.
106
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The Two-wire Serial Interface
(Slave) Address Register –
TWAR
Bit
7
6
5
4
3
2
1
0
TWA6
TWA5
TWA4
TWA3
TWA2
TWA1
TWA0
TWGCE
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
1
1
1
1
1
1
1
0
$02 ($22)
TWAR
• Bits 7..1 – TWA: Two-wire Serial Interface (Slave) Address Register
These seven bits constitute the slave address of the Two-wire Serial Bus unit.
• Bit 0 – TWGCE: Two-wire Serial Interface General Call Recognition Enable bit
This bit enables, if set, the recognition of the General Call given over the Two-wire Serial
Bus.
The TWAR should be loaded with the 7-bit slave address (in the seven most significant
bits of TWAR) to which the Two-wire Serial Interface will respond when programmed as
a Slave Transmitter or Receiver, and not needed in the Master modes. The LSB of
TWAR is used to enable recognition of the general call address ($00). There is an associated address comparator that looks for the slave address (or general call address if
enabled) in the received serial address. If a match is found, an interrupt request is
generated.
Two-wire Serial Interface
Modes
The Two-wire Serial Interface can operate in four different modes:
•
Master Transmitter
•
Master Receiver
•
Slave Receiver
•
Slave Transmitter
Data transfer in each mode of operation is shown in Figure 55 to Figure 58. These figures contain the following abbreviations:
S: START condition
R: Read bit (high level at SDA)
W: Write bit (low level at SDA)
A: Acknowledge bit (low level at SDA)
A: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 55 to Figure 58, circles are used to indicate that the Two-wire Serial Interface
Interrupt Flag is set. The numbers in the circles show the status code held in TWSR. At
these points, actions must be taken by the application to continue or complete the Twowire Serial Bus transfer. The Two-wire Serial Bus transfer is suspended until the Twowire Serial Interface Interrupt Flag is cleared by software.
The Two-wire Serial Interface Interrupt Flag is not automatically cleared by hardware
when executing the interrupt routine. Software has to clear the flag to continue the Twowire transfer. Also note that the Two-wire Serial Interface starts execution as soon as
this bit is cleared, so that all access to TWAR, TWDR, and TWSR must have been completed before clearing this flag.
107
1457G–AVR–09/03
When the Two-wire Serial Interface Interrupt Flag is set, the status code in TWSR is
used to determine the appropriate software action. For each status code, the required
software action and details of the following serial transfer are given in Table 37 to Table
44.
Master Transmitter Mode In the Master Transmitter mode, a number of data bytes are transmitted to a Slave
Receiver (see Figure 55). Before Master Transmitter mode can be entered, the TWCR
must be initialized as follows:
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
Value
0
X
0
0
0
1
0
X
TWEN must be set to enable the Two-wire Serial Interface, TWSTA and TWSTO must
be cleared.
The Master Transmitter mode may now be entered by setting the TWSTA bit. The Twowire Serial Interface logic will then test the Two-wire Serial Bus and generate a START
condition as soon as the bus becomes free. When a START condition is transmitted, the
Two-wire Serial Interface Interrupt Flag (TWINT) is set by hardware, and the status code
in TWSR will be $08. TWDR must then be loaded with the slave address and the Data
Direction bit (SLA+W). Clearing the TWINT bit in software will continue the transfer. The
TWINT Flag is cleared by writing a logic one to the flag.
When the slave address and the direction bit have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of status codes in
TWSR are possible. Possible status codes in Master mode are $18, $20, or $38. The
appropriate action to be taken for each of these status codes is detailed in Table 37. The
data must be loaded when TWINT is high only. If not, the access will be discarded, and
the Write Collision bit – TWWC will be set in the TWCR Register. This scheme is
repeated until the last byte is sent and the transfer is ended by generating a STOP condition or a repeated START condition. A STOP condition is generated by setting
TWSTO, a repeated START condition is generated by setting TWSTA and TWSTO.
After a repeated START condition (state $10) the Two-wire Serial Interface can access
the same Slave again, or a new Slave without transmitting a STOP condition. Repeated
START enables the Master to switch between Slaves, Master Transmitter mode and
Master Receiver mode without loosing control over the bus.
Assembly code illustrating operation of the Master Transmitter mode is given at the end
of the TWI section.
Master Receiver Mode
In the Master Receiver mode, a number of data bytes are received from a Slave Transmitter (see Figure 56). The transfer is initialized as in the Master Transmitter mode.
When the START condition has been transmitted, the TWINT Flag is set by hardware.
The software must then load TWDR with the 7-bit slave address and the Data Direction
bit (SLA+R). The transfer will then continue when the TWINT Flag is cleared by
software.
When the slave address and the direction bit have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of status codes in
TWSR are possible. Possible status codes in Master mode are $40, $48, or $38. The
appropriate action to be taken for each of these status codes is detailed in Table .
Received data can be read from the TWDR Register when the TWINT Flag is set high
by hardware. This scheme is repeated until the last byte has been received and a STOP
condition is transmitted by writing a logic one to the TWSTO bit in the TWCR Register.
108
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
After a repeated START condition (state $10), the Two-wire Serial Interface may switch
to the Master Transmitter mode by loading TWDR with SLA+W or access a new Slave
as Master Receiver or Transmitter.
Assembly code illustrating operation of the Master Receiver mode is given at the end of
the TWI section.
Slave Receiver Mode
In the Slave Receiver mode, a number of data bytes are received from a Master Transmitter (see Figure 57). To initiate the Slave Receiver mode, TWAR and TWCR must be
initialized as follows:
TWAR
TWA6
TWA5
TWA4
Value
TWA3
TWA2
TWA1
TWA0
TWGCE
Device’s Own Slave Address
The upper seven bits are the address to which the Two-wire Serial Interface will respond
when addressed by a Master. If the LSB is set, the Two-wire Serial Interface will
respond to the general call address ($00), otherwise it will ignore the general call
address.
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
Value
0
1
0
0
0
1
0
X
TWEN must be set to enable the Two-wire Serial Interface. The TWEA bit must be set to
enable the acknowledgement of the device’s own slave address or the general call
address. TWSTA and TWSTO must be cleared.
When TWAR and TWCR have been initialized, the Two-wire Serial Interface waits until
it is addressed by its own slave address (or the general call address if enabled) followed
by the Data Direction bit which must be “0” (write) for the Two-wire Serial Interface to
operate in the Slave Receiver mode. After its own slave address and the write bit have
been received, the Two-wire Serial Interface Interrupt Flag is set and a valid status code
can be read from TWSR. The status code is used to determine the appropriate software
action. The appropriate action to be taken for each status code is detailed in Table 42.
The Slave Receiver mode may also be entered if arbitration is lost while the Two-wire
Serial Interface is in the Master mode (see states $68 and $78).
If the TWEA bit is reset during a transfer, the Two-wire Serial Interface will return a “Not
Acknowledge” (“1”) to SDA after the next received data byte. While TWEA is reset, the
Two-wire Serial Interface does not respond to its own slave address. However, the Twowire Serial Bus is still monitored and address recognition may resume at any time by
setting TWEA. This implies that the TWEA bit may be used to temporarily isolate the
Two-wire Serial Interface from the Two-wire Serial Bus.
In ADC Noise Reduction mode, Power-down mode, and Power-save mode, the clock
system to the Two-wire Serial Interface is turned off. If the Slave Receive mode is
enabled, the interface can still acknowledge a general call and its own slave address by
using the Two-wire Serial Bus clock as a clock source. The part will then wake up from
sleep and the Two-wire Serial Interface will hold the SCL clock will low during the wake
up and until the TWINT Flag is cleared.
Note that the Two-wire Serial Interface Data Register – TWDR does not reflect the last
byte present on the bus when waking up from these sleep modes.
Assembly code illustrating operation of the Slave Receiver mode is given at the end of
the TWI section.
109
1457G–AVR–09/03
Slave Transmitter Mode
In the Slave Transmitter mode, a number of data bytes are transmitted to a Master
Receiver (see Figure 58). The transfer is initialized as in the Slave Receiver mode.
When TWAR and TWCR have been initialized, the Two-wire Serial Interface waits until
it is addressed by its own slave address (or the general call address if enabled) followed
by the Data Direction bit which must be “1” (read) for the Two-wire Serial Interface to
operate in the Slave Transmitter mode. After its own slave address and the read bit
have been received, the Two-wire Serial Interface Interrupt Flag is set and a valid status
code can be read from TWSR. The status code is used to determine the appropriate
software action. The appropriate action to be taken for each status code is detailed in
Table 43. The Slave Transmitter mode may also be entered if arbitration is lost while the
Two-wire Serial Interface is in the Master mode (see state $B0).
If the TWEA bit is reset during a transfer, the Two-wire Serial Interface will transmit the
last byte of the transfer and enter state $C0 or state $C8. the Two-wire Serial Interface
is switched to the not addressed Slave mode, and will ignore the Master if it continues
the transfer. Thus the Master Receiver receives all “1” as serial data. While TWEA is
reset, the Two-wire Serial Interface does not respond to its own slave address. However, the Two-wire Serial Bus is still monitored and address recognition may resume at
any time by setting TWEA. This implies that the TWEA bit may be used to temporarily
isolate the Two-wire Serial Interface from the Two-wire Serial Bus.
Assembly code illustrating operation of the Slave Receiver mode is given at the end of
the TWI section.
Miscellaneous States
There are two status codes that do not correspond to a defined Two-wire Serial Interface state, see Table 37.
Status $F8 indicates that no relevant information is available because the Two-wire
Serial Interface Interrupt Flag (TWINT) is not set yet. This occurs between other states,
and when the Two-wire Serial Interface is not involved in a serial transfer.
Status $00 indicates that a bus error has occurred during a Two-wire Serial Bus transfer. A bus error occurs when a START or STOP condition occurs at an illegal position in
the format frame. Examples of such illegal positions are during the serial transfer of an
address byte, a data byte or an acknowledge bit. When a bus error occurs, TWINT is
set. To recover from a bus error, the TWSTO Flag must set and TWINT must be cleared
by writing a logic one to it. This causes the Two-wire Serial Interface to enter the not
addressed Slave mode and to clear the TWSTO Flag (no other bits in TWCR are
affected). The SDA and SCL lines are released and no STOP condition is transmitted.
110
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 37. Miscellaneous States
Application Software Response
Status Code
(TWSR)
Status of the Two-wire Serial
Bus and Two-wire Serial Interface Hardware
To TWCR
To/from TWDR
STA
STO
TWINT
TWEA
Next Action Taken by Two-wire Serial Interface Hardware
$08
A START condition has been
transmitted
Load SLA+W
X
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
$10
A repeated START condition
has been transmitted
Load SLA+W or
X
0
1
X
Load SLA+R
X
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+R will be transmitted;
Logic will switch to Master Receiver mode
Load data byte or
0
0
1
X
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Load data byte or
0
0
1
X
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Load data byte or
0
0
1
X
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
Load data byte or
0
0
1
X
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
No TWDR action or
0
0
1
X
No TWDR action
1
0
1
X
$18
$20
$28
$30
$38
SLA+W has been transmitted;
ACK has been received
SLA+W has been transmitted;
NOT ACK has been received
Data byte has been transmitted;
ACK has been received
Data byte has been transmitted;
NOT ACK has been received
Arbitration lost in SLA+W or
data bytes
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Two-wire Serial Bus will be released and not addressed
Slave mode entered
A START condition will be transmitted when the bus becomes free
111
1457G–AVR–09/03
Figure 55. Formats and States in the Master Transmitter Mode
MT
Successfull
Transmission
to a Slave
Receiver
S
SLA
W
A
DATA
$18
$08
A
P
$28
Next Transfer
Started with a
Repeated Start
Condition
S
SLA
W
$10
Not Acknowledge
Received after the
Slave Address
A
R
P
$20
MR
Not Acknowledge
Received after a Data
Byte
A
P
$30
Arbitration Lost in Slave
Address or Data Byte
A or A
Other Master
Continues
$38
Arbitration Lost and
Addressed as Slave
A
$68
From Master to Slave
From Slave to Master
Assembly Code Example –
Master Transmitter Mode
A or A
Other Master
Continues
$38
Other Master
Continues
$78
DATA
To Corresponding
States in Slave Mode
$B0
A
n
Any Number of Data Bytes
and their Associated Acknowledge Bits
This Number (Contained in TWSR) Corresponds
to a Defined State of the Two-wire Serial Bus
;The Slave being addressed has address 0x64. The code examples also assumes
some sort of error handling routine named ERROR.
;Part specific include file and TWI include file must be included.
; <Initialize registers, including TWAR, TWBR and TWCR>
ldi
r16, (1<<TWSTA) | (1<<TWEN)
out
TWCR, r16
; Send START condition
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait1: in
sbrs r16,TWINT
; the START condition has been transmitted
rjmp wait1
in
r16, TWSR
; Check value of TWI Status Register.
cpi
r16, START
; If status different from START go to ERROR
brne ERROR
112
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
ldi
r16, 0xc8
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
wait2: in
r16, TWCR
; Load SLA+W into TWDR Register
; Clear TWINT bit in TWCR to start transmission
; of address
; Wait for TWINT Flag set. This indicates that
sbrs r16, TWINT
; SLA+W has been transmitted, and ACK/NACK has
rjmp wait2
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MT_SLA_ACK
; different from MT_SLA_ACK, go to ERROR
brne ERROR
ldi
r16, 0x33
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
wait3: in
r16, TWCR
; Load data (here, data=0x33) into TWDR
; Register
; Clear TWINT bit in TWCR to start transmission
; of data
; Wait for TWINT Flag set. This indicates that
sbrs r16, TWINT
; data has been transmitted, and ACK/NACK has
rjmp wait3
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MT_DATA_ACK ; different from MT_DATA_ACK, go to ERROR
brne ERROR
ldi
r16, 0x44
; Load data (here, data = 0x44) into TWDR
; Register
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start transmission
; of data
;<send more data bytes if needed>
wait4: in
r16, TWCR
; Wait for TWINT Flag set. This indicates that
sbrs r16, TWINT
; data has been transmitted, and ACK/NACK has
rjmp wait4
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MT_DATA_ACK ; different from MT_DATA_ACK, go to ERROR
brne ERROR
ldi
r16, (1<<TWINT) | (1<<TWSTO) | (1<<TWEN)
out
TWCR, r16
; Transmit STOP condition
113
1457G–AVR–09/03
Table 38. Miscellaneous States
Application Software Response
Status Code
(TWSR)
Status of the Two-wire Serial
Bus and Two-wire Serial Interface hardware
To TWCR
To/from TWDR
STA
STO
TWINT
TWEA
Next Action Taken by Two-wire Serial Interface Hardware
$08
A START condition has been
transmitted
Load SLA+R
X
0
1
X
SLA+R will be transmitted
ACK or NOT ACK will be received
$10
A repeated START condition
has been transmitted
Load SLA+R or
X
0
1
X
Load SLA+W
X
0
1
X
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+W will be transmitted
Logic will switch to Master Transmitter mode\
No TWDR action or
0
0
1
X
No TWDR action
1
0
1
X
No TWDR action or
0
0
1
0
No TWDR action
0
0
1
1
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
0
0
1
0
$38
$40
$48
Arbitration lost in SLA+R or
NOT ACK bit
SLA+R has been transmitted;
ACK has been received
SLA+R has been transmitted;
NOT ACK has been received
$50
Data byte has been received;
ACK has been returned
Read data byte or
Read data byte
0
0
1
1
$58
Data byte has been received;
NOT ACK has been returned
Read data byte or
Read data byte or
1
0
0
1
1
1
X
X
Read data byte
1
1
1
X
114
Two-wire Serial Bus will be released and not addressed
Slave mode will be entered
A START condition will be transmitted when the bus
becomes free
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Repeated START will be transmitted
STOP condition will be transmitted and TWSTO Flag
will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Repeated START will be transmitted
STOP condition will be transmitted and TWSTO Flag
will be reset
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 56. Formats and States in the Master Receiver Mode
MR
Successfull
Reception
from a Slave
Receiver
S
SLA
R
$08
A
DATA
A
$40
DATA
$50
A
P
$58
Next Transfer
Started with a
Repeated Start
Condition
S
SLA
R
$10
Not Acknowledge
Received after the
Slave Address
A
W
P
$48
MT
Arbitration Lost in Slave
Address or Data Byte
Other Master
Continues
A or A
A
$38
Arbitration Lost and
Addressed as Slave
$38
Other Master
Continues
A
$68
$78
DATA
From Master to Slave
From Slave to Master
Assembly Code Example –
Master Receiver Mode
Other Master
Continues
To Corresponding
States in Slave Mode
$B0
A
n
Any Number of Data Bytes
and their Associated Acknowledge Bits
This Number (Contained in TWSR) Corresponds
to a Defined State of the Two-wire Serial Bus
;Part specific include file and TWI include file must be included.
; <Initialize registers TWAR and TWBR>
ldi
r16, (1<<TWINT) | (1<<TWSTA) | (1<<TWEN)
out
wait5:in
TWCR, r16
r16,TWCR
sbrs r16, TWINT
;Send START condition
; Wait for TWINT Flag set. This indicates that
; the START condition has been transmitted
rjmp wait5
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, START
; different from START, go to ERROR
brne ERROR
ldi
r16, 0xc9
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start transmission
; of SLA+R
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait6:in
; Load SLA+R into TWDR Register
sbrs r16, TWINT
; SLA+R has been transmitted, and ACK/NACK has
rjmp wait6
; been received
115
1457G–AVR–09/03
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MR_SLA_ACK
; different from MR_SLA_ACK, go to ERROR
brne ERROR
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start reception of
; data. Setting TWEA causes ACK to be returned
; after reception of data byte
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait7:in
sbrs r16, TWINT
; data has been received and ACK returned
rjmp wait7
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MR_DATA_ACK
; different from MR_DATA_ACK, go to ERROR
brne ERROR
in
r16, TWDR
nop
; Input received data from TWDR.
;<do something with received data>
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start reception of
; data. Setting TWEA causes ACK to be returned
;after reception of data byte
;<Receive more data bytes if needed>
;receive next to last data byte.
wait8:in
r16,TWCR
sbrs r16, TWINT
; Wait for TWINT Flag set. This indicates that
; data has been received and ACK returned
rjmp wait8
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MR_DATA_ACK
; different from MR_DATA_ACK, go to ERROR
brne ERROR
in
r16, TWDR
nop
; Input received data from TWDR.
;<do something with received data>
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
;
;
;
;
;
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait9:in
sbrs r16, TWINT
Clear TWINT bit in TWCR to start reception of
data. Not setting TWEA causes NACK to be
returned after reception of next data byte
receive last data byte. Signal this to Slave
by returning NACK
; data has been received and NACK returned
rjmp wait9
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, MR_DATA_NACK
; different from MR_DATA_NACK, go to ERROR
brne ERROR
116
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
in
r16, TWDR
; Input received data from TWDR.
nop
;<do something with received data>
ldi
r16, (1<<TWINT) | (1<<TWSTO) | (1<<TWEN)
out
TWCR, r16
; Send STOP signal
Table 39. Miscellaneous States
Application Software Response
Status Code
(TWSR)
Status of the Two-wire Serial Bus
and Two-wire Serial Interface
Hardware
To TWCR
To/from TWDR
STA
STO
TWINT
TWEA
No TWDR action or
X
0
1
0
$60
Own SLA+W has been received;
ACK has been returned
No TWDR action
X
0
1
1
$68
Arbitration lost in SLA+R/W as
Master; own SLA+W has been
received; ACK has been returned
No TWDR action or
X
0
1
0
No TWDR action
X
0
1
1
$70
General call address has been
received; ACK has been returned
No TWDR action or
X
0
1
0
No TWDR action
X
0
1
1
$78
Arbitration lost in SLA+R/W as
Master; General call address has
been received; ACK has been
returned
No TWDR action or
X
0
1
0
No TWDR action
X
0
1
1
$80
Previously addressed with own
SLA+W; data has been received;
ACK has been returned
Read data byte or
X
0
1
0
Read data byte
X
0
1
1
$88
Previously addressed with own
SLA+W; data has been received;
NOT ACK has been returned
Read data byte or
0
0
1
0
Read data byte or
0
0
1
1
Read data byte or
1
0
1
0
Read data byte
1
0
1
1
$90
Previously addressed with
general call; data has been received; ACK has been returned
Read data byte or
X
0
1
0
Read data byte
X
0
1
1
$98
Previously addressed with
general call; data has been
received; NOT ACK has been
returned
Read data byte or
0
0
1
0
Read data byte or
0
0
1
1
Read data byte or
1
0
1
0
Read data byte
1
0
1
1
Read data byte or
0
0
1
0
Read data byte or
0
0
1
1
Read data byte or
1
0
1
0
Read data byte
1
0
1
1
$A0
A STOP condition or repeated
START condition has been
received while still addressed as
Slave
Next Action Taken by Two-wire Serial Interface Hardware
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
117
1457G–AVR–09/03
Figure 57. Formats and States in the Slave Receiver Mode
Reception of the Own
Slave Address and One or
more Data Bytes. All are
Acknowledged
S
SLA
W
A
DATA
$60
A
DATA
$80
Last Data Byte Received
is not Acknowledged
A
P or S
$80
$A0
A
P or S
$88
Arbitration Lost as Master
and Addressed as Slave
A
$68
Reception of the General Call
Address and One or more Data
Bytes
General Call
A
DATA
$70
A
DATA
$90
Last Data Byte received is
not Acknowledged
A
P or S
$90
$A0
A
P or S
$98
Arbitration Lost as Master and
Addressed as Slave by General Call
A
$78
From Master to Slave
From Slave to Master
Assembly Code Example –
Slave Receiver Mode
DATA
A
n
Any Number of Data Bytes
and their Associated Acknowledge Bits
This Number (Contained in TWSR) Corresponds
to a Defined State of the Two-wire Serial Bus
;Part specific include file and TWI include file must be included.
; <Initialize registers TWAR and TWBR>
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Enable TWI in Slave Receiver Mode
; <Receive START condition and SLA+W>
wait10:in
r16,TWCR
sbrs r16, TWINT
; Wait for TWINT Flag set. This indicates that
; START followed by SLA+W has been received
rjmp wait10
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, SR_SLA_ACK
; different from SR_SLA_ACK, go to ERROR
brne ERROR
118
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start reception of
; first data byte. Setting TWEA indicates that
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
; ACK should be returned after receiving first
; data byte
wait12:in
r16,TWCR
sbrs r16, TWINT
; Wait for TWINT Flag set. This indicates that
; data has been received and ACK returned
rjmp wait12
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, SR_DATA_ACK
; different from SR_DATA_ACK, go to ERROR
brne ERROR
in
r16, TWDR
nop
; Input received data from TWDR.
;<do something with received data>
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start reception of
; data. Not setting TWEA causes NACK to be
; returned after reception of next data byte
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait13:in
sbrs r16, TWINT
; data has been received and NACK returned
rjmp wait13
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, SR_DATA_NACK
; different from SR_DATA_NACK, go to ERROR
brne ERROR
in
r16, TWDR
nop
; Input received data from TWDR.
;<do something with received data>
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
;
;
;
;
Clear TWINT bit in TWCR to start reception of
data. Setting TWEA causes TWI unit to enter
not addressed Slave mode with recognition of
own SLA
;<Wait for next data transmission or do something else>
119
1457G–AVR–09/03
Table 40. Miscellaneous States
Application Software Response
Status Code
(TWSR)
$A8
$B0
$B8
$C0
$C8
120
Status of the Two-wire Serial Bus
and Two-wire Serial Interface
Hardware
Own SLA+R has been received;
ACK has been returned
To TWCR
To/from TWDR
STA
STO
TWINT
TWEA
Load data byte or
X
0
1
0
Load data byte
X
0
1
1
Arbitration lost in SLA+R/W as
Master; own SLA+R has been
received; ACK has been returned
Load data byte or
X
0
1
0
Load data byte
X
0
1
1
Data byte in TWDR has been
transmitted; ACK has been
received
Load data byte or
X
0
1
0
Load data byte
X
0
1
1
Data byte in TWDR has been
transmitted; NOT ACK has been
received
No TWDR action or
0
0
1
0
No TWDR action or
0
0
1
1
No TWDR action or
1
0
1
0
No TWDR action
1
0
1
1
No TWDR action or
0
0
1
0
No TWDR action or
0
0
1
1
No TWDR action or
1
0
1
0
No TWDR action
1
0
1
1
Last data byte in TWDR has been
transmitted (TWEA = “0”); ACK
has been received
Next Action Taken by Two-wire Serial Interface Hardware
Last data byte will be transmitted and NOT ACK should
be received
Data byte will be transmitted and ACK should be received
Last data byte will be transmitted and NOT ACK should
be received
Data byte will be transmitted and ACK should be received
Last data byte will be transmitted and NOT ACK should
be received
Data byte will be transmitted and ACK should be received
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 58. Formats and States in the Slave Transmitter Mode
Reception of the
Own Slave Address
and One or
More Data Bytes
S
SLA
R
A
DATA
$A8
Arbitration Lost as Master
and Addressed as Slave
A
DATA
$B8
A
P or S
$C0
A
$B0
Last Data Byte Transmitted.
Switched to not Addressed
Slave (TWEA = '0')
A
All 1's
P or S
$C8
From Master to Slave
DATA
From Slave to Master
Assembly Code Example –
Slave Transmitter Mode
A
n
Any Number of Data Bytes
and their Associated Acknowledge Bits
This Number (Contained in TWSR) Corresponds
to a Defined State of the Two-wire Serial Bus
; Part specific include file and TWI include file must be included.
; <Initialize registers, including TWAR, TWBR and TWCR>
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Enable TWI in Slave Transmitter mode
; <Receive START condition and SLA+R>
wait14:in
r16,TWCR
; Wait for TWINT Flag set. This indicates that
sbrs r16, TWINT
; SLA+R has been received, and ACK/NACK has
rjmp wait14
; been returned
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, ST_SLA_ACK
; different from ST_SLA_ACK, go to ERROR
brne ERROR
ldi
r16, 0x33
out
TWDR, r16
; Load data(here, data=0x33)into TWDR Register
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start transmission
; of data. Setting TWEA indicates that ACK
; should be received when transfer finished
; <Send more data bytes if needed>
wait15:in
r16,TWCR
; Wait for TWINT Flag set. This indicates that
sbrs r16, TWINT
; data has been transmitted, and ACK/NACK has
rjmp wait15
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, ST_DATA_ACK
; different from ST_DATA_ACK, go to ERROR
brne ERROR
121
1457G–AVR–09/03
ldi
r16, 0x44
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Clear TWINT bit in TWCR to start transmission
; of data. Setting TWEA indicates that ACK
; should be received when transfer finished
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait16:in
; Load data(here, data=0x44)into TWDR Register
sbrs r16, TWINT
; data has been transmitted, and ACK/NACK has
rjmp wait16
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, ST_DATA_ACK
; different from ST_DATA_ACK, go to ERROR
brne ERROR
ldi
r16, 0x55
out
TWDR, r16
ldi
r16, (1<<TWINT) | (1<<TWEN)
out
TWCR, r16
;
;
;
;
r16,TWCR
; Wait for TWINT Flag set. This indicates that
wait17:in
; Load data(here, data=0x55)into TWDR Register
Clear TWINT bit in TWCR to start transmission
of data. Not setting TWEA indicates that
NACK should be received after data byte
Master signalling end of transmission)
sbrs r16, TWINT
; data has been transmitted, and ACK/NACK has
rjmp wait17
; been received
in
r16, TWSR
; Check value of TWI Status Register. If status
cpi
r16, ST_LAST_DATA
; different from ST_LAST_DATA, go to ERROR
brne ERROR
ldi
r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out
TWCR, r16
; Continue address recognition in Slave
; Transmitter mode
Table 41. Miscellaneous States
Application Software Response
Status Code
(TWSR)
Status of the Two-wire Serial
Bus and Two-wire Serial Interface Hardware
To TWCR
To/from TWDR
$F8
No relevant state information
available; TWINT = “0”
No TWDR action
$00
Bus error due to an illegal
START or STOP condition
No TWDR action
TWI Include File
STA
STO
TWINT
TWEA
No TWCR action
0
1
1
Next Action Taken by Two-wire Serial Interface Hardware
Wait or proceed current transfer
X
Only the internal hardware is affected, no STOP condition is sent on the bus. In all cases, the bus is released
and TWSTO is cleared.
;***** General Master status codes *****
.equ
START
=$08
;START has been transmitted
.equ
REP_START
=$10
;Repeated START has been transmitted
;***** Master Transmitter status codes *****
122
.equ
MT_SLA_ACK
=$18
;SLA+W has been transmitted and ACK received
.equ
MT_SLA_NACK
=$20
;SLA+W has been transmitted and NACK received
.equ
MT_DATA_ACK
=$28
;Data byte has been transmitted and ACK
;received
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
.equ
MT_DATA_NACK
=$30
;Data byte has been transmitted and NACK
;received
.equ
MT_ARB_LOST
=$38
;Arbitration lost in SLA+W or data bytes
;***** Master Receiver status codes *****
.equ
MR_ARB_LOST
=$38
;Arbitration lost in SLA+R or NACK bit
.equ
MR_SLA_ACK
=$40
;SLA+R has been transmitted and ACK received
.equ
MR_SLA_NACK
=$48
;SLA+R has been transmitted and NACK received
.equ
MR_DATA_ACK
=$50
;Data byte has been received and ACK returned
.equ
MR_DATA_NACK
=$58
;Data byte has been received and NACK
;transmitted
;***** Slave Transmitter status codes *****
.equ
ST_SLA_ACK
.equ
ST_ARB_LOST_SLA_ACK=$B0 ;Arbitration lost in SLA+R/W as Master. Own
;SLA+W has been received and ACK returned
=$A8
;Own SLA+R has been received and ACK returned
.equ
ST_DATA_ACK
=$B8
;Data byte has been transmitted and ACK
;received
.equ
ST_DATA_NACK
=$C0
;Data byte has been transmitted and NACK
;received
.equ
ST_LAST_DATA
=$C8
;Last byte in I2DR has been transmitted
;(TWEA = “0”), ACK has been received
;***** Slave Receiver status codes *****
.equ
SR_SLA_ACK
=$60
.equ
SR_ARB_LOST_SLA_ACK=$68;Arbitration lost in SLA+R/W as Master. Own
;SLA+R has been received and ACK returned
.equ
SR_GCALL_ACK
.equ
SR_ARB_LOST_GCALL_ACK=$78;Arbitration lost in SLA+R/W as Master.
;General Call has been received and ACK
;returned
.equ
SR_DATA_ACK
=$80
;Previously addressed with own SLA+W. Data byte
;has been received and ACK returned
.equ
SR_DATA_NACK
=$88
;Previously addressed with own SLA+W. Data byte
;has been received and NACK returned
.equ
SR_GCALL_DATA_ACK=$90 ;Previously addressed with General Call.Data
;byte has been received and ACK returned
.equ
SR_GCALL_DATA_NACK=$98 ;Previously addressed with General Call. Data
;byte has been received and NACK returned
.equ
SR_STOP
=$70
=$A0
;SLA+R has been received and ACK returned
;General call has been received and ACK
;returned
;A STOP condition or repeated START condition
;has been received while still addressed as a
;Slave
;***** Miscellaneous States *****
.equ
NO_INFO
=$F8
;No relevant state information; TWINT =
.equ
BUS_ERROR
=$00
;Bus error due to illegal START or STOP
;condition
“0”
123
1457G–AVR–09/03
The Analog
Comparator
The Analog Comparator compares the input values on the positive pin PB2 (AIN0) and
negative pin PB3 (AIN1). When the voltage on the positive pin PB2 (AIN0) is higher than
the voltage on the negative pin PB3 (AIN1), the Analog Comparator Output, ACO, is set
(one). 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 59.
Figure 59. Analog Comparator Block Diagram
BANDGAP
REFERENCE
ACBG
ACME
ADEN
ADC MULTIPLEXER
1)
OUTPUT
Note:
124
See Figure 60 on page 128.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The Analog Comparator
Control and Status Register –
ACSR
Bit
7
6
5
4
3
2
1
0
$08 ($28)
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
• Bit 7 – ACD: Analog Comparator Disable
When this bit is set(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 voltage of nominally 1.22 ± 0.10V replaces the positive input to the Analog Comparator. When this bit is cleared, AIN0 is applied to the
positive input of the Analog Comparator. See “Internal Voltage Reference” on page 31.
• Bit 5 – ACO: Analog Comparator Output
ACO is directly connected to the comparator output.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set (one) 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 (one) and the I-bit in SREG is set (one). 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 set (one) and the I-bit in the Status Register is set (one), the analog comparator interrupt is activated. When cleared (zero), the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When set (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
cleared (zero), no connection between the Analog Comparator and the Input Capture
function is given. To make the comparator trigger the Timer/Counter1 Input Capture
Interrupt, the TICIE1 bit in the Timer Interrupt Mask Register (TIMSK) must be set (one).
125
1457G–AVR–09/03
• 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 42.
Table 42. 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.
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 SFIOR) 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 43. If ACME is cleared (zero) or ADEN is set (one),
PB3 (AIN1) is applied to the negative input to the Analog Comparator.
Table 43. Analog Comparator Multiplexed Input
126
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
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Analog to Digital
Converter
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
10-bit Resolution
0.5 LSB Integral Non-linearity
±2 LSB Absolute Accuracy
65 - 260 µs Conversion Time
Up to 15 kSPS at Maximum Resolution
Up to 76 kSPS at 8-bit Resolution
Eight Multiplexed Single Ended Input Channels
Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
Selectable 2.56V ADC Reference Voltage
Free Run or Single Conversion Mode
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
The ATmega323 features a 10-bit successive approximation ADC. The ADC is connected to an 8-channel Analog Multiplexer which allows each pin of Port A to be used as
input for the ADC.
The ADC contains a Sample and Hold Amplifier 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 60.
The ADC has two separate analog supply voltage pins, AVCC and AGND. AGND must
be connected to GND, and the voltage on AVCC must not differ more than ±0.3V from
VCC. See the paragraph ADC Noise Canceling Techniques on how to connect these
pins.
Internal reference voltages of nominally 2.56V or AVCC are provided On-chip. The
2.56V reference may be externally decoupled at the AREF pin by a capacitor for better
noise performance. See “Internal Voltage Reference” on page 31 for a description of the
internal voltage reference.
127
1457G–AVR–09/03
Figure 60. Analog to Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
ADC[9:0]
ADPS1
0
ADC DATA REGISTER
(ADCH/ADCL)
ADPS0
ADPS2
ADIF
ADFR
ADEN
ADSC
MUX1
15
ADC CTRL. & STATUS
REGISTER (ADCSR)
MUX0
MUX2
MUX4
MUX3
REFS0
ADLAR
REFS1
ADC MULTIPLEXER
SELECT (ADMUX)
ADIE
ADIF
8-BIT DATA BUS
PRESCALER
CHANNEL SELECTION
MUX DECODER
AVCC
CONVERSION LOGIC
INTERNAL 2.56 V
REFERENCE
SAMPLE & HOLD
COMPARATOR
AREF
10-BIT DAC
+
AGND
1.22 V BANDGAP
REFERENCE
ADC7
ADC6
ADC5
INPUT
MUX
ADC MULTIPLEXER
OUTPUT
ADC4
ADC3
ADC2
ADC1
ADC0
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive
approximation. The minimum value represents AGND and the maximum value represents the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or an internal 2.56V
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
eight ADC input pins ADC7..0, as well as AGND and a fixed bandgap voltage reference
of nominally 1.22 V (VBG), can be selected as single ended inputs to the ADC.
The ADC can operate in two modes – Single Conversion and Free Running mode. In
Single Conversion mode, each conversion will have to be initiated by the user. In Free
Running mode, the ADC is constantly sampling and updating the ADC Data Register.
The ADFR bit in ADCSR selects between the two available modes.
128
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSR. 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.
A 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 set to zero 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.
The ADC generates a 10-bit result, which are 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
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.
Prescaling and
Conversion Timing
Figure 61. ADC Prescaler
ADEN
Reset
7-BIT ADC PRESCALER
CK/64
CK/128
CK/32
CK/8
CK/16
CK/4
CK/2
CK
ADPS0
ADPS1
ADPS2
ADC CLOCK SOURCE
The successive approximation circuitry requires an input clock frequency between
50 kHz and 200 kHz to achieve maximum resolution. If a lower resolution than 10 bits is
required, the input clock frequency to the ADC can be higher than 200 kHz to achieve a
higher sampling rate. See “ADC Characteristics – Preliminary Data” on page 136 for
more details. The ADC module contains a prescaler, which divides the system clock to
an acceptable ADC clock frequency.
The ADPS bits in ADCSR are used to generate a proper ADC clock input frequency
from any XTAL frequency above 100 kHz. The prescaler starts counting from the
moment the ADC is switched on by setting the ADEN bit in ADCSR. The prescaler
129
1457G–AVR–09/03
keeps running for as long as the ADEN bit is set, and is continuously reset when ADEN
is low.
When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at
the following rising edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. In certain situations, the ADC needs
more clock cycles to initialization and minimize offset errors. Extended conversions take
25 ADC clock cycles and occur as the first conversion after the ADC is switched on
(ADEN in ADCSR is set). Additionally, when changing voltage reference, the user may
improve accuracy by disregarding the first conversion result after the reference or MUX
setting was changed.
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 extended 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. In Free Running mode, a new conversion will be started immediately after the
conversion completes, while ADSC remains high. Using Free Running mode and an
ADC clock frequency of 200 kHz gives the lowest conversion time with a maximum resolution, 65 µs, equivalent to 15 kSPS. For a summary of conversion times, see Table
43.
Figure 62. ADC Timing Diagram, Extended Conversion (Single Conversion Mode)
Next
Conversion
Extended Conversion
Cycle Number
1
2
12
13
14
15
16
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 63. 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
MUX and REFS
Update
130
Conversion
Complete
MUX and REFS
Update
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 64. ADC Timing Diagram, Free Run 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 44. ADC Conversion Time
Sample & Hold (Cycles from
Start of Conversion)
Conversion
Time (Cycles)
Conversion
Time (µs)
Extended Conversion
13.5
25
125 - 500
Normal Conversions
1.5
13
65 - 260
Condition
ADC Noise Canceler
Function
The ADC features a noise canceler that enables conversion during ADC Noise Reduction mode (see “Sleep Modes” on page 39) to reduce noise induced from the CPU core
and other I/O peripherals. If other I/O peripherals must be active during conversion, this
mode works equivalently for 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.
ADEN = 1
ADSC = 0
ADFR = 0
ADIE = 1
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.
131
1457G–AVR–09/03
The ADC Multiplexer Selection
Register – ADMUX
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
$07 ($27)
ADMUX
• Bit 7, 6 – REFS1..0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 22. If these bits
are changed during a conversion, the change will not go in effect until this conversion is
complete (ADIF in ADCSR is set). The user should disregard the first conversion result
after changing these bits to obtain maximum accuracy. The internal voltage reference
options may not be used if an external reference voltage is being applied to the AREF
pin.
Table 45. 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 2.56V 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. If ADLAR is cleared, the result is right adjusted. If ADLAR is set, the result is
left 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 “The
ADC Data Register – ADCL and ADCH” on page 134.
• Bits 4..0 – MUX4..MUX0: Analog Channel Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. See Table 46 for details. If these bits are changed during a conversion, the
change will not go in effect until this conversion is complete (ADIF in ADCSR is set).
Table 46. Input Channel Selections
132
MUX4..0
Single-ended Input
00000
ADC0
00001
ADC1
00010
ADC2
00011
ADC3
00100
ADC4
00101
ADC5
00110
ADC6
00111
ADC7
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 46. Input Channel Selections (Continued)
The ADC Control and Status
Register – ADCSR
Bit
MUX4..0
Single-ended Input
01000..11101
Reserved
11110
1.22V (VBG)
11111
0V (AGND)
7
6
5
4
3
2
1
0
ADEN
ADSC
ADFR
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
$06 ($26)
ADCSR
• Bit 7 – ADEN: ADC Enable
Writing a logical “1” to this bit enables the ADC. By clearing this bit 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, a logical “1” must be written to this bit to start each conversion. In Free Running mode, a logical “1” must be written to this bit to start the first
conversion. The first time ADSC has been written after the ADC has been enabled, or if
ADSC is written at the same time as the ADC is enabled, an extended conversion will
precede the initiated conversion. This extended 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. When a extended conversion precedes a real conversion,
ADSC will stay high until the real conversion completes. Writing a 0 to this bit has no
effect.
• Bit 5 – ADFR: ADC Free Running Select
When this bit is set (one) the ADC operates in Free Running mode. In this mode, the
ADC samples and updates the Data Registers continuously. Clearing this bit (zero) will
terminate Free Running mode.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set (one) when an ADC conversion completes and the Data Registers are
updated. The ADC Conversion Complete Interrupt is executed if the ADIE bit and the Ibit in SREG are set (one). 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 ADCSR, 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 set (one) and the I-bit in SREG is set (one), the ADC Conversion Complete Interrupt is activated.
133
1457G–AVR–09/03
• 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 47. 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
The ADC Data Register –
ADCL and ADCH
ADLAR = 0
Bit
15
14
13
12
11
10
9
8
$05 ($25)
SIGN
–
–
–
–
–
ADC9
ADC8
ADCH
$04 ($24)
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
$05 ($25)
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
$04 ($24)
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 affects 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. $000 represents analog ground,
and $3FF represents the selected reference voltage minus one LSB.
134
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Scanning Multiple
Channels
Since change of analog channel always is delayed until a conversion is finished, the
Free Running mode can be used to scan multiple channels without interrupting the converter. Typically, the ADC Conversion Complete interrupt will be used to perform the
channel shift. However, the user should take the following fact into consideration:
The interrupt triggers once the result is ready to be read. In Free Running mode, the
next conversion will start immediately when the interrupt triggers. If ADMUX is changed
after the interrupt triggers, the next conversion has already started, and the old setting is
used.
ADC Noise Canceling
Techniques
Digital circuitry inside and outside the ATmega323 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. The analog part of the ATmega323 and all analog components in the application
should have a separate analog ground plane on the PCB. This ground plane is
connected to the digital ground plane via a single point on the PCB.
2. 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.
3. The AVCC pin on the ATmega323 should be connected to the digital VCC supply
voltage via an LC network as shown in Figure 65.
4. Use the ADC noise canceler function to reduce induced noise from the CPU.
5. If some Port A pins are used as digital outputs, it is essential that these do not
switch while a conversion is in progress.
PA3 (ADC3)
35
34
Analog Ground Plane
PA2 (ADC2)
36
33
PA4 (ADC4)
32
PA5 (ADC5)
31
PA6 (ADC6)
30
PA7 (ADC7)
29
AREF
28
27
26
AGND
AVCC
10µΗ
PA1 (ADC1)
37
100nF
PA0 (ADC0)
38
ATmega32
39
VCC
GND
Figure 65. ADC Power Connections
PC7
135
1457G–AVR–09/03
ADC Characteristics – Preliminary Data
Symbol
Min(2)
Condition
Resolution
Single-ended Conversion
10
Absolute accuracy
VREF = 4V
ADC clock = 200 kHz
1
Absolute accuracy
VREF = 4V
ADC clock = 1 MHz
4
LSB
Absolute accuracy
VREF = 4V
ADC clock = 2 MHz
16
LSB
Integral Non-linearity
VREF > 2V
0.5
LSB
Differential Non-linearity
VREF > 2V
0.5
LSB
Zero Error (Offset)
VREF > 2V
1
LSB
Conversion Time
Free Running Conversion
Clock Frequency
Typ
Max(3)
Parameter
Units
Bits
2
LSB
65
260
µs
50
200
kHz
VCC - 0.3(2)
VCC + 0.3(3)
V
AVCC
V
AVCC
Analog Supply Voltage
VREF
Reference Voltage
2V
VINT
Internal Voltage Reference
2.35
2.56
2.77
V
VBG
Bandgap Voltage Reference
1.12
1.22
1.32
V
RREF
Reference Input Resistance
6
10
13
kΩ
AREF
V
VIN
RAIN
Notes:
136
Input Voltage
Analog Input Resistance
AGND
100
MΩ
1. Values are guidelines only. Actual values are TBD.
2. Minimum for AVCC is 2.7V.
3. Maximum for AVCC is 5.5V.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
I/O Ports
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 for changing drive value (if configured as output) or enabling/disabling of
pull-up resistors (if configured as input).
Port A
Port A is an 8-bit bi-directional I/O port with optional internal pull-ups.
Three I/O Memory address locations are allocated for Port A, one each for the Data
Register – PORTA, $1B($3B), Data Direction Register – DDRA, $1A($3A) and the Port
A Input Pins – PINA, $19($39). The Port A Input Pins address is read only, while the
Data Register and the Data Direction Register are read/write.
All port pins have individually selectable pull-up resistors. The Port A output buffers can
sink 20 mA and thus drive LED displays directly. When pins PA0 to PA7 are used as
inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.
Port A has an alternate function as analog inputs for the ADC. If some Port A 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.
During Power-down mode, the Schmitt Trigger of the digital input is disconnected. This
allows analog signals that are close to VCC/2 to be present during Power-down without
causing excessive power consumption.
The Port A Data Register –
PORTA
The Port A Data Direction
Register – DDRA
The Port A Input Pins Address
– PINA
Bit
7
6
5
4
3
2
1
0
$1B ($3B)
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
$1A ($3A)
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
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$19 ($39)
PORTA
DDRA
PINA
The Port A Input Pins address – PINA – is not a register, and this address enables
access to the physical value on each Port A pin. When reading PORTA the Port A Data
Latch is read, and when reading PINA, the logical values present on the pins are read.
137
1457G–AVR–09/03
Port A as General Digital I/O
All 8-bits in Port A are equal when used as digital I/O pins.
PAn, General I/O pin: The DDAn bit in the DDRA Register selects the direction of this
pin, if DDAn is set (one), PAn is configured as an output pin. If DDAn is cleared (zero),
PAn is configured as an input pin. If PORTAn is set (one) when the pin configured as an
input pin, the MOS pull up resistor is activated. To switch the pull up resistor off, the
PORTAn has to be cleared (zero), the pin has to be configured as an output pin, or the
PUD bit has to be set. The Port A pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Table 48. DDAn Effects on Port A Pins(1)
DDAn
PORTAn
PUD
(in SFIOR)
I/O
Pull Up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
PAn will source current if ext. pulled
low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Push-pull Zero Output
1
1
X
Output
No
Push-pull One Output
Note:
Port A Schematics
Comment
1. n: 7,6…0, pin number.
Note that all port pins are synchronized. The synchronization latches are not shown in
the figure.
Figure 66. Port A Schematic Diagrams (Pins PA0 - PA7)
RD
MOS
PULLUP
PUD
RESET
Q
D
DDAn
WD
RESET
Q
D
PORTAn
C
PDn
RL
PWRDN
WP
RP
TO ADC MUX
WP:
WD:
RL:
RP:
RD:
n:
PUD:
138
DATA BUS
C
ADCn
WRITE PORTA
WRITE DDRA
READ PORTA LATCH
READ PORTA PIN
READ DDRA
0-7
PULL-UP DISABLE
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Port B
Port B is an 8-bit bi-directional I/O port with optional internal pull-ups.
Three I/O Memory address locations are allocated for Port B, one each for the Data
Register – PORTB, $18($38), Data Direction Register – DDRB, $17($37) and the Port B
Input Pins – PINB, $16($36). The Port B Input Pins address is read only, while the Data
Register and the Data Direction Register are read/write.
All port pins have individually selectable pull-up resistors. The Port B output buffers can
sink 20 mA and thus drive LED displays directly. When pins PB0 to PB7 are used as
inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.
The Port B pins with alternate functions are shown in Table 49.:
Table 49. Port B Pins Alternate Functions
Port Pin
Alternate Functions
PB0
T0 (Timer/Counter 0 External Counter Input)
XCK (USART External Clock Input/Output)
PB1
T1 (Timer/Counter 1 External Counter Input)
PB2
AIN0 (Analog Comparator Positive Input)
INT2 (External Interrupt 2 Input)
PB3
AIN1 (Analog Comparator Negative Input)
OC0 (Timer/Counter0 Output Compare Match Output)
PB4
SS (SPI Slave Select Input)
PB5
MOSI (SPI Bus Master Output/Slave Input)
PB6
MISO (SPI Bus Master Input/Slave Output)
PB7
SCK (SPI Bus Serial Clock)
When the pins are used for the alternate function, the DDRB and PORTB Registers
have to be set according to the alternate function description.
The Port B Data Register –
PORTB
Bit
7
6
5
4
3
2
1
0
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
$18 ($38)
The Port B Data Direction
Register – DDRB
Bit
7
6
5
4
3
2
1
0
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
$17 ($37)
The Port B Input Pins Address
– PINB
Bit
7
6
5
4
3
2
1
0
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$16 ($36)
PORTB
DDRB
PINB
139
1457G–AVR–09/03
The Port B Input Pins address – PINB – is not a register, and this address enables
access to the physical value on each Port B pin. When reading PORTB, the Port B Data
Latch is read, and when reading PINB, the logical values present on the pins are read.
Port B As General Digital I/O
All eight bits in Port B are equal when used as digital I/O pins. PBn, General I/O pin: The
DDBn bit in the DDRB Register selects the direction of this pin, if DDBn is set (one), PBn
is configured as an output pin. If DDBn is cleared (zero), PBn is configured as an input
pin. If PORTBn is set (one) when the pin configured as an input pin, the MOS pull up
resistor is activated. To switch the pull up resistor off, the PORTBn has to be cleared
(zero), the pin has to be configured as an output pin, or the PUD bit has to be set. The
Port B pins are tri-stated when a reset condition becomes active, even if the clock is not
running.
Table 50. DDBn Effects on Port B Pins(1)
DDBn
PORTBn
PUD
(in SFIOR)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
PBn will Source Current if Ext. Pulled
Low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Push-Pull Zero Output
1
1
X
Output
No
Push-Pull One Output
Note:
Alternate Functions of Port B
Comment
1. n: 7,6…0, pin number.
The alternate pin configuration is as follows:
• SCK – Port B, Bit 7
SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is
enabled as a Slave, this pin is configured as an input regardless of the setting of DDB7.
When the SPI is enabled as a Master, the data direction of this pin is controlled by
DDB7. When the pin is forced to be an input, the pull-up can still be controlled by the
PORTB7 bit. See the description of the SPI port for further details.
• MISO – Port B, Bit 6
MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is
enabled as a Master, this pin is configured as an input regardless of the setting of
DDB6. When the SPI is enabled as a Slave, the data direction of this pin is controlled by
DDB6. When the pin is forced to be an input, the pull-up can still be controlled by the
PORTB6 bit. See the description of the SPI port for further details.
• MOSI – Port B, Bit 5
MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is
enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5.
When the SPI is enabled as a Master, the data direction of this pin is controlled by
DDB5. When the pin is forced to be an input, the pull-up can still be controlled by the
PORTB5 bit. See the description of the SPI port for further details.
140
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
• SS – Port B, Bit 4
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 DDB4. 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 DDB4. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB4 bit. See the description of the SPI port for further details.
• AIN1/OC0 – Port B, Bit 3
AIN1, Analog Comparator Negative Input. When configured as an input (DDB3 is
cleared (zero)) and with the internal MOS pull up resistor switched off (PB3 is cleared
(zero)), this pin also serves as the negative input of the On-chip Analog Comparator.
During Power-down mode, the Schmitt Trigger of the digital input is disconnected. This
allows analog signals which are close to VCC/2 to be present during Power-down without
causing excessive power consumption.
OC0, Output Compare Match output: The PB3 pin can serve as an external output for
the Timer/Counter0 Compare Match. The PB3 pin has to be configured as an output
(DDB3 set (one)) to serve this function. See “8-bit Timers/Counters Timer/Counter0 and
Timer/Counter2” on page 45 for further details, and how to enable the output. The OC0
pin is also the output pin for the PWM mode timer function.
• AIN0/INT2 – Port B, Bit 2
AIN0, Analog Comparator Positive Input. When configured as an input (DDB2 is cleared
(zero)) and with the internal MOS pull up resistor switched off (PB2 is cleared (zero)),
this pin also serves as the positive input of the On-chip Analog Comparator. During
Power-down mode, the Schmitt Trigger of the digital input is disconnected if INT2 is not
enabled. This allows analog signals which are close to VCC /2 to be present during
Power-down without causing excessive power consumption.
INT2, External Interrupt Source 2: The PB2 pin can serve as an external interrupt
source to the MCU. See “MCU Control and Status Register – MCUCSR” on page 30 for
further details.
• T1 – Port B, Bit 1
T1, Timer/Counter1 Counter Source. See the timer description for further details.
• T0/XCK – Port B, Bit 0
T0, Timer/Counter0 Counter Source. See the timer description for further details.
XCK, USART external clock. See the USART description for further details.
141
1457G–AVR–09/03
Port B Schematics
Note that all port pins are synchronized. The synchronization latches are not shown in
the figures.
Figure 67. Port B Schematic Diagram (Pin PB0)
PUD
DDB0
UMSEL
XCK OUTPUT
1
PB0
0
PORTB0
TIMER0 CLOCK
SOURCE MUX
PUD: PULL-UP DISABLE
CS02 CS01 CS00
XCK INPUT
Figure 68. Port B Schematic Diagram (Pin PB1)
PUD
DDB1
PB1
PORTB1
TIMER1 CLOCK
SOURCE MUX
PUD: PULL-UP DISABLE
CS12 CS11 CS10
142
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 69. Port B Schematic Diagram (Pin PB2)
RD
MOS
PULLUP
PUD
RESET
Q
R
D
DDB2
WD
RESET
R
Q
D
PORTB2
PB2
DATA BUS
C
C
RL
INT2 ENABLE
WP
RP
PWRDN
'1'
WP:
WD:
RL:
RP:
RD:
PUD:
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
PULL-UP DISABLE
D
C
INT2
Q
R
HW CLEAR
SW CLEAR
ISC2
TO COMPARATOR
AIN0
Figure 70. Port B Schematic Diagram (Pin PB3)
PUD
DDB3
PB3
PORTB3
PWRDN
WP:
WD:
RL:
RP:
RD:
PUD:
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
PULL-UP DISABLE
COM00
COM01
COMP. MATCH 0
PWM0
FOC0
TO COMPARATOR
AIN1
143
1457G–AVR–09/03
Figure 71. Port B Schematic Diagram (Pin PB4)
RD
MOS
PULLUP
PUD
RESET
Q
D
DDB4
C
DATA BUS
WD
RESET
Q
D
PORTB4
C
PB4
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
MSTR:
SPE:
PUD:
MSTR
SPE
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
SPI MASTER ENABLE
SPI ENABLE
PULL-UP DISABLE
SPI SS
Figure 72. Port B Schematic Diagram (Pin PB5)
RD
MOS
PULLUP
PUD
RESET
Q
R
D
DDB5
WD
RESET
R
Q
D
PORTB5
PB5
DATA BUS
C
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
SPE:
MSTR:
PUD:
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
SPI ENABLE
MASTER SELECT
PULL-UP DISABLE
MSTR
SPE
SPI MASTER
OUT
SPI SLAVE
IN
144
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 73. Port B Schematic Diagram (Pin PB6)
RD
MOS
PULLUP
PUD
RESET
R
Q
D
DDB6
WD
RESET
R
Q
D
PORTB6
PB6
DATA BUS
C
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
SPE:
MSTR
PUD:
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
SPI ENABLE
MASTER SELECT
PULL-UP DISABLE
MSTR
SPE
SPI SLAVE
OUT
SPI MASTER
IN
Figure 74. Port B Schematic Diagram (Pin PB7)
RD
MOS
PULLUP
PUD
RESET
Q
R
D
DDB7
WD
RESET
R
Q
D
PORTB7
PB7
DATA BUS
C
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
SPE:
MSTR
PUD:
WRITE PORTB
WRITE DDRB
READ PORTB LATCH
READ PORTB PIN
READ DDRB
SPI ENABLE
MASTER SELECT
PULL-UP DISABLE
MSTR
SPE
SPI ClLOCK
OUT
SPI CLOCK
IN
145
1457G–AVR–09/03
Port C
Port C is an 8-bit bi-directional I/O port with optional internal pull-ups.
Three I/O Memory address locations are allocated for the Port C, one each for the Data
Register – PORTC, $15($35), Data Direction Register – DDRC, $14($34) and the Port C
Input Pins – PINC, $13($33). The Port C Input Pins address is read only, while the Data
Register and the Data Direction Register are read/write.
All port pins have individually selectable pull-up resistors. The Port C output buffers can
sink 20mA and thus drive LED displays directly. When pins PC0 to PC7 are used as
inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.
Table 51. Port C Pins Alternate Functions
Port Pin
The Port C Data Register –
PORTC
PC0
SCL (Two-wire Serial Bus Clock Line)
PC1
SDA (Two-wire Serial Bus Data Input/Output Line)
PC2
TCK (JTAG Test Clock)
PC3
TMS (JTAG Test Mode Select)
PC4
TDO (JTAG Test Data Out)
PC5
TDI (JTAG Test Data In)
PC6
TOSC1 (Timer Oscillator Pin 1)
PC7
TOSC2 (Timer Oscillator Pin 2)
Bit
7
6
5
4
3
2
1
0
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
$15 ($35)
The Port C Data Direction
Register – DDRC
Bit
7
6
5
4
3
2
1
0
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
$14 ($34)
The Port C Input Pins Address
– PINC
Alternate Function
Bit
7
6
5
4
3
2
1
0
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$13 ($33)
PORTC
DDRC
PINC
The Port C Input Pins address – PINC – is not a register, and this address enables
access to the physical value on each Port C pin. When reading PORTC, the Port C Data
Latch is read, and when reading PINC, the logical values present on the pins are read.
Port C As General Digital I/O
All 8 bits in Port C are equal when used as digital I/O pins.
PCn, General I/O pin: The DDCn bit in the DDRC Register selects the direction of this
pin, if DDCn is set (one), PCn is configured as an output pin. If DDCn is cleared (zero),
PCn is configured as an input pin. If PORTCn is set (one) when the pin configured as an
input pin, the MOS pull up resistor is activated. To switch the pull up resistor off,
146
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
PORTCn has to be cleared (zero), the pin has to be configured as an output pin, or the
PUD bit has to be set. The Port C pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Table 52. DDCn Effects on Port C Pins(1)
DDCn
PORTCn
PUD
(in SFIOR)
I/O
Pull-up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
PCn will Source Current if Ext. Pulled
Low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Push-pull Zero Output
1
1
X
Output
No
Push-pull One Output
Note:
Comments
1. n: 7…0, pin number
If the JTAG Interface is enabled, the pull-up resistors on pins PC5 (TDI), PC3 (TMS) and
PC2 (TCK) will be activated even if a reset occurs.
Alternate Functions of Port C
• TOSC2 – Port C, Bit 7
TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set (one) to enable asynchronous clocking of Timer/Counter2, pin PC7 is disconnected from the port, and
becomes the inverting output of the Oscillator amplifier. In this mode, a crystal Oscillator
is connected to this pin, and the pin can not be used as an I/O pin.
• TOSC1 – Port C, Bit 6
TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set (one) to enable asynchronous clocking of Timer/Counter1, pin PC6 is disconnected from the port, and
becomes the input of the inverting Oscillator amplifier. In this mode, a crystal Oscillator
is connected to this pin, and the pin can not be used as an I/O pin.
• TDI – Port C, Bit 5
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. Refer to the section “JTAG Interface and the On-chip Debug System” on page 157 for details on operation of the JTAG interface.
• TDO – Port C, Bit 4
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. Refer to
the section “JTAG Interface and the On-chip Debug System” on page 157 for details on
operation of the JTAG interface.
• TMS – Port C, Bit 3
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. Refer to the section “JTAG Interface and the On-chip Debug System” on page 157
for details on operation of the JTAG interface.
147
1457G–AVR–09/03
• TCK – Port C, Bit 2
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. Refer to the section “JTAG
Interface and the On-chip Debug System” on page 157 for details on operation of the
JTAG interface.
• SDA – Port C, Bit 1
SDA, Two-wire Serial Interface Data: When the TWEN bit in TWCR is set (one) to
enable the Two-wire Serial Interface, pin PC1 is disconnected from the port and
becomes the Serial Data I/O pin for the Two-wire Serial Interface. In this mode, there is
a spike filter on the pin to capture spikes shorter than 50 ns on the input signal, and the
pin is driven by an open collector driver with slew rate limitation.
• SCL – Port C, Bit 0
SCL, Two-wire Serial Interface Clock: When the TWEN bit in TWCR is set (one) to
enable the Two-wire Serial Interface, pin PC1 is disconnected from the port and
becomes the Serial Clock I/O pin for the Two-wire Serial Interface. In this mode, there is
a spike filter on the pin to capture spikes shorter than 50 ns on the input signal.
Port C Schematics
Note that all port pins are synchronized. The synchronization latches are not shown in
the figure.
Figure 75. Port C Schematic Diagram (Pins PC0 - PC1)
0
DDCn
PUD
1
0
0
1
PCn
n
SCL/SDA out
SCL/SDA in
TWEN
PUD: PULL-UP DISABLE
n = 0, 1
148
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 76. Port C Schematic Diagram (Pins PC2 - PC5). The JTAG interface on these
pins is not shown in the figure.
RD
MOS
PULLUP
PUD
RESET
Q
R
D
DDCn
C
DATA BUS
WD
RESET
R
Q
D
PORTCn
PCn
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
PUD:
n:
WRITE PORTC
WRITE DDRC
READ PORTC LATCH
READ PORTC PIN
READ DDRC
PULL-UP DISABLE
2..5
Figure 77. Port C Schematic Diagram (Pins PC6)
RD
PUD
MOS
PULLUP
RESET
Q
R
D
DDC6
WD
RESET
R
Q
D
PORTC6
PC6
DATA BUS
C
C
RL
WP
RP
0
1
AS2
T/C2 OSC
AMP INPUT
WP:
WD:
RL:
RP:
RD:
AS2:
PUD:
WRITE PORTC
WRITE DDRC
READ PORTC LATCH
READ PORTC PIN
READ DDRC
ASYNCH SELECT T/C2
PULL-UP DISABLE
149
1457G–AVR–09/03
Figure 78. Port C Schematic Diagram (Pins PC7)
PUD
0
1
WP:
WD:
RL:
RP:
RD:
AS2:
PUD:
150
WRITE PORTC
WRITE DDRC
READ PORTC LATCH
READ PORTC PIN
READ DDRC
ASYNCH SELECT T/C2
PULL-UP DISABLE
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Port D
Port D is an 8-bit bi-directional I/O port with optional internal pull-up resistors.
Three I/O Memory address locations are allocated for Port D, one each for the Data
Register – PORTD, $12($32), Data Direction Register – DDRD, $11($31) and the Port D
Input Pins – PIND, $10($30). The Port D Input Pins address is read only, while the Data
Register and the Data Direction Register are read/write.
The Port D output buffers can sink 20 mA. As inputs, Port D pins that are externally
pulled low will source current if the pull-up resistors are activated. Some Port D pins
have alternate functions as shown in Table 53.
Table 53. Port D Pins Alternate Functions
Port Pin
The Port D Data Register –
PORTD
PD0
RXD (USART Input Pin)
PD1
TXD (USART Output Pin)
PD2
INT0 (External Interrupt 0 Input)
PD3
INT1 (External Interrupt 1 Input)
PD4
OC1B (Timer/Counter1 Output Compare B Match Output)
PD5
OC1A (Timer/Counter1 Output Compare A Match Output)
PD6
ICP (Timer/Counter1 Input Capture Pin)
PD7
OC2 (Timer/Counter2 Output Compare Match Output)
Bit
$12 ($32)
Read/Write
Initial
ue
The Port D Data Direction
Register – DDRD
Val-
Bit
7
6
5
4
3
2
1
0
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
7
6
5
4
3
2
1
0
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
$11 ($31)
The Port D Input Pins Address
– PIND
Alternate Function
Bit
7
6
5
4
3
2
1
0
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
$10 ($30)
PORTD
DDRD
PIND
The Port D Input Pins address – PIND – is not a register, and this address enables
access to the physical value on each Port D pin. When reading PORTD, the Port D Data
Latch is read, and when reading PIND, the logical values present on the pins are read.
151
1457G–AVR–09/03
Port D As General Digital I/O
PDn, General I/O pin: The DDDn bit in the DDRD Register selects the direction of this
pin. If DDDn is set (one), PDn is configured as an output pin. If DDDn is cleared (zero),
PDn is configured as an input pin. If PDn is set (one) when configured as an input pin
the MOS pull up resistor is activated. To switch the pull up resistor off the PDn has to be
cleared (zero), the pin has to be configured as an output pin, or the PUD bit has to be
set. The Port D pins are tri-stated when a reset condition becomes active, even if the
clock is not running.
Table 54. DDDn Effects on Port D Pins
DDDn
PORTDn
PUD
(in SFIOR)
I/O
Pull Up
0
0
X
Input
No
Tri-state (Hi-Z)
0
1
0
Input
Yes
PDn will Source Current if Ext. Pulled
Low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Push-pull Zero Output
1
1
X
Output
No
Push-pull One Output
Note:
Alternate Functions of Port D
Comment
n: 7,6…0, pin number.
• OC2 – Port D, Bit 7
OC2, Timer/Counter2 Output Compare Match output: The PD7 pin can serve as an
external output for the Timer/Counter2 Output Compare. The pin has to be configured
as an output (DDD7 set (one)) to serve this function. See the timer description on how to
enable this function. The OC2 pin is also the output pin for the PWM mode timer
function.
• ICP – Port D, Bit 6
ICP – Input Captur e Pin: The PD6 pin can act as an Input Capture Pin for
Timer/Counter1. The pin has to be configured as an input (DDD6 cleared(zero)) to serve
this function. See the timer description on how to enable this function.
• OC1A – Port D, Bit 5
OC1A, Output Compare Match A output: The PD5 pin can serve as an external output
for the Timer/Counter1 Output Compare A. The pin has to be configured as an output
(DDD5 set (one)) to serve this function. See the timer description on how to enable this
function. The OC1A pin is also the output pin for the PWM mode timer function.
• OC1B – Port D, Bit 4
OC1B, Output Compare Match B output: The PD4 pin can serve as an external output
for the Timer/Counter1 Output Compare B. The pin has to be configured as an output
(DDD4 set (one)) to serve this function. See the timer description on how to enable this
function. The OC1B pin is also the output pin for the PWM mode timer function.
• INT1 – Port D, Bit 3
INT1, External Interrupt Source 1: The PD3 pin can serve as an external interrupt
source to the MCU. See the interrupt description for further details, and how to enable
the source.
152
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
• INT0 – Port D, Bit 2
INT0, External Interrupt Source 0: The PD2 pin can serve as an external interrupt
source to the MCU. See the interrupt description for further details, and how to enable
the source.
• TXD – Port D, Bit 1
TXD, Transmit Data (Data output pin for the USART). When the USART Transmitter is
enabled, this pin is configured as an output regardless of the value of DDD1.
• RXD – Port D, Bit 0
RXD, 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 DDD0. When the
USART forces this pin to be an input, a logical one in PORTD0 will turn on the internal
pull-up.
Port D Schematics
Note that all port pins are synchronized. The synchronization latches are not shown in
the figures.
Figure 79. Port D Schematic Diagram (Pin PD0)
RD
MOS
PULLUP
PUD
RESET
Q
D
DDD0
C
DATA BUS
WD
RESET
Q
D
PORTD0
C
PD0
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
RXD:
RXEN:
PUD:
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
UART RECEIVE DATA
UART RECEIVE ENABLE
PULL-UP DISABLE
RXEN
RXD
153
1457G–AVR–09/03
Figure 80. Port D Schematic Diagram (Pin PD1)
RD
PUD
MOS
PULLUP
RESET
Q
R
D
DDD1
C
DATA BUS
WD
RESET
R
Q
D
PORTD1
PD1
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
TXD:
TXEN:
PUD:
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
UART TRANSMIT DATA
UART TRANSMIT ENABLE
PULL-UP DISABLE
TXEN
TXD
Figure 81. Port D Schematic Diagram (Pins PD2 and PD3)
PUD
WP:
WD:
RL:
RP:
RD:
PUD:
n:
m:
154
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
PULL-UP DISABLE
2, 3
0, 1
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 82. Port D Schematic Diagram (Pins PD4 and PD5)
PUD
WP:
WD:
RL:
RP:
RD:
PUD:
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
PULL-UP DISABLE
Figure 83. Port D Schematic Diagram (Pin PD6)
RD
MOS
PULLUP
PUD
RESET
Q
R
D
DDD6
WD
RESET
R
Q
D
PORTD6
PD6
DATA BUS
C
C
RL
WP
RP
WP:
WD:
RL:
RP:
RD:
ACIC:
ACO:
PUD:
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
COMPARATOR IC ENABLE
COMPARATOR OUTPUT
PULL-UP DISABLE
0
NOISE CANCELER
EDGE SELECT
ICNC1
ICES1
ICF1
1
ACIC
ACO
155
1457G–AVR–09/03
Figure 84. Port D Schematic Diagram (Pin PD7)
PUD
WP:
WD:
RL:
RP:
RD:
PUD:
156
WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
PULL-UP DISABLE
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
JTAG Interface and
the On-chip Debug
System
Features
• JTAG (IEEE std. 1149.1 Compliant) Interface
• Boundary-Scan Capabilities According to the 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
– 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 202 and “IEEE 1149.1 (JTAG)
Boundary-Scan” on page 164, respectively. The On-chip Debug support is considered
being private JTAG instructions, and distributed within ATMEL and to selected third
party vendors only.
Figure 85 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.
Of the Data Registers, the ID-Register, Bypass Register, and the Boundary-Scan Chain
are 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 Onchip debugging only.
157
1457G–AVR–09/03
The Test Access Port –
TAP
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
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 input signals are internally pulled high and the JTAG is enabled for
Boundary-scan and programming. In this case, the TAP output pin (TDO) is left floating
in states where the JTAG TAP controller is not shifting data, and must therefore be connected to a pull-up resistor or other hardware having pull-ups (for instance the TDI-input
of the next device in the scan chain). The device is shipped with this fuse programmed.
For the On-chip Debug system, in addition 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 reset line are used in
the application.
158
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 85. Block Diagram
PORT A
DEVICE BOUNDARY
BOUNDARY SCAN CHAIN
TDI
TDO
TCK
TMS
JTAG PROGRAMMING
INTERFACE
TAP
CONTROLLER
AVR CPU
M
U
X
BREAKPOINT
UNIT
BYPASS
REGISTER
INTERNAL
SCAN
CHAIN
PC
Instruction
FLOW CONTROL
UNIT
DIGITAL
PERIPHERAL
UNITS
BREAKPOINT
SCAN CHAIN
ADDRESS
DECODER
JTAG / AVR CORE
COMMUNICATION
INTERFACE
OCD STATUS
AND CONTROL
ANALOG
PERIPHERIAL
UNITS
Analog inputs
ID
REGISTER
Address
Data
Control & Clock lines
INSTRUCTION
REGISTER
FLASH
MEMORY
PORT B
159
1457G–AVR–09/03
Figure 86. 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 86 depends 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
•
160
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 TMS is low, shift the 4-bit JTAG
instructions into the JTAG Instruction Register from the TDI input at the rising edge
of TCK, while the captured IR-state 0x01 is shifts 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.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
•
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
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 TMS is low, 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. At the same time, the parallel inputs to
the Data Register captured in the Capture-DR state shifts 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 5 TCK clock periods.
For detailed information on the JTAG specification, refer to the literature listed in “Bibliography” on page 163.
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 164.
Using the On-chip Debug As shown in Figure 85, 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 4 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 list of the On-chip Debug specific JTAG instructions is given in “On-chip Debug Specific JTAG Instructions” on page 162. Note that Atmel supports the On-chip Debug
system with the AVR Studio front-end software for PCs. The details on hardware imple-
161
1457G–AVR–09/03
mentation and JTAG instructions are therefore irrelevant for the user of the On-chip
Debug system.
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. The disabling of the On-chip debug system when any Lock
bits are set is a security feature. 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 3rd party vendors’ compilers.
AVR Studio runs under Microsoft® Windows® 95/98/2000 and Microsoft Windows NT®.
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 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 opcode listed for
reference.
PRIVATE0; $8
Private JTAG instruction for accessing On-chip debug system.
PRIVATE1; $9
Private JTAG instruction for accessing On-chip debug system.
PRIVATE2; $A
Private JTAG instruction for accessing On-chip debug system.
PRIVATE3; $B
Private JTAG instruction for accessing On-chip debug system.
162
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
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 MCUSR 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.
A description of the programming specific JTAG instructions is given in “Programming
specific JTAG instructions” on page 202. The details on programming through the JTAG
interface is given in the section “Programming via the JTAG Interface” on page 202
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, AddisonWesley, 1992
163
1457G–AVR–09/03
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. 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
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 MCUSR
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.
164
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Data Registers
The Data Registers are selected by the JTAG Instruction Registers described in section
“Boundary-Scan Specific JTAG Instructions” on page 166. The Data Registers relevant
for Boundary-Scan operations are:
•
Bypass Register
•
Device Identification Register
•
Reset Register
•
Boundary-Scan Chain
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 87 shows the structure of the Device Identification Register.
Figure 87. The format of the Device Identification Register
MSB
Bit
Device ID
Version
31
LSB
28
27
12
11
1
0
Version
Part Number
Manufacturer ID
1
4 bits
16 bits
11 bits
1 bit
Version is a 4-bit number identifying the revision of the component. The relevant version
numbers are shown in Table 55.
Table 55. JTAG Version Numbers
Part Number
Version
JTAG Version number (Binary digits)
ATmega323 revision B
0010
The part number is a 16 bit code identifying the component. The JTAG Part Number for
AVR devices are listed in Table 56.
Table 56. AVR JTAG Part Number
Manufacturer ID
Part number
JTAG Part Number (Hex)
ATmega323
0x9501
The manufacturer ID for ATMEL is 0x01F (11 bit).
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1457G–AVR–09/03
Reset Register
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 TimeOut Period (refer to Table 6 on page 27) 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 88.
Figure 88. 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.
See “Boundary-Scan Chain” on page 168 for a complete description.
Boundary-Scan Specific
JTAG Instructions
The Instruction Register is four 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 high-impedant state by using the AVR_RESET instruction, since the initial state for all
port pins is tri-state.
As a definition in this datasheet, 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; $0
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 by the EXTEST instruction.
The active states are:
166
•
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.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
•
IDCODE; $1
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 ID Register 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:
SAMPLE_PRELOAD; $2
•
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.
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; $C
•
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; $F
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.
167
1457G–AVR–09/03
Boundary-Scan Chain
The Boundary-Scan chain has the capability of driving and observing the logic levels on
the digital I/O pins.
Note:
Scanning the Digital Port Pins
Compatibility issues regarding future devices: Future devices, included replacements for
ATmega323 will have Pull-Up Enable signals instead of the Pull-Up Disable signals in the
scan path (i.e. inverted logic). The scan cell for the reset signal will have the same logic
level as the external pin (i.e. inverted logic). The length of the scan-chain is likely to
change in future devices.
Figure 89 shows the Boundary-Scan Cell for Bidirectional Port Pins with Pull-up function. The cell consists of a standard Boundary-Scan cell for the Pull-up function, and a
Bidirectional pin cell that combines the three signals Output Control – OC, Output Data
– OD, and Input Data – ID, into only a two-stage Shift Register.
Figure 89. Boundary-Scan Cell For bidirectional Port Pin with Pull-up Function.
ShiftDR
To Next Cell
EXTEST
Pullup Disable (PLD)
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
The Boundary-Scan logic is not included in the figures in the datasheet. Figure 90
shows a simple digital Port Pin as described in the section “I/O Ports” on page 137. The
Boundary-Scan details from Figure 89 replaces the dashed box in Figure 90.
168
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 90. General Port Pin Schematic diagram
See Boundary Scan
description for details
RD
MOS
PULLUP
PLD
PUD
RESET
Q
D
DDXn
WD
OC
RESET
OD
PXn
ID
Q
D
PORTXn
C
RL
DATA BUS
C
WP
RP
WP:
WD:
RL:
RP:
RD:
n:
PUD:
WRITE PORTX
WRITE DDRX
READ PORTX LATCH
READ PORTX PIN
READ DDRX
0-7
PULL-UP DISABLE
PuD: JTAG PULL-UP DISABLE
OC: JTAG OUTPUT CONTROL
OD: JTAG OUTPUT DATA
ID: JTAG INPUT DATA
When no alternate port function is present, the Input Data – ID corresponds to the PINn
Register value, Output Data corresponds to the PORTn Register, Output Control corresponds to the Data Direction – DDn Register, and the PuLL-up Disable – PLD –
corresponds to logic expression (DDn OR NOT(PORTBn)).
Digital alternate port functions are connected outside the dotted box in Figure 90 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 circuit.
Scanning RESET
The RESET pin accepts 5V active low logic for standard reset operation. An observeonly cell as shown in Figure 91 is inserted at the output from the Reset Detector; RST.
Note:
The scanned signal is active high, i.e., the RST signal is the inverse of the external
RESET pin.
169
1457G–AVR–09/03
Figure 91. Observe-only Cell
To
next
cell
ShiftDR
From system pin
To system logic
FF1
0
D
Q
1
From
previous
cell
Internal signals
ClockDR
ATmega323 contains a lot of scan chains for internal signals. The description of these
signals are not public. However, the user must apply safe values to these cells before
applying the Update-DR state of the TAP controller.
Note:
Incorrect setting of the scan cells for internal signals may cause signal contention and
can damage the part. Make sure the safe values are used.
Table 57. Boundary-Scan signals for the ADC
170
Signal Name
Type of scan cell
Recommended input when not in use
SIG_PRIVATE0
General Scan Cell
1
SIG_PRIVATE1
General Scan Cell
0
SIG_PRIVATE2
General Scan Cell
0
SIG_PRIVATE3
General Scan Cell
0
SIG_PRIVATE4
General Scan Cell
0
SIG_PRIVATE5
General Scan Cell
0
SIG_PRIVATE6
General Scan Cell
0
SIG_PRIVATE7
General Scan Cell
0
SIG_PRIVATE8
General Scan Cell
0
SIG_PRIVATE9
General Scan Cell
0
SIG_PRIVATE10
General Scan Cell
0
SIG_PRIVATE11
General Scan Cell
1
SIG_PRIVATE12
General Scan Cell
0
SIG_PRIVATE13
General Scan Cell
0
SIG_PRIVATE14
General Scan Cell
0
SIG_PRIVATE15
General Scan Cell
0
SIG_PRIVATE16
General Scan Cell
0
SIG_PRIVATE17
General Scan Cell
0
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 57. Boundary-Scan signals for the ADC (Continued)
Signal Name
Type of scan cell
Recommended input when not in use
SIG_PRIVATE18
General Scan Cell
0
SIG_PRIVATE19
General Scan Cell
0
SIG_PRIVATE20
General Scan Cell
0
SIG_PRIVATE21
General Scan Cell
1
SIG_PRIVATE22
General Scan Cell
0
SIG_PRIVATE23
General Scan Cell
0
SIG_PRIVATE24
General Scan Cell
0
SIG_PRIVATE25
General Scan Cell
1
SIG_PRIVATE26
General Scan Cell
0
SIG_PRIVATE27
General Scan Cell
0
SIG_PRIVATE28
General Scan Cell
0
SIG_PRIVATE29
General Scan Cell
0
SIG_PRIVATE30
General Scan Cell
0
SIG_PRIVATE31
General Scan Cell
0
SIG_PRIVATE32
General Scan Cell
0
SIG_PRIVATE33
General Scan Cell
0
SIG_PRIVATE34
General Scan Cell
1
SIG_PRIVATE35
General Scan Cell
0
SIG_PRIVATE36
General Scan Cell
0
SIG_PRIVATE37
General Scan Cell
0
SIG_PRIVATE38
General Scan Cell
1
SIG_PRIVATE39
General Scan Cell
1
SIG_PRIVATE40
General Scan Cell
0
SIG_PRIVATE41
General Scan Cell
0
SIG_PRIVATE42
General Scan Cell
0
SIG_PRIVATE43
Observe Only
X
SIG_PRIVATE44
Observe Only
X
SIG_PRIVATE45
Observe Only
X
SIG_PRIVATE46
Observe Only
X
171
1457G–AVR–09/03
ATmega323 BoundaryScan Order
Table 64 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 pinout 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
89, PXn.Data corresponds to FF0, PXn.Control corresponds to FF1, and PXn.
Pullup_dissable corresponds to FF2. Bit 2, 3, 4, and 5 of Port C is not in the scan chain,
since these pins constitute the TAP pins when the JTAG is enabled
Table 58. ATmega323 Boundary-Scan Order
Bit Number
Signal Name
131
SIG_PRIVATE0
130
SIG_PRIVATE1
129
SIG_PRIVATE2
128
SIG_PRIVATE3
127
SIG_PRIVATE4
126
SIG_PRIVATE5
125
SIG_PRIVATE6
124
SIG_PRIVATE7
123
SIG_PRIVATE8
122
SIG_PRIVATE9
121
SIG_PRIVATE10
120
SIG_PRIVATE11
119
SIG_PRIVATE12
118
SIG_PRIVATE13
117
SIG_PRIVATE14
116
SIG_PRIVATE15
115
SIG_PRIVATE16
114
SIG_PRIVATE17
113
SIG_PRIVATE18
112
SIG_PRIVATE19
111
SIG_PRIVATE20
110
SIG_PRIVATE21
109
SIG_PRIVATE22
108
SIG_PRIVATE23
107
SIG_PRIVATE24
106
SIG_PRIVATE25
105
SIG_PRIVATE26
Module
Private Section 1
172
Private Section 2
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 58. ATmega323 Boundary-Scan Order (Continued)
Bit Number
Signal Name
104
SIG_PRIVATE27
103
SIG_PRIVATE28
102
SIG_PRIVATE29
101
SIG_PRIVATE30
100
SIG_PRIVATE31
99
SIG_PRIVATE32
98
SIG_PRIVATE33
97
SIG_PRIVATE34
96
SIG_PRIVATE35
95
SIG_PRIVATE36
94
SIG_PRIVATE37
93
SIG_PRIVATE38
92
SIG_PRIVATE39
91
SIG_PRIVATE40
90
SIG_PRIVATE41
89
SIG_PRIVATE42
88
PB0.Data
87
PB0.Control
86
PB0.PuLLup_Disable
85
PB1.Data
84
PB1.Control
83
PB1.PuLLup_Disable
82
PB2.Data
81
PB2.Control
80
PB2.PuLLup_Disable
79
PB3.Data
78
PB3.Control
77
PB3.PuLLup_Disable
76
PB4.Data
75
PB4.Control
74
PB4.PuLLup_Disable
Module
Private Section 2 (Cont.)
Port B
173
1457G–AVR–09/03
Table 58. ATmega323 Boundary-Scan Order (Continued)
174
Bit Number
Signal Name
73
PB5.Data
72
PB5.Control
71
PB5.PuLLup_Disable
70
PB6.Data
69
PB6.Control
68
PB6.PuLLup_Disable
67
PB7.Data
66
PB7.Control
65
PB7.PuLLup_Disable
64
RSTT
63
SIG_PRIVATE43
62
SIG_PRIVATE44
61
SIG_PRIVATE45
60
SIG_PRIVATE46
59
PD0.Data
58
PD0.Control
57
PD0.PuLLup_Disable
56
PD1.Data
55
PD1.Control
54
PD1.PuLLup_Disable
53
PD2.Data
52
PD2.Control
51
PD2.PuLLup_Disable
50
PD3.Data
49
PD3.Control
48
PD3.PuLLup_Disable
47
PD4.Data
46
PD4.Control
45
PD4.PuLLup_Disable
Module
Port B
Observe-Only cells
Port D
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 58. ATmega323 Boundary-Scan Order (Continued)
Bit Number
Signal Name
44
PD5.Data
43
PD5.Control
42
PD5.PuLLup_Disable
41
PD6.Data
40
PD6.Control
39
PD6.PuLLup_Disable
38
PD7.Data
37
PD7.Control
36
PD7.PuLLup_Disable
35
PC0.Data
34
PC0.Control
33
PC0.PuLLup_Disable
32
PC1.Data
31
PC1.Control
30
PC1.PuLLup_Disable
29
PC6.Data
28
PC6.Control
27
PC6.PuLLup_Disable
26
PC7.Data
25
PC7.Control
24
PC7.PuLLup_Disable
23
PA7.Data
22
PA7.Control
21
PA7.PuLLup_Disable
20
PA6.Data
19
PA6.Control
18
PA6.PuLLup_Disable
17
PA5.Data
16
PA5.Control
15
PA5.PuLLup_Disable
14
PA4.Data
13
PA4.Control
12
PA4.PuLLup_Disable
Module
Port D
Port C
Port A
175
1457G–AVR–09/03
Table 58. ATmega323 Boundary-Scan Order (Continued)
Bit Number
Signal Name
11
PA3.Data
10
PA3.Control
9
PA3.PuLLup_Disable
8
PA2.Data
7
PA2.Control
6
PA2.PuLLup_Disable
5
PA1.Data
4
PA1.Control
3
PA1.PuLLup_Disable
2
PA0.Data
1
PA0.Control
0
PA0.PuLLup_Disable
Module
Port A
Boundary-Scan
Description Language
Files
176
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 ATmega323 is available.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Memory
Programming
Boot Loader Support
The ATmega323 provides a 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. This makes it possible to program the AVR in a target system without access to its SPI pins. The Boot Loader
program can use any available data interface and associated protocol, such as USART
serial bus interface, to input or output program code, and write (program) that code into
the Flash memory, or read the code from the Flash memory.
The ATmega323 Flash memory is organized in two main sections:
•
The Application Flash section
•
The Boot Loader Flash section
The Application Flash section and the Boot Loader Flash section have separate Boot
Lock bits. Thus the user can select different levels of protection for the two sections. The
Store Program memory (SPM) instruction can only be executed from the Boot Loader
Flash section.
The program Flash memory in ATmega323 is divided into 256 pages of 64 words each.
The Boot Loader Flash section is located at the high address space of the Flash, and
can be configured through the BOOTSZ Fuses as shown in Table 59.
Table 59. Boot Size Configuration
Pages
Application
Flash Addresses
256
words
4
$0000 - $3EFF
$3F00 $3FFF
$3F00
0
512
words
8
$0000 - $3DFF
$3E00 $3FFF
$3E00
0
1
1024
words
16
$0000 - $3BFF
$3C00 $3FFF
$3C00
0
0
2048
words
32
$0000 - $37FF
$3800 $3FFF
$3800
BOOTSZ1
BOOTSZ0
1
1
1
Boot
Size
Boot Flash
Addresses
Boot Reset
Address
177
1457G–AVR–09/03
Figure 92. Memory Sections
Pages
Program Memory
BOOTSZ = '11'
Pages
Program Memory
BOOTSZ = '10'
$0000
$0000
252
Application Flash Section
(16128 x 16)
4
Boot Flash Section
(256 x 16)
Pages
Program Memory
BOOTSZ = '01'
248
$3EFF
$3F00
8
$3FFF
Pages
Application Flash Section
(15872 x 16)
$3DFF
$3E00
Boot Flash Section
(512 x 16)
$3FFF
Program Memory
BOOTSZ = '00'
$0000
$0000
240
Application Flash Section
(15360 x 16)
224
$37FF
$3800
$3BFF
$3C00
16
32
Boot Flash Section
(1024 x 16)
$3FFF
178
Application Flash Section
(14336 x 16)
Boot Flash Section
(2048 x 16)
$3FFF
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Entering the Boot Loader The SPM instruction can access the entire Flash, but can only be executed from the
Boot Loader Flash section. If no Boot Loader capability is needed, the entire Flash is
Program
available for application code. Entering the Boot Loader takes place by a jump or call
from the application program. This may be initiated by some trigger such as a command
received via USART or SPI interface, for example. 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 60. Boot Reset Fuse
BOOTRST
Reset Address
0
Reset Vector = Application Reset (address $0000)
1
Reset Vector = Boot Loader Reset (see Table 59)
Capabilities of the Boot
Loader
The program code within the Boot Loader section has the capability to read from and
write into the entire Flash, including the Boot Loader Memory. This allows the user to
update both the Application code and the Boot Loader code that handles the software
update. The Boot Loader can thus even modify itself, and it can also erase itself from
the code if the feature is not needed anymore.
Self-programming the
Flash
Programming of the Flash is executed one page at a time. The Flash page must be
erased first for correct programming. The general Write Lock (Lock bit 2) does not control the programming of the Flash memory by SPM instruction. Similarly, the general
Read/Write Lock (Lock bit 1) does not control reading nor writing by LPM/SPM, if it is
attempted.
The Program memory can only be updated page by page, not word by word. One page
is 128 bytes (64 words). The Program memory will be modified by first performing page
erase, then filling the temporary page buffer one word at a time using SPM, and
then executing page write. If only part of the page needs to be changed, the other parts
must be stored (for example in internal SRAM) before the erase, and then be rewritten.
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 “Assembly code example for a Boot Loader” on page 185 for an
assembly code example.
Performing Page Erase by
SPM
To execute Page Erase, set up the address in the Z-pointer, write “00011” to the five
LSB in SPMCR and execute SPM within four clock cycles after writing SPMCR. The
data in R1 and R0 is ignored. The page address must be written to Z14:Z7. Other bits in
the Z-pointer will be ignored during this operation. It is recommended that the interrupts
are disabled during the Page Erase operation.
Fill the Temporary Buffer
(Page Load)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00001” to the five LSB in SPMCR and execute SPM within four clock cycles after writing SPMCR. The content of Z6:Z1 is used to address the data in the temporary buffer.
Z14:Z7 must point to the page that is supposed to be written.
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Perform a Page Write
To execute page write, set up the address in the Z-pointer, write “00101” to the five LSB
in SPMCR and execute SPM within four clock cycles after writing SPMCR. The data in
R1 and R0 is ignored. The page address must be written to Z14:Z7. During this operation, Z6:Z0 must be zero to ensure that the page is written correctly. It is recommended
that the interrupts are disabled during the page write operation.
Consideration while Updating
the Boot Loader Section
Special care must be taken if the user allows the Boot Loader section to be updated by
leaving Boot Lock bit 11 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 bit 11 to protect the Boot Loader software from any internal software
changes.
Wait for SPM Instruction to
Complete
Though the CPU is halted during Page Write, Page Erase or Lock bit write, for future
compatibility, the user software must poll for SPM complete by reading the SPMCR
Register and loop until the SPMEN bit is cleared after a programming operation. See
“Assembly code example for a Boot Loader” on page 185 for a code example.
Instruction Word Read after
Page Erase, Page Write, and
Lock Bit Write
To ensure proper instruction pipelining after programming action (Page Erase, Page
Write, or Lock bit write), the SPM instruction must be followed with the sequence (.dw
$FFFF - NOP) as shown below:
spm
.dw $FFFF
nop
If not, the instruction following SPM might fail. It is not necessary to add this sequence
when the SPM instruction only loads the temporary buffer.
Avoid Reading the Application
Section During Selfprogramming
During Self-programming (either Page Erase or Page Write), the user software should
not read the application section. The user software itself must prevent addressing this
section during the Self-programming operations. This implies that interrupts must be disabled or moved to the Boot Loader section. Before addressing the application section
after the programming is completed, for future compatibility, the user software must
write”10001” to the five LSB in SPMCR and execute SPM within four clock cycles. Then
the user software should verify that the ASB bit is cleared. See “Assembly code example for a Boot Loader” on page 185 for an example. Though the ASB and ASRE bits
have no special function in this device, it is important for future code compatibility that
they are treated as described above.
Boot Loader Lock Bits
ATmega323 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 only protect the Boot Loader Flash section from a software update by the MCU.
•
To only protect application Flash section from a software update by the MCU.
•
Allowing software update in the entire Flash.
See Table 61 for further details. The Boot Lock bits can be set in software and in Serial
or Parallel Programming mode, but they can only be cleared by a chip erase command.
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Table 61. 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 62. 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:
Setting the Boot Loader Lock
Bits by SPM
Protection
1. “1” means unprogrammed, “0” means programmed
To set the Boot Loader Lock bits, write the desired data to R0, write “00001001” to
SPMCR and execute SPM within four clock cycles after writing SPMCR. The only
accessible Lock bits are the Boot Lock bits that may prevent the Application and Boot
Loader section from any software update by the MCU.
Bit
7
6
5
4
3
2
1
0
R0
1
1
BLB12
BLB11
BLB02
BLB01
1
1
If bits 5..2 in R0 are cleared (zero), the corresponding Boot Lock Bit will be programmed
if an SPM instruction is executed within four cycles after BLBSET and SPMEN are set in
SPMCR.
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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 $0001 and set the BLBSET and SPMEN bits in SPMCR. When
an LPM instruction is executed within five CPU cycles after the BLBSET and SPMEN
bits are set in SPMCR, 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 SPM, or LPM, instruction is executed within four, respectively five, CPU
cycles. When BLBSET and SPMEN are cleared, LPM will work as described in “Constant Addressing Using the LPM and SPM Instructions” on page 16 and 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 bits is similar to the one described above for
reading the Lock bits. To read the Fuse Low bits, load the Z-pointer with $0000 and set
the BLBSET and SPMEN bits in SPMCR. When an LPM instruction is executed within
five cycles after the BLBSET and SPMEN bits are set in the SPMCR, the value of the
Fuse Low bits will be loaded in the destination register as shown below.
Bit
7
6
5
4
3
2
1
0
Rd
BODLEVEL
BODEN
–
–
CKSEL3
CKSEL2
CKSEL1
CKSEL0
Similarly, when reading the Fuse High bits, load $0003 in the Z-pointer. When an LPM
instruction is executed within five cycles after the BLBSET and SPMEN bits are set in
the SPMCR, the value of the Fuse High bits will be loaded in the destination register as
shown below.
Bit
7
6
5
4
3
2
1
0
Rd
OCDEN
JTAGEN
SPIEN
–
EESAVE
BOOTSZ1
BOOTSZ0
BOOTRST
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that
are unprogrammed, will be read as one.
In all cases, the read value of unused bit positions are undefined.
EEPROM Write Prevents
Writing to SPMCR
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 SPMCR
Register. If EEPROM writing is performed inside an interrupt routine, the user software
should disable that interrupt before checking the EEWE status bit.
Addressing the Flash During
Self-programming
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
Z15
always ignored
Z14:Z7
page select, for page erase and page write
Z6:Z1
word select, for filling temp buffer (must be zero during page write operation)
Z0
should be zero for all SPM commands, byte select for the LPM instruction.
The only 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.
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Note that the page erase and page write operation is 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.
The LPM instruction also uses 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. See
page 16 for a detailed description.
Store Program Memory
Control Register – SPMCR
The Store Program memory Control Register contains the control bits needed to control
the programming of the Flash from internal code execution.
Bit
7
6
5
4
3
2
1
0
$37 ($57)
–
ASB
–
ASRE
BLBSET
PGWRT
PGERS
SPMEN
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
x
0
0
0
0
0
0
0
SPMCR
• Bit 7 – Res: Reserved Bit
This bit is a reserved bit in the ATmega323 and always reads as zero. This bit should be
written to zero when writing SPMCR.
• Bit 6 – ASB: Application Section Busy
Before entering the Application section after a Boot Loader operation (Page Erase or
Page Write) the user software must verify that this bit is cleared. In future devices, this
bit will be set to “1” by page erase and page write. In ATmega323, this bit always reads
as zero.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the ATmega323 and always reads as zero. This bit should be
written to zero when writing SPMCR.
• Bit 4 – ASRE: Application Section Read Enable
Before re-entering the application section, the user software must set this bit together
with the SPMEN bit and execute SPM within four clock cycles.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is set at the same time as SPMEN, the next SPM instruction within four clock
cycles will set Boot Lock bits. Alternatively, an LPM instruction within five cycles will
read either the Lock bits or the Fuse bits. The BLBSET bit will auto-clear upon completion of the SPM or LPM instruction, or if no SPM, or LPM, instruction is executed within
four, respectively five, clock cycles.
• Bit 2 – PGWRT: Page Write
If this bit is set 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.
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• Bit 1 – PGERS: Page Erase
If this bit is set 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 the Zpointer. 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 erase operation.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If set together with
either ASRE, BLBSET, PGWRT, or PGERS, the following SPM instruction will have a
special meaning, see description above. If only SPMEN is set, 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”, or “00001” in the lower
five bits will have no effect.
Preventing Flash
Corruption
During periods of low VCC, the Flash 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 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. Keep the AVR RESET active (low) during periods of insufficient power supply
voltage. This can be done be 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. The total reset time must be longer than the Flash write
time. This can be achieved by holding the External Reset, or by selecting a long
reset timeout.
2. 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 Flash from unintentional writes.
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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 (lowest address) the first
; data location in Flash is pointed to by the Z-pointer (lowest address)
; - error handling is not included – the routine must be placed inside the
; boot space. Only code inside boot loader section should be read during
; self-programming.
;- registers used: r0, r1, temp1, temp2, looplo, loophi, spmcrval 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 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 Application Section
ldi
spmcrval, (1<<ASRE) + (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 Application Section
ldi
spmcrval, (1<<ASRE) + (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
sbiw loophi:looplo, 2
;use subi for PAGESIZEB<=256
brne Rdloop
; return to Application Section
; verify that Application Section is safe to read
Return:
in
temp1, SPMCR
sbrs temp1, ASB
; If ASB is set, the AS is not ready yet
ret
; re-enable the Applicaiton Section
ldi
spmcrval, (1<<ASRE) + (1<<SPMEN)
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call Do_spm
rjmp Return
Do_spm:
; input: spmcrval determines SPM action
; check that no EEPROM write access is running
Wait_ee:
sbic EECR, EEWE
rjmp Wait_ee
; SPM timed sequence
out
SPMCR, spmcrval
spm
.dw $FFFF
nop
; check for SPM complete
Wait_spm:
in
temp1, SPMCR
sbrc temp1, SPMEN
rjmp Wait_spm
ret
Program and Data
Memory Lock Bits
; ensure proper pipelining
; of next instruction
The ATmega323 provides six Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 63. The Lock bits can
only be erased to “1” with the Chip Erase command.
Table 63. Lock Bit Protection Modes
Memory Lock Bits
186
LB mode
LB2
LB1
Protection Type
1
1
1
No memory lock features enabled for parallel, serial, and
JTAG programming.
2
1
0
Further programming of the Flash and EEPROM is
disabled in parallel, serial, and JTAG programming mode.
The Fuse bits are locked in both serial and parallel
programming mode.(1)
3
0
0
Further programming and verification of the Flash and
EEPROM is disabled in parallel, serial, and JTAG
programming mode. The Fuse bits are locked in both
serial and parallel programming mode.(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.
BLB1 mode
BLB12
BLB11
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ATmega323(L)
Table 63. Lock Bit Protection Modes
Memory Lock Bits
LB mode
LB2
LB1
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:
Fuse Bits
Protection Type
1. Program the Fuse bits before programming the Lock bits.
The ATmega323 has 13 Fuse bits, divided in two groups. The Fuse High bits are
OCDEN, JTAGEN, SPIEN, EESAVE, BOOTSZ1..0, and BOOTRST, and the Fuse Low
bits are BODLEVEL, BODEN, and CKSEL3..0. All Fuses are accessible in Parallel Programming mode and when programming via the JTAG interface. In Serial Programming
mode, all but the SPIEN Fuse is accessible.
•
When the OCDEN Fuse is programmed, the On-chip debug system is enabled if the
JTAGEN Fuse is programmed. If the JTAGEN Fuse is unprogrammed, the OCDEN
Fuse has no visible effect.Never ship a product with the OCDEN Fuse programmed.
Regardless of the setting of Lock bits and the JTAGEN Fuse, a programmed
OCDEN Fuse enables some parts of the clock system be running in all sleep
modes. This may increase the power consumption. Default value is unprogrammed
(“1”).
•
When the JTAGEN Fuse is programmed, the JTAG interface is enabled on port C
pins PC5..2. Default value is programmed (“0”).
•
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.
•
When the SPIEN Fuse is programmed (“0”), Serial Program and Data Downloading
are enabled. Default value is programmed (“0”). The SPIEN Fuse is not accessible
in SPI Serial Programming mode.
•
When EESAVE is programmed, the EEPROM Memory is preserved through the
Chip Erase cycle. Default value is unprogrammed (“1”). The EESAVE Fuse bit can
not be programmed if any of the Lock bits are programmed.
•
BOOTSZ1..0 select the size and start address of the Boot Flash section according
to Table on page 177. Default value is “11” (both unprogrammed).
•
When BOOTRST is programmed (“0”), the Reset Vector is set to the start address of
the Boot Flash section, as selected by the BOOTSZ Fuses according to Table 59 on
page 177. If the BOOTRST is unprogrammed (“1”), the Reset Vector is set to
address $0000. Default value is unprogrammed (“1”).
•
The BODLEVEL Fuse selects the Brown-out Detection Level and changes the Startup times, according to Table 5 on page 26 and Table 6 on page 27, respectively.
Default value is unprogrammed (“1”).
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•
When the BODEN Fuse is programmed (“0”), the Brown-out Detector is enabled.
See “Reset and Interrupt Handling” on page 22. Default value is unprogrammed
(“1”).
•
CKSEL3..0 select the clock source and the start-up delay after reset, according to
Table 1 on page 6 and Table 6 on page 27. Default value is “0010” (Internal RC
Oscillator, slowly rising power).
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.
Signature Bytes
All Atmel microcontrollers have a 3-byte signature code which identifies the device. This
code can be read in both serial and parallel mode. The three bytes reside in a separate
address space.
For the ATmega323 the signature bytes are:
1. $000: $1E (indicates manufactured by Atmel)
2. $001: $95 (indicates 32KB Flash memory)
3. $002: $01 (indicates ATmega323 device when $001 is $95)
Calibration Byte
The ATmega323 has a one byte calibration value for the internal RC Oscillator. This
byte resides in the High Byte of address $000 in the signature address space. To make
use of this byte, it should be read from this location and written into the normal Flash
Program memory by the external programmer. At start-up, the user software must read
this Flash location and write the value to the OSCCAL Register.
Parallel Programming
This section describes how to parallel program and verify Flash Program memory,
EEPROM Data memory + Program And Data memory Lock bits and Fuse bits in the
ATmega323. Pulses are assumed to be at least 500ns unless otherwise noted.
Signal Names
In this section, some pins of the ATmega323 are referenced by signal names describing
their functionality during parallel programming, see Figure 93 and Table 64. 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 are shown in Table 65.
When pulsing WR or OE, the command loaded determines the action executed. The
Command is a byte where the different bits are assigned functions as shown in Table
66.
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Figure 93. Parallel Programming
ATmega323
+5V
RDY/BSY
PD1
OE
PD2
WR
PD3
BS1
PD4
XA0
PD5
XA1
PD6
VCC
PB7 - PB0
PAGEL
+12 V
BS2
DATA
PD7
RESET
PA0
XTAL1
GND
Table 64. 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 Page Load
BS2
PA0
I
Byte Select 2 (“0” Selects Low Byte, “1” Selects 2
nd High Byte)
DATA
PB7 - 0
I/O
Bidirectional Data Bus (Output When OE is Low)
Table 65. 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
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Table 66. Command Byte Bit Coding
Command Byte
Enter Programming Mode
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
0000 0100
Read Fuse and Lock bits
0000 0010
Read Flash
0000 0011
Read EEPROM
The following algorithm puts the device in Parallel Programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET and BS1 pins to “0” and wait at least 100 ns.
3. Apply 11.5 - 12.5V to RESET. Any activity on BS1 within 100 ns after +12V has
been applied to RESET, will cause the device to fail entering programming mode.
Chip Erase
The Chip Erase command will erase the Flash and EEPROM memories and the 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 is
reprogrammed.
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.
4. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
5. Wait until RDY/BSY goes high before loading a new command.
Programming the Flash
The Flash is organized as 256 pages of 128 bytes each. 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 ($00 - $FF).
4. Give XTAL1 a positive pulse. This loads the address Low Byte.
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C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data Low Byte ($00 - $FF).
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 ($00 - $FF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data High and Low Byte
1. Set BS1 to “1”.
2. Give PAGEL a positive pulse. See Figure 94 for signal waveforms.
F. Repeat B through F 64 Times to Fill the Page Buffer.
To address a page in the Flash, 8 bits are needed (256 pages). The 6 most significant
bits are read from address High Byte as described in section “H” below. The two least
significant page address bits however, are the two most significant bits (bit7 and bit6) of
the latest loaded address Low Byte as described in section “B”.
G. Load Address High Byte
1. 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 ($00 - $3F).
4. Give XTAL1 a positive pulse. This loads the address High Byte.
H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of
data. RDY/BSYgoes low.
2. Wait until RDY/BSY goes high.
(See Figure 95 for signal waveforms)
I. 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.
J. Repeat A through I 256 Times or Until All Data Has Been Programmed.
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Figure 94. Programming the Flash Waveforms
$10
DATA
ADDR. LOW
ADDR. HIGH
DATA LOW
XA1
XA2
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
BS2
PAGEL
Figure 95. Programming the Flash Waveforms (continued)
DATA
DA TA HIGH
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET
+12V
OE
PAGEL
BS2
Programming the EEPROM
The programming algorithm for the EEPROM Data memory is as follows (refer to “Programming the Flash” on page 190 for details on Command, Address and Data loading):
1. A: Load Command “0001 0001”.
2. H: Load Address High Byte ($00 - $03)
3. B: Load Address Low Byte ($00 - $FF)
4. C: Load Data Low Byte ($00 - $FF)
K: Write Data Low Byte
1. Set BS1 to “0”. This selects low data.
2. Give WR a negative pulse. This starts programming of the data byte. RDY/BSY
goes low.
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3. Wait until to RDY/BSY goes high before programming the next byte.
(See Figure 96 for signal waveforms)
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.
•
Address High Byte needs only be loaded before programming a new 256 byte
window in the EEPROM.
•
Skip writing the data value $FF, that is the contents of the entire EEPROM after a
Chip Erase.
These considerations also applies to Flash, EEPROM and Signature bytes reading.
Figure 96. Programming the EEPROM Waveforms
DATA
$11
ADDR. HIGH
ADDR. LOW
DA TA LOW
XA1
XA2
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
BS2
PAGEL
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the
Flash” on page 190 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. H: Load Address High Byte ($00 - $3F)
3. B: Load Address Low Byte ($00 - $FF)
4. Set OE to “0”, and BS1 to “0”. The Flash word Low Byte can now be read at
DATA.
5. Set BS 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 190 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. H: Load Address High Byte ($00 - $03)
3. B: Load Address ($00 - $FF)
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at
DATA.
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5. Set OE to “1”.
Programming the Fuse Low
Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming
the Flash” on page 190 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.
Bit 7 = BODLEVEL Fuse bit
Bit 6 = BODEN Fuse bit
Bit 3..0 = CKSEL3..0 Fuse bits
Bit 5,4 = “1”. This bit is reserved and should be left unprogrammed (“1”).
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 190 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.
Bit 7 = OCDEN Fuse bit
Bit 6 = JTAGEN Fuse bit
Bit 5 = SPIEN Fuse bit
Bit 3 = EESAVE Fuse bit
Bit 2..1 = BOOTSZ1..0 Fuse bits
Bit 0 = BOOTRST Fuse bit
Bit 7,6,4 = “1”. These bits are reserved and should be left unprogrammed (“1”).
3. Set BS1 to “1”. 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 Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” on page 190 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.
Bit 5 = Boot Lock bit12
Bit 4 = Boot Lock bit11
Bit 3 = Boot Lock bit02
Bit 2 = Boot Lock bit01
Bit 1 = Lock bit2
Bit 0 = Lock bit1
Bit 7..6 = “1”. These bits are reserved and should be left unprogrammed (“1”).
3. L: Write Data Low Byte.
The Lock bits can only be cleared by executing Chip Erase.
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 190 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).
Bit 7 = BODLEVEL Fuse bit
Bit 6 = BODEN Fuse bit
Bit 3..0 = CKSEL3..0 Fuse bits
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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).
Bit 7 = OCDEN Fuse bit
Bit 6 = JTAGEN Fuse bit
Bit 5 = SPIEN Fuse bit
Bit 3 = EESAVE Fuse bit
Bit 2..1 = BOOTSZ1..0 Fuse bits
Bit 0 = BOOTRST Fuse bit
4. 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).
Bit 5 = Boot Lock bit12
Bit 4 = Boot Lock bit11
Bit 3 = Boot Lock bit02
Bit 2 = Boot Lock bit01
Bit 1 = Lock bit2
Bit 0 = Lock bit1
5. Set OE to “1”.
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to Programming the
Flash for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. C: Load Address Low Byte ($00 - $02).
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 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. C: Load Address Low Byte, $00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Parallel Programming
Characteristics
Figure 97. Parallel Programming Timing
tXLWL
tXHXL
XTAL1
tDVXH
tXLDX
Data & Contol
(DATA, XA0/1, BS1, BS2)
tPLBX t BVWL
tBVPH
PAGEL
tRHBX
tPHPL
Write
tWLWH
WR
tPLWL
WLRL
RDY/BSY
DATA
tXLOL
tOLDV
tOHDZ
Read
tWLRH
OE
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Table 67. Parallel Programming Characteristics, TA = 25°C ± 10%, VCC = 5 V ± 10%
Symbol
Parameter
Min
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXHXL
XTAL1 Pulse Width High
67
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
67
ns
tBVPH
BS1 Valid before PAGEL High
67
ns
tPHPL
PAGEL Pulse Width High
67
ns
tPLBX
BS1 Hold after PAGEL Low
67
ns
tPLWL
PAGEL Low to WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tRHBX
BS1 Hold after RDY/BSY High
67
ns
tWLWH
WR Pulse Width Low
67
ns
tWLRL
WR Low to RDY/BSY Low
0
tWLRH (1)
WR Low to RDY/BSY High(1)
tWLRH_CE
(2)
tWLRH_FLASH
XTAL1 Low to OE Low
tOLDV
OE Low to DATA Valid
tOHDZ
OE High to DATA Tri-stated
Notes:
196
1.
2.
3.
Units
12.5
V
250
µA
2.5
µs
1
1.5
1.9
ms
16
23
30
ms
(3)
8
12
15
ms
WR Low to RDY/BSY High for Write Flash
tXLOL
Max
(2)
WR Low to RDY/BSY High for Chip Erase
(3)
Typ
67
ns
20
ns
20
ns
tWLRH is valid for the Write EEPROM, Write Fuse bits and Write Lock bits commands.
tWLRH_CE is valid for the Chip Erase command.
tWLRH_FLASH is valid for the Write Flash command.
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ATmega323(L)
Serial Downloading
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.
Figure 98. Serial Programming and Verify
ATmega323
2.7 - 5.5V
VCC
MOSI
PB5
MISO
PB6
SCK
PB7
RESET
GND
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 $FF.
The Program and EEPROM Memory arrays have separate address spaces:
$0000 to $3FFF for Program memory and $0000 to $03FF for EEPROM Memory.
The device can be clocked by any clock option during Low Voltage Serial Programming.
The minimum low and high periods for the serial clock (SCK) input are defined as
follows:
Low: > 2 CPU clock cycles
High: > 2 CPU clock cycles
Serial Programming
Algorithm
When writing serial data to the ATmega323, data is clocked on the rising edge of SCK.
When reading data from the ATmega323, data is clocked on the falling edge of SCK.
See Figure 99, Figure 100, and Table 70 for timing details.
To program and verify the ATmega323 in the Serial Programming mode, the following
sequence is recommended (See four byte instruction formats in Table 69):
1. Power-up sequence:
Apply power between V CC and GND while RESET and SCK are set to “0”. The
RESET and SCK are set to “0”. In accordance with the setting of CKSEL Fuses,
apply a crystal/resonator, external clock or RC network, or let the device run on the
internal RC Oscillator. 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 XTAL1 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/PB5.
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3. The Serial Programming instructions will not work if the communication is out of
synchronization. When in sync. the second byte ($53), 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 $53 did
not echo back, give SCK a positive pulse and issue a new Programming Enable
command. If the $53 is not seen within 32 attempts, there is no functional device
connected.
4. If a chip erase is performed (must be done to erase the Flash), wait 2•tWD_FLASH
after the instruction, give RESET a positive pulse, and start over from Step 2.
See Table 68 for the tWD_FLASH figure.
5. The Flash is programmed one page at a time. 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. 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. (Please refer to Table 68). Accessing the Serial Programming
interface before the Flash write operation completes can result in incorrect
programming.
6. 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 is not
used, the user must wait at least tWD_EEPROM before issuing the next byte. (Please
refer to Table 68). In a chip erased device, no $FFs in the data file(s) need to be
programmed.
7. Any memory location can be verified by using the Read instruction which returns
the content at the selected address at serial output MISO/PB6.
8. At the end of the programming session, RESET can be set high to commence
normal operation.
9. Power-off sequence (if needed):
Set XTAL1 to “0” (if a crystal is not used).
Set RESET to “1”.
Turn VCC power off
Data Polling Flash
When a page is being programmed into the Flash, reading an address location within
the page being programmed will give the value $FF. At the time the device is ready for a
new page, the programmed value will read correctly. This is used to determine when the
next page can be written. Note that the entire page is written simultaneously and any
address within the page can be used for polling. Data polling of the Flash will not work
for the value $FF, so when programming this value, the user will have to wait for at least
tWD_FLASH before programming the next page. As a Chip Erased device contains $FF in
all locations, programming of addresses that are meant to contain $FF, can be skipped.
See Table 68 tWD_FLASH.
Data Polling EEPROM
When a new byte has been written and is being programmed into EEPROM, reading the
address location being programmed will give the value $FF. At the time the device is
ready for a new byte, the programmed value will read correctly. This is used to determine when the next byte can be written. This will not work for the value $FF, but the user
should have the following in mind: As a Chip Erased device contains $FF in all locations,
programming of addresses that are meant to contain $FF, can be skipped. This does
not apply if the EEPROM is re-programmed without Chip Erasing the device. In this
case, data polling cannot be used for the value $FF, and the user will have to wait at
least tWD_EEPROM before programming the next byte. See Table 68 for tWD_EEPROM.
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Programming Times for Nonvolatile Memory
The internal RC Oscillator is used to control programming time when programming or
erasing Flash, EEPORM, Fuses and Lock bits. During Parallel or Serial Programming,
the device is in reset, and this Oscillator runs at its initial, uncalibrated frequency, which
may vary from 0.5 MHz to 1.0 MHz. In software it is possible to calibrate this Oscillator to
1.0 MHz (see “Calibrated Internal RC Oscillator” on page 41). Consequently, programming times will be shorter and more accurate when programming or erasing non-volatile
memory from software, using SPM or the EEPROM interface. See Table 68 for a summary of programming times.
Table 68. Maximum Programming Times for Non-volatile Memory
Parallel/Serial
Programming
Number of
RC Oscillator
Cycles
Selfprogramming
2.7V
5.0V
(1)
Operation
Symbol
Chip Erase
tWD_CE
16K
32 ms
30 ms
17 ms
Flash Write
tWD_FLASH
8K
16 ms
15 ms
8.5 ms
EEPROM
Write(2)
tWD_EEPROM
2K
4 ms
3.8 ms
2.2 ms
Fuse/Lock
bit write
tWD_FUSE
1K
2 ms
1.9 ms
1.1 ms
Notes:
1. Includes variation over voltage and temperature after RC Oscillator has been calibrated to 1.0 MHz
2. Parallel EEPROM programming takes 1K cycles
Figure 99. Serial Programming Waveforms
SERIAL DATA INPUT
PB5 (MOSI)
MSB
LSB
SERIAL DATA OUTPUT
PB6 (MISO)
MSB
LSB
SERIAL CLOCK INPUT
PB7(SCK)
SAMPLE
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1457G–AVR–09/03
.
Table 69. Serial Programming Instruction Set
Instruction Format
Instruction
Byte 1
Byte 2
Byte 3
Byte4
Programming Enable
1010 1100
0101 0011
xxxx xxxx
xxxx xxxx
Enable Serial Programming after
RESET goes low.
Chip Erase
1010 1100
100x xxxx
xxxx xxxx
xxxx xxxx
Chip Erase EEPROM and Flash.
Read Program Memory
0010 H000
xxaa aaaa
bbbb bbbb
oooo oooo
Read H (high or low) data o from
Program memory at word address
a:b.
Load Program Memory
Page
0100 H000
xxxx xxxx
xxbb bbbb
iiii iiii
Write H (high or low) data i to
Program memory page at word
address b.
Write Program Memory
Page
0100 1100
xxaa aaaa
bbxx xxxx
xxxx xxxx
Write Program memory Page at
address a:b.
Read EEPROM Memory
1010 0000
xxxx xxaa
bbbb bbbb
oooo oooo
Read data o from EEPROM
Memory at address a:b.
Write EEPROM Memory
1100 0000
xxxx xxaa
bbbb bbbb
iiii iiii
Write data i to EEPROM Memory
at address a:b.
Read Lock Bits
0101 1000
0000 0000
xxxx xxxx
xx65 4321
Read Lock bits. “0” = programmed,
“1” = unprogrammed.
Write Lock Bits
1010 1100
111x xxxx
xxxx xxxx
1165 4321
Write Lock bits. Set bits 6 - 1 = “0”
to program Lock bits.
Read Signature Byte
0011 0000
xxxx xxxx
xxxx xxbb
oooo oooo
Read Signature Byte o at address
b.
Write Fuse Bits
1010 1100
1010 0000
xxxx xxxx
CB11 A987
Set bits C - A, 9 - 7 = “0” to
program, “1” to unprogram
Write Fuse High Bits
1010 1100
1010 1000
xxxx xxxx
IH11 GFED
Set bits F - D = “0” to program, “1”
to unprogram
Read Fuse Bits
0101 0000
0000 0000
xxxx xxxx
CBxx A987
Read Fuse bits. “0” = programmed,
“1” = unprogrammed
Read Fuse High Bits
0101 1000
0000 1000
xxxx xxxx
IHxx GFED
Read Fuse high bits. “0” = programmed, “1” = unprogrammed
Read Calibration Byte
0011 1000
xxxx xxxx
0000 0000
oooo oooo
Read Signature Byte o at address
b.
Note:
200
Operation
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;
1 = lock bit 1; 2 = lock bit 2; 3 = Boot Lock Bit01; 4 = Boot Lock Bit02; 5 = Boot Lock Bit11; 6 = Boot Lock Bit12;
7 = CKSEL0 Fuse; 8 = CKSEL1 Fuse; 9 = CKSEL2 Fuse; A = CKSEL3 Fuse; B = BODEN Fuse; C = BODLEVEL Fuse;
D = BOOTRST Fuse; E = BOOTSZ0 Fuse; F = BOOTSZ1 Fuse; G = EESAVE Fuse; H = JTAGEN Fuse; and I = OCDEN Fuse
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Serial Programming
Characteristics
Figure 100. Serial Programming Timing
MOSI
tOVSH
SCK
tSHOX
tSLSH
tSHSL
MISO
tSLIV
Table 70. Serial Programming Characteristics
TA = -40°C to 85°C, VCC = 2.7V - 5.5V (Unless otherwise noted)
Symbol
Parameter
1/tCLCL
Oscillator Frequency (VCC = 2.7 - 5.5 V)
tCLCL
1/tCLCL
Oscillator Period (VCC = 2.7 - 5.5 V)
Oscillator Frequency (VCC = 4.0 - 5.5 V)
tCLCL
Oscillator Period (VCC = 4.0 - 5.5 V)
tSHSL
Min
Typ
0
Max
Units
4
MHz
250
ns
0
8
MHz
125
ns
SCK Pulse Width High
2 tCLCL
ns
tSLSH
SCK Pulse Width Low
2 tCLCL
ns
tOVSH
MOSI Setup to SCK High
tCLCL
ns
tSHOX
MOSI Hold after SCK High
2 tCLCL
ns
tSLIV
SCK Low to MISO Valid
10
16
32
ns
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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
On-chip Debug. In these cases the JTAG pins must be dedicated for this purpose.
As a definition in this datasheet, the LSB is shifted in and out first of all Shift Registers.
Programming specific
JTAG instructions
The Instruction Register is four 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.
AVR_RESET ($C)
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 ($4)
PROG_COMMANDS ($5)
PROG_PAGELOAD ($6)
202
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.
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 71 below).
The AVR specific public JTAG instruction to directly load the Flash data page via the
JTAG port. The 1024 bit Virtual Flash Page Load Register is selected as Data Register.
This is a virtual scan chain with length equal to the number of bits in one Flash page.
Internally the Shift Register is 8-bit. Unlike most JTAG instructions, the Update-DR state
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ATmega323(L)
is not used to transfer data from the Shift Register. The data are automatically transferred to the Flash page buffer byte-by-byte in the Shift-DR state by an internal state
machine. This is the only active state:
•
PROG_PAGEREAD ($7)
The AVR specific public JTAG instruction to read one full Flash data page via the JTAG
port. The 1,032 bit Virtual Flash Page Read Register is selected as Data Register. This
is a virtual scan chain with length equal to the number of bits in one Flash page plus
eight. Internally the Shift Register is 8-bit. Unlike most JTAG instructions, the CaptureDR state is not used to transfer data to the Shift Register. The data are automatically
transferred from the Flash page buffer byte-by-byte in the Shift-DR state by an internal
state machine. This is the only active state:
•
Data Registers
Reset Register
Shift-DR: Flash page data are shifted in from TDI by the TCK input, and
automatically loaded into the Flash page one byte at a time.
Shift-DR: Flash data are automatically read one byte at a time and shifted out on
TDO by the TCK input. The TDI input is ignored.
The Data Registers are selected by the JTAG Instruction Registers described in section
“Programming specific JTAG instructions” on page 202. The Data Registers relevant for
programming operations are:
•
Reset Register
•
Programming Enable Register
•
Programming Command Register
•
Virtual Flash Page Load Register
•
Virtual Flash Page Read 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 TimeOut Period (refer to Table 6 on page 27) 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 93 on page 189.
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 1010_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.
203
1457G–AVR–09/03
Figure 101. Programming Enable Register
TDI
D
A
T
A
$A370
=
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 71. The
state sequence when shifting in the programming commands is illustrated in Figure 102.
Figure 102. 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
204
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table 71. JTAG Programming Instruction Set
Instruction
TDI sequence
TDO sequence
Notes
1a. Chip erase
0100011_10000000
0110001_10000000
0110011_10000000
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_00aaaaaa
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 Page
0110111_00000000
0110101_00000000
0110111_00000000
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_00aaaaaa
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_000000aa
xxxxxxx_xxxxxxxx
4c. Load Address Low Byte
0000011_bbbbbbbb
xxxxxxx_xxxxxxxx
4d. Load Data Byte
0010011_iiiiiiii
xxxxxxx_xxxxxxxx
4e. Write EEPROM byte
0110011_00000000
0110001_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4f. Poll for Byte Write complete
0110011_00000000
xxxxxox_xxxxxxxx
(2)
5a. Enter EEPROM Read
0100011_00000011
xxxxxxx_xxxxxxxx
5b. Load Address High Byte
0000111_000000aa
xxxxxxx_xxxxxxxx
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
6a. Enter Fuse Write
0100011_01000000
xxxxxxx_xxxxxxxx
6b. Load Data High Byte
0010011_IH11GFED
xxxxxxx_xxxxxxxx
(2)
Low Byte
High Byte
(3)
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Table 71. JTAG Programming Instruction Set (Continued)
Instruction
TDI sequence
TDO sequence
6c. Write Fuse High Byte
0110111_00000000
0110101_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6d. Poll for Fuse Write complete
0110111_00000000
xxxxxox_xxxxxxxx
(2)
6e. Load Data Low Byte
0010011_CB11A987
xxxxxxx_xxxxxxxx
(3)
6f. Write Fuse Low Byte
0110011_00000000
0110001_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6g. Poll for Fuse Write complete
0110011_00000000
xxxxxox_xxxxxxxx
(2)
7a. Enter Lock Bit Write
0100011_00100000
xxxxxxx_xxxxxxxx
7b. Load Data Byte
0010011_11654321
xxxxxxx_xxxxxxxx
(4)
7c. Write Lock Bits
0110011_00000000
0110001_00000000
0110011_00000000
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 Fuse High Byte
0111110_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_IHxxGFED
8c. Read Fuse Low Byte
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_CBxxA987
8d. Read Lock Bits
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xx654321
(5)
8e. Read Fuses and Lock Bits
0111110_00000000
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
(5)
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:
206
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.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
4. Set bits to “0” to program the corresponding lock bit, “1” to leave the lock bit
unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. a = address High Byte; b = address Low Byte; i = data in; o = data out; 1 = lock bit 1;
2 = lock bit 2; 3 = Boot Lock Bit01;
4 = Boot Lock Bit02; 5 = Boot Lock Bit11; 6 = Boot Lock Bit12; 7 = CKSEL0 Fuse; 8 =
CKSEL1 Fuse; 9 = CKSEL2 Fuse;
A = CKSEL3 Fuse; B = BODEN Fuse; C = BODLEVEL Fuse; D = BOOTRST Fuse; E
= BOOTSZ0 Fuse; F = BOOTSZ1 Fuse; G = EESAVE Fuse; H = JTAGEN Fuse; I =
OCDEN Fuse
Figure 103. 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
0
1
1
Capture-DR
Capture-IR
0
0
Shift-DR
Shift-IR
0
1
Exit1-DR
1
Exit1-IR
0
0
Pause-DR
0
0
Pause-IR
1
1
0
Exit2-DR
Exit2-IR
1
1
Update-DR
1
0
1
1
0
1
Update-IR
0
1
0
207
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Virtual Flash Page
Load Register
The Virtual Flash Page Load Register is a virtual scan chain with length equal to the
number of bits in one Flash page, 1,024. Internally the Shift Register is 8-bit, and the
data are automatically transferred to the Flash page buffer byte-by-byte. Shift in all
instruction words in the page, starting with the LSB of the instruction with page address
0 and ending with the MSB of the instruction with page address 3F. This provides an
efficient way to load the entire Flash page buffer before executing Page Write.
Figure 104. Virtual Flash Page Load Register
STROBES
State
machine
ADDRESS
TDI
Flash
EEPROM
Fuses
Lock Bits
D
A
T
A
TDO
208
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1457G–AVR–09/03
ATmega323(L)
Virtual Flash Page Read
Register
The Virtual Flash Page Read Register is a virtual scan chain with length equal to the
number of bits in one Flash page plus eight, 1,032 in total. Internally the Shift Register is
8-bit, and the data are automatically transferred from the Flash data page byte-by-byte.
The first eight cycles are used to transfer the first byte to the internal Shift Register, and
the bits that are shifted out during these eight cycles should be ignored. Following this
initialization, data are shifted out starting with the LSB of the instruction with page
address 0 and ending with the MSB of the instruction with page address 3F. This provides an efficient way to read one full Flash page to verify programming.
Figure 105. Virtual Flash Page Read Register
STROBES
State
machine
TDI
ADDRESS
Flash
EEPROM
Fuses
Lock Bits
D
A
T
A
TDO
Programming algorithm
All references below of type “1a”, “1b”, and so on, refer to Table 71.
Entering programming mode
1. Enter JTAG instruction AVR_RESET and shift 1 in the Reset Register.
2. Enter instruction PROG_ENABLE and shift 1010_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 0000_0000_0000_0000 in the programming Enable Register.
4. Enter JTAG instruction AVR_RESET and shift 0 in the Reset Register.
If PROG_ENABLE instruction is not followed by the AVR_RESET instruction, the following algorithm should be used:
1. Enter JTAG instruction PROG_COMMANDS.
2. Disable all programming instructions by using no operation instruction 11a.
3. Enter instruction PROG_ENABLE and shift 0000_0000_0000_0000 in the Programming Enable Register.
4. Enter instruction PROG_ENABLE and shift 0000_0000_0000_0000 in the Programming Enable Register.
5. Wait until the selected Oscillator has started before applying more commands.
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1457G–AVR–09/03
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 67 on page 196).
Programming the Flash
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load address using programming instructions 2b and 2c.
4. Load data using programming instructions 2d, 2e and 2f.
5. Repeat step 3 and 4 for all 64 instruction words in the page.
6. Write the page using programming instruction 2g.
7. Poll for Flash write complete using programming instruction 2h, or wait for
tWLRH_FLASH (refer to Table 67 on page 196).
8. 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. The 6 LSB
are 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, starting with
the LSB of the first instruction in the page and ending with the MSB of the last
instruction in the page.
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_FLASH (refer to Table 67 on page 196).
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. The 6 LSB
are used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGEREAD.
5. Read the entire page by shifting out all instruction words in the page, starting
with the LSB of the instruction with page address 0 and ending with the MSB of
the instruction with page address 3F. Remember that the first eight bits should be
ignored.
210
ATmega323(L)
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ATmega323(L)
6. Enter JTAG instruction PROG_COMMANDS.
7. Repeat steps 3 to 6 until all data have been read.
Programming the EEPROM
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM write using programming instruction 4a.
3. Load address using programming instructions 4b and 4c.
4. Load data using programming instructions 4d.
5. Write the data using programming instruction 4e.
6. Poll for EEPROM write complete using programming instruction 4f, or wait for
tWLRH (refer to Table 67 on page 196).
7. Repeat steps 3 to 6 until all data have been programmed.
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.
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 67 on page 196).
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 67 on page 196).
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 67 on page 196).
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.
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Reading the Signature Bytes
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Signature byte read using programming instruction 9a.
3. Load address $00 using programming instruction 9b.
4. Read first signature byte using programming instruction 9c.
5. Repeat steps 3 and 4 with address $01 and address $02 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 $00 using programming instruction 10b.
4. Read the calibration byte using programming instruction 10c.
212
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ATmega323(L)
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 = 2.7V to 5.5V (Unless Otherwise Noted)
Symbol
VIL
VIL1
VIH
VIH1
Parameter
Condition
Min
Typ
Max
Units
Input Low Voltage
(Except XTAL1)
-0.5
0.3
VCC(1)
V
(XTAL1), CKSEL3 Fuse
programmed
-0.5
0.3
VCC(1)
V
(XTAL1), CKSEL3 Fuse
unprogrammed
-0.5
0.2
VCC(1)
V
(Except XTAL1, RESET)
0.6 VCC(2)
VCC + 0.5
V
(XTAL1), CKSEL3 Fuse
programmed
0.6 VCC(2)
VCC + 0.5
V
(XTAL1), CKSEL3 Fuse
unprogrammed
0.8 VCC(2)
VCC + 0.5
V
0.9 VCC(2)
VCC + 0.5
V
0.6
0.5
V
V
Input Low Voltage
Input High Voltage
Input High Voltage
VIH2
Input High Voltage
(RESET)
VOL
Output Low Voltage(3)
(Ports A,B,C,D)
IOL = 20 mA, VCC = 5V
IOL = 10 mA, VCC = 3V
VOH
Output High Voltage(4)
(Ports A,B,C,D)
IOH = -3 mA, VCC = 5V
IOH = -1.5 mA, VCC = 3V
IIL
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin low
(absolute value)
8.0
µA
IIH
Input Leakage
Current I/O Pin
Vcc = 5.5V, pin high
(absolute value)
980
nA
4.2
2.3
V
V
RRST
Reset Pull-up Resistor
100
500
kΩ
RI/O
I/O Pin Pull-up Resistor
35
120
kΩ
213
1457G–AVR–09/03
DC Characteristics (Continued)
TA = -40°C to 85°C, VCC = 2.7V to 5.5V (Unless Otherwise Noted)
Symbol
Parameter
Condition
Min
Typ
Active 4 MHz, VCC = 3V
(ATmega323L)
Active 8 MHz, VCC = 5V
(ATmega323)
Max
Units
5
mA
15
mA
2.5
mA
8
mA
Power Supply Current
Idle 4 MHz, VCC = 3V
(ATmega323L)
ICC
Idle 8 MHz, VCC = 5V
(ATmega323)
Power-down mode(5)
WDT enabled, VCC = 3V
9
15.0
µA
WDT disabled, VCC = 3V
<1
4.0
µA
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
Initialization Delay
VCC = 2.7V
VCC = 4.0V
Note:
-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 (20mA at Vcc = 5V, 10mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed – PDIP Package:
1] The sum of all IOL, for all ports, should not exceed 200 mA.
2] The sum of all IOL, for port A0 - A7, should not exceed 100 mA.
3] The sum of all IOL, for ports B0 - B7,C0 - C7, D0 - D7 and XTAL2, should not exceed 100 mA – TQFP 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, should not exceed 100 mA.
3] The sum of all IOL, for ports B0 - B3, should not exceed 100 mA.
4] The sum of all IOL, for ports B4 - B7, should not exceed 100 mA.
5] The sum of all IOL, for ports C0 - C3, should not exceed 100 mA.
6] The sum of all IOL, for ports C4 - C7, should not exceed 100 mA.
7] The sum of all IOL, for ports D0 - D3 and XTAL2, should not exceed 100 mA.
8] The sum of all IOL, for ports D4 - D7, 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 (3mA at Vcc = 5V, 1.5mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed – PDIP Package:
1] The sum of all IOH, for all ports, should not exceed 200 mA.
2] The sum of all IOH, for port A0 - A7, should not exceed 100 mA.
3] The sum of all IOH, for ports B0 - B7,C0 - C7, D0 - D7 and XTAL2, should not exceed 100 mA – TQFP Package:
1] The sum of all IOH, for all ports, should not exceed 400 mA.
2] The sum of all IOH, for ports A0 - A7, should not exceed 100 mA.
3] The sum of all IOH, for ports B0 - B3, should not exceed 100 mA.
4] The sum of all IOH, for ports B4 - B7, should not exceed 100 mA.
5] The sum of all IOH, for ports C0 - C3, should not exceed 100 mA.
6] The sum of all IOH, for ports C4 - C7, should not exceed 100 mA.
7] The sum of all IOH, for ports D0 - D3 and XTAL2, should not exceed 100 mA.
8] The sum of all IOH, for ports D4 - D7, 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. Minimum VCC for Power-down is 2.5V.
214
ATmega323(L)
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ATmega323(L)
External Clock Drive
Waveforms
Figure 106. External Clock Drive Waveforms
lH1
lL1
External Clock Drive
Table 72. External Clock Drive
VCC = 2.7V to 5.5V
VCC = 4.0V to 5.5V
Symbol
Parameter
Min
Max
Min
Max
Units
1/tCLCL
Oscillator Frequency
0
4
0
8
MHz
tCLCL
Clock Period
250
125
ns
tCHCX
High Time
100
50
ns
tCLCX
Low Time
100
50
ns
tCLCH
Rise Time
1.6
0.5
µs
tCHCL
Fall Time
1.6
0.5
µs
Table 73. External RC Oscillator, Typical Frequencies
Note:
R [kΩ]
C [pF]
f
100
70
TBD
31.5
20
TBD
6.5
20
TBD
R should be in the range 3kΩ - 100kΩ, and C should be at least 20pF. The C values
given in the table includes pin capacitance. This will vary with package type.
215
1457G–AVR–09/03
Two-wire Serial Interface Characteristics
Table 74 describes the requirements for devices connected to the Two-wire Serial Bus. The ATmega323 Two-wire Serial
Interface meets or exceeds these requirements under the noted conditions.
Timing symbols refer to Figure 107.
Table 74. Two-wire Serial Bus Requirements
Symbol
Parameter
VIL
VIH
VOL
tof
Min
Max
Units
Input Low-voltage
-0.5
0.3 VCC
V
Input High-voltage
0.7 VCC
VCC + 0.5
V
0.05 VCC(2)
–
V
0
0.4
V
250
ns
0
50(2)
ns
-10
10
µA
–
10
pF
0
400
kHz
fSCL ≤ 100 kHz
4.0
–
µs
fSCL > 100 kHz
(1)
Hysteresis of Schmitt Trigger Inputs
(1)
Output Low-voltage
Vhys
(1)
(1)
Spikes Suppressed by Input Filter
Ii
Input Current each I/O Pin
(1)
SCL Clock Frequency
tHD;STA
Hold Time (repeated) START Condition
tLOW
Low Period of the SCL Clock
tHIGH
High period of the SCL clock
tSU;STA
Set-up time for a repeated START condition
tHD;DAT
Data hold time
tSU;DAT
Data setup time
tSU;STO
Setup time for STOP condition
tBUF
Bus free time between a STOP and START
condition
216
(3)
10 pF < Cb < 400 pF
20 + 0.1Cb
0.1VCC < Vi < 0.9VCC
Capacitance for each I/O Pin
fSCL
Notes:
3 mA sink current
Output Fall Time from VIHmin to VILmax
tSP
Ci
Condition
fCK
(4)
(5)
> max(16fSCL, 250kHz)
(3)(2)
0.6
–
µs
(6)
4.7
–
µs
(7)
1.3
–
µs
fSCL ≤ 100 kHz
4.0
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL ≤ 100 kHz
4.7
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL ≤ 100 kHz
0
3.45
µs
fSCL > 100 kHz
0
0.9
µs
fSCL ≤ 100 kHz
250
–
ns
fSCL > 100 kHz
100
–
ns
fSCL ≤ 100 kHz
4.0
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL ≤ 100 kHz
4.7
–
µs
fSCL > 100 kHz
1.3
–
µs
fSCL ≤ 100 kHz
fSCL > 100 kHz
1.
2.
3.
4.
5.
In ATmega323, this parameter is characterized and not 100% tested.
Required only for fSCL > 100 kHz.
Cb = capacitance of one bus line in pF.
fCK = CPU clock frequency
This requirement applies to all ATmega323 Two-wire Serial Interface operation. Other devices connected to the Two-wire
Serial Bus need only obey the general fSCL requirement.
6. The actual low period generated by the ATmega323 Two-wire Serial Interface is (1/fSCL - 2/fCK), thus fCK must be greater than
6 MHz for the low time requirement to be strictly met at fSCL = 100 kHz.
7. The actual low period generated by the ATmega323 Two-wire Serial Interface is (1/fSCL - 2/fCK), thus the low time requirement will not be strictly met for fSCL > 308 kHz when fCK = 8 MHz. Still, ATmega323 devices connected to the bus may
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
communicate at full speed (400 kHz) with other ATmega323 devices, as well as any other device with a proper tLOW acceptance margin.
Figure 107. Two-wire Serial Bus timing
tof
tHIGH
tLOW
tLOW
SCL
tSU;STA
tHD;STA
tHD;DAT
tSU;DAT
tSU;STO
SDA
tBUF
217
1457G–AVR–09/03
ATmega323 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.
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.
Figure 108. Active Supply Current vs. Frequency
ACTIVE SUPPLY CURRENT vs. FREQUENCY
TA= 25˚C
60
Vcc= 6V
50
Vcc= 5.5V
I cc(mA)
40
Vcc= 5V
30
Vcc= 4.5V
Vcc= 4V
20
Vcc= 3.6V
Vcc= 3.3V
Vcc= 3.0V
10
Vcc= 2.7V
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Frequency (MHz)
218
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 109. Active Supply Current vs. VCC
ACTIVE SUPPLY CURRENT vs. Vcc
FREQUENCY = 4 MHz
20
18
TA = 85˚C
16
TA = 25˚C
14
I cc(mA)
12
10
8
6
4
2
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 110. Active Supply Current vs. VCC, Device Clocked by Internal Oscillator
ACTIVE SUPPLY CURRENT vs. Vcc
DEVICE CLOCKED BY 1.0MHz INTERNAL RC OSCILLATOR
5
4.5
TA = 85˚C
4
TA = 25˚C
3.5
I cc(mA)
3
2.5
2
1.5
1
0.5
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
219
1457G–AVR–09/03
Figure 111. Active Supply Current vs. VCC, Device Clocked by External 32kHz Crystal
ACTIVE SUPPLY CURRENT vs. Vcc
DEVICE CLOCKED BY 32KHz CRYSTAL
1.4
TA = 25˚C
1.2
TA = 85˚C
1
I cc(mA)
0.8
0.6
0.4
0.2
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 112. Idle Supply Current vs. Frequency
IDLE SUPPLY CURRENT vs. FREQUENCY
TA= 25˚C
35
Vcc= 6V
30
Vcc= 5.5V
I cc(mA)
25
20
Vcc= 5V
Vcc= 4.5V
15
Vcc= 4V
10
Vcc= 3.6V
Vcc= 3.3V
Vcc= 3.0V
Vcc= 2.7V
5
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Frequency (MHz)
220
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 113. Idle Supply Current vs. VCC
IDLE SUPPLY CURRENT vs. Vcc
FREQUENCY = 4 MHz
12
10
TA = 85˚C
TA = 25˚C
I cc(mA)
8
6
4
2
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 114. Idle Supply Current vs. VCC, Device Clocked by Internal Oscillator
IDLE SUPPLY CURRENT vs. Vcc
DEVICE CLOCKED BY 1.0MHz INTERNAL RC OSCILLATOR
2.5
2
TA = 85˚C
TA = 25˚C
I cc(mA)
1.5
1
0.5
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
221
1457G–AVR–09/03
Figure 115. Idle Supply Current vs. VCC, Device Clocked by External 32kHz Crystal
IDLE SUPPLY CURRENT vs. Vcc
DEVICE CLOCKED BY 32KHz CRYSTAL
100
90
TA = 85˚C
80
TA = 25˚C
70
I cc(µA)
60
50
40
30
20
10
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 116. Power-down Supply Current vs. VCC
POWER DOWN SUPPLY CURRENT vs. Vcc
WATCHDOG TIMER DISABLED
8
TA = 85˚C
7
6
I cc(µA)
5
4
3
TA = 70˚C
2
1
TA = 45˚C
TA = 25˚C
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
222
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 117. Power-down Supply Current vs. VCC
POWER DOWN SUPPLY CURRENT vs. Vcc
WATCHDOG TIMER ENABLED
100
90
TA = 25˚C
80
70
TA = 85˚C
I cc(µA)
60
50
40
30
20
10
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 118. Power-save Supply Current vs. VCC
POWER SAVE SUPPLY CURRENT vs. Vcc
WATCHDOG TIMER DISABLED
30
25
TA = 85˚C
20
I cc(µA)
TA = 25˚C
15
10
5
0
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
223
1457G–AVR–09/03
Figure 119. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. Vcc
0.9
0.8
0.7
TA = 25˚C
0.6
I cc(mA)
TA = 85˚C
0.5
0.4
0.3
0.2
0.1
0
2
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Analog comparator offset voltage is measured as absolute offset
Figure 120. Analog Comparator Offset Voltage vs. Common Mode Voltage
ANALOG COMPARATOR OFFSET VOLTAGE vs.
COMMON MODE VOLTAGE
Vcc = 5V
18
16
TA = 25˚C
Offset Voltage (mV)
14
12
TA = 85˚C
10
8
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Common Mode Voltage (V)
224
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 121. Analog Comparator Offset voltage vs. Common Mode Voltage
ANALOG COMPARATOR OFFSET VOLTAGE vs.
COMMON MODE VOLTAGE
Vcc = 2.7V
10
TA = 25˚C
Offset Voltage (mV)
8
6
TA = 85˚C
4
2
0
0
0.5
1
1.5
2
2.5
3
Common Mode Voltage (V)
Figure 122. Analog Comparator Input Leakage Current
ANALOG COMPARATOR INPUT LEAKAGE CURRENT
VCC = 6V
TA = 25˚C
60
50
30
I
ACLK
(nA)
40
20
10
0
-10
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
VIN (V)
225
1457G–AVR–09/03
Figure 123. Calibrated RC Oscillator Frequency vs. VCC
CALIBRATED RC OSCILLATOR FREQUENCY vs.
OPERATING VOLTAGE
1.02
TA = 25˚C
TA = 45˚C
TA = 70˚C
1
TA = 85˚C
FRc (MHz)
0.98
0.96
0.94
0.92
0.9
0.88
2
2.5
3
3.5
4
4.5
5
5.5
6
Vcc(V)
Figure 124. Watchdog Oscillator Frequency vs. VCC
WATCHDOG OSCILLATOR FREQUENCY vs. Vcc
1600
TA = 25˚C
1400
TA = 85˚C
F RC (KHz)
1200
1000
800
600
400
200
0
2
2.5
3
3.5
4
4.5
5
5.5
6
Vcc (V)
Sink and source capabilities of I/O ports are measured on one pin at a time.
226
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 125. Pull-Up Resistor Current vs. Input Voltage
PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5V
120
TA = 25˚C
100
TA = 85˚C
I
OP (µA)
80
60
40
20
0
0
0.5
1
1.5
2
2.5
VOP (V)
3
3.5
4
4.5
5
Figure 126. Pull-Up Resistor Current vs. Input Voltage
PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7V
30
TA = 25˚C
25
TA = 85˚C
15
I
OP (µA)
20
10
5
0
0
0.5
1
1.5
2
2.5
3
VOP (V)
227
1457G–AVR–09/03
Figure 127. I/O Pin Sink Current vs. Output Voltage
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
70
TA = 25˚C
60
TA = 85˚C
50
30
I
OL (mA)
40
20
10
0
0
0.5
1
1.5
2
2.5
3
VOL (V)
Figure 128. I/O Pin Source Current vs. Output Voltage
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
20
TA = 25˚C
18
16
TA = 85˚C
14
I
OH (mA)
12
10
8
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VOH (V)
228
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Figure 129. I/O Pin Sink Current vs. Output Voltage
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
25
TA = 25˚C
20
TA = 85˚C
10
I
OL (mA)
15
5
0
0
0.5
1
1.5
2
VOL (V)
Figure 130. I/O Pin Source Current vs. Output Voltage
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
6
TA = 25˚C
5
TA = 85˚C
3
I
OH (mA)
4
2
1
0
0
0.5
1
1.5
2
2.5
3
VOH (V)
229
1457G–AVR–09/03
Figure 131. I/O Pin Input Threshold Voltage vs. VCC
I/O PIN INPUT THRESHOLD VOLTAGE vs. Vcc
TA = 25˚C
2.5
Threshold Voltage (V)
2
1.5
1
0.5
0
2.7
4.0
5.0
Vcc
Figure 132. I/O Pin Input Hysteresis vs. VCC
I/O PIN INPUT HYSTERESIS vs. Vcc
TA = 25˚C
0.18
0.16
Input hysteresis (V)
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
2.7
4.0
5.0
Vcc
230
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Register Summary
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
$3F ($5F)
SREG
I
T
H
S
V
N
Z
C
page 21
$3E ($5E)
SPH
–
–
–
–
SP11
SP10
SP9
SP8
page 22
$3D ($5D)
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
page 22
$3C ($5C)
OCR0
$3B ($5B)
GICR
INT1
INT0
INT2
–
–
–
IVSEL
IVCE
$3A ($5A)
GIFR
INTF1
INTF0
INTF2
–
–
–
–
–
page 34
$39 ($59)
TIMSK
OCIE2
TOIE2
TICIE1
OCIE1A
OCIE1B
TOIE1
OCIE0
TOIE0
page 36
$38 ($58)
TIFR
OCF2
TOV2
ICF1
OCF1A
OCF1B
TOV1
OCF0
TOV0
page 36
$37 ($57)
SPMCR
–
ASB
–
ASRE
BLBSET
PGWRT
PGERS
SPMEN
page 183
Timer/Counter0 Output Compare Register
page 47
page 33
$36 ($56)
TWCR
TWINT
TWEA
TWSTA
TWSTO
TWWC
TWEN
–
TWIE
page 104
$35 ($55)
MCUCR
SE
SM2
SM1
SM0
ISC11
ISC10
ISC01
ISC00
page 37
$34 ($54)
MCUCSR
JTD
ISC2
–
JTRF
WDRF
BORF
EXTRF
PORF
page 30
$33 ($53)
TCCR0
FOC0
PWM0
COM01
COM00
CTC0
CS02
CS01
CS00
page 47
$32 ($52)
$31 ($51)
TCNT0
Timer/Counter0 (8 Bits)
page 49
OSCCAL
Oscillator Calibration Register
page 41
OCRD
On-chip Debug Register
page 161
$30 ($50)
SFIOR
–
–
–
–
ACME
PUD
PSR2
PSR10
$2F ($4F)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1B0
FOC1A
FOC1B
PWM11
PWM10
page 56
$2E ($4E)
TCCR1B
ICNC1
ICES1
–
–
CTC1
CS12
CS11
CS10
page 57
$2D ($4D)
TCNT1H
Timer/Counter1 – Counter Register High Byte
page 58
$2C ($4C)
TCNT1L
Timer/Counter1 – Counter Register Low Byte
page 58
$2B ($4B)
OCR1AH
Timer/Counter1 – Output Compare Register A High Byte
page 59
$2A ($4A)
OCR1AL
Timer/Counter1 – Output Compare Register A Low Byte
page 59
$29 ($49)
OCR1BH
Timer/Counter1 – Output Compare Register B High Byte
page 59
$28 ($48)
OCR1BL
Timer/Counter1 – Output Compare Register B Low Byte
page 59
$27 ($47)
ICR1H
Timer/Counter1 – Input Capture Register High Byte
page 60
$26 ($46)
ICR1L
Timer/Counter1 – Input Capture Register Low Byte
$25 ($45)
TCCR2
$24 ($44)
TCNT2
Timer/Counter2 (8 Bits)
page 49
$23 ($43)
OCR2
Timer/Counter2 Output Compare Register
page 49
FOC2
PWM2
COM21
COM20
CTC2
page 60
CS22
CS21
CS20
$22 ($42)
ASSR
–
–
–
–
AS2
TCN2UB
OCR2UB
TCR2UB
$21 ($41)
WDTCR
–
–
–
WDTOE
WDE
WDP2
WDP1
WDP0
UBRRH
URSEL
–
–
–
$20 ($40)
page 45
UBRR[11:8]
page 47
page 52
page 64
page 98
UCSRC
URSEL
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
page 97
$1F ($3F)
EEARH
–
–
–
–
–
–
EEAR9
EEAR8
page 66
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
page 66
page 67
$1E ($3E)
EEARL
$1D ($3D)
EEDR
$1C ($3C)
EECR
–
–
–
–
EERIE
EEMWE
EEWE
EERE
$1B ($3B)
PORTA
PORTA7
PORTA6
PORTA5
PORTA4
PORTA3
PORTA2
PORTA1
PORTA0
page 137
$1A ($3A)
DDRA
DDA7
DDA6
DDA5
DDA4
DDA3
DDA2
DDA1
DDA0
page 137
EEPROM Data Register
page 66
$19 ($39)
PINA
PINA7
PINA6
PINA5
PINA4
PINA3
PINA2
PINA1
PINA0
page 137
$18 ($38)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
page 139
$17 ($37)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
page 139
$16 ($36)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
page 139
$15 ($35)
PORTC
PORTC7
PORTC6
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
page 146
$14 ($34)
DDRC
DDC7
DDC6
DDC5
DDC4
DDC3
DDC2
DDC1
DDC0
page 146
page 146
$13 ($33)
PINC
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
$12 ($32)
PORTD
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
page 151
$11 ($31)
DDRD
DDD7
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
page 151
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
page 151
$10 ($30)
PIND
$0F ($2F)
SPDR
$0E ($2E)
SPSR
SPIF
WCOL
–
–
–
–
–
SPI2X
page 72
$0D ($2D)
SPCR
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
page 71
$0C ($2C)
UDR
$0B ($2B)
UCSRA
RXC
TXC
UDRE
$0A ($2A)
UCSRB
RXCIE
TXCIE
UDRIE
$09 ($29)
UBRRL
$08 ($28)
ACSR
ACD
ACBG
ACO
ACI
ACIE
$07 ($27)
ADMUX
REFS1
REFS0
ADLAR
MUX4
MUX3
MUX2
MUX1
MUX0
page 132
$06 ($26)
ADCSR
ADEN
ADSC
ADFR
ADIF
ADIE
ADPS2
ADPS1
ADPS0
page 133
$05 ($25)
ADCH
ADC Data Register High Byte
page 134
$04 ($24)
ADCL
ADC Data Register Low Byte
page 134
$03 ($23)
TWDR
$02 ($22)
TWAR
SPI Data Register
page 73
USART I/O Data Register
page 94
FE
DOR
PE
U2X
MPCM
page 94
RXEN
TXEN
UCSZ2
RXB8
TXB8
page 96
ACIC
ACIS1
ACIS0
page 125
USART Baud Rate Register Low Byte
page 98
Two-wire Serial Interface Data Register
TWA6
TWA5
TWA4
TWA3
TWA2
page 106
TWA1
TWA0
TWGCE
page 107
231
1457G–AVR–09/03
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
$01 ($21)
TWSR
TWS7
TWS6
TWS5
TWS4
TWS3
–
–
–
page 106
$00 ($20)
TWBR
Notes:
232
Two-wire Serial Interface Bit Rate Register
page 104
1. When the OCDEN Fuse is unprogrammed, the OSCCAL Register is always accessed on this address. Refer to the debugger specific documentation for details on how to use the OCDR Register.
2. Refer to the USART description for details on how to access UBRRH and UCSRC.
3. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O Memory addresses
should never be written.
4. Some of the Status Flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate on
all bits in the I/O Register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI instructions
work with registers $00 to $1F only.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
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
1
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
COM
Rd
One’s Complement
Rd ← $FF − Rd
Z,C,N,V
1
NEG
Rd
Two’s Complement
Rd ← $00 − Rd
Z,C,N,V,H
1
SBR
Rd,K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
1
1
CBR
Rd,K
Clear Bit(s) in Register
Rd ← Rd • ($FF - K)
Z,N,V
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 ← $FF
None
1
MUL
Rd, Rr
Multiply Unsigned
R1:R0 ← Rd x Rr
Z,C
2
2
MULS
Rd, Rr
Multiply Signed
R1:R0 ← Rd x Rr
Z,C
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) <<
Z,C
2
FMULS
Rd, Rr
Fractional Multiply Signed
Z,C
2
FMULSU
Rd, Rr
Fractional Multiply Signed with Unsigned
1
R1:R0 ← (Rd x Rr) << 1
R1:R0 ← (Rd x Rr) << 1
Z,C
2
Relative Jump
PC ← PC + k + 1
None
2
Indirect Jump to (Z)
PC ← Z
None
2
Direct Jump
PC ← k
None
3
BRANCH INSTRUCTIONS
RJMP
k
IJMP
JMP
k
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
ICALL
CALL
k
4
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
1/2/3
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
233
1457G–AVR–09/03
Mnemonics
Operands
Description
Operation
Flags
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ← PC + k + 1
None
#Clocks
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ← PC + k + 1
None
1/2
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
Rd ← Rr
None
1
MOVW
Rd, Rr
Copy Register Word
Rd+1:Rd ← Rr+1:Rr
None
1
LDI
Rd, K
Load Immediate
Rd ← K
None
1
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
LD
Rd, - X
Load Indirect and Pre-Dec.
X ← X - 1, Rd ← (X)
None
2
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
2
ST
- Y, Rr
Store Indirect and Pre-Dec.
Y ← Y - 1, (Y) ← Rr
None
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
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 Port
Rd ← P
None
1
LPM
SPM
IN
Rd, P
OUT
P, Rr
Out Port
P ← Rr
None
1
PUSH
Rr
Push Register on Stack
Stack ← Rr
None
2
POP
Rd
Pop Register from Stack
Rd ← Stack
None
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
Set Half Carry Flag in SREG
H←1
H
1
234
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Mnemonics
Description
Operation
Flags
CLH
Operands
Clear Half Carry Flag in SREG
H←0
H
#Clocks
1
NOP
No Operation
None
1
SLEEP
Sleep
(see specific descr. for Sleep function)
None
1
WDR
Watchdog Reset
(see specific descr. for WDR/timer)
None
1
BREAK
Break
For On-chip Debug Only
None
N/A
235
1457G–AVR–09/03
Ordering Information
Speed (MHz)
Power Supply
4
2.7 - 5.5V
8
4.0 - 5.5V
Ordering Code
Package
Operation Range
ATmega323L-4AC
ATmega323L-4PC
44A
40P6
Commercial
(0°C to 70°C)
ATmega323L-4AI
ATmega323L-4PI
44A
40P6
Industrial
(-40°C to 85°C)
ATmega323-8AC
ATmega323-8PC
44A
40P6
Commercial
(0°C to 70°C)
ATmega323-8AI
ATmega323-8PI
44A
40P6
Industrial
(-40°C to 85°C)
Package Type
44A
44-lead, Thin (1.0 mm) Plastic Gull Wing Quad Flat Package (TQFP)
40P6
40-pin, 0.600” Wide, Plastic Dual Inline Package (PDIP)
236
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Packaging Information
44A
D
Marked Pin# 1 ID
E
SEATING PLANE
A1
TOP VIEW
A3
A
L
Pin #1 Corner
D2
SIDE VIEW
COMMON DIMENSIONS
(Unit of Measure = mm)
E2
SYMBOL
MIN
NOM
MAX
A
0.80
0.90
1.00
A1
–
0.02
0.05
A3
b
0.25 REF
0.18
D
b
e
D2
E2
5.00
L
0.30
5.20
5.40
7.00 BSC
5.00
e
Notes: 1. JEDEC Standard MO-220, Fig. 1 (SAW Singulation) VKKD-1.
0.23
7.00 BSC
E
BOTTOM VIEW
NOTE
5.20
5.40
0.50 BSC
0.35
0.55
0.75
01/15/03
R
TITLE
2325 Orchard Parkway
44M1, 44-pad, 7 x 7 x 1.0 mm Body, Lead Pitch 0.50 mm
San Jose, CA 95131
Micro Lead Frame Package (MLF)
DRAWING NO. REV.
44M1
C
237
1457G–AVR–09/03
40P6
D
PIN
1
E1
A
SEATING PLANE
A1
L
B1
B
e
E
0º ~ 15º REF
C
eB
Notes:
COMMON DIMENSIONS
(Unit of Measure = mm)
1. This package conforms to JEDEC reference MS-011, Variation AC.
2. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25 mm (0.010").
SYMBOL
MIN
NOM
MAX
A
–
–
4.826
NOTE
A1
0.381
–
D
52.070
–
52.578 Note 2
E
15.240
–
15.875
E1
13.462
–
13.970 Note 2
B
0.356
–
0.559
B1
1.041
–
1.651
L
3.048
–
3.556
C
0.203
–
0.381
eB
15.494
–
17.526
e
–
2.540 TYP
09/28/01
R
238
2325 Orchard Parkway
San Jose, CA 95131
TITLE
40P6, 40-lead (0.600"/15.24 mm Wide) Plastic Dual
Inline Package (PDIP)
DRAWING NO. REV.
40P6
B
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Errata for ATmega323
Rev. B
•
•
•
•
•
•
•
Interrupts Abort TWI Power-down
TWI Master Does not Accept Spikes on Bus Lines
TWCR Write Operations Ignored when Immediately Repeated
PWM not Phase Correct
TWI is Speed Limited in Slave Mode
Problems with UBRR Settings
Missing OverRun Flag and Fake Frame Error in USART
7. Interrupts Abort TWI Power-down
TWI Power-down operation may wake up by other interrupts. If an interrupt (e.g.,
INT0) occurs during TWI Power-down address watch and wakes up the CPU, the
TWI aborts operation and returns to its idle state.
If the interrupt occurs in the middle of a Power-down Address Match (i.e., during
reading of a slave address), the received address will be lost and the Slave will not
return an ACN.
Problem Fix/Workaround
Ensure that the TWI Address Match is the only enabled interrupt when entering
Power-down.
The Master can handle this by resending the request if NACH is received.
6. TWI Master Does not Accept Spikes on Bus Lines
When the part operates as Master, and the bus is idle (SDA = 1; SCL = 1), generating a short spike on SDA (SDA = 0 for a short interval), no interrupt is generated,
and the status code is still $F8 (idle). But when the software initiates a new start
condition and clears TWINT, nothing happens on SDA or SCL, and TWINT is never
set again.
Problem Fix/Workaround
Either of the following:
1. Ensure no spikes occur on SDA or SCL lines.
2. Generate a valid START condition followed by a STOP condition on the bus.
This provokes a bus error reported as a TWI interrupt with status code $00.
3. In a Single-master system, the user should write the TWSTO bit immediately
before writing the TWSTA bit.
5. TWCR Write Operation Ignored when Immediately Repeated
Repeated write to TWCR must be delayed. If a write operation to TWCR is immediately followed by another write operation to TWCR, the first write operation may be
ignored.
Problem Fix/Workaround
Ensure at least one instruction (e.g., NOP) is executed between two writes to
TWCR.
4. PWM not Phase Correct
In phase-correct PWM mode, a change from OCRx = TOP to anything less than
TOP does not change the OCx output. This gives a phase error in the following
period.
Problem Fix/Workaround
Make sure this issue is not harmful to the application.
239
1457G–AVR–09/03
3. TWI is Speed Limited in Slave Mode
When the Two-wire Serial Interface operates in Slave mode, frames may be undetected if the CPU frequency is less than 64 times the bus frequency.
Problem Fix/Workaround
Ensure that the CPU frequency is at least 64 times the TWI bus frequency.
2. Problems with UBRR Settings
The baud rate corresponding to the previous UBRR setting is used for the first transmitted/received bit when either UBRRH or UBRRL is written. This will disturb
communication if the UBRR is changed from a very high to a very low baud rate setting, as the internal baud rate counter will have to count down to zero before using
the new setting.
In addition, writing to UBRRL incorrectly clears the UBRRH setting.
Problem Fix/Workaround
UBRRH must be written after UBRRL because setting UBRRL clears UBRRH. By
doing an additional dummy write to UBRRH, the baud rate is set correctly. The following is an example on how to set UBRR. UBRRH is updated first for upward
compatibility with corrected devices.
ldi r17, HIGH(baud)
ldi r16, LOW(baud)
out UBRRH, r17
; Added for upward compatibility
out UBRRL, r16
; Set new UBRRL, UBRRH incorrectly cleared
out UBRRH, r17
; Set new UBRRH
out UBRRH, r17
; Loads the baud rate counter with new (correct) value
1. Missing OverRun Flag and Fake Frame Error in USART
When the USART has received three characters without any of them been read, the
USART FIFO is full. If the USART detects the start bit of a fourth character, the Data
OverRun (DOR) Flag will be set for the third character. However, if a read from the
USART Data Register is performed just after the start bit of the fourth byte is
received, a Frame Error is generated for character three. If the USART Data Register is read between the reception of the first data bit and the end of the fourth
character, the Data OverRun Flag of character three will be lost.
Problem Fix/Workaround
The user should design the application to never completely fill the USART FIFO. If
this is not possible, the user must use a high-level protocol to be able to detect if any
characters were lost and request a retransmission if this happens.
The following is not errata for ATmega323, all revisions. However, a proposal for solving
problems regarding the JTAG instruction IDCODE is presented below.
IDCODE masks data from TDI input
The public but optional JTAG instruction IDCODE is not implemented correctly
according to IEEE1149.1; a logic one is scanned into the shift register instead of the
TDI input while shifting the Device ID Register. Hence, captured data from the preceding devices in the boundary scan chain are lost and replaced by all-ones, and
data to succeeding devices are replaced by all-ones during Update-DR.
If ATmega323 is the only device in the scan chain, the problem is not visible.
240
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Problem Fix / Workaround
Select the Device ID Register of the ATmega323 (Either by issuing the IDCODE
instruction or by entering the Test-Logic-Reset state of the TAP controller) to read
out the contents of its Device ID Register and possibly data from succeeding
devices of the scan chain. Note that data to succeeding devices cannot be entered
during this scan, but data to preceding devices can. Issue the BYPASS instruction
to the ATmega323 to select its Bypass Register while reading the Device ID Registers of preceding devices of the boundary scan chain. Never read data from
succeeding devices in the boundary scan chain or upload data to the succeeding
devices while the Device ID Register is selected for the ATmega323. Note that the
IDCODE instruction is the default instruction selected by the Test-Logic-Reset state
of the TAP-controller.
Alternative Problem Fix / Workaround
If the Device IDs of all devices in the boundary scan chain must be captured simultaneously (for instance if blind interrogation is used), the boundary scan chain can
be connected in such way that the ATmega323 is the fist device in the chain.
Update-DR will still not work for the succeeding devices in the boundary scan chain
as long as IDCODE is present in the JTAG Instruction Register, but the Device ID
registered cannot be uploaded in any case.
241
1457G–AVR–09/03
Datasheet Change
Log for ATmega323
This document contains a log on the changes made to the datasheet for ATmega323.
Changes from Rev.
1457F – 09/02 to Rev.
1457G – 09/03
1. Removed “Preliminary” from the .
2. Updated “The Test Access Port – TAP” on page 158 regarding JTAGEN.
3. Updated description for the JTD bit on page 30.
4. Added extra information regarding the JTAGEN interface to “Fuse Bits” on
page 187.
5. Updated some values in “Electrical Characteristics” on page 213.
5. Added a proposal for solving problems regarding the JTAG instruction
IDCODE in “Errata for ATmega323 Rev. B” on page 239.
Changes from Rev.
1457E – 11/01 to Rev.
1457F – 09/02
242
1. Added watermark: “Not recommended for new designs. Use ATmega32”.
2. Added “Errata for ATmega323 Rev. B” on page 239.
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Table of Contents
Features................................................................................................ 1
Pin Configurations............................................................................... 2
Overview ............................................................................................... 3
Block Diagram ...................................................................................................... 3
Pin Descriptions.................................................................................................... 4
Clock Options ...................................................................................... 6
Internal RC Oscillator............................................................................................
Crystal Oscillator...................................................................................................
External Clock.......................................................................................................
External RC Oscillator ..........................................................................................
Timer Oscillator.....................................................................................................
6
6
7
7
7
Architectural Overview........................................................................ 8
The General Purpose Register File ....................................................................
The ALU – Arithmetic Logic Unit.........................................................................
The In-System Reprogrammable Flash Program Memory .................................
The SRAM Data Memory....................................................................................
The Program and Data Addressing Modes ........................................................
The EEPROM Data Memory ..............................................................................
Memory Access Times and Instruction Execution Timing ..................................
I/O Memory .........................................................................................................
Reset and Interrupt Handling..............................................................................
Sleep Modes.......................................................................................................
11
12
12
12
13
17
17
18
22
39
Calibrated Internal RC Oscillator ..................................................... 41
Timer/Counters .................................................................................. 43
Timer/Counter Prescalers................................................................................... 43
8-bit Timers/Counters Timer/Counter0 and Timer/Counter2 .............................. 45
16-bit Timer/Counter1......................................................................................... 54
Watchdog Timer................................................................................. 64
EEPROM Read/Write Access............................................................ 66
Preventing EEPROM Corruption ........................................................................ 68
Serial Peripheral Interface – SPI....................................................... 69
SS Pin Functionality............................................................................................ 70
Data Modes ........................................................................................................ 71
USART ................................................................................................ 74
Overview............................................................................................................. 74
ATmega323 USART Pin Specification ............................................................... 75
i
1457G–AVR–09/03
About Code Examples ........................................................................................ 75
AVR USART vs. AVR UART – Compatibility...................................................... 75
Clock Generation ............................................................................... 76
Frame Formats ...................................................................................................
Parity Bit Calculation...........................................................................................
USART Initialization............................................................................................
Data Transmission – The USART Transmitter ...................................................
Data Reception – The USART Receiver ............................................................
Asynchronous Data Reception ...........................................................................
Multi-processor Communication Mode ...............................................................
Accessing UBRRH/UCSRC Registers................................................................
USART Register Description ..............................................................................
Examples of Baud Rate Setting..........................................................................
78
79
79
81
84
88
91
92
94
99
Two-wire Serial Interface (Byte Oriented) ..................................... 102
Two-wire Serial Interface Modes ......................................................................
Master Transmitter Mode..................................................................................
Master Receiver Mode......................................................................................
Slave Receiver Mode........................................................................................
Slave Transmitter Mode....................................................................................
Miscellaneous States........................................................................................
107
108
108
109
110
110
The Analog Comparator.................................................................. 124
Analog Comparator Multiplexed Input .............................................................. 126
Analog to Digital Converter ............................................................ 127
Features............................................................................................................
Operation ..........................................................................................................
Prescaling and Conversion Timing ...................................................................
ADC Noise Canceler Function..........................................................................
Scanning Multiple Channels .............................................................................
ADC Noise Canceling Techniques ...................................................................
ADC Characteristics – Preliminary Data...........................................................
127
128
129
131
135
135
136
I/O Ports............................................................................................ 137
Port A................................................................................................................
Port B................................................................................................................
Port C................................................................................................................
Port D................................................................................................................
137
139
146
151
JTAG Interface and the On-chip Debug System ........................... 157
Features............................................................................................................
Overview...........................................................................................................
The Test Access Port – TAP ............................................................................
Using the Boundary-Scan Chain ......................................................................
ii
157
157
158
161
ATmega323(L)
1457G–AVR–09/03
ATmega323(L)
Using the On-chip Debug System .................................................................... 161
On-chip Debug Specific JTAG Instructions ...................................................... 162
Using the JTAG Programming Capabilities ...................................................... 163
IEEE 1149.1 (JTAG) Boundary-Scan .............................................. 164
Features............................................................................................................
System Overview..............................................................................................
Data Registers ..................................................................................................
Boundary-Scan Specific JTAG Instructions......................................................
Boundary-Scan Chain.......................................................................................
ATmega323 Boundary-Scan Order ..................................................................
Boundary-Scan Description Language Files ....................................................
164
164
165
166
168
172
176
Memory Programming..................................................................... 177
Boot Loader Support.........................................................................................
Entering the Boot Loader Program ...................................................................
Capabilities of the Boot Loader.........................................................................
Self-programming the Flash .............................................................................
Boot Loader Lock Bits.......................................................................................
EEPROM Write Prevents Writing to SPMCR ...................................................
Preventing Flash Corruption .............................................................................
Program and Data Memory Lock Bits...............................................................
Parallel Programming .......................................................................................
Serial Downloading...........................................................................................
177
179
179
179
180
182
184
186
188
197
Programming via the JTAG Interface ............................................ 202
Programming specific JTAG instructions..........................................................
Data Registers ..................................................................................................
Reset Register ..................................................................................................
Programming Enable Register..........................................................................
Programming Command Register ....................................................................
202
203
203
203
204
Virtual Flash Page Load Register................................................... 208
Virtual Flash Page Read Register .................................................................... 209
Programming algorithm .................................................................................... 209
Electrical Characteristics................................................................ 213
Absolute Maximum Ratings*.............................................................................
DC Characteristics............................................................................................
External Clock Drive Waveforms ......................................................................
External Clock Drive .........................................................................................
213
213
215
215
Two-wire Serial Interface Characteristics ..................................... 216
ATmega323 Typical Characteristics – Preliminary Data .............. 218
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1457G–AVR–09/03
Register Summary ........................................................................... 231
Instruction Set Summary ................................................................ 233
Ordering Information ....................................................................... 236
Packaging Information .................................................................... 237
44A ................................................................................................................... 237
40P6 ................................................................................................................. 238
Errata for ATmega323 Rev. B ......................................................... 239
Datasheet Change Log for ATmega323......................................... 242
Changes from Rev. 1457F – 09/02 to Rev. 1457G – 09/03 ............................. 242
Changes from Rev. 1457E – 11/01 to Rev. 1457F – 09/02.............................. 242
Table of Contents ................................................................................. i
iv
ATmega323(L)
1457G–AVR–09/03
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1457G–AVR–09/03