ATMEL AT90PWM3 8-bit microcontroller with 8k bytes in-system programmable flash Datasheet

Features
• High Performance, Low Power AVR ® 8-bit Microcontroller
• Advanced RISC Architecture
•
•
•
•
•
•
•
– 129 Powerful Instructions - Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 1 MIPS throughput per MHz
– On-chip 2-cycle Multiplier
Data and Non-Volatile Program Memory
– 8K Bytes Flash of In-System Programmable Program Memory
• Endurance: 10,000 Write/Erase Cycles
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
– 512 Bytes of In-System Programmable EEPROM
Endurance: 100,000 Write/Erase Cycles
– 512 Bytes Internal SRAM
– Programming Lock for Flash Program and EEPROM Data Security
On Chip Debug Interface (debugWIRE)
Peripheral Features
– Two or three 12-bit High Speed PSC (Power Stage Controllers) with 4-bit
Resolution Enhancement
• Non Overlapping Inverted PWM Output Pins With Flexible Dead-Time
• Variable PWM duty Cycle and Frequency
• Synchronous Update of all PWM Registers
• Auto Stop Function for Event Driven PFC Implementation
• Less than 25 Hz Step Width at 150 kHz Output Frequency
• PSC2 with four Output Pins and Output Matrix
– One 8-bit General purpose Timer/Counter with Separate Prescaler and Capture
Mode
– One 16-bit General purpose Timer/Counter with Separate Prescaler, Compare
Mode and Capture Mode
– Programmable Serial USART
• Standard UART mode
• 16/17 bit Biphase Mode for DALI Communications
– Master/Slave SPI Serial Interface
– 10-bit ADC
• Up To 11 Single Ended Channels and 2 Fully Differential ADC Channel Pairs
• Programmable Gain (5x, 10x, 20x, 40x on Differential Channels)
• Internal Reference Voltage
– 10-bit DAC
– Two or three Analog Comparator with Resistor-Array to Adjust Comparison
Voltage
– 4 External Interrupts
– Programmable Watchdog Timer with Separate On-Chip Oscillator
Special Microcontroller Features
– Low Power Idle, Noise Reduction, and Power Down Modes
– Power On Reset and Programmable Brown Out Detection
– Flag Array in Bit-programmable I/O Space (4 bytes)
8-bit
Microcontroller
with 8K Bytes
In-System
Programmable
Flash
AT90PWM2
AT90PWM3
AT90PWM2B
AT90PWM3B
4317I–AVR–01/08
– In-System Programmable via SPI Port
– Internal Calibrated RC Oscillator ( 8 MHz)
– On-chip PLL for fast PWM ( 32 MHz, 64 MHz) and CPU (16 MHz)
• Operating Voltage: 2.7V - 5.5V
• Extended Operating Temperature:
– -40°C to +105°
Product
Package
12 bit PWM with
deadtime
ADC
Input
ADC
Diff
Analog
Compar
Application
AT90PWM2
AT90PWM2B
SO24
2x2
8
1
2
One fluorescent ballast
AT90PWM3
AT90PWM3B
SO32,
QFN32
3x2
11
2
3
HID ballast, fluorescent ballast,
Motor control
1. History
Product
Revision
AT90PWM2
AT90PWM3
First revision of parts, only for running production.
Second revision of parts, for all new developments.
The major changes are :
• complement the PSCOUT01, PSCOUT11, PSCOUT21 polarity in
centered mode - See “PSCn0 & PSCn1 Basic Waveforms in Center
Aligned Mode” on page 139.
AT90PWM2B
AT90PWM3B
• Add the PSC software triggering capture - See “PSC 0 Input Capture
Register – PICR0H and PICR0L” on page 170.
• Add bits to read the PSC output activity - See “PSC0 Interrupt Flag
Register – PIFR0” on page 172.
• Add some clock configurations - See “Device Clocking Options Select
AT90PWM2B/3B” on page 31.
• Change Amplifier Synchonization - See “Amplifier” on page 252. and
See “” on page 255.
• Correction of the Errata - See “Errata” on page 350.
This datasheet deals with product characteristics of AT90PW2 and AT90WM3. It will be updated
as soon as characterization will be done.
2. Disclaimer
Typical values contained in this datasheet are based on simulations and characterization of
other AVR microcontrollers manufactured on the same process technology. Min and Max values will be available after the device is characterized.
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AT90PWM2/3/2B/3B
3. Pin Configurations
Figure 3-1.
SOIC 24-pin Package
(PSCOUT00/XCK/SS_A) PD0
(RESET/OCD) PE0
(PSCIN0/CLKO) PD1
(PSCIN2/OC1A/MISO_A) PD2
(TXD/DALI/OC0A/SS/MOSI_A) PD3
VCC
GND
(MISO/PSCOUT20) PB0
(MOSI/PSCOUT21) PB1
(OC0B/XTAL1) PE1
(ADC0/XTAL2) PE2
ADC1/RXD/DALI/ICP1A/SCK_A) PD4
Figure 3-2.
AT90PWM2/2B
SOIC24
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
PB7(ADC4/PSCOUT01/SCK)
PB6 (ADC7/ICP1B)
PB5 (ADC6/INT2)
PB4 (AMP0+)
PB3 (AMP0-)
AREF
GND
AVCC
PB2 (ADC5/INT1)
PD7 (ACMP0)
PD6 (ADC3/ACMPM/INT0)
PD5 (ADC2/ACMP2)
SOIC 32-pin Package
AT90PWM3/3B
SOIC 32
(PSCOUT00/XCK/SS_A) PD0
(INT3/PSCOUT10) PC0
(RESET/OCD) PE0
(PSCIN0/CLKO) PD1
(PSCIN2/OC1A/MISO_A) PD2
(TXD/DALI/OC0A/SS/MOSI_A) PD3
(PSCIN1/OC1B) PC1
VCC
GND
(T0/PSCOUT22) PC2
(T1/PSCOUT23) PC3
(MISO/PSCOUT20) PB0
(MOSI/PSCOUT21) PB1
(OC0B/XTAL1) PE1
(ADC0/XTAL2) PE2
(ADC1/RXD/DALI/ICP1A/SCK_A) PD4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
PB7(ADC4/PSCOUT01/SCK)
PB6 (ADC7/PSCOUT11/ICP1B)
PB5 (ADC6/INT2)
PC7 (D2A)
PB4 (AMP0+)
PB3 (AMP0-)
PC6 (ADC10/ACMP1)
AREF
GND
AVCC
PC5 (ADC9/AMP1+)
PC4 (ADC8/AMP1-)
PB2 (ADC5/INT1)
PD7 (ACMP0)
PD6 (ADC3/ACMPM/INT0)
PD5 (ADC2/ACMP2)
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Figure 3-3.
QFN32 (7*7 mm) Package.
PB7 (ADC4/PSCOUT01/SCK)
PB6 (ADC7/PSCOUT11/ICP1B)
PB5 (ADC6/INT2)
PC7 (D2A)
PD0 (PSCOUT00/XCK/SS_A)
PC0(INT3/PSCOUT10)
PE0 (RESET/OCD)
32
31
30
29
28
27
26
25
PD1(PSCIN0/CLKO)
AT90PWM3/3B QFN 32
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
PB4 (AMP0+)
PB3 (AMP0-)
PC6 (ADC10/ACMP1)
AREF
AGND
AVCC
PC5 (ADC9/AMP1+)
PC4 (ADC8/AMP1-)
(MOSI/PSCOUT21) PB1
(OC0B/XTAL1) PE1
(ADC0/XTAL2) PE2
(ADC1/RXD/DALI/ICP1_A/SCK_A) PD4
(ADC2/ACMP2 ) PD5
(ADC3/ACMPM/INT0) PD6
(ACMP0) PD7
(ADC5/INT1) PB2
9
10
11
12
13
14
15
16
(PSCIN2/OC1A/MISO_A) PD2
(TXD/DALI/OC0A/SS/MOSI_A) PD3
(PSCIN1/OC1B) PC1
VCC
GND
(T0/PSCOUT22) PC2
(T1/PSCOUT23) PC3
(MISO/PSCOUT20) PB0
3.1
Pin Descriptions
:
Table 3-1.
4
Pin out description
S024 Pin
Number
SO32 Pin
Number
QFN32 Pin
Number
Mnemonic
Type
7
9
5
GND
Power
Ground: 0V reference
18
24
20
AGND
Power
Analog Ground: 0V reference for analog part
Name, Function & Alternate Function
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 3-1.
Pin out description (Continued)
S024 Pin
Number
SO32 Pin
Number
QFN32 Pin
Number
Mnemonic
Type
6
8
4
VCC
power
Power Supply:
17
23
19
AVCC
Power
Analog Power Supply: This is the power supply voltage for analog
part
Name, Function & Alternate Function
For a normal use this pin must be connected.
Analog Reference : reference for analog converter . This is the
reference voltage of the A/D converter. As output, can be used by
external analog
19
25
21
AREF
Power
8
12
8
PBO
I/O
9
13
9
PB1
I/O
16
20
16
PB2
I/O
20
27
23
PB3
I/O
AMP0- (Analog Differential Amplifier 0 Input Channel )
21
28
24
PB4
I/O
AMP0+ (Analog Differential Amplifier 0 Input Channel )
22
30
26
PB5
I/O
23
31
27
PB6
I/O
MISO (SPI Master In Slave Out)
PSCOUT20 output
MOSI (SPI Master Out Slave In)
PSCOUT21 output
ADC5 (Analog Input Channel5 )
INT1
ADC6 (Analog Input Channel 6)
INT 2
ADC7 (Analog Input Channel 7)
ICP1B (Timer 1 input capture alternate input)
PSCOUT11 output (see note 1)
PSCOUT01 output
24
32
28
PB7
I/O
ADC4 (Analog Input Channel 4)
SCK (SPI Clock)
2
30
PC0
I/O
7
3
PC1
I/O
10
6
PC2
I/O
11
7
PC3
I/O
21
17
PC4
22
18
PC5
I/O
26
22
PC6
I/O
29
25
PC7
I/O
NA
I/O
PSCOUT10 output (see note 1)
INT3
PSCIN1 (PSC 1 Digital Input)
OC1B (Timer 1 Output Compare B)
T0 (Timer 0 clock input)
PSCOUT22 output
T1 (Timer 1 clock input)
PSCOUT23 output
ADC8 (Analog Input Channel 8)
AMP1- (Analog Differential Amplifier 1 Input Channel )
ADC9 (Analog Input Channel 9)
AMP1+ (Analog Differential Amplifier 1 Input Channel )
ADC10 (Analog Input Channel 10)
ACMP1 (Analog Comparator 1 Positive Input )
D2A : DAC output
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Table 3-1.
Pin out description (Continued)
S024 Pin
Number
SO32 Pin
Number
QFN32 Pin
Number
Mnemonic
Type
1
1
29
PD0
I/O
Name, Function & Alternate Function
PSCOUT00 output
XCK (UART Transfer Clock)
SS_A (Alternate SPI Slave Select)
3
4
32
PD1
I/O
4
5
1
PD2
I/O
PSCIN0 (PSC 0 Digital Input )
CLKO (System Clock Output)
PSCIN2 (PSC 2 Digital Input)
OC1A (Timer 1 Output Compare A)
MISO_A (Programming & alternate SPI Master In Slave Out)
TXD (Dali/UART Tx data)
5
6
2
PD3
I/O
OC0A (Timer 0 Output Compare A)
SS (SPI Slave Select)
MOSI_A (Programming & alternate Master Out SPI Slave In)
ADC1 (Analog Input Channel 1)
12
16
12
PD4
I/O
RXD (Dali/UART Rx data)
ICP1A (Timer 1 input capture)
SCK_A (Programming & alternate SPI Clock)
13
17
13
PD5
I/O
14
18
14
PD6
I/O
ADC2 (Analog Input Channel 2)
ACMP2 (Analog Comparator 2 Positive Input )
ADC3 (Analog Input Channel 3 )
ACMPM reference for analog comparators
INT0
15
19
15
PD7
I/O
2
3
31
PE0
I/O or I
10
14
10
PE1
I/O
11
15
11
PE2
I/O
ACMP0 (Analog Comparator 0 Positive Input )
RESET (Reset Input)
OCD (On Chip Debug I/O)
XTAL1: XTAL Input
OC0B (Timer 0 Output Compare B)
XTAL2: XTAL OuTput
ADC0 (Analog Input Channel 0)
1. PSCOUT10 & PSCOUT11 are not present on 24 pins package
4. Overview
The AT90PWM2/2B/3/3B 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
AT90PWM2/2B/3/3B achieves throughputs approaching 1 MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
4.1
Block Diagram
Figure 4-1.
Block Diagram
Data Bus 8-bit
8Kx8 Flash
Program
Memory
Program
Counter
Status
and Control
SPI
Unit
32 x 8
General
Purpose
Registrers
Instruction
Register
Watchdog
Timer
Direct Addressing
Indirect Addressing
3 Analog
Comparators
Instruction
Decoder
Control Lines
Interrupt
Unit
ALU
DALI USART
Timer 0
Timer 1
Data
SRAM
512 bytes
EEPROM
512 bytes
I/O Lines
ADC
DAC
PSC 2/1/0
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 AT90PWM2/2B/3/3B provides the following features: 8K bytes of In-System Programmable
Flash with Read-While-Write capabilities, 512 bytes EEPROM, 512 bytes SRAM, 53 general
purpose I/O lines, 32 general purpose working registers,three Power Stage Controllers, two flexible Timer/Counters with compare modes and PWM, one USART with DALI mode, an 11channel 10-bit ADC with two differential input stage with programmable gain, a 10-bit DAC, a
programmable Watchdog Timer with Internal Oscillator, an SPI serial port, an On-chip Debug
system and four software selectable power saving modes.
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4317I–AVR–01/08
The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, SPI ports 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. The
ADC Noise Reduction mode stops the CPU and all I/O modules except ADC, to minimize switching noise during ADC conversions. In Standby mode, the Crystal/Resonator Oscillator is running
while the rest of the device is sleeping. This allows very fast start-up combined with low power
consumption.
The device is manufactured using Atmel’s high-density nonvolatile memory technology. The Onchip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial
interface, by a conventional nonvolatile memory programmer, or by an On-chip Boot program
running on the AVR core. The boot program can use any interface to download the application
program in the application Flash memory. Software in the Boot Flash section will continue to run
while the Application Flash section is updated, providing true Read-While-Write operation. By
combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip,
the Atmel AT90PWM2/3 is a powerful microcontroller that provides a highly flexible and cost
effective solution to many embedded control applications.
The AT90PWM2/3 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.
4.2
4.2.1
Pin Descriptions
VCC
Digital supply voltage.
4.2.2
GND
Ground.
4.2.3
Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the AT90PWM2/2B/3/3B as listed
on page 69.
4.2.4
Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port C output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port C is not available on 24 pins package.
Port C also serves the functions of special features of the AT90PWM2/2B/3/3B as listed on page
72.
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AT90PWM2/3/2B/3B
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AT90PWM2/3/2B/3B
4.2.5
Port D (PD7..PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port D also serves the functions of various special features of the AT90PWM2/2B/3/3B as listed
on page 74.
4.2.6
Port E (PE2..0) RESET/ XTAL1/
XTAL2
Port E is an 3-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port E output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port E pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port E pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
If the RSTDISBL Fuse is programmed, PE0 is used as an I/O pin. Note that the electrical characteristics of PE0 differ from those of the other pins of Port C.
If the RSTDISBL Fuse is unprogrammed, PE0 is used as a Reset input. A low level on this pin
for longer than the minimum pulse length will generate a Reset, even if the clock is not running.
The minimum pulse length is given in Table 9-1 on page 47. Shorter pulses are not guaranteed
to generate a Reset.
Depending on the clock selection fuse settings, PE1 can be used as input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
Depending on the clock selection fuse settings, PE2 can be used as output from the inverting
Oscillator amplifier.
The various special features of Port E are elaborated in “Alternate Functions of Port E” on page
77 and “Clock Systems and their Distribution” on page 29.
4.2.7
AVCC
AVCC is the supply voltage pin for 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 lowpass filter.
4.2.8
AREF
This is the analog reference pin for the A/D Converter.
4.3
About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation for more details.
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AT90PWM2/3/2B/3B
5. AVR CPU Core
5.1
Introduction
This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
5.2
Architectural Overview
Figure 5-1.
Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
Control Lines
Direct Addressing
Instruction
Decoder
Indirect Addressing
Instruction
Register
Interrupt
Unit
SPI
Unit
Watchdog
Timer
ALU
Analog
Comparator
I/O Module1
Data
SRAM
I/O Module 2
I/O Module n
EEPROM
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions to be executed
in every clock cycle. The program memory is In-System Reprogrammable Flash memory.
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4317I–AVR–01/08
The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word format. Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM (Store Program Memory) instruction that writes into the Application Flash
memory section must reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher is the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F. In addition, the
AT90PWM2/2B/3/3B has Extended I/O space from 0x60 - 0xFF in SRAM where only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
5.3
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, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
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5.4
Status Register
The Status Register contains information about the result of the most recently executed arithmetic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
The AVR Status Register – SREG – is defined as:
Bit
7
6
5
4
3
2
1
I
T
H
S
V
N
Z
0
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 to enabled the interrupts. The individual interrupt
enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the negative flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
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4317I–AVR–01/08
• 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.
5.5
General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 5-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 5-2.
AVR CPU General Purpose Working Registers
7
0
Addr.
R0
0x00
R1
0x01
R2
0x02
…
R13
0x0D
General
R14
0x0E
Purpose
R15
0x0F
Working
R16
0x10
Registers
R17
0x11
…
R26
0x1A
R27
0x1B
X-register Low Byte
X-register High Byte
R28
0x1C
Y-register Low Byte
R29
0x1D
Y-register High Byte
R30
0x1E
Z-register Low Byte
R31
0x1F
Z-register High Byte
Most of the instructions operating on the Register File have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 5-2, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
5.5.1
The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 5-3.
Figure 5-3.
The X-, Y-, and Z-registers
15
14
XH
XL
0
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AT90PWM2/3/2B/3B
X-register
7
0
R27 (0x1B)
15
Y-register
0
YH
YL
7
0
R29 (0x1D)
Z-register
7
R26 (0x1A)
0
7
0
R28 (0x1C)
15
ZH
7
0
ZL
7
R31 (0x1F)
0
0
R30 (0x1E)
In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
5.6
Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x100. The Stack Pointer is decremented by one when data is pushed onto the
Stack with the PUSH instruction, and it is decremented by two when the return address is
pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one
when data is popped from the Stack with the POP instruction, and it is incremented by two when
data is popped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
Bit
Read/Write
Initial Value
5.7
15
14
13
12
11
10
9
8
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
SPL
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
Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
Figure 5-4 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.
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4317I–AVR–01/08
Figure 5-4.
The Parallel Instruction Fetches and Instruction Executions
T1
T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 5-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destination register.
Figure 5-5.
Single Cycle ALU Operation
T1
T2
T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
5.8
Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory Programming” on page 279 for details.
The lowest addresses in the program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 57. 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 PSC2 CAPT – the PSC2 Capture
Event. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the
IVSEL bit in the MCU Control Register (MCUCR). Refer to “Interrupts” on page 57 for more information. The Reset Vector can also be moved to the start of the Boot Flash section by
programming the BOOTRST Fuse, see “Boot Loader Support – Read-While-Write Self-Programming” on page 265.
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5.8.1
Interrupt Behavior
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
interrupt flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector
in order to execute the interrupt handling routine, and hardware clears the corresponding interrupt flag. Interrupt flags can also be cleared by writing a logic one to the flag bit position(s) to be
cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared,
the interrupt flag will be set and remembered until the interrupt is enabled, or the flag is cleared
by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable
bit is cleared, the corresponding interrupt flag(s) will be set and remembered until the Global
Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have interrupt flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence..
Assembly Code Example
in r16, SREG
; store SREG value
cli
; disable interrupts during timed sequence
sbi EECR, EEMWE
; start EEPROM write
sbi EECR, EEWE
out SREG, r16
; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG;
/* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG;
/* restore SREG value (I-bit) */
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in this example.
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Assembly Code Example
sei
; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
5.8.2
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 is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is increased by four clock cycles. This increase comes in addition to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and the I-bit in SREG is set.
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AT90PWM2/3/2B/3B
6. Memories
This section describes the different memories in the AT90PWM2/2B/3/3B. The AVR architecture
has two main memory spaces, the Data Memory and the Program Memory space. In addition,
the AT90PWM2/2B/3/3B features an EEPROM Memory for data storage. All three memory
spaces are linear and regular.
6.1
In-System Reprogrammable Flash Program Memory
The AT90PWM2/2B/3/3B contains 8K bytes On-chip In-System Reprogrammable Flash memory
for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as
4K x 16. For software security, the Flash Program memory space is divided into two sections,
Boot Program section and Application Program section.
The Flas h memory has an endur ance of at leas t 10,000 write/eras e cyc les. The
AT90PWM2/2B/3/3B Program Counter (PC) is 12 bits wide, thus addressing the 4K program
memory locations. The operation of Boot Program section and associated Boot Lock bits for
software protection are described in detail in “Boot Loader Support – Read-While-Write Self-Programming” on page 265. “Memory Programming” on page 279 contains a detailed description
on Flash programming in SPI or Parallel programming mode.
Constant tables can be allocated within the entire program memory address space (see the LPM
– Load Program Memory.
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 15.
Figure 1. Program Memory Map
Program Memory
0x0000
Application Flash Section
Boot Flash Section
0x0FFF
6.2
SRAM Data Memory
Figure 2 shows how the AT90PWM2/2B/3/3B SRAM Memory is organized.
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4317I–AVR–01/08
The AT90PWM2/2B/3/3B is a complex microcontroller with more peripheral units than can be
supported within the 64 locations reserved in the Opcode for the IN and OUT instructions. For
the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.
The lower 768 data memory locations address both the Register File, the I/O memory, Extended
I/O memory, and the internal data SRAM. The first 32 locations address the Register File, the
next 64 location the standard I/O memory, then 160 locations of Extended I/O memory, and the
next 512 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register
File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address given
by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and
the 512 bytes of internal data SRAM in the AT90PWM2/2B/3/3B are all accessible through all
these addressing modes. The Register File is described in “General Purpose Register File” on
page 14.
Figure 2. Data Memory Map
Data Memory
32 Registers
64 I/O Registers
160 Ext I/O Reg.
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
0x0100
Internal SRAM
(512 x 8)
0x02FF
6.2.1
SRAM Data Access Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figure 3.
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AT90PWM2/3/2B/3B
Figure 3. On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address
Address valid
Compute Address
Write
Data
WR
Read
Data
RD
Memory Access Instruction
6.3
Next Instruction
EEPROM Data Memory
The AT90PWM2/2B/3/3B contains 512 bytes of data EEPROM memory. It is organized as a
separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register.
For a detailed description of SPI and Parallel data downloading to the EEPROM, see “Serial
Downloading” on page 294, and “Parallel Programming Parameters, Pin Mapping, and Commands” on page 283 respectively.
6.3.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 6-2. A self-timing function, however,
lets the user software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, VCC is likely to rise or fall slowly on power-up/down. This causes the device for some
period of time to run at a voltage lower than specified as minimum for the clock frequency used.
For details on how to avoid problems in these situations seeSee “Preventing EEPROM Corruption” on page 26.
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.
6.3.2
The EEPROM Address Registers – EEARH and EEARL
Bit
15
14
13
12
11
10
9
8
–
–
–
–
–
–
–
EEAR8
EEARH
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EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
7
6
5
4
3
2
1
0
Read/Write
R
R
R
R
R
R
R
R/W
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
X
X
X
X
X
X
X
X
X
EEARL
• Bits 15..9 – Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bits 8..0 – EEAR8..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the
512 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
511. The initial value of EEAR is undefined. A proper value must be written before the EEPROM
may be accessed.
6.3.3
The EEPROM Data Register – EEDR
Bit
7
6
5
4
3
2
1
0
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
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.
6.3.4
The EEPROM Control Register – EECR
Bit
7
6
5
4
3
2
1
0
–
–
EEPM1
EEPM0
EERIE
EEMWE
EEWE
EERE
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
X
X
0
0
X
0
EECR
• Bits 7..6 – Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bits 5..4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bit setting defines which programming action that will be triggered when writing EEWE. It is possible to program data in one atomic operation (erase the old
value and program the new value) or to split the Erase and Write operations in two different
operations. The Programming times for the different modes are shown in Table 6-1. While
EEWE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to
0b00 unless the EEPROM is busy programming.
Table 6-1.
22
EEPROM Mode Bits
EEPM1
EEPM0
Programming
Time
0
0
3.4 ms
Erase and Write in one operation (Atomic Operation)
0
1
1.8 ms
Erase Only
1
0
1.8 ms
Write Only
1
1
–
Operation
Reserved for future use
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AT90PWM2/3/2B/3B
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a constant interrupt when EEWE is cleared. The interrupt will not be generated during EEPROM write or SPM.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written.
When EEMWE is set, setting EEWE within four clock cycles will write data to the EEPROM at
the selected address If EEMWE is zero, setting EEWE will have no effect. When EEMWE has
been written to one by software, hardware clears the bit to zero after four clock cycles. See the
description of the EEWE bit for an EEPROM write procedure.
• Bit 1 – EEWE: EEPROM Write Enable
The EEPROM Write Enable Signal EEWE is the write strobe to the EEPROM. When address
and data are correctly set up, the EEWE bit must be written to one to write the value into the
EEPROM. The EEMWE bit must be written to one before a logical one is written to EEWE, otherwise no EEPROM write takes place. The following procedure should be followed when writing
the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEWE becomes zero.
2. Wait until SPMEN (Store Program Memory Enable) in SPMCSR (Store Program Memory
Control and Status Register) becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.
6. Within four clock cycles after setting EEMWE, write a logical one to EEWE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The software
must check that the Flash programming is completed before initiating a new EEPROM write.
Step 2 is only relevant if the software contains a Boot Loader allowing the CPU to program the
Flash. If the Flash is never being updated by the CPU, step 2 can be omitted. See “Boot Loader
Support – Read-While-Write Self-Programming” on page 265 for details about Boot
programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM is
interrupting another EEPROM access, the EEAR or EEDR Register will be modified, causing the
interrupted EEPROM access to fail. It is recommended to have the Global Interrupt Flag cleared
during all the steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared by hardware. The user software can poll this bit and wait for a zero before writing the next byte. When EEWE has been set,
the CPU is halted for two cycles before the next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct
address is set up in the EEAR Register, the EERE bit must be written to a logic one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed.
The user should poll the EEWE bit before starting the read operation. If a write operation is in
progress, it is neither possible to read the EEPROM, nor to change the EEAR Register.
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The calibrated Oscillator is used to time the EEPROM accesses. Table 6-2 lists the typical programming time for EEPROM access from the CPU.
Table 6-2.
EEPROM Programming Time.
Symbol
Number of Calibrated RC Oscillator Cycles
Typ Programming Time
26368
3.3 ms
EEPROM write
(from CPU)
The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these functions. The examples also
assume that no Flash Boot Loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
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Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to data register
out EEDR,r16
; Write logical one to EEMWE
sbi EECR,EEMWE
; Start eeprom write by setting EEWE
sbi EECR,EEWE
ret
C Code Example
void EEPROM_write (unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address and data registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from data register
in
r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
6.3.5
Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can
be done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal
BOD does not match the needed detection level, an external low VCC reset Protection circuit can
be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient.
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6.4
I/O Memory
The I/O space definition of the AT90PWM2/2B/3/3B is shown in “Register Summary” on page
337.
All AT90PWM2/2B/3/3B I/Os and peripherals are placed in the I/O space. All I/O locations may
be accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the
32 general purpose working registers and the I/O space. I/O registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the
value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, the
I/O addresses 0x00 - 0x3F must be used. When addressing I/O registers as data space using
LD and ST instructions, 0x20 must be added to these addresses. The AT90PWM2/2B/3/3B is a
complex microcontroller with more peripheral units than can be supported within the 64 location
reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other
AVR’s, the CBI and SBI instructions will only operate on the specified bit, and can therefore be
used on registers containing such status flags. The CBI and SBI instructions work with registers
0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
6.5
General Purpose I/O Registers
The AT90PWM2/2B/3/3B contains four General Purpose I/O Registers. These registers can be
used for storing any information, and they are particularly useful for storing global variables and
status flags.
The General Purpose I/O Registers, within the address range 0x00 - 0x1F, are directly bitaccessible using the SBI, CBI, SBIS, and SBIC instructions.
6.5.1
General Purpose I/O Register 0 – GPIOR0
Bit
7
6
5
4
3
2
1
0
GPIOR07 GPIOR06 GPIOR05 GPIOR04 GPIOR03 GPIOR02 GPIOR01 GPIOR00
6.5.2
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
5
4
3
2
1
0
General Purpose I/O Register 1 – GPIOR1
Bit
7
6
GPIOR17 GPIOR16 GPIOR15 GPIOR14 GPIOR13 GPIOR12 GPIOR11 GPIOR10
6.5.3
GPIOR0
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
5
4
3
2
1
0
GPIOR1
General Purpose I/O Register 2 – GPIOR2
Bit
7
6
GPIOR27 GPIOR26 GPIOR25 GPIOR24 GPIOR23 GPIOR22 GPIOR21 GPIOR20
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
GPIOR2
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4317I–AVR–01/08
6.5.4
General Purpose I/O Register 3– GPIOR3
Bit
7
6
5
4
3
2
1
0
GPIOR37 GPIOR36 GPIOR35 GPIOR34 GPIOR33 GPIOR32 GPIOR31 GPIOR30
28
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
GPIOR3
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
7. System Clock
7.1
Clock Systems and their Distribution
Figure 7-1 presents the principal clock systems in the AVR and their distribution. All of the clocks
need not be active at a given time. In order to reduce power consumption, the clocks to unused
modules can be halted by using different sleep modes, as described in “Power Management and
Sleep Modes” on page 41. The clock systems are detailed below.
Figure 7-1.
Clock Distribution AT90PWM2/3
PSC0/1/2
General I/O
Modules
CLK PLL
ADC
CPU Core
RAM
Flash and
EEPROM
clkADC
PLL
clkI/O
clkCPU
AVR Clock
Control Unit
clkFLASH
Reset Logic
Source Clock
Clock
Multiplexer
External Clock
Watchdog Timer
Watchdog Clock
Watchdog
Oscillator
(Crystal
Oscillator)
Calibrated RC
Oscillator
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4317I–AVR–01/08
Figure 7-2.
Clock Distribution AT90PWM2B/3B
PSC0/1/2
General I/O
Modules
CLK PLL
ADC
CPU Core
RAM
Flash and
EEPROM
clkADC
PLL
clkI/O
clkCPU
AVR Clock
Control Unit
clkFLASH
Reset Logic
Source Clock
PLL Input
Multiplexer
Clock
Multiplexer
External Clock
7.1.1
Watchdog Timer
Watchdog Clock
Watchdog
Oscillator
(Crystal
Oscillator)
Calibrated RC
Oscillator
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and the
data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
7.1.2
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, USART. The
I/O clock is also used by the External Interrupt module, but note that some external interrupts
are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O clock
is halted.
7.1.3
Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.
7.1.4
PLL Clock – clkPLL
The PLL clock allows the PSC modules to be clocked directly from a 64/32 MHz clock. A 16 MHz
clock is also derived for the CPU.
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AT90PWM2/3/2B/3B
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AT90PWM2/3/2B/3B
7.1.5
ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion
results.
7.2
Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as illustrated
Table 7-1. The clock from the selected source is input to the AVR clock generator, and routed to
the appropriate modules.
Table 7-1.
Device Clocking Options Select(1) AT90PWM2/3
Device Clocking Option
CKSEL3..0
External Crystal/Ceramic Resonator
1111 - 1000
Reserved
0111- 0100
PLL output divided by 4 : 16 MHz
0011
Calibrated Internal RC Oscillator
0010
Reserved
0001
External Clock
Note:
1. For all fuses “1” means unprogrammed while “0” means programmed.
Table 7-2.
0000
Device Clocking Options Select AT90PWM2B/3B
Device Clocking Option
System
Clock
PLL Input
CKSEL3..0
(1)
External Crystal/Ceramic Resonator
Ext Osc (2)
RC Osc (3)
1111 - 1000
PLL output divided by 4 : 16 MHz / PLL driven by External
Crystal/Ceramic Resonator
Ext Osc
Ext Osc
0100
PLL output divided by 4 : 16 MHz / PLL driven by External
Crystal/Ceramic Resonator
PLL / 4
Ext Osc
0101
Reserved
N/A
N/A
PLL output divided by 4 : 16 MHz
PLL / 4
RC Osc
0011
Calibrated Internal RC Oscillator
RC Osc
RC Osc
0010
PLL output divided by 4 : 16 MHz / PLL driven by External
clock
PLL / 4
Ext Clk (4)
0001
External Clock
Ext Clk
RC Osc
0000
0111- 0110
1.For all fuses “1” means unprogrammed while “0” means programmed
2.Ext Osc : External Osc
3.RC Osc : Internal RC Oscillator
4.Ext Clk : External Clock Input
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down or Power-save, the selected clock source is used to time the startup, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts
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4317I–AVR–01/08
from reset, there is an additional delay allowing the power to reach a stable level before starting
normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up
time. The number of WDT Oscillator cycles used for each time-out is shown in Table 7-3. The
frequency of the Watchdog Oscillator is voltage dependent as shown in “Watchdog Oscillator
Frequency vs. VCC” on page 330.
Table 7-3.
7.3
Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V)
Typ Time-out (VCC = 3.0V)
Number of Cycles
4.1 ms
4.3 ms
4K (4,096)
65 ms
69 ms
64K (65,536)
Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is the Internal RC Oscillator with longest start-up time and an initial system
clock prescaling of 8. This default setting ensures that all users can make their desired clock
source setting using an In-System or Parallel programmer.
7.4
Low Power 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 7-3. Either a quartz crystal or a
ceramic resonator may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the lowest power consumption, but is not capable of driving other clock inputs.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in Table 7-4. For ceramic resonators, the capacitor values given by
the manufacturer should be used. For more information on how to choose capacitors and other
details on Oscillator operation, refer to the Multi-purpose Oscillator Application Note.
Figure 7-3.
Crystal Oscillator Connections
C2
C1
XTAL2
XTAL1
GND
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 7-4.
Table 7-4.
Crystal Oscillator Operating Modes
CKSEL3..1
Frequency Range(1) (MHz)
Recommended Range for Capacitors C1 and
C2 for Use with Crystals (pF)
100(2)
0.4 - 0.9
–
101
0.9 - 3.0
12 - 22
110
3.0 - 8.0
12 - 22
111
8.0 -16.0
12 - 22
Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
7-5.
Table 7-5.
CKSEL0
SUT1..0
Start-up Time from
Power-down and
Power-save
0
00
258 CK(1)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
258 CK(1)
14CK + 65 ms
Ceramic resonator, slowly
rising power
0
10
1K CK(2)
14CK
Ceramic resonator, BOD
enabled
0
11
1K CK(2)
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K CK(2)
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
Notes:
7.5
Start-up Times for the Oscillator Clock Selection
Additional Delay
from Reset
(VCC = 5.0V)
Recommended Usage
Crystal Oscillator, slowly
rising power
1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum frequency of the device, and if frequency stability at start-up is not important for the application.
11
16K CK
14CK + 65 ms
Calibrated Internal RC Oscillator
By default, the Internal RC OScillator provides an approximate 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. The device
is shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 38 for
more details.
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4317I–AVR–01/08
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 7-6. If selected, it will operate with no external components. During reset, hardware loads
the pre-programmed calibration value into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 26-2 on page 302.
By changing the OSCCAL register from SW, see “Oscillator Calibration Register – OSCCAL” on
page 34, it is possible to get a higher calibration accuracy than by using the factory calibration.
The accuracy of this calibration is shown as User calibration in Table 26-2 on page 302.
When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the
Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed calibration value, see the section “Calibration Byte” on page 283.
Internal Calibrated RC Oscillator Operating Modes(1)(2)
Table 7-6.
Notes:
Frequency Range (MHz)
CKSEL3..0
7.3 - 8.1
0010
1. The device is shipped with this option selected.
2. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-7 on page 34.
Table 7-7.
Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
SUT1..0
BOD enabled
6 CK
14CK(1)
00
Fast rising power
6 CK
14CK + 4.1 ms
Power Conditions
Slowly rising power
01
(1)
6 CK
14CK + 65 ms
10
Reserved
Note:
11
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1 ms to ensure programming mode can be entered.
2. The device is shipped with this option selected.
Table 7-8.
Bit
Read/Write
Oscillator Calibration Register – OSCCAL
7
6
5
4
3
2
1
0
CAL7
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
OSCCAL
Device Specific Calibration Value
• Bits 7..0 – CAL7..0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator frequency of 8.0 MHz at 25°C.
The application software can write this register to change the oscillator frequency. The oscillator
can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1% accuracy. Calibration
outside that range is not guaranteed.
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the
range. Incrementing CAL6..0 by 1 will give a frequency increment of less than 2% in the frequency range 7.3 - 8.1 MHz.
7.6
PLL
To generate high frequency and accurate PWM waveforms, the ‘PSC’s need high frequency
clock input. This clock is generated by a PLL. To keep all PWM accuracy, the frequency factor of
PLL must be configurable by software. With a system clock of 8 MHz, the PLL output is 32Mhz
or 64Mhz.
7.6.1
Internal PLL for PSC
The internal PLL in AT90PWM2/2B/3/3B generates a clock frequency that is 64x multiplied from
nominally 1 MHz input. The source of the 1 MHz PLL input clock is the output of the internal RC
Oscillator which is divided down to 1 MHz. See the Figure 7-4 on page 36.
The PLL is locked on the RC Oscillator and adjusting the RC Oscillator via OSCCAL Register
will adjust the fast peripheral clock at the same time. However, even if the possibly divided RC
Oscillator is taken to a higher frequency than 1 MHz, the fast peripheral clock frequency saturates at 70 MHz (worst case) and remains oscillating at the maximum frequency. It should be
noted that the PLL in this case is not locked any more with the RC Oscillator clock.
Therefore it is recommended not to take the OSCCAL adjustments to a higher frequency than 1
MHz in order to keep the PLL in the correct operating range. The internal PLL is enabled only
when the PLLE bit in the register PLLCSR is set. The bit PLOCK from the register PLLCSR is
set when PLL is locked.
Both internal 1 MHz RC Oscillator and PLL are switched off in Power-down and Standby sleep
modes
.
Table 7-9.
CKSEL
3..0
0011
RC Osc
Start-up Times when the PLL is selected as system clock
SUT1..0
Start-up Time from Power-down
and Power-save
Additional Delay from Reset
(VCC = 5.0V)
00
1K CK
14CK
01
1K CK
14CK + 4 ms
10
1K CK
14CK + 64 ms
11
16K CK
14CK
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4317I–AVR–01/08
Table 7-9.
CKSEL
3..0
0101
Ext Osc
0001
Ext Clk
Start-up Times when the PLL is selected as system clock
SUT1..0
Start-up Time from Power-down
and Power-save
Additional Delay from Reset
(VCC = 5.0V)
00
1K CK
14CK
01
1K CK
14CK + 4 ms
10
16K CK
14CK + 4 ms
11
16K CK
14CK + 64 ms
00
6 CK (1)
14CK
01
6 CK
(2)
14CK + 4 ms
6 CK
(3)
14CK + 64 ms
10
11
Reserved
1.
This value do not provide a proper restart ; do not use PD in this clock scheme
2.
This value do not provide a proper restart ; do not use PD in this clock scheme
3.
This value do not provide a proper restart ; do not use PD in this clock scheme
Figure 7-4.
PCK Clocking System AT90PWM2/3
OSCCAL
PLLF
PLLE
PLOCK
Lock
Detector
RC OSCILLATOR 8 MHz
DIVIDE
BY 8
PLL
64x
DIVIDE
BY 2
CLK PLL
DIVIDE
BY 4
CK SOURCE
XTAL1
XTAL2
36
OSCILLATORS
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 7-5.
PCK Clocking System AT90PWM2B/3B
OSCCAL
PLLF
PLLE
CKSEL3..0
PLOCK
Lock
Detector
RC OSCILLATOR
PLL
64x
DIVIDE
BY 8
8 MHz
CLK PLL
DIVIDE
BY 2
DIVIDE
BY 4
CK SOURCE
XTAL1
XTAL2
7.6.2
OSCILLATORS
PLL Control and Status Register – PLLCSR
Bit
7
6
5
4
3
2
1
0
$29 ($29)
–
–
–
–
–
PLLF
PLLE
PLOCK
Read/Write
R
R
R
R
R
R/W
R/W
R
Initial Value
0
0
0
0
0
0
0/1
0
PLLCSR
• Bit 7..3 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and always read as zero.
• Bit 2 – PLLF: PLL Factor
The PLLF bit is used to select the division factor of the PLL.
If PLLF is set, the PLL output is 64Mhz.
If PLLF is clear, the PLL output is 32Mhz.
• Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started and if not yet started the internal RC Oscillator is
started as PLL reference clock. If PLL is selected as a system clock source the value for this bit
is always 1.
• Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock, and it is safe to enable
CLKPLL for PSC. After the PLL is enabled, it takes about 100 ms for the PLL to lock.
7.7
128 kHz Internal Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The frequency is nominal at 3V and 25°C. This clock is used by the Watchdog Oscillator.
7.8
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in Figure
7-6. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
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4317I–AVR–01/08
Figure 7-6.
External Clock Drive Configuration
NC
XTAL2
External
Clock
Signal
XTAL1
GND
Table 7-10.
External Clock Frequency
CKSEL3..0
Frequency Range
0000
0 - 16 MHz
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-11.
Table 7-11.
Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Powerdown and Power-save
Additional Delay from
Reset (VCC = 5.0V)
00
6 CK
14CK
01
6 CK
14CK + 4.1 ms
Fast rising power
10
6 CK
14CK + 65 ms
Slowly rising power
11
Recommended Usage
BOD enabled
Reserved
When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
38 for details.
7.9
Clock Output Buffer
When the CKOUT Fuse is programmed, the system Clock will be output on CLKO. This mode is
suitable when chip clock is used to drive other circuits on the system. The clock will be output
also during reset and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including internal RC Oscillator, can be selected when CLKO
serves as clock output. If the System Clock Prescaler is used, it is the divided system clock that
is output (CKOUT Fuse programmed).
7.10
System Clock Prescaler
The AT90PWM2/2B/3/3B system clock can be divided by setting the Clock Prescale Register –
CLKPR. This feature can be used to decrease power consumption when the requirement for
processing power is low. This can be used with all clock source options, and it will affect the
clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH
are divided by a factor as shown in Table 7-12.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occurs in the clock system. It also ensures that no intermediate frequency is higher than
neither the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting. The ripple counter that implements the prescaler runs at the
frequency of the undivided clock, which may be faster than the CPU's clock frequency. Hence, it
is not possible to determine the state of the prescaler - even if it were readable, and the exact
time it takes to switch from one clock division to the other cannot be exactly predicted. From the
time the CLKPS values are written, it takes between T1 + T2 and T1 + 2 * T2 before the new
clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period corresponding to the new prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is
not interrupted.
7.10.1
Clock Prescaler Register – CLKPR
Bit
7
6
5
4
3
2
1
0
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Read/Write
R/W
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
CLKPR
See Bit Description
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE
bit is only updated when the other bits in CLKPR are simultaniosly written to zero. CLKPCE is
cleared by hardware four cycles after it is written or when CLKPS bits are written. Rewriting the
CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the
CLKPCE bit.
• Bits 3..0 – CLKPS3..0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As the divider divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given in
Table 7-12.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to
“0011”, giving a division factor of 8 at start up. This feature should be used if the selected clock
source has a higher frequency than the maximum frequency of the device at the present operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8
Fuse setting. The Application software must ensure that a sufficient division factor is chosen if
39
4317I–AVR–01/08
the selcted clock source has a higher frequency than the maximum frequency of the device at
the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed.
Table 7-12.
40
Clock Prescaler Select
CLKPS3
CLKPS2
CLKPS1
CLKPS0
Clock Division Factor
0
0
0
0
1
0
0
0
1
2
0
0
1
0
4
0
0
1
1
8
0
1
0
0
16
0
1
0
1
32
0
1
1
0
64
0
1
1
1
128
1
0
0
0
256
1
0
0
1
Reserved
1
0
1
0
Reserved
1
0
1
1
Reserved
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
8. Power Management and Sleep Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving
power. The AVR provides various sleep modes allowing the user to tailor the power consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a
SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select
which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save, or Standby) will be
activated by the SLEEP instruction. See Table 8-1 for a summary. If an enabled interrupt occurs
while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles in
addition to the start-up time, executes the interrupt routine, and resumes execution from the
instruction following SLEEP. The contents of the register file and SRAM are unaltered when the
device wakes up from sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the Reset Vector.
Figure 7-1 on page 29 presents the different clock systems in the AT90PWM2/2B/3/3B, and their
distribution. The figure is helpful in selecting an appropriate sleep mode.
8.0.1
Sleep Mode Control Register – SMCR
The Sleep Mode Control Register contains control bits for power management.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
SM2
SM1
SM0
SE
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SMCR
• Bits 3..1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 8-1.
Table 8-1.
Sleep Mode Select
SM2
SM1
SM0
Sleep Mode
0
0
0
Idle
0
0
1
ADC Noise Reduction
0
1
0
Power-down
0
1
1
Reserved
1
0
0
Reserved
1
0
1
Reserved
1
1
0
Standby(1)
1
1
1
Reserved
Note: 1. Standby mode is only recommended for use with external crystals or resonators.
• Bit 1 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s
purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.
8.1
Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing SPI, USART, Analog Comparator, ADC, Timer/Counters,
41
4317I–AVR–01/08
Watchdog, and the interrupt system to continue operating. This sleep mode basically halt clkCPU
and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow and USART Transmit Complete interrupts. If wake-up from the
Analog Comparator interrupt is not required, the Analog Comparator can be powered down by
setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will
reduce power consumption in Idle mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
8.2
ADC Noise Reduction Mode
When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter ADC
Noise Reduction mode, stopping the CPU but allowing the ADC, the External Interrupts,
Timer/Counter (if their clock source is external - T0 or T1) and the Watchdog to continue
operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing
the other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If
the ADC is enabled, a conversion starts automatically when this mode is entered. Apart from the
ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out
Reset, a Timer/Counter interrupt, an SPM/EEPROM ready interrupt, an External Level Interrupt
on INT3:0 can wake up the MCU from ADC Noise Reduction mode.
8.3
Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Powerdown mode. In this mode, the External Oscillator is stopped, while the External Interrupts and
the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a
Brown-out Reset, a PSC Interrupt, an External Level Interrupt on INT3:0 can wake up the MCU.
This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 81
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL fuses that define the
Reset Time-out period, as described in “Clock Sources” on page 31.
8.4
Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
with the exception that the Oscillator is kept running. From Standby mode, the device wakes up
in six clock cycles.
Table 8-2.
Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
Oscillator
s
clkADC
clkPLL
Main Clock
Source Enabled
INT3..0
PSC
SPM/EEPROM
Ready
ADC
WDT
OtherI/O
X
X
X
X
X
X
X
X
X
X
X
X
X
X(2)
X
X
X
X
X(2)
X
Sleep
Mode
Idle
Wake-up Sources
clkIO
clkFLASH
clkCPU
Active Clock Domains
ADC
Noise
Reduction
Powerdown
X
X
X(2)
Standby(1)
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. Only level interrupt.
8.5
X
Power Reduction Register
The Power Reduction Register, PRR, provides a method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/O
registers can not be read or written. Resources used by the peripheral when stopping the clock
will remain occupied, hence the peripheral should in most cases be disabled before stopping the
clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the
same state as before shutdown.
A full predictible behaviour of a peripheral is not guaranteed during and after a cycle of stopping
and starting of its clock. So its recommended to stop a peripheral before stopping its clock with
PRR register.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.
8.5.1
Power Reduction Register - PRR
Bit
7
6
5
4
3
2
1
0
PRPSC2
PRPSC1
PRPSC0
PRTIM1
PRTIM0
PRSPI
PRUSART
PRADC
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
PRR
• Bit 7 - PRPSC2: Power Reduction PSC2
Writing a logic one to this bit reduces the consumption of the PSC2 by stopping the clock to this
module. When waking up the PSC2 again, the PSC2 should be re initialized to ensure proper
operation.
• Bit 6 - PRPSC1: Power Reduction PSC1
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4317I–AVR–01/08
Writing a logic one to this bit reduces the consumption of the PSC1 by stopping the clock to this
module. When waking up the PSC1 again, the PSC1 should be re initialized to ensure proper
operation.
• Bit 5 - PRPSC0: Power Reduction PSC0
Writing a logic one to this bit reduces the consumption of the PSC0 by stopping the clock to this
module. When waking up the PSC0 again, the PSC0 should be re initialized to ensure proper
operation.
• Bit 4 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit reduces the consumption of the Timer/Counter1 module. When the
Timer/Counter1 is enabled, operation will continue like before the setting of this bit.
• Bit 3 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit reduces the consumption of the Timer/Counter0 module. When the
Timer/Counter0 is enabled, operation will continue like before the setting of this bit.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit reduces the consumption of the Serial Peripheral Interface by stopping the clock to this module. When waking up the SPI again, the SPI should be re initialized to
ensure proper operation.
• Bit 1 - PRUSART0: Power Reduction USART0
Writing a logic one to this bit reduces the consumption of the USART by stopping the clock to
this module. When waking up the USART again, the USART should be re initialized to ensure
proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit reduces the consumption of the ADC by stopping the clock to this
module. The ADC must be disabled before using this function. The analog comparator cannot
use the ADC input MUX when the clock of ADC is stopped.
8.6
Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
8.6.1
Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “CROSS REFERENCE REMOVED” for
details on ADC operation.
8.6.2
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering
ADC Noise Reduction mode, the Analog Comparator should be disabled. In other sleep modes,
the Analog Comparator is automatically disabled. However, if the Analog Comparator is set up
to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all
sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep
mode. Refer to “Analog Comparator” on page 227 for details on how to configure the Analog
Comparator.
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
8.6.3
Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned off. If
the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep
modes, and hence, always consume power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Brown-out Detection” on page 49 for details
on how to configure the Brown-out Detector.
8.6.4
Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When
turned on again, the user must allow the reference to start up before the output is used. If the
reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal Voltage Reference” on page 51 for details on the start-up time.
8.6.5
Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Watchdog Timer” on page 52 for details on how to configure the Watchdog Timer.
8.6.6
Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important is then to ensure that no pins drive resistive loads. In sleep modes where both
the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device will
be disabled. This ensures that no power is consumed by the input logic when not needed. In
some cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section “I/O-Ports” on page 62 for details on which pins are enabled. If the
input buffer is enabled and the input signal is left floating or have an analog signal level close to
VCC/2, the input buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to VCC/2 on an input pin can cause significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and
DIDR0). Refer to “Digital Input Disable Register 1– DIDR1” and “Digital Input Disable Register 0
– DIDR0” on page 232 and page 252 for details.
8.6.7
On-chip Debug System
If the On-chip debug system is enabled by OCDEN Fuse and the chip enter sleep mode, the
main clock source is enabled, and hence, always consumes power. In the deeper sleep modes,
this will contribute significantly to the total current consumption.
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4317I–AVR–01/08
9. System Control and Reset
9.0.1
Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a JMP – Absolute
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. This is also the case if the Reset Vector is in the Application section while the Interrupt
Vectors are in the Boot section or vice versa. The circuit diagram in Figure 9-1 shows the reset
logic. Table 9-1 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The different selections for the delay period are presented in “Clock Sources” on page 31.
9.0.2
Reset Sources
The AT90PWM2/2B/3/3B has four sources of reset:
46
•
Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
•
External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
•
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog is enabled.
•
Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 9-1.
Reset Logic
DATA BUS
PORF
BORF
EXTRF
WDRF
MCU Status
Register (MCUSR)
Power-on Reset
Circuit
Brown-out
Reset Circuit
BODLEVEL [2..0]
Pull-up Resistor
Spike
Filter
Watchdog
Oscillator
Clock
Generator
CK
Delay Counters
TIMEOUT
CKSEL[3:0]
SUT[1:0]
Table 9-1.
Symbol
VPOT
VRST
tRST
Notes:
9.0.3
Reset Characteristics(1)
Parameter
Typ.
Max.
Units
Power-on Reset Threshold
Voltage (rising)
1.4
2.3
V
Power-on Reset Threshold
Voltage (falling)(2)
1.3
2.3
V
0.85Vcc
V
RESET Pin Threshold Voltage
Condition
Min.
0.2Vcc
Minimum pulse width on RESET
400
ns
Pin
1. Values are guidelines only..
2. The Power-on Reset will not work unless the supply voltage has been below VPOT (falling)
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in Table 9-1. The POR is activated whenever VCC is below the detection level. The
POR circuit can be used to trigger the start-up Reset, as well as to detect a failure in supply
voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay,
when VCC decreases below the detection level.
47
4317I–AVR–01/08
Figure 9-2.
MCU Start-up, RESET Tied to VCC
VCC
RESET
VPOT
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
Figure 9-3.
MCU Start-up, RESET Extended Externally
VCC
VPOT
RESET
TIME-OUT
VRST
tTOUT
INTERNAL
RESET
9.0.4
External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the
minimum pulse width (see Table 9-1) will generate a reset, even if the clock is not running.
Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the
Reset Threshold Voltage – VRST – on its positive edge, the delay counter starts the MCU after
the Time-out period – tTOUT – has expired.
Figure 9-4.
External Reset During Operation
CC
48
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
9.0.5
Brown-out Detection
AT90PWM2/2B/3/3B has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC
level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can
be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free
Brown-out Detection. The hysteresis on the detection level should be interpreted as V BOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
Table 9-2.
BODLEVEL Fuse Coding(1)(2)
BODLEVEL 2..0 Fuses
Min VBOT
111
Notes:
Typ VBOT
Max VBOT
Units
BOD Disabled
110
4.5
V
101
2.7
V
100
4.3
V
011
4.4
V
010
4.2
V
001
2.8
V
000
2.6
V
1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guarantees that a Brown-Out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed. The test is performed using
BODLEVEL = 010 for Low Operating Voltage and BODLEVEL = 101 for High Operating Voltage .
2. Values are guidelines only.
Table 9-3.
Brown-out Characteristics(1)
Symbol
Parameter
VHYST
Brown-out Detector Hysteresis
70
mV
tBOD
Min Pulse Width on Brown-out Reset
2
µs
Notes:
Min.
Typ.
Max.
Units
1. Values are guidelines only.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure
9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(V BOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for
longer than tBOD given in Table 9-3.
49
4317I–AVR–01/08
Figure 9-5.
Brown-out Reset During Operation
VCC
VBOT+
VBOT-
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
9.0.6
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
page 51 for details on operation of the Watchdog Timer.
Figure 9-6.
Watchdog Reset During Operation
CC
CK
9.0.7
MCU Status Register – MCUSR
The MCU Status Register provides information on which reset source caused an MCU reset.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
WDRF
BORF
EXTRF
PORF
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
MCUSR
See Bit Description
• 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
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset flags to identify a reset condition, the user should read and then reset
the MCUSR as early as possible in the program. If the register is cleared before another reset
occurs, the source of the reset can be found by examining the reset flags.
9.1
Internal Voltage Reference
AT90PWM2/2B/3/3B features an internal bandgap reference (1.1V). This reference is used for
Brown-out Detection. A 2.56V voltage reference is generated thanks to the bandgap, it can be used as
a voltage reference for the DAC and/or the ADC, and can also be used as analog input for the
analog comparators. In order to use the internal Vref, it is necessary to configure it thanks to the
REFS1 and REFS0 bits in the ADMUX register and to set an analog feature which requires it.
9.1.1
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 9-4. To save power, the reference is not always turned on. The
reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
3. When the ADC is enabled.
4. When the DAC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC or the DAC,
the user must always allow the reference to start up before the output from the Analog Comparator or ADC or DAC is used. To reduce power consumption in Power-down mode, the user can
avoid the three conditions above to ensure that the reference is turned off before entering
Power-down mode.
9.1.2
Voltage Reference Characteristics
Table 9-4.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
VBG
Bandgap reference voltage
1.1
V
tBG
Bandgap reference start-up time
40
µs
15
µA
IBG
Note:
9.2
Internal Voltage Reference Characteristics(1)
Bandgap reference current
consumption
1. Values are guidelines only.
Watchdog Timer
AT90PWM2/2B/3/3B has an Enhanced Watchdog Timer (WDT). The main features are:
• Clocked from separate On-chip Oscillator
• 3 Operating modes
– Interrupt
– System Reset
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4317I–AVR–01/08
– Interrupt and System Reset
• Selectable Time-out period from 16ms to 8s
• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
Figure 9-7.
Watchdog Timer
OSC/8K
OSC/2K
OSC/4K
128 KHz
OSCILLATOR
WDP3
MCU RESET
WDIF
INTERRUPT
WDIE
The Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 kHz oscillator.
The WDT gives an interrupt or a system reset when the counter reaches a given time-out value.
In normal operation mode, it is required that the system uses the WDR - Watchdog Timer Reset
- instruction to restart the counter before the time-out value is reached. If the system doesn't
restart the counter, an interrupt or system reset will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used
to wake the device from sleep-modes, and also as a general system timer. One example is to
limit the maximum time allowed for certain operations, giving an interrupt when the operation
has run longer than expected. In System Reset mode, the WDT gives a reset when the timer
expires. This is typically used to prevent system hang-up in case of runaway code. The third
mode, Interrupt and System Reset mode, combines the other two modes by first giving an interrupt and then switch to System Reset mode. This mode will for instance allow a safe shutdown
by saving critical parameters before a system reset.
The “Watchdog Timer Always On” (WDTON) fuse, if programmed, will force the Watchdog Timer
to System Reset mode. With the fuse programmed the System Reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure program security,
alterations to the Watchdog set-up must follow timed sequences. The sequence for clearing
WDE and changing time-out configuration is as follows:
1. In the same operation, write a logic one to the Watchdog change enable bit (WDCE) and
WDE. A logic one must be written to WDE regardless of the previous value of the WDE
bit.
2. Within the next four clock cycles, write the WDE and Watchdog prescaler bits (WDP) as
desired, but with the WDCE bit cleared. This must be done in one operation.
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The following code example shows one assembly and one C function for turning off the Watchdog Timer. The example assumes that interrupts are controlled (e.g. by disabling interrupts
globally) so that no interrupts will occur during the execution of these functions.
Assembly Code Example(1)
WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
in
r16, MCUSR
andi
r16, (0xff & (0<<WDRF))
out
MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional time-out
lds r16, WDTCSR
ori
r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; Turn off WDT
ldi
r16, (0<<WDE)
sts WDTCSR, r16
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_off(void)
{
__disable_interrupt();
__watchdog_reset();
/* Clear WDRF in MCUSR */
MCUSR &= ~(1<<WDRF);
/* Write logical one to WDCE and WDE */
/* Keep old prescaler setting to prevent unintentional time-out */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
}
Note:
1. The example code assumes that the part specific header file is included.
Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out
condition, the device will be reset and the Watchdog Timer will stay enabled. If the code is not
set up to handle the Watchdog, this might lead to an eternal loop of time-out resets. To avoid this
situation, the application software should always clear the Watchdog System Reset Flag
(WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.
53
4317I–AVR–01/08
The following code example shows one assembly and one C function for changing the time-out
value of the Watchdog Timer.
Assembly Code Example(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
lds r16, WDTCSR
ori
r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; --
Got four cycles to set the new values from here -
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi
r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
sts WDTCSR, r16
; --
Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed
equence */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR
= (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Note:
1. The example code assumes that the part specific header file is included.
Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change
in the WDP bits can result in a time-out when switching to a shorter time-out period;
9.2.1
Watchdog Timer Control Register - WDTCSR
Bit
7
6
5
4
3
2
1
0
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
X
0
0
0
WDTCSR
• Bit 7 - WDIF: Watchdog Interrupt Flag
This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is configured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt
handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in
SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.
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AT90PWM2/3/2B/3B
• Bit 6 - WDIE: Watchdog Interrupt Enable
When this bit is written to one and the I-bit in the Status Register is set, the Watchdog Interrupt is
enabled. If WDE is cleared in combination with this setting, the Watchdog Timer is in Interrupt
Mode, and the corresponding interrupt is executed if time-out in the Watchdog Timer occurs.
If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. The first time-out in
the Watchdog Timer will set WDIF. Executing the corresponding interrupt vector will clear WDIE
and WDIF automatically by hardware (the Watchdog goes to System Reset Mode). This is useful for keeping the Watchdog Timer security while using the interrupt. To stay in Interrupt and
System Reset Mode, WDIE must be set after each interrupt. This should however not be done
within the interrupt service routine itself, as this might compromise the safety-function of the
Watchdog System Reset mode. If the interrupt is not executed before the next time-out, a System Reset will be applied.
Table 9-5.
WDTON
Note:
(1)
Watchdog Timer Configuration
WDE
WDIE
Mode
Action on Time-out
0
0
0
Stopped
None
0
0
1
Interrupt Mode
Interrupt
0
1
0
System Reset Mode
Reset
0
1
1
Interrupt and System Reset
Mode
Interrupt, then go to System
Reset Mode
1
x
x
System Reset Mode
Reset
1. For the WDTON Fuse “1” means unprogrammed while “0” means programmed.
• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit,
and/or change the prescaler bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is
set. To clear WDE, WDRF must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the failure.
• Bit 5, 2..0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP3..0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is running. The different prescaling values and their corresponding time-out periods are shown in
Table 9-6 on page 56.
55
4317I–AVR–01/08
.
Table 9-6.
Watchdog Timer Prescale Select
WDP3
WDP2
WDP1
WDP0
Number of WDT Oscillator
Cycles
Typical Time-out at
VCC = 5.0V
0
0
0
0
2K (2048) cycles
16 ms
0
0
0
1
4K (4096) cycles
32 ms
0
0
1
0
8K (8192) cycles
64 ms
0
0
1
1
16K (16384) cycles
0.125 s
0
1
0
0
32K (32768) cycles
0.25 s
0
1
0
1
64K (65536) cycles
0.5 s
0
1
1
0
128K (131072) cycles
1.0 s
0
1
1
1
256K (262144) cycles
2.0 s
1
0
0
0
512K (524288) cycles
4.0 s
1
0
0
1
1024K (1048576) cycles
8.0 s
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
Reserved
56
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
10. Interrupts
This section describes the specifics of the interrupt handling as performed in
AT90PWM2/2B/3/3B. For a general explanation of the AVR interrupt handling, refer to “Reset
and Interrupt Handling” on page 16.
10.1
Interrupt Vectors in AT90PWM2/2B/3/3B
Table 10-1.
Reset and Interrupt Vectors
Vector
No.
Program
Address
1
0x0000
2
0x0001
PSC2 CAPT
PSC2 Capture Event
3
0x0002
PSC2 EC
PSC2 End Cycle
4
0x0003
PSC1 CAPT
PSC1 Capture Event
5
0x0004
PSC1 EC
PSC1 End Cycle
6
0x0005
PSC0 CAPT
PSC0 Capture Event
7
0x0006
PSC0 EC
PSC0 End Cycle
8
0x0007
ANACOMP 0
Analog Comparator 0
9
0x0008
ANACOMP 1
Analog Comparator 1
10
0x0009
ANACOMP 2
Analog Comparator 2
11
0x000A
INT0
External Interrupt Request 0
12
0x000B
TIMER1 CAPT
Timer/Counter1 Capture Event
13
0x000C
TIMER1 COMPA
Timer/Counter1 Compare Match A
14
0x000D
TIMER1 COMPB
Timer/Counter1 Compare Match B
15
0x000E
16
0x000F
TIMER1 OVF
Timer/Counter1 Overflow
17
0x0010
TIMER0 COMPA
Timer/Counter0 Compare Match A
18
0x0011
TIMER0 OVF
Timer/Counter0 Overflow
19
0x0012
ADC
ADC Conversion Complete
20
0x0013
INT1
External Interrupt Request 1
21
0x0014
SPI, STC
SPI Serial Transfer Complete
22
0x0015
USART0, RX
USART0, Rx Complete
23
0x0016
USART0, UDRE
USART0 Data Register Empty
24
0x0017
USART0, TX
USART0, Tx Complete
25
0x0018
INT2
External Interrupt Request 2
26
0x0019
WDT
Watchdog Time-Out Interrupt
27
0x001A
EE READY
EEPROM Ready
28
0x001B
TIMER0 COMPB
Timer/Counter0 Compare Match B
Source
RESET
Interrupt Definition
External Pin, Power-on Reset, Brown-out Reset,
Watchdog Reset, and Emulation AVR Reset
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4317I–AVR–01/08
Table 10-1.
Reset and Interrupt Vectors
Vector
No.
Program
Address
29
0x001C
30
0x001D
31
0x001E
32
0x001F
Notes:
Source
Interrupt Definition
INT3
External Interrupt Request 3
SPM READY
Store Program Memory Ready
1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at
reset, see “Boot Loader Support – Read-While-Write Self-Programming” on page 265.
2. When the IVSEL bit in MCUCR is set, Interrupt Vectors will be moved to the start of the Boot
Flash Section. The address of each Interrupt Vector will then be the address in this table
added to the start address of the Boot Flash Section.
Table 10-2 shows reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the Interrupt
Vectors are not used, and regular program code can be placed at these locations. This is also
the case if the Reset Vector is in the Application section while the Interrupt Vectors are in the
Boot section or vice versa.
Table 10-2.
Reset and Interrupt Vectors Placement in AT90PWM2/2B/3/3B(1)
BOOTRST
IVSEL
1
Note:
Reset Address
Interrupt Vectors Start Address
0
0x000
0x001
1
1
0x000
Boot Reset Address + 0x001
0
0
Boot Reset Address
0x001
0
1
Boot Reset Address
Boot Reset Address + 0x001
1. The Boot Reset Address is shown in Table 37 on page 278. For the BOOTRST Fuse “1”
means unprogrammed while “0” means programmed.
The most typical and general program setup for the Reset and Interrupt Vector Addresses in
AT90PWM2/2B/3/3B is:
Address Labels Code
58
Comments
0x000
rjmp
RESET
; Reset Handler
0x001
rjmp
PSC2_CAPT
; PSC2 Capture event Handler
0x002
rjmp
PSC2_EC
; PSC2 End Cycle Handler
0x003
rjmp
PSC1_CAPT
; PSC1 Capture event Handler
0x004
rjmp
PSC1_EC
; PSC1 End Cycle Handler
0x005
rjmp
PSC0_CAPT
; PSC0 Capture event Handler
0x006
rjmp
PSC0_EC
; PSC0 End Cycle Handler
0x007
rjmp
ANA_COMP_0
; Analog Comparator 0 Handler
0x008
rjmp
ANA_COMP_1
; Analog Comparator 1 Handler
0x009
rjmp
ANA_COMP_2
; Analog Comparator 2 Handler
0x00A
rjmp
EXT_INT0
; IRQ0 Handler
0x00B
rjmp
TIM1_CAPT
; Timer1 Capture Handler
0x00C
rjmp
TIM1_COMPA
; Timer1 Compare A Handler
0x00D
rjmp
TIM1_COMPB
; Timer1 Compare B Handler
0x00F
rjmp
TIM1_OVF
; Timer1 Overflow Handler
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
0x010
rjmp
TIM0_COMPA
; Timer0 Compare A Handler
0x011
rjmp
TIM0_OVF
; Timer0 Overflow Handler
0x012
rjmp
ADC
; ADC Conversion Complete Handler
0x013
rjmp
EXT_INT1
; IRQ1 Handler
0x014
rjmp
SPI_STC
; SPI Transfer Complete Handler
0x015
rjmp
USART_RXC
; USART, RX Complete Handler
0x016
rjmp
USART_UDRE
; USART, UDR Empty Handler
0x017
rjmp
USART_TXC
; USART, TX Complete Handler
0x018
rjmp
EXT_INT2
; IRQ2 Handler
0x019
rjmp
WDT
; Watchdog Timer Handler
0x01A
rjmp
EE_RDY
; EEPROM Ready Handler
0x01B
rjmp
TIM0_COMPB
; Timer0 Compare B Handler
0x01C
rjmp
EXT_INT3
; IRQ3 Handler
0x01F
rjmp
SPM_RDY
; Store Program Memory Ready Handler
;
0x020RESET:
ldi
r16, high(RAMEND); Main program start
0x021
out
SPH,r16
0x022
ldi
r16, low(RAMEND)
0x023
0x024
out
sei
0x025
...
SPL,r16
; Enable interrupts
<instr>
...
...
; Set Stack Pointer to top of RAM
xxx
...
When the BOOTRST Fuse is unprogrammed, the Boot section size set to 2K bytes and the
IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most typical and
general program setup for the Reset and Interrupt Vector Addresses in AT90PWM2/2B/3/3B is:
Address Labels Code
Comments
0x000
RESET: ldi
r16,high(RAMEND); Main program start
0x001
out
SPH,r16
0x002
ldi
r16,low(RAMEND)
0x003
0x004
out
sei
SPL,r16
0x005
<instr>
; Set Stack Pointer to top of RAM
; Enable interrupts
xxx
;
.org 0xC01
0xC01
rjmp
PSC2_CAPT
; PSC2 Capture event Handler
0xC02
rjmp
PSC2_EC
; PSC2 End Cycle Handler
...
...
...
;
0xC1F
rjmp
SPM_RDY
; Store Program Memory Ready Handler
When the BOOTRST Fuse is programmed and the Boot section size set to 2K bytes, the most
typical and general program setup for the Reset and Interrupt Vector Addresses in
AT90PWM2/2B/3/3B is:
Address Labels Code
Comments
.org 0x001
0x001
rjmp
PSC2_CAPT
; PSC2 Capture event Handler
0x002
rjmp
PSC2_EC
; PSC2 End Cycle Handler
...
...
...
;
0x01F
rjmp
SPM_RDY
; Store Program Memory Ready Handler
59
4317I–AVR–01/08
;
.org 0xC00
0xC00
RESET: ldi
r16,high(RAMEND); Main program start
0xC01
out
SPH,r16
0xC02
ldi
r16,low(RAMEND)
0xC03
0xC04
out
sei
SPL,r16
0xC05
<instr>
; Set Stack Pointer to top of RAM
; Enable interrupts
xxx
When the BOOTRST Fuse is programmed, the Boot section size set to 2K bytes and the IVSEL
bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general
program setup for the Reset and Interrupt Vector Addresses in AT90PWM2/2B/3/3B is:
Address Labels Code
Comments
;
.org 0xC00
0xC00
rjmp
RESET
; Reset handler
0xC01
rjmp
PSC2_CAPT
; PSC2 Capture event Handler
0xC02
rjmp
PSC2_EC
; PSC2 End Cycle Handler
...
...
...
;
0xC1F
rjmp
SPM_RDY
; Store Program Memory Ready Handler
;
10.1.1
0xC20
RESET: ldi
r16,high(RAMEND); Main program start
0xC21
out
SPH,r16
0xC22
ldi
r16,low(RAMEND)
0xC23
0xC24
out
sei
SPL,r16
0xC25
<instr>
; Set Stack Pointer to top of RAM
; Enable interrupts
xxx
Moving Interrupts Between Application and Boot Space
The MCU Control Register controls the placement of the Interrupt Vector table.
10.1.2
MCU Control Register – MCUCR
Bit
7
6
5
4
3
2
1
0
SPIPS
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash
memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot
Loader section of the Flash. The actual address of the start of the Boot Flash Section is determined by the BOOTSZ Fuses. Refer to the section “Boot Loader Support – Read-While-Write
Self-Programming” on page 265 for details. To avoid unintentional changes of Interrupt Vector
tables, a special write procedure must be followed to change the IVSEL bit:
1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled
in the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status
Register is unaffected by the automatic disabling.
Note:
If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed, interrupts are disabled while executing from the Application section. If Interrupt Vectors
are placed in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while executing from the Boot Loader section. Refer to the section “Boot Loader Support –
Read-While-Write Self-Programming” on page 265 for details on Boot Lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by
hardware four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disable
interrupts, as explained in the IVSEL description above. See Code Example below.
Assembly Code Example
Move_interrupts:
; Enable change of Interrupt Vectors
ldi r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ldi r16, (1<<IVSEL)
out MCUCR, r16
ret
C Code Example
void Move_interrupts(void)
{
/* Enable change of Interrupt Vectors */
MCUCR = (1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR = (1<<IVSEL);
}
61
4317I–AVR–01/08
11. I/O-Ports
11.1
Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as
input). Each output buffer has symmetrical drive characteristics with both high sink and source
capability. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both VCC and Ground as indicated in Figure
11-1. Refer to “Electrical Characteristics(1)” on page 299 for a complete list of parameters.
Figure 11-1. I/O Pin Equivalent Schematic
Rpu
Pxn
Logic
Cpin
See Figure
"General Digital I/O" for
Details
All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for the port, and a lower case “n” represents the bit number. However,
when using the register or bit defines in a program, the precise form must be used. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description for I/O-Ports”.
Three I/O memory address locations are allocated for each port, one each for the Data Register
– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register and the Data Direction Register are read/write.
However, writing a logic one to a bit in the PINx Register, will result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables the
pull-up function for all pins in all ports when set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O”. Most port
pins are multiplexed with alternate functions for the peripheral features on the device. How each
alternate function interferes with the port pin is described in “Alternate Port Functions” on page
67. Refer to the individual module sections for a full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the port as general digital I/O.
11.2
Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 11-2 shows a functional description of one I/O-port pin, here generically called Pxn.
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AT90PWM2/3/2B/3B
Figure 11-2. General Digital I/O(1)
PUD
Q
D
DDxn
Q CLR
WDx
RESET
1
Q
Pxn
D
0
PORTxn
Q CLR
WPx
DATA BUS
RDx
RESET
WRx
RRx
SLEEP
SYNCHRONIZER
D
Q
L
Q
D
RPx
Q
PINxn
Q
clk I/O
PUD: PULLUP DISABLE
SLEEP: SLEEP CONTROL
clkI/O : I/O CLOCK
Note:
11.2.1
WDx:
RDx:
WRx:
RRx:
RPx:
WPx:
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.
Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description for I/O-Ports” on page 78, the DDxn bits are accessed at the DDRx I/O address, the
PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one,
Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input
pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is
activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to
be configured as an output pin
The port pins are tri-stated when reset condition becomes active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven
high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port
pin is driven low (zero).
63
4317I–AVR–01/08
11.2.2
Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port.
11.2.3
Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}
= 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output
low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully acceptable, as a high-impedant environment will not notice the difference between a strong high driver
and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all
pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}
= 0b11) as an intermediate step.
Table 11-1 summarizes the control signals for the pin value.
Table 11-1. Port Pin Configurations
11.2.4
DDxn
PORTxn
PUD
(in MCUCR)
I/O
Pull-up
0
0
X
Input
No
Default configuration after Reset.
Tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled low.
0
1
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output Low (Sink)
1
1
X
Output
No
Output High (Source)
Comment
Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 11-2, the PINxn Register bit and the preceding latch constitute a synchronizer. This is needed to avoid metastability if the physical pin changes value
near the edge of the internal clock, but it also introduces a delay. Figure 11-3 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and
minimum propagation delays are denoted tpd,max and tpd,min respectively.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 11-3. Synchronization when Reading an Externally Applied Pin value
SYSTEM CLK
INSTRUCTIONS
XXX
XXX
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd, max
t pd, min
Consider the clock period starting shortly after the first falling edge of the system clock. The latch
is closed when the clock is low, and goes transparent when the clock is high, as indicated by the
shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed
between ½ and 1½ system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 11-4. The out instruction sets the “SYNC LATCH” signal at the positive edge of
the clock. In this case, the delay tpd through the synchronizer is 1 system clock period.
Figure 11-4. Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
0xFF
out PORTx, r16
nop
in r17, PINx
SYNC LATCH
PINxn
r17
0x00
0xFF
t pd
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The resulting pin
65
4317I–AVR–01/08
values are read back again, but as previously discussed, a nop instruction is included to be able
to read back the value recently assigned to some of the pins.
TABLE 2.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi
r16, (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi
r17, (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out
PORTB, r16
out
DDRB, r17
; Insert nop for synchronization
nop
; Read port pins
in
r16, PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINB;
...
Note:
11.2.5
1. For the assembly program, two temporary registers are used to minimize the time from pullups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3
as low and redefining bits 0 and 1 as strong high drivers.
Digital Input Enable and Sleep Modes
As shown in Figure 11-2, the digital input signal can be clamped to ground at the input of the
schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down mode, Power-save mode, and Standby mode to avoid high power consumption if
some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt
request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various
other alternate functions as described in “Alternate Port Functions” on page 67.
If a logic high level (“one”) is present on an Asynchronous External Interrupt pin configured as
“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from the
above mentioned sleep modes, as the clamping in these sleep modes produces the requested
logic change.
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AT90PWM2/3/2B/3B
11.3
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 11-5
shows how the port pin control signals from the simplified Figure 11-2 can be overridden by
alternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
Figure 11-5. Alternate Port Functions(1)
PUOExn
PUOVxn
1
PUD
0
DDOExn
DDOVxn
1
Q D
DDxn
0
Q CLR
WDx
PVOExn
RESET
RDx
1
1
Pxn
Q
0
D
0
PORTxn
PTOExn
Q CLR
DIEOExn
DATA BUS
PVOVxn
WPx
DIEOVxn
RESET
WRx
1
0
RRx
SLEEP
SYNCHRONIZER
D
SET
Q
RPx
Q
D
PINxn
L
CLR
Q
CLR
Q
clk I/O
DIxn
AIOxn
PUOExn: Pxn PULL-UP OVERRIDE ENABLE
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE
Note:
PUD: PULLUP DISABLE
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clkI/O:
DIxn:
AIOxn:
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.
Table 11-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 11-5 are not shown in the succeeding tables. The overriding signals are generated internally
in the modules having the alternate function.
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4317I–AVR–01/08
Table 11-2.
Generic Description of Overriding Signals for Alternate Functions
Signal Name
Full Name
Description
PUOE
Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, PUD} = 0b010.
PUOV
Pull-up Override
Value
If PUOE is set, the pull-up is enabled/disabled when PUOV is
set/cleared, regardless of the setting of the DDxn, PORTxn,
and PUD Register bits.
DDOE
Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled by the
DDOV signal. If this signal is cleared, the Output driver is
enabled by the DDxn Register bit.
DDOV
Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled when
DDOV is set/cleared, regardless of the setting of the DDxn
Register bit.
PVOE
Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the port
value is controlled by the PVOV signal. If PVOE is cleared, and
the Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.
PVOV
Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless of the
setting of the PORTxn Register bit.
PTOE
Port Toggle
Override Enable
If PTOE is set, the PORTxn Register bit is inverted.
DIEOE
Digital Input
Enable Override
Enable
If this bit is set, the Digital Input Enable is controlled by the
DIEOV signal. If this signal is cleared, the Digital Input Enable
is determined by MCU state (Normal mode, sleep mode).
DIEOV
Digital Input
Enable Override
Value
If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state (Normal
mode, sleep mode).
DI
Digital Input
This is the Digital Input to alternate functions. In the figure, the
signal is connected to the output of the schmitt trigger but
before the synchronizer. Unless the Digital Input is used as a
clock source, the module with the alternate function will use its
own synchronizer.
AIO
Analog
Input/Output
This is the Analog Input/output to/from alternate functions. The
signal is connected directly to the pad, and can be used bidirectionally.
The following subsections shortly describe the alternate functions for each port, and relate the
overriding signals to the alternate function. Refer to the alternate function description for further
details.
11.3.1
MCU Control Register – MCUCR
Bit
7
6
5
4
3
2
1
0
SPIPS
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 4 – PUD: Pull-up Disable
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). Se
11.3.2
Alternate Functions of Port B
The Port B pins with alternate functions are shown in Table 11-3.
Table 11-3.
Port Pin
Port B Pins Alternate Functions
Alternate Functions
PB7
PSCOUT01 output
ADC4 (Analog Input Channel 4)
SCK (SPI Bus Serial Clock)
PB6
ADC7 (Analog Input Channel 7)
ICP1B (Timer 1 input capture alternate input)
PSCOUT11 output (see note 4)
PB5
ADC6 (Analog Input Channel 6)
INT2
PB4
AMP0+ (Analog Differential Amplifier 0 Input Channel )
PB3
AMP0- (Analog Differential Amplifier 0 Input Channel )
PB2
ADC5 (Analog Input Channel5 )
INT1
PB1
MOSI (SPI Master Out Slave In)
PSCOUT21 output
PB0
MISO (SPI Master In Slave Out)
PSCOUT20 output
The alternate pin configuration is as follows:
• PSCOUT01/ADC4/SCK – Bit 7
PSCOUT01: Output 1 of PSC 0.
ADC4, Analog to Digital Converter, input channel 4.
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.
• ADC7/ICP1B/PSCOUT11 – Bit 6
ADC7, Analog to Digital Converter, input channel 7.
ICP1B, Input Capture Pin: The PB6 pin can act as an Input Capture Pin for Timer/Counter1.
PSCOUT11: Output 1 of PSC 1.
• ADC6/INT2 – Bit 5
ADC6, Analog to Digital Converter, input channel 6.
INT2, External Interrupt source 2. This pin can serve as an External Interrupt source to the MCU.
• APM0+ – Bit 4
AMP0+, Analog Differential Amplifier 0 Positive Input Channel.
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4317I–AVR–01/08
• AMP0- – Bit 3
AMP0-, Analog Differential Amplifier 0 Negative Input Channel.
• ADC5/INT1 – Bit 2
ADC5, Analog to Digital Converter, input channel 5.
INT1, External Interrupt source 1. This pin can serve as an external interrupt source to the MCU.
• MOSI/PSCOUT21 – Bit 1
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 DDB1 When the SPI is
enabled as a master, the data direction of this pin is controlled by DDB1. When the pin is forced
to be an input, the pull-up can still be controlled by the PORTB1 and PUD bits.
PSCOUT21: Output 1 of PSC 2.
• MISO/PSC20 – Bit 0
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 DDB0. When the SPI is
enabled as a slave, the data direction of this pin is controlled by DDB0. When the pin is forced to
be an input, the pull-up can still be controlled by the PORTB0 and PUD bits.
PSCOUT20: Output 0 of PSC 2.
Table 11-4 and Table 11-5 relates the alternate functions of Port B to the overriding signals
shown in Figure 11-5 on page 67.
Table 11-4.
70
Overriding Signals for Alternate Functions in PB7..PB4
Signal Name
PB7/ADC4/
PSCOUT01/SCK
PB6/ADC7/
PSCOUT11/
ICP1B
PUOE
SPE • MSTR • SPIPS
0
0
0
PUOV
PB7 • PUD • SPIPS
0
0
0
DDOE
SPE • MSTR • SPIPS
+ PSCen01
PSCen11
0
0
DDOV
PSCen01
1
0
0
PVOE
SPE • MSTR • SPIPS
PSCen11
0
0
PVOV
PSCout01 • SPIPS +
PSCout01 •
PSCen01 • SPIPS
+ PSCout01 •
PSCen01 • SPIPS
PSCOUT11
0
0
DIEOE
ADC4D
ADC7D
ADC6D + In2en
AMP0ND
DIEOV
0
0
In2en
0
DI
SCKin • SPIPS •
ireset
ICP1B
INT2
AIO
ADC4
ADC7
ADC6
PB5/ADC6/
INT2
PB4/AMP0+
AMP0+
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 11-5.
Overriding Signals for Alternate Functions in PB3..PB0
Signal Name
PB3/AMP0-
PB2/ADC5/INT1
PB1/MOSI/
PSCOUT21
PB0/MISO/
PSCOUT20
PUOE
0
0
–
–
PUOV
0
0
–
–
DDOE
0
0
–
–
DDOV
0
0
–
–
PVOE
0
0
–
–
PVOV
0
0
–
–
DIEOE
AMP0ND
ADC5D + In1en
0
0
DIEOV
0
In1en
0
0
INT1
MOSI_IN • SPIPS
• ireset
MISO_IN • SPIPS
• ireset
ADC5
–
–
DI
AIO
11.3.3
AMP0-
Alternate Functions of Port C
The Port C pins with alternate functions are shown in Table 11-6.
Table 11-6.
Port C Pins Alternate Functions
Port Pin
Alternate Function
PC7
D2A : DAC output
PC6
ADC10 (Analog Input Channel 10)
ACMP1 (Analog Comparator 1 Positive Input )
PC5
ADC9 (Analog Input Channel 9)
AMP1+ (Analog Differential Amplifier 1 Input Channel )
PC4
ADC8 (Analog Input Channel 8)
AMP1- (Analog Differential Amplifier 1 Input Channel )
PC3
T1 (Timer 1 clock input)
PSCOUT23 output
PC2
T0 (Timer 0 clock input)
PSCOUT22 output
PC1
PSCIN1 (PSC 1 Digital Input)
OC1B (Timer 1 Output Compare B)
PC0
PSCOUT10 output (see note 4)
INT3
The alternate pin configuration is as follows:
• D2A – Bit 7
D2A, Digital to Analog output
• ADC10/ACMP1 – Bit 6
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4317I–AVR–01/08
ADC10, Analog to Digital Converter, input channel 10.
ACMP1, Analog Comparator 1 Positive Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
• ADC9/AMP1+ – Bit 5
ADC9, Analog to Digital Converter, input channel 9.
AMP1+, Analog Differential Amplifier 1 Positive Input Channel.
• ADC8/AMP1- – Bit 4
ADC8, Analog to Digital Converter, input channel 8.
AMP1-, Analog Differential Amplifier 1 Negative Input Channel.
• T1/PSCOUT23 – Bit 3
T1, Timer/Counter1 counter source.
PSCOUT23: Output 3 of PSC 2.
• T0/PSCOUT22 – Bit 2
T0, Timer/Counter0 counter source.
PSCOUT22: Output 2 of PSC 2.
• PSCIN1/OC1B, Bit 1
PCSIN1, PSC 1 Digital Input.
OC1B, Output Compare Match B output: This pin can serve as an external output for the
Timer/Counter1 Output Compare B. The pin has to be configured as an output (DDC1 set “one”)
to serve this function. This pin is also the output pin for the PWM mode timer function.
• PSCOUT10/INT3 – Bit 0
PSCOUT10: Output 0 of PSC 1.
INT3, External Interrupt source 3: This pin can serve as an external interrupt source to the MCU.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 11-7 and Table 11-8 relate the alternate functions of Port C to the overriding signals
shown in Figure 11-5 on page 67.
Table 11-7.
Overriding Signals for Alternate Functions in PC7..PC4
Signal Name
PC7/D2A
PC6/ADC10/
ACMP1
PC5/ADC9/
AMP1+
PC4/ADC8/
AMP1-
PUOE
0
0
0
PUOV
0
0
0
DDOE
DAEN
0
0
0
DDOV
0
0
0
0
PVOE
0
0
0
–
PVOV
0
0
0
–
DIEOE
DAEN
ADC10D
ADC9D
ADC8D
DIEOV
0
0
0
0
–
ADC10 Amp1
ADC9 Amp1+
ADC8 Amp1-
DI
AIO
Table 11-8.
Overriding Signals for Alternate Functions in PC3..PC0
Signal Name
PC3/T1/
PSCOUT23
PC2/T0/
PSCOUT22
PC1/PSCIN1/
OC1B
PC0/INT3/
PSCOUT10
PUOE
0
0
0
0
PUOV
0
0
0
0
DDOE
PSCen23
PSCen22
0
PSCen10
DDOV
1
1
0
1
PVOE
PSCen23
PSCen22
OC1Ben
PSCen10
PVOV
PSCout23
PSCout22
OC1B
PSCout10
DIEOE
In3en
DIEOV
In3en
DI
T1
T0
PSCin1
INT3
AIO
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4317I–AVR–01/08
11.3.4
Alternate Functions of Port D
The Port D pins with alternate functions are shown in Table 11-9.
Table 11-9.
Port Pin
Port D Pins Alternate Functions
Alternate Function
PD7
ACMP0 (Analog Comparator 0 Positive Input )
PD6
ADC3 (Analog Input Channel 3 )
ACMPM reference for analog comparators
INT0
PD5
ADC2 (Analog Input Channel 2)
ACMP2 (Analog Comparator 2 Positive Input )
PD4
ADC1 (Analog Input Channel 1)
RXD (Dali/UART Rx data)
ICP1 (Timer 1 input capture)
SCK_A (Programming & alternate SPI Clock)
PD3
TXD (Dali/UART Tx data)
OC0A (Timer 0 Output Compare A)
SS (SPI Slave Select)
MOSI_A (Programming & alternate SPI Master Out Slave In)
PD2
PSCIN2 (PSC 2 Digital Input)
OC1A (Timer 1 Output Compare A)
MISO_A (Programming & alternate Master In SPI Slave Out)
PD1
PSCIN0 (PSC 0 Digital Input )
CLKO (System Clock Output)
PD0
PSCOUT00 output
XCK (UART Transfer Clock)
SS_A (Alternate SPI Slave Select)
The alternate pin configuration is as follows:
• ACMP0 – Bit 7
ACMP0, Analog Comparator 0 Positive Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
• ADC3/ACMPM/INT0 – Bit 6
ADC3, Analog to Digital Converter, input channel 3.
ACMPM, Analog Comparators Negative Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
INT0, External Interrupt source 0. This pin can serve as an external interrupt source to the MCU.
• ADC2/ACMP2 – Bit 5
ADC2, Analog to Digital Converter, input channel 2.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
ACMP2, Analog Comparator 1 Positive Input. Configure the port pin as input with the internal
pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
• ADC1/RXD/ICP1/SCK_A – Bit 4
ADC1, Analog to Digital Converter, input channel 1.
RXD, USART Receive Pin. Receive Data (Data input pin for the USART). When the USART
receiver is enabled this pin is configured as an input regardless of the value of DDRD4. When
the USART forces this pin to be an input, a logical one in PORTD4 will turn on the internal pullup.
ICP1 – Input Capture Pin1: This pin can act as an input capture pin for Timer/Counter1.
SCK_A: 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 DDD4. When the SPI is
enabled as a master, the data direction of this pin is controlled by DDD4. When the pin is forced
to be an input, the pull-up can still be controlled by the PORTD4 bit.
• TXD/OC0A/SS/MOSI_A, Bit 3
TXD, UART Transmit pin. Data output pin for the USART. When the USART Transmitter is
enabled, this pin is configured as an output regardless of the value of DDD3.
OC0A, Output Compare Match A output: This pin can serve as an external output for the
Timer/Counter0 Output Compare A. The pin has to be configured as an output (DDD3 set “one”)
to serve this function. The OC0A pin is also the output pin for the PWM mode
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 DDD3. 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 DDD3.
When the pin is forced to be an input, the pull-up can still be controlled by the PORTD3 bit.
MOSI_A: 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 DDD3 When the SPI is
enabled as a master, the data direction of this pin is controlled by DDD3. When the pin is forced
to be an input, the pull-up can still be controlled by the PORTD3 bit.
• PSCIN2/OC1A/MISO_A, Bit 2
PCSIN2, PSC 2 Digital Input.
OC1A, Output Compare Match A output: This pin can serve as an external output for the
Timer/Counter1 Output Compare A. The pin has to be configured as an output (DDD2 set “one”)
to serve this function. The OC1A pin is also the output pin for the PWM mode timer function.
MISO_A: 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 DDD2. When the SPI is
enabled as a slave, the data direction of this pin is controlled by DDD2. When the pin is forced to
be an input, the pull-up can still be controlled by the PORTD2 bit.
• PSCIN0/CLKO – Bit 1
PCSIN0, PSC 0 Digital Input.
CLKO, Divided System Clock: The divided system clock can be output on this pin. The divided
system clock will be output if the CKOUT Fuse is programmed, regardless of the PORTD1 and
DDD1 settings. It will also be output during reset.
• PSCOUT00/XCK/SS_A – Bit 0
PSCOUT00: Output 0 of PSC 0.
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XCK, USART External clock. The Data Direction Register (DDD0) controls whether the clock is
output (DDD0 set) or input (DDD0 cleared). The XCK0 pin is active only when the USART operates in Synchronous mode.
SS_A: Slave Port Select input. When the SPI is enabled as a slave, this pin is configured as an
input regardless of the setting of DDD0. 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 DDD0.
When the pin is forced to be an input, the pull-up can still be controlled by the PORTD0 bit.
Table 11-10 and Table 11-11 relates the alternate functions of Port D to the overriding signals
shown in Figure 11-5 on page 67.
Table 11-10. Overriding Signals for Alternate Functions PD7..PD4
76
Signal Name
PD7/
ACMP0
PD6/ADC3/
ACMPM/INT0
PD5/ADC2/
ACMP2
PD4/ADC1/RXD/
ICP1A/SCK_A
PUOE
0
0
0
RXEN + SPE •
MSTR • SPIPS
PUOV
0
0
0
PD4 •
PUD
DDOE
0
0
0
RXEN + SPE •
MSTR • SPIPS
DDOV
0
0
0
0
PVOE
0
0
0
SPE • MSTR •
SPIPS
PVOV
0
0
0
–
DIEOE
ACMP0D
ADC3D + In0en
ADC2D
ADC1D
DIEOV
0
In0en
0
0
DI
–
INT0
AIO
ACOMP0
ADC3
ACMPM
ICP1A
ADC2
ACOMP2
ADC1
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 11-11. Overriding Signals for Alternate Functions in PD3..PD0
PD3/TXD/OC0A/
SS/MOSI_A
PD2/PSCIN2/
OC1A/MISO_A
PD1/PSCIN0/
CLKO
PD0/PSCOUT00/X
CK/SS_A
PUOE
TXEN + SPE •
MSTR • SPIPS
–
0
SPE •
MSTR • SPIPS
PUOV
TXEN • SPE • MSTR
• SPIPS • PD3 • PUD
–
0
PD0 • PUD
DDOE
TXEN + SPE •
MSTR • SPIPS
–
0
PSCen00 + SPE •
MSTR • SPIPS
DDOV
TXEN
0
0
PSCen00
PVOE
TXEN + OC0en +
SPE •
MSTR • SPIPS
–
0
PSCen00 + UMSEL
PVOV
TXEN • TXD + TXEN
• (OC0en • OC0 +
OC0en • SPIPS •
MOSI)
–
0
–
DIEOE
0
0
0
0
DIEOV
0
0
0
0
DI
SS
MOSI_Ain
Signal Name
SS_A
AIO
11.3.5
Alternate Functions of Port E
The Port E pins with alternate functions are shown in Table 11-12.
Table 11-12. Port E Pins Alternate Functions
Port Pin
Alternate Function
PE2
XTAL2: XTAL Output
ADC0 (Analog Input Channel 0)
PE1
XTAL1: XTAL Input
OC0B (Timer 0 Output Compare B)
PE0
RESET# (Reset Input)
OCD (On Chip Debug I/O)
The alternate pin configuration is as follows:
• XTAL2/ADC0 – Bit 2
XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency
crystal Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
ADC0, Analog to Digital Converter, input channel 0.
• XTAL1/OC0B – Bit 1
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4317I–AVR–01/08
XTAL1: Chip clock Oscillator pin 1. Used for all chip clock sources except internal calibrated RC
Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.
OC0B, Output Compare Match B output: This pin can serve as an external output for the
Timer/Counter0 Output Compare B. The pin has to be configured as an output (DDE1 set “one”)
to serve this function. This pin is also the output pin for the PWM mode timer function.
• RESET/OCD – Bit 0
RESET, Reset pin: When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O
pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources.
When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the
pin can not be used as an I/O pin.
If PE0 is used as a reset pin, DDE0, PORTE0 and PINE0 will all read 0.
Table 11-13 relates the alternate functions of Port E to the overriding signals shown in Figure
11-5 on page 67.
Table 11-13. Overriding Signals for Alternate Functions in PE2..PE0
Signal Name
PE2/ADC0/
XTAL2
PE1/OC0B
PE0/RESET/
OCD
PUOE
0
0
0
PUOV
0
0
0
DDOE
0
0
0
DDOV
0
0
0
PVOE
0
OC0Ben
0
PVOV
0
OC0B
0
DIEOE
ADC0D
0
0
DIEOV
0
0
0
Osc Output
ADC0
Osc / Clock input
DI
AIO
11.4
11.4.1
Register Description for I/O-Ports
Port B Data Register – PORTB
Bit
11.4.2
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
Port B Data Direction Register – DDRB
Bit
Read/Write
78
PORTB
7
6
5
4
3
2
1
0
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
DDRB
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Initial Value
11.4.3
0
5
4
3
2
1
0
PINB4
PINB3
PINB2
PINB1
PINB0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PINB
Port C Data Register – PORTC
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
PORTC
Port C Data Direction Register – DDRC
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
DDRC
Port C Input Pins Address – PINC
7
6
5
4
3
2
1
0
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PINC
Port D Data Register – PORTD
7
6
5
4
3
2
1
0
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PORTD
Port D Data Direction Register – DDRD
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
DDRD
Port D Input Pins Address – PIND
Bit
11.4.10
0
PINB5
Bit
11.4.9
0
6
Bit
11.4.8
0
PINB6
Bit
11.4.7
0
7
Bit
11.4.6
0
PINB7
Bit
11.4.5
0
Port B Input Pins Address – PINB
Bit
11.4.4
0
7
6
5
4
3
2
1
0
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
7
6
5
4
3
2
1
0
–
–
–
–
–
PORTE2
PORTE1
PORTE0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
PIND
Port E Data Register – PORTE
Bit
PORTE
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11.4.11
Port E Data Direction Register – DDRE
Bit
11.4.12
7
6
5
4
3
2
1
0
–
–
–
–
–
DDE2
DDE1
DDE0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
7
6
5
4
3
2
1
0
–
–
–
–
–
PINE2
PINE1
PINE0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
N/A
N/A
N/A
Port E Input Pins Address – PINE
Bit
80
DDRE
PINE
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
12. External Interrupts
The External Interrupts are triggered by the INT3:0 pins. Observe that, if enabled, the interrupts
will trigger even if the INT3:0 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. This is set up as indicated in the specification for the External Interrupt Control Registers – EICRA (INT3:0). When the external interrupt is enabled and is configured as level
triggered, the interrupt will trigger as long as the pin is held low. Note that recognition of falling or
rising edge interrupts on INT3:0 requires the presence of an I/O clock, described in “Clock Systems and their Distribution” on page 29. The I/O clock is halted in all sleep modes except Idle
mode.
Note that if a level triggered interrupt is used for wake-up from Power-down 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. 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(1)” on page 299. The MCU
will wake up if the input has the required level during this sampling or if it is held until the end of
the start-up time. The start-up time is defined by the SUT fuses as described in “System Clock”
on page 29. If the level is sampled twice by the Watchdog Oscillator clock but disappears before
the end of the start-up time, the MCU will still wake up, but no interrupt will be generated. The
required level must be held long enough for the MCU to complete the wake up to trigger the level
interrupt.
12.0.1
External Interrupt Control Register A – EICRA
Bit
7
6
5
4
3
2
1
0
ISC31
ISC30
ISC21
ISC20
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
EICRA
• Bits 7..0 – ISC31, ISC30 – ISC01, ISC00: External Interrupt 3 - 0 Sense Control Bits
The External Interrupts 3 - 0 are activated by the external pins INT3:0 if the SREG I-flag and the
corresponding interrupt mask in the EIMSK is set. The level and edges on the external pins that
activate the interrupts are defined in Table 12-1. Edges on INT3..INT0 are registered asynchronously.The value on the INT3:0 pins are 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. Observe that CPU clock frequency
can be lower than the XTAL frequency if the XTAL divider is enabled. If low level interrupt is
selected, the low level must be held until the completion of the currently executing instruction to
generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt request as
long as the pin is held low.
Interrupt Sense Control(1)
Table 12-1.
ISCn1
ISCn0
Description
0
0
The low level of INTn generates an interrupt request.
0
1
Any logical change on INTn generates an interrupt request
1
0
The falling edge between two samples of INTn generates an interrupt request.
1
1
The rising edge between two samples of INTn generates an interrupt request.
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Note:
12.0.2
1. n = 3, 2, 1 or 0.
When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt
Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.
External Interrupt Mask Register – EIMSK
Bit
7
6
5
4
3
2
1
0
-
-
-
-
INT3
INT2
INT1
IINT0
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
EIMSK
• Bits 3..0 – INT3 – INT0: External Interrupt Request 3 - 0 Enable
When an INT3 – INT0 bit is written to one and the I-bit in the Status Register (SREG) is set
(one), the corresponding external pin interrupt is enabled. The Interrupt Sense Control bits in the
External Interrupt Control Register – EICRA – defines whether the external interrupt is activated
on rising or falling edge or level sensed. Activity on any of these pins will trigger an interrupt
request even if the pin is enabled as an output. This provides a way of generating a software
interrupt.
12.0.3
External Interrupt Flag Register – EIFR
Bit
7
6
5
4
3
2
1
0
-
-
-
-
INTF3
INTF2
INTF1
IINTF0
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
EIFR
• Bits 3..0 – INTF3 - INTF0: External Interrupt Flags 3 - 0
When an edge or logic change on the INT3:0 pin triggers an interrupt request, INTF3:0 becomes
set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT3:0 in EIMSK, are
set (one), the MCU will jump to the 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. These flags are
always cleared when INT3:0 are configured as level interrupt.
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13. Timer/Counter0 and Timer/Counter1 Prescalers
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the Timer/Counters
can have different prescaler settings. The description below applies to both Timer/Counter1 and
Timer/Counter0.
13.0.1
Internal Clock Source
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024.
13.0.2
Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. Since the prescaler is
not affected by the Timer/Counter’s clock select, the state of the prescaler will have implications
for situations where a prescaled clock is used. One example of prescaling artifacts occurs when
the timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The number of system clock
cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system
clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution. However, care must be taken if the other Timer/Counter that shares the same prescaler
also uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is
connected to.
13.0.3
External Clock Source
An external clock source applied to the Tn/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0). The Tn/T0 pin is sampled once every system clock cycle by the pin synchronization
logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 13-1
shows a functional equivalent block diagram of the Tn/T0 synchronization and edge detector
logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch
is transparent in the high period of the internal system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative
(CSn2:0 = 6) edge it detects.
Figure 13-1. Tn/T0 Pin Sampling
Tn
D
Q
D
Q
D
Tn_sync
(To Clock
Select Logic)
Q
LE
clk I/O
Synchronization
Edge Detector
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the Tn/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn/T0 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
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Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is
recommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 13-2. Prescaler for Timer/Counter0 and Timer/Counter1(1)
clk I/O
Clear
PSRSYNC
T0
Synchronization
T1
Synchronization
clkT1
Note:
13.0.4
clkT0
1. The synchronization logic on the input pins (Tn/T0) is shown in Figure 13-1.
General Timer/Counter Control Register – GTCCR
Bit
7
6
5
4
3
2
1
0
TSM
ICPSEL1
–
–
–
–
–
PSRSYNC
Read/Write
R/W
R/W
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
GTCCR
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the
value that is written to the PSRSYNC bit is kept, hence keeping the corresponding prescaler
reset signals asserted. This ensures that the corresponding Timer/Counters are halted and can
be configured to the same value without the risk of one of them advancing during configuration.
When the TSM bit is written to zero, the PSRSYNC bit is cleared by hardware, and the
Timer/Counters start counting simultaneously.
• Bit6 – ICPSEL1: Timer 1 Input Capture selection
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AT90PWM2/3/2B/3B
Timer 1 capture function has two possible inputs ICP1A (PD4) and ICP1B (PB6). The selection
is made thanks to ICPSEL1 bit as described in Table .
Table 13-1.
ICPSEL1
ICPSEL1
Description
0
Select ICP1A as trigger for timer 1 input capture
1
Select ICP1B as trigger for timer 1 input capture
• Bit 0 – PSRSYNC: Prescaler Reset
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This bit is normally cleared immediately by hardware, except if the TSM bit is set. Note that Timer/Counter1
and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both
timers.
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14. 8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and with PWM support. It allows accurate program execution timing (event management) and wave generation. The main features are:
•
•
•
•
•
•
•
14.1
Two Independent Output Compare Units
Double Buffered Output Compare Registers
Clear Timer on Compare Match (Auto Reload)
Glitch Free, Phase Correct Pulse Width Modulator (PWM)
Variable PWM Period
Frequency Generator
Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. For the actual
placement of I/O pins, refer to “Pin Descriptions” on page 9. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “8-bit Timer/Counter Register Description” on page 96.
The PRTIM0 bit in “Power Reduction Register” on page 43 must be written to zero to enable
Timer/Counter0 module.
Figure 14-1. 8-bit Timer/Counter Block Diagram
count
TOVn
(Int.Req.)
clear
Control Logic
direction
clk Tn
Clock Select
Edge
Detector
DATA BUS
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCRnx
OCnB
(Int.Req.)
Fixed
TOP
Values
=
OCnA
Waveform
Generation
OCnB
OCRnx
TCCRnA
14.1.1
TCCRnB
Definitions
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Compare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
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The definitions in Table 14-1 are also used extensively throughout the document.
Table 14-1. Definitions
14.1.2
BOTTOM
The counter reaches the BOTTOM when it becomes 0x00.
MAX
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be the fixed value 0xFF
(MAX) or the value stored in the OCR0A Register. The assignment is dependent on the mode of operation.
Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the
Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkT0).
The double buffered Output Compare Registers (OCR0A and OCR0B) are compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and
OC0B). See “Using the Output Compare Unit” on page 113. for details. The compare match
event will also set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compare interrupt request.
14.2
Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 83.
14.3
Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
14-2 shows a block diagram of the counter and its surroundings.
Figure 14-2. Counter Unit Block Diagram
TOVn
(Int.Req.)
DATA BUS
Clock Select
count
TCNTn
clear
Control Logic
clkTn
Edge
Detector
Tn
direction
( From Prescaler )
bottom
top
Signal description (internal signals):
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4317I–AVR–01/08
count
Increment or decrement TCNT0 by 1.
direction
Select between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clkTn
Timer/Counter clock, referred to as clkT0 in the following.
top
Signalize that TCNT0 has reached maximum value.
bottom
Signalize that TCNT0 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT0). clkT0 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the
timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of
whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in
the Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter
Control Register B (TCCR0B). There are close connections between how the counter behaves
(counts) and how waveforms are generated on the Output Compare outputs OC0A and OC0B.
For more details about advanced counting sequences and waveform generation, see “Modes of
Operation” on page 91.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by
the WGM02:0 bits. TOV0 can be used for generating a CPU interrupt.
14.4
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers
(OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a
match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock
cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output
Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit
location. The Waveform Generator uses the match signal to generate an output according to
operating mode set by the WGM02:0 bits and Compare Output mode (COM0x1:0) bits. The max
and bottom signals are used by the Waveform Generator for handling the special cases of the
extreme values in some modes of operation (“Modes of Operation” on page 91).
Figure 14-3 shows a block diagram of the Output Compare unit.
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Figure 14-3. Output Compare Unit, Block Diagram
DATA BUS
OCRnx
TCNTn
= (8-bit Comparator )
OCFnx (Int.Req.)
top
bottom
Waveform Generator
OCnx
FOCn
WGMn1:0
COMnx1:0
The OCR0x Registers are double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR0x Compare
Registers to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR0x Buffer Register, and if double buffering is disabled the CPU will access the OCR0x directly.
14.4.1
Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOC0x) bit. Forcing compare match will not set the
OCF0x Flag or reload/clear the timer, but the OC0x pin will be updated as if a real compare
match had occurred (the COM0x1:0 bits settings define whether the OC0x pin is set, cleared or
toggled).
14.4.2
Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any compare match that occur in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.
14.4.3
Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT0 when using the Output Compare Unit,
independently of whether the Timer/Counter is running or not. If the value written to TCNT0
equals the OCR0x value, the compare match will be missed, resulting in incorrect waveform
generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is
downcounting.
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The setup of the OC0x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0x value is to use the Force Output Compare (FOC0x) strobe bits in Normal mode. The OC0x Registers keep their values even when
changing between Waveform Generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value.
Changing the COM0x1:0 bits will take effect immediately.
14.5
Compare Match Output Unit
The Compare Output mode (COM0x1:0) bits have two functions. The Waveform Generator uses
the COM0x1:0 bits for defining the Output Compare (OC0x) state at the next compare match.
Also, the COM0x1:0 bits control the OC0x pin output source. Figure 14-4 shows a simplified
schematic of the logic affected by the COM0x1:0 bit setting. The I/O Registers, I/O bits, and I/O
pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR
and PORT) that are affected by the COM0x1:0 bits are shown. When referring to the OC0x
state, the reference is for the internal OC0x Register, not the OC0x pin. If a system reset occur,
the OC0x Register is reset to “0”.
Figure 14-4. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCn
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform
Generator if either of the COM0x1:0 bits are set. However, the OC0x pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0x state before the output is enabled. Note that some COM0x1:0 bit settings are reserved for certain modes of
operation. See “8-bit Timer/Counter Register Description” on page 96.
14.5.1
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0x1:0 bits differently in Normal, CTC, and PWM modes.
For all modes, setting the COM0x1:0 = 0 tells the Waveform Generator that no action on the
OC0x Register is to be performed on the next compare match. For compare output actions in the
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non-PWM modes refer to Table 14-2 on page 97. For fast PWM mode, refer to Table 14-3 on
page 97, and for phase correct PWM refer to Table 14-4 on page 97.
A change of the COM0x1:0 bits state will have effect at the first compare match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC0x strobe bits.
14.6
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGM02:0) and Compare Output
mode (COM0x1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM0x1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM0x1:0 bits control whether the output should be set, cleared, or toggled at a compare
match (See “Compare Match Output Unit” on page 90.).
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 95.
14.6.1
Normal Mode
The simplest mode of operation is the Normal mode (WGM02:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the same
timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV0 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using the Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
14.6.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used to
manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter
value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter, hence
also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 14-5. The counter value (TCNT0)
increases until a compare match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
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Figure 14-5. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set
TCNTn
OCn
(Toggle)
Period
(COMnx1:0 = 1)
1
2
3
4
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the compare match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the compare match can
occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction for
the pin is set to output. The waveform generated will have a maximum frequency of f OC0 =
fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following
equation:
f clk_I/O
f OCnx = -------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnx )
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
14.6.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM option by
its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the compare match
between TCNT0 and OCR0x, and set at BOTTOM. In inverting Compare Output mode, the output is set on compare match and cleared at BOTTOM. Due to the single-slope operation, the
operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 14-6. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
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inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare
matches between OCR0x and TCNT0.
Figure 14-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
TCNTn
OCn
(COMnx1:0 = 2)
OCn
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins.
Setting the COM0x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM0x1:0 to three: Setting the COM0A1:0 bits to one allows
the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not available
for the OC0B pin (see Table 14-6 on page 98). The actual OC0x value will only be visible on the
port pin if the data direction for the port pin is set as output. The PWM waveform is generated by
setting (or clearing) the OC0x Register at the compare match between OCR0x and TCNT0, and
clearing (or setting) the OC0x Register at the timer clock cycle the counter is cleared (changes
from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = -----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will result
in a constantly high or low output (depending on the polarity of the output set by the COM0A1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical level on each compare match (COM0x1:0 = 1). The waveform
generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is set to zero. This
feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
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14.6.4
Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dual-slope
operation. The counter counts repeatedly from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the compare match
between TCNT0 and OCR0x while upcounting, and set on the compare match while downcounting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation has
lower maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP.
When the counter reaches TOP, it changes the count direction. The TCNT0 value will be equal
to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown
on Figure 14-7. The TCNT0 value is in the timing diagram shown as a histogram for illustrating
the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The
small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0x
and TCNT0.
Figure 14-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC0x pins. Setting the COM0x1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0x1:0 to three: Setting the COM0A0 bits to
one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is
not available for the OC0B pin (see Table 14-7 on page 98). The actual OC0x value will only be
visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is
generated by clearing (or setting) the OC0x Register at the compare match between OCR0x and
TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at compare
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match between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the
output when using phase correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = -----------------N ⋅ 510
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 14-7 OCnx has a transition from high to low even though
there is no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a transition without Compare Match.
14.7
•
OCRnx changes its value from MAX, like in Figure 14-7. When the OCR0A value is MAX the
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCnx value at MAX must correspond to the result of an upcounting Compare Match.
•
The timer starts counting from a value higher than the one in OCRnx, and for that reason
misses the Compare Match and hence the OCnx change that would have happened on the
way up.
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable signal in the following figures. The figures include information on when interrupt
flags are set. Figure 14-8 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 14-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
MAX - 1
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 14-9 shows the same timing data, but with the prescaler enabled.
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Figure 14-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
MAX - 1
TCNTn
MAX
BOTTOM
BOTTOM + 1
TOVn
Figure 14-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC
mode and PWM mode, where OCR0A is TOP.
Figure 14-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 14-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast
PWM mode where OCR0A is TOP.
Figure 14-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
(CTC)
TOP - 1
TOP
OCRnx
BOTTOM
BOTTOM + 1
TOP
OCFnx
14.8
8-bit Timer/Counter Register Description
14.8.1
Timer/Counter Control Register A – TCCR0A
Bit
96
7
6
5
4
3
2
1
0
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0A
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• Bits 7:6 – COM0A1:0: Compare Match Output A Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A1:0
bits are set, the OC0A output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0A pin
must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM02:0 bit setting. Table 14-2 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 14-2.
Compare Output Mode, non-PWM Mode
COM0A1
COM0A0
Description
0
0
Normal port operation, OC0A disconnected.
0
1
Toggle OC0A on Compare Match
1
0
Clear OC0A on Compare Match
1
1
Set OC0A on Compare Match
Table 14-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Table 14-3.
Compare Output Mode, Fast PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match, set OC0A at TOP
1
Note:
Description
1
Set OC0A on Compare Match, clear OC0A at TOP
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 92
for more details.
Table 14-4 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 14-4.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1
COM0A0
0
0
Normal port operation, OC0A disconnected.
0
1
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
1
0
Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.
1
Note:
Description
Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 118 for more details.
1
• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
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These bits control the Output Compare pin (OC0B) behavior. If one or both of the COM0B1:0
bits are set, the OC0B output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0B pin
must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the
WGM02:0 bit setting. Table 14-5 shows the COM0B1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 14-5.
Compare Output Mode, non-PWM Mode
COM0B1
COM0B0
Description
0
0
Normal port operation, OC0B disconnected.
0
1
Toggle OC0B on Compare Match
1
0
Clear OC0B on Compare Match
1
1
Set OC0B on Compare Match
Table 14-6 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM
mode.
Table 14-6.
Compare Output Mode, Fast PWM Mode(1)
COM0B1
COM0B0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match, set OC0B at TOP
1
Note:
Description
1
Set OC0B on Compare Match, clear OC0B at TOP
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 92
for more details.
Table 14-7 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 14-7.
Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1
COM0B0
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.
1
Note:
Description
Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 93 for more details.
1
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
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Combined with the WGM02 bit found in the TCCR0B Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 14-8. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode, and two types of
Pulse Width Modulation (PWM) modes (see “Modes of Operation” on page 91).
Table 14-8.
Timer/Count
er Mode of
Operation
TOP
Update of
OCRx at
TOV Flag
Set on(1)(2)
Mode
WGM02
WGM01
WGM00
0
0
0
0
Normal
0xFF
Immediate
MAX
1
0
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
2
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
TOP
MAX
4
1
0
0
Reserved
–
–
–
5
1
0
1
PWM, Phase
Correct
OCRA
TOP
BOTTOM
6
1
1
0
Reserved
–
–
–
7
1
1
1
Fast PWM
OCRA
TOP
TOP
Notes:
14.8.2
Waveform Generation Mode Bit Description
1. MAX
= 0xFF
2. BOTTOM = 0x00
Timer/Counter Control Register B – TCCR0B
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
Read/Write
W
W
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR0B
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0A bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0A output is
changed according to its COM0A1:0 bits setting. Note that the FOC0A bit is implemented as a
strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the
forced compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0B bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0B output is
changed according to its COM0B1:0 bits setting. Note that the FOC0B bit is implemented as a
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strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the
forced compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR0A” on page 96.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 14-9.
Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
No clock source (Timer/Counter stopped)
0
0
1
clkI/O/(No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on T0 pin. Clock on falling edge.
1
1
1
External clock source on T0 pin. Clock on rising edge.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
14.8.3
Timer/Counter Register – TCNT0
Bit
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers.
14.8.4
Output Compare Register A – OCR0A
Bit
7
6
5
4
3
2
1
0
OCR0A[7:0]
OCR0A
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0A pin.
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14.8.5
Output Compare Register B – OCR0B
Bit
7
6
5
4
3
2
1
0
OCR0B[7:0]
OCR0B
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Register B contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0B pin.
14.8.6
Timer/Counter Interrupt Mask Register – TIMSK0
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
OCIE0B
OCIE0A
TOIE0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter Compare Match B interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter
Interrupt Flag Register – TIFR0.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the
Timer/Counter 0 Interrupt Flag Register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter 0 Interrupt Flag Register – TIFR0.
14.8.7
Timer/Counter 0 Interrupt Flag Register – TIFR0
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
OCF0B
OCF0A
TOV0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bit 2 – OCF0B: Timer/Counter 0 Output Compare B Match Flag
The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in
OCR0B – Output Compare Register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable),
and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed.
• Bit 1 – OCF0A: Timer/Counter 0 Output Compare A Match Flag
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The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable),
and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by
writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt
Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed.
The setting of this flag is dependent of the WGM02:0 bit setting. Refer to Table 14-8, “Waveform
Generation Mode Bit Description” on page 99.
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15. 16-bit Timer/Counter1 with PWM
The 16-bit Timer/Counter unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement. The main features are:
• True 16-bit Design (i.e., Allows 16-bit PWM)
• Two independent Output Compare Units
• Double Buffered Output Compare Registers
• One Input Capture Unit
• Input Capture Noise Canceler
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• External Event Counter
• Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1)
15.1
Overview
Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit
channel. However, when using the register or bit defines in a program, the precise form must be
used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 15-1. For the actual
placement of I/O pins, refer to “Pin Descriptions” on page 5. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “16-bit Timer/Counter Register Description” on page 123.
The PRTIM1 bit in “Power Reduction Register” on page 43 must be written to zero to enable
Timer/Counter1 module.
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Figure 15-1. 16-bit Timer/Counter Block Diagram(1)
Count
Clear
Direction
TOVn
(Int.Req.)
Control Logic
clkTn
Clock Select
Edge
Detector
TOP
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=0
OCnA
(Int.Req.)
Waveform
Generation
=
OCnA
OCRnA
OCnB
(Int.Req.)
DATA BUS
Fixed
TOP
Values
Waveform
Generation
=
OCRnB
ICPSEL1
ICFn (Int.Req.)
Edge
Detector
ICRn
TCCRnA
Note:
15.1.1
OCnB
Noise
Canceler
0
1
ICPnA
ICPnB
TCCRnB
1. Refer toTable on page 5 for Timer/Counter1 pin placement and description.
Registers
The Timer/Counter (TCNTn), Output Compare Registers (OCRnx), and Input Capture Register
(ICRn) are all 16-bit registers. Special procedures must be followed when accessing the 16-bit
registers. These procedures are described in the section “Accessing 16-bit Registers” on page
105. The Timer/Counter Control Registers (TCCRnx) are 8-bit registers and have no CPU
access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all visible
in the Timer Interrupt Flag Register (TIFRn). All interrupts are individually masked with the Timer
Interrupt Mask Register (TIMSKn). TIFRn and TIMSKn are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the Tn pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkTn).
The double buffered Output Compare Registers (OCRnx) are compared with the Timer/Counter
value at all time. The result of the compare can be used by the Waveform Generator to generate
a PWM or variable frequency output on the Output Compare pin (OCnx). See “Output Compare
Units” on page 111. The compare match event will also set the Compare Match Flag (OCFnx)
which can be used to generate an Output Compare interrupt request.
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The Input Capture Register can capture the Timer/Counter value at a given external (edge triggered) event on either the Input Capture pin (ICPn). The Input Capture unit includes a digital
filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined
by either the OCRnA Register, the ICRn Register, or by a set of fixed values. When using
OCRnA as TOP value in a PWM mode, the OCRnA Register can not be used for generating a
PWM output. However, the TOP value will in this case be double buffered allowing the TOP
value to be changed in run time. If a fixed TOP value is required, the ICRn Register can be used
as an alternative, freeing the OCRnA to be used as PWM output.
15.1.2
Definitions
The following definitions are used extensively throughout the section:
15.2
BOTTOM
The counter reaches the BOTTOM when it becomes 0x0000.
MAX
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be one of the fixed values: 0x00FF, 0x01FF,
or 0x03FF, or to the value stored in the OCRnA or ICRn Register. The assignment is
dependent of the mode of operation.
Accessing 16-bit Registers
The TCNTn, OCRnx, and ICRn are 16-bit registers that can be accessed by the AVR CPU via
the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations.
Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16-bit
access. The same temporary register is shared between all 16-bit registers within each 16-bit
timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a
16-bit register is written by the CPU, the high byte stored in the temporary register, and the low
byte written are both copied into the 16-bit register in the same clock cycle. When the low byte of
a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the temporary register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCRnx 16-bit
registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
The following code examples show how to access the 16-bit Timer Registers assuming that no
interrupts updates the temporary register. The same principle can be used directly for accessing
the OCRnx and ICRn Registers. Note that when using “C”, the compiler handles the 16-bit
access.
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Assembly Code Examples(1)
...
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNTnH,r17
out TCNTnL,r16
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
...
C Code Examples(1)
unsigned int i;
...
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
...
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit Timer Registers, then the result of the access outside the interrupt will be corrupted. Therefore, when both
the main code and the interrupt code update the temporary register, the main code must disable
the interrupts during the 16-bit access.
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The following code examples show how to do an atomic read of the TCNTn Register contents.
Reading any of the OCRnx or ICRn Registers can be done by using the same principle.
Assembly Code Example(1)
TIM16_ReadTCNTn:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
unsigned int TIM16_ReadTCNTn( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNTn into i */
i = TCNTn;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
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The following code examples show how to do an atomic write of the TCNTn Register contents.
Writing any of the OCRnx or ICRn Registers can be done by using the same principle.
Assembly Code Example(1)
TIM16_WriteTCNTn:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNTn to r17:r16
out TCNTnH,r17
out TCNTnL,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
void TIM16_WriteTCNTn( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNTn to i */
TCNTn = i;
/* Restore global interrupt flag */
SREG = sreg;
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNTn.
15.2.1
Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.
15.3
Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CSn2:0) bits
located in the Timer/Counter control Register B (TCCRnB). For details on clock sources and
prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 83.
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15.4
Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.
Figure 15-2 shows a block diagram of the counter and its surroundings.
Figure 15-2. Counter Unit Block Diagram
DATA BUS (8-bit)
TOVn
(Int.Req.)
TEMP (8-bit)
Clock Select
Count
TCNTnH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
Clear
Direction
Control Logic
clkTn
Edge
Detector
Tn
( From Prescaler )
TOP
BOTTOM
Signal description (internal signals):
Count
Increment or decrement TCNTn by 1.
Direction
Select between increment and decrement.
Clear
Clear TCNTn (set all bits to zero).
clkTn
Timer/Counter clock.
TOP
Signalize that TCNTn has reached maximum value.
BOTTOM
Signalize that TCNTn has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNTnH) containing the upper eight bits of the counter, and Counter Low (TCNTnL) containing the lower eight
bits. The TCNTnH Register can only be indirectly accessed by the CPU. When the CPU does an
access to the TCNTnH I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNTnH value when the TCNTnL is read, and
TCNTnH is updated with the temporary register value when TCNTnL is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNTn Register when the
counter is counting that will give unpredictable results. The special cases are described in the
sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkTn). The clkTn can be generated from an external or internal clock source,
selected by the Clock Select bits (CSn2:0). When no clock source is selected (CSn2:0 = 0) the
timer is stopped. However, the TCNTn value can be accessed by the CPU, independent of
whether clkTn is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits
(WGMn3:0) located in the Timer/Counter Control Registers A and B (TCCRnA and TCCRnB).
There are close connections between how the counter behaves (counts) and how waveforms
are generated on the Output Compare outputs OCnx. For more details about advanced counting
sequences and waveform generation, see “16-bit Timer/Counter1 with PWM” on page 103.
The Timer/Counter Overflow Flag (TOVn) is set according to the mode of operation selected by
the WGMn3:0 bits. TOVn can be used for generating a CPU interrupt.
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15.5
Input Capture Unit
The Timer/Counter incorporates an Input Capture unit that can capture external events and give
them a time-stamp indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICPn pin or alternatively, via the analog-comparator unit. The
time-stamps can then be used to calculate frequency, duty-cycle, and other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 15-3. The elements of
the block diagram that are not directly a part of the Input Capture unit are gray shaded. The
small “n” in register and bit names indicates the Timer/Counter number.
Figure 15-3. Input Capture Unit Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
ICRnH (8-bit)
WRITE
ICRnL (8-bit)
TCNTnH (8-bit)
ICRn (16-bit Register)
ICPSEL1
TCNTnL (8-bit)
TCNTn (16-bit Counter)
ICNC
ICES
Noise
Canceler
Edge
Detector
ICPnA
ICFn (Int.Req.)
ICPnB
When a change of the logic level (an event) occurs on the Input Capture pin (ICPn), alternatively
on the Analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter
(TCNTn) is written to the Input Capture Register (ICRn). The Input Capture Flag (ICFn) is set at
the same system clock as the TCNTn value is copied into ICRn Register. If enabled (ICIEn = 1),
the Input Capture Flag generates an Input Capture interrupt. The ICFn Flag is automatically
cleared when the interrupt is executed. Alternatively the ICFn Flag can be cleared by software
by writing a logical one to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICRn) is done by first reading the low
byte (ICRnL) and then the high byte (ICRnH). When the low byte is read the high byte is copied
into the high byte temporary register (TEMP). When the CPU reads the ICRnH I/O location it will
access the TEMP Register.
The ICRn Register can only be written when using a Waveform Generation mode that utilizes
the ICRn Register for defining the counter’s TOP value. In these cases the Waveform Generation mode (WGMn3:0) bits must be set before the TOP value can be written to the ICRn
Register. When writing the ICRn Register the high byte must be written to the ICRnH I/O location
before the low byte is written to ICRnL.
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For more information on how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 105.
15.5.1
Input Capture Trigger Source
The trigger sources for the Input Capture unit arethe Input Capture pin (ICP1A & ICP1B).
Be aware that changing trigger source can trigger a capture. The Input Capture Flag must therefore be cleared after the change.
The Input Capture pin (ICPn) IS sampled using the same technique as for the Tn pin (Figure 131 on page 83). The edge detector is also identical. However, when the noise canceler is
enabled, additional logic is inserted before the edge detector, which increases the delay by four
system clock cycles. Note that the input of the noise canceler and edge detector is always
enabled unless the Timer/Counter is set in a Waveform Generation mode that uses ICRn to
define TOP.
An Input Capture can be triggered by software by controlling the port of the ICPn pin.
15.5.2
Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The
noise canceler input is monitored over four samples, and all four must be equal for changing the
output that in turn is used by the edge detector.
The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNCn) bit in
Timer/Counter Control Register B (TCCRnB). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied to the input, to the update of the
ICRn Register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
15.5.3
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICRn Register before the next event occurs, the ICRn will be
overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICRn Register should be read as early in the interrupt handler routine as possible. Even though the Input Capture interrupt has relatively high
priority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.
Using the Input Capture unit in any mode of operation when the TOP value (resolution) is
actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICRn
Register has been read. After a change of the edge, the Input Capture Flag (ICFn) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICFn Flag is not required (if an interrupt handler is used).
15.6
Output Compare Units
The 16-bit comparator continuously compares TCNTn with the Output Compare Register
(OCRnx). If TCNT equals OCRnx the comparator signals a match. A match will set the Output
Compare Flag (OCFnx) at the next “timer clock cycle”. If enabled (OCIEnx = 1), the Output Compare Flag generates an Output Compare interrupt. The OCFnx Flag is automatically cleared
when the interrupt is executed. Alternatively the OCFnx Flag can be cleared by software by writ-
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ing a logical one to its I/O bit location. The Waveform Generator uses the match signal to
generate an output according to operating mode set by the Waveform Generation mode
(WGMn3:0) bits and Compare Output mode (COMnx1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (See “16-bit Timer/Counter1 with PWM” on page 103.)
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value (i.e.,
counter resolution). In addition to the counter resolution, the TOP value defines the period time
for waveforms generated by the Waveform Generator.
Figure 15-4 shows a block diagram of the Output Compare unit. The small “n” in the register and
bit names indicates the device number (n = n for Timer/Counter n), and the “x” indicates Output
Compare unit (x). The elements of the block diagram that are not directly a part of the Output
Compare unit are gray shaded.
Figure 15-4. Output Compare Unit, Block Diagram
DATA BUS
(8-bit)
TEMP (8-bit)
OCRnxH Buf. (8-bit)
OCRnxL Buf. (8-bit)
TCNTnH (8-bit)
OCRnx Buffer (16-bit Register)
OCRnxH (8-bit)
TCNTnL (8-bit)
TCNTn (16-bit Counter)
OCRnxL (8-bit)
OCRnx (16-bit Register)
= (16-bit Comparator )
OCFnx (Int.Req.)
TOP
BOTTOM
Waveform Generator
WGMn3:0
OCnx
COMnx1:0
The OCRnx Register is double buffered when using any of the twelve Pulse Width Modulation
(PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, the
double buffering is disabled. The double buffering synchronizes the update of the OCRnx Compare Register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCRnx Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCRnx Buffer Register, and if double buffering is disabled the CPU will access the OCRnx directly. The content of the OCR1x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as when
accessing other 16-bit registers. Writing the OCRnx Registers must be done via the TEMP Register since the compare of all 16 bits is done continuously. The high byte (OCRnxH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
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updated by the value written. Then when the low byte (OCRnxL) is written to the lower eight bits,
the high byte will be copied into the upper 8-bits of either the OCRnx buffer or OCRnx Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 105.
15.6.1
Force Output Compare
In non-PWM Waveform Generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOCnx) bit. Forcing compare match will not set the
OCFnx Flag or reload/clear the timer, but the OCnx pin will be updated as if a real compare
match had occurred (the COMn1:0 bits settings define whether the OCnx pin is set, cleared or
toggled).
15.6.2
Compare Match Blocking by TCNTn Write
All CPU writes to the TCNTn Register will block any compare match that occurs in the next timer
clock cycle, even when the timer is stopped. This feature allows OCRnx to be initialized to the
same value as TCNTn without triggering an interrupt when the Timer/Counter clock is enabled.
15.6.3
Using the Output Compare Unit
Since writing TCNTn in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNTn when using any of the Output Compare
channels, independent of whether the Timer/Counter is running or not. If the value written to
TCNTn equals the OCRnx value, the compare match will be missed, resulting in incorrect waveform generation. Do not write the TCNTn equal to TOP in PWM modes with variable TOP
values. The compare match for the TOP will be ignored and the counter will continue to 0xFFFF.
Similarly, do not write the TCNTn value equal to BOTTOM when the counter is downcounting.
The setup of the OCnx should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OCnx value is to use the Force Output Compare (FOCnx) strobe bits in Normal mode. The OCnx Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COMnx1:0 bits are not double buffered together with the compare value.
Changing the COMnx1:0 bits will take effect immediately.
15.7
Compare Match Output Unit
The Compare Output mode (COMnx1:0) bits have two functions. The Waveform Generator uses
the COMnx1:0 bits for defining the Output Compare (OCnx) state at the next compare match.
Secondly the COMnx1:0 bits control the OCnx pin output source. Figure 15-5 shows a simplified
schematic of the logic affected by the COMnx1:0 bit setting. The I/O Registers, I/O bits, and I/O
pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers
(DDR and PORT) that are affected by the COMnx1:0 bits are shown. When referring to the
OCnx state, the reference is for the internal OCnx Register, not the OCnx pin. If a system reset
occur, the OCnx Register is reset to “0”.
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Figure 15-5. Compare Match Output Unit, Schematic
COMnx1
COMnx0
FOCnx
Waveform
Generator
D
Q
1
OCnx
DATA BUS
D
0
OCnx
Pin
Q
PORT
D
Q
DDR
clk I/O
The general I/O port function is overridden by the Output Compare (OCnx) from the Waveform
Generator if either of the COMnx1:0 bits are set. However, the OCnx pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OCnx pin (DDR_OCnx) must be set as output before the OCnx value is visible on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. Refer to Table 15-2, Table 15-3 and Table 15-4 for
details.
The design of the Output Compare pin logic allows initialization of the OCnx state before the output is enabled. Note that some COMnx1:0 bit settings are reserved for certain modes of
operation. See “16-bit Timer/Counter Register Description” on page 123.
The COMnx1:0 bits have no effect on the Input Capture unit.
15.7.1
Compare Output Mode and Waveform Generation
The Waveform Generator uses the COMnx1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COMnx1:0 = 0 tells the Waveform Generator that no action on the
OCnx Register is to be performed on the next compare match. For compare output actions in the
non-PWM modes refer to Table 15-2 on page 124. For fast PWM mode refer to Table 15-3 on
page 124, and for phase correct and phase and frequency correct PWM refer to Table 15-4 on
page 124.
A change of the COMnx1:0 bits state will have effect at the first compare match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOCnx strobe bits.
15.8
Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGMn3:0) and Compare Output
mode (COMnx1:0) bits. The Compare Output mode bits do not affect the counting sequence,
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while the Waveform Generation mode bits do. The COMnx1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COMnx1:0 bits control whether the output should be set, cleared or toggle at a compare
match (See “Compare Match Output Unit” on page 113.)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 122.
15.8.1
Normal Mode
The simplest mode of operation is the Normal mode (WGMn3:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOVn) will be set in
the same timer clock cycle as the TCNTn becomes zero. The TOVn Flag in this case behaves
like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow
interrupt that automatically clears the TOVn Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new counter value can be
written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval
between events are too long, the timer overflow interrupt or the prescaler must be used to
extend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
15.8.2
Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGMn3:0 = 4 or 12), the OCRnA or ICRn Register
are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNTn) matches either the OCRnA (WGMn3:0 = 4) or the ICRn (WGMn3:0 =
12). The OCRnA or ICRn define the top value for the counter, hence also its resolution. This
mode allows greater control of the compare match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 15-6. The counter value (TCNTn)
increases until a compare match occurs with either OCRnA or ICRn, and then counter (TCNTn)
is cleared.
Figure 15-6. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnA
(Toggle)
Period
(COMnA1:0 = 1)
1
2
3
4
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An interrupt can be generated at each time the counter value reaches the TOP value by either
using the OCFnA or ICFn Flag according to the register used to define the TOP value. If the
interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none or a
low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new value written to OCRnA or ICRn is lower than the current value of
TCNTn, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode
using OCRnA for defining TOP (WGMn3:0 = 15) since the OCRnA then will be double buffered.
For generating a waveform output in CTC mode, the OCnA output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COMnA1:0 = 1). The OCnA value will not be visible on the port pin unless the data direction for
the pin is set to output (DDR_OCnA = 1). The waveform generated will have a maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). The waveform frequency is
defined by the following equation:
f clk_I/O
f OCnA = --------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnA )
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOVn Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
15.8.3
Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGMn3:0 = 5, 6, 7, 14, or 15) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is set on
the compare match between TCNTn and OCRnx, and cleared at TOP. In inverting Compare
Output mode output is cleared on compare match and set at TOP. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the phase correct
and phase and frequency correct PWM modes that use dual-slope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICRn or
OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can be
calculated by using the following equation:
log ( TOP + 1 )
R FPWM = ----------------------------------log ( 2 )
In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 =
14), or the value in OCRnA (WGMn3:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in Figure 15-7. The figure
shows fast PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the
timing diagram shown as a histogram for illustrating the single-slope operation. The diagram
includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNTn
slopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will
be set when a compare match occurs.
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Figure 15-7. Fast PWM Mode, Timing Diagram
OCRnx/TOP Update and
TOVn Interrupt Flag Set and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
5
6
7
8
The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches TOP. In addition
the OCnA or ICFn Flag is set at the same timer clock cycle as TOVn is set when either OCRnA
or ICRn is used for defining the TOP value. If one of the interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNTn and the OCRnx.
Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCRnx Registers are written.
The procedure for updating ICRn differs from updating OCRnA when used for defining the TOP
value. The ICRn Register is not double buffered. This means that if ICRn is changed to a low
value when the counter is running with none or a low prescaler value, there is a risk that the new
ICRn value written is lower than the current value of TCNTn. The result will then be that the
counter will miss the compare match at the TOP value. The counter will then have to count to the
MAX value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
The OCRnA Register however, is double buffered. This feature allows the OCRnA I/O location
to be written anytime. When the OCRnA I/O location is written the value written will be put into
the OCRnA Buffer Register. The OCRnA Compare Register will then be updated with the value
in the Buffer Register at the next timer clock cycle the TCNTn matches TOP. The update is done
at the same timer clock cycle as the TCNTn is cleared and the TOVn Flag is set.
Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,
if the base PWM frequency is actively changed (by changing the TOP value), using the OCRnA
as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins.
Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COMnx1:0 to three (see Table on page 124). The actual OCnx
value will only be visible on the port pin if the data direction for the port pin is set as output
(DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx Register at
the compare match between OCRnx and TCNTn, and clearing (or setting) the OCnx Register at
the timer clock cycle the counter is cleared (changes from TOP to BOTTOM).
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The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ----------------------------------N ⋅ ( 1 + TOP )
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCRnx is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCRnx equal to TOP
will result in a constant high or low output (depending on the polarity of the output set by the
COMnx1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OCnA to toggle its logical level on each compare match (COMnA1:0 = 1). This applies only
if OCR1A is used to define the TOP value (WGM13:0 = 15). The waveform generated will have
a maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). This feature is
similar to the OCnA toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
15.8.4
Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGMn3:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a dualslope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from
TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is
cleared on the compare match between TCNTn and OCRnx while upcounting, and set on the
compare match while downcounting. In inverting Output Compare mode, the operation is
inverted. The dual-slope operation has lower maximum operation frequency than single slope
operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes
are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined
by either ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to
0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can be calculated by using the following equation:
log ( TOP + 1 )
R PCPWM = ----------------------------------log ( 2 )
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 1, 2, or 3), the value in ICRn
(WGMn3:0 = 10), or the value in OCRnA (WGMn3:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNTn value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 15-8. The figure
shows phase correct PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn
value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The
diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on
the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set when a compare match occurs.
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Figure 15-8. Phase Correct PWM Mode, Timing Diagram
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches BOTTOM. When
either OCRnA or ICRn is used for defining the TOP value, the OCnA or ICFn Flag is set accordingly at the same timer clock cycle as the OCRnx Registers are updated with the double buffer
value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNTn and the OCRnx.
Note that when using fixed TOP values, the unused bits are masked to zero when any of the
OCRnx Registers are written. As the third period shown in Figure 15-8 illustrates, changing the
TOP actively while the Timer/Counter is running in the phase correct mode can result in an
unsymmetrical output. The reason for this can be found in the time of update of the OCRnx Register. Since the OCRnx update occurs at TOP, the PWM period starts and ends at TOP. This
implies that the length of the falling slope is determined by the previous TOP value, while the
length of the rising slope is determined by the new TOP value. When these two values differ the
two slopes of the period will differ in length. The difference in length gives the unsymmetrical
result on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct
mode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COMnx1:0 to three (See Table on page 124). The
actual OCnx value will only be visible on the port pin if the data direction for the port pin is set as
output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx Register at the compare match between OCRnx and TCNTn when the counter increments, and
clearing (or setting) the OCnx Register at compare match between OCRnx and TCNTn when
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the counter decrements. The PWM frequency for the output when using phase correct PWM can
be calculated by the following equation:
f clk_I/O
f OCnxPCPWM = ---------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output
will toggle with a 50% duty cycle.
15.8.5
Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM
mode (WGMn3:0 = 8 or 9) provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the
Output Compare (OCnx) is cleared on the compare match between TCNTn and OCRnx while
upcounting, and set on the compare match while downcounting. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCRnx Register is updated by the OCRnx Buffer Register, (see Figure 158 and Figure 15-9).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either
ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and
the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can
be calculated using the following equation:
log ( TOP + 1 )
R PFCPWM = ----------------------------------log ( 2 )
In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICRn (WGMn3:0 = 8), or the value in OCRnA (WGMn3:0 = 9). The
counter has then reached the TOP and changes the count direction. The TCNTn value will be
equal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency
correct PWM mode is shown on Figure 15-9. The figure shows phase and frequency correct
PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes noninverted and inverted PWM outputs. The small horizontal line marks on the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set when a
compare match occurs.
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Figure 15-9. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/TOP Updateand
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
OCnx
(COMnx1:0 = 2)
OCnx
(COMnx1:0 = 3)
Period
1
2
3
4
The Timer/Counter Overflow Flag (TOVn) is set at the same timer clock cycle as the OCRnx
Registers are updated with the double buffer value (at BOTTOM). When either OCRnA or ICRn
is used for defining the TOP value, the OCnA or ICFn Flag set when TCNTn has reached TOP.
The Interrupt Flags can then be used to generate an interrupt each time the counter reaches the
TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNTn and the OCRnx.
As Figure 15-9 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the OCRnx Registers are updated at BOTTOM, the length of the rising
and the falling slopes will always be equal. This gives symmetrical output pulses and is therefore
frequency correct.
Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,
if the base PWM frequency is actively changed by changing the TOP value, using the OCRnA as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and
an inverted PWM output can be generated by setting the COMnx1:0 to three (See Table on
page 124). The actual OCnx value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing)
the OCnx Register at the compare match between OCRnx and TCNTn when the counter increments, and clearing (or setting) the OCnx Register at compare match between OCRnx and
TCNTn when the counter decrements. The PWM frequency for the output when using phase
and frequency correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPFCPWM = ---------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
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The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be set to high for noninverted PWM mode. For inverted PWM the output will have the opposite logic values. If OCR1A
is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output will toggle
with a 50% duty cycle.
15.9
Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkTn) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set, and when the OCRnx Register is updated with the OCRnx buffer value (only for
modes utilizing double buffering). Figure 15-10 shows a timing diagram for the setting of OCFnx.
Figure 15-10. Timer/Counter Timing Diagram, Setting of OCFnx, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
OCRnx - 1
OCRnx
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 15-11 shows the same timing data, but with the prescaler enabled.
Figure 15-11. Timer/Counter Timing Diagram, Setting of OCFnx, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O /8)
TCNTn
OCRnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
OCFnx
Figure 15-12 shows the count sequence close to TOP in various modes. When using phase and
frequency correct PWM mode the OCRnx Register is updated at BOTTOM. The timing diagrams
will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1 and so on.
The same renaming applies for modes that set the TOVn Flag at BOTTOM.
122
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 15-12. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn
(clkI/O /1)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
New OCRnx Value
Old OCRnx Value
(Update at TOP)
Figure 15-13 shows the same timing data, but with the prescaler enabled.
Figure 15-13. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1
TOP
BOTTOM
BOTTOM + 1
TOP - 1
TOP
TOP - 1
TOP - 2
TOVn (FPWM)
and ICF n (if used
as TOP)
OCRnx
Old OCRnx Value
(Update at TOP)
New OCRnx Value
15.10 16-bit Timer/Counter Register Description
15.10.1
Timer/Counter1 Control Register A – TCCR1A
Bit
7
6
5
4
3
2
1
0
COM1A1
COM1A0
COM1B1
COM1B0
–
–
WGM11
WGM10
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR1A
• Bit 7:6 – COMnA1:0: Compare Output Mode for Channel A
• Bit 5:4 – COMnB1:0: Compare Output Mode for Channel B
The COMnA1:0 and COMnB1:0 control the Output Compare pins (OCnA and OCnB respectively) behavior. If one or both of the COMnA1:0 bits are written to one, the OCnA output
overrides the normal port functionality of the I/O pin it is connected to. If one or both of the
COMnB1:0 bit are written to one, the OCnB output overrides the normal port functionality of the
123
4317I–AVR–01/08
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to the OCnA or OCnB pin must be set in order to enable the output driver.
When the OCnA or OCnB is connected to the pin, the function of the COMnx1:0 bits is dependent of the WGMn3:0 bits setting. Table 15-2 shows the COMnx1:0 bit functionality when the
WGMn3:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 15-1.
Compare Output Mode, non-PWM
COMnA1/COMnB1
COMnA0/COMnB0
Description
0
0
Normal port operation, OCnA/OCnB disconnected.
0
1
Toggle OCnA/OCnB on Compare Match.
1
0
Clear OCnA/OCnB on Compare Match (Set output to
low level).
1
1
Set OCnA/OCnB on Compare Match (Set output to
high level).
Table 15-3 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the fast
PWM mode.
Table 15-2.
Compare Output Mode, Fast PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
0
0
Normal port operation, OCnA/OCnB disconnected.
0
1
WGMn3:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port operation).
For all other WGM1 settings, normal port operation,
OC1A/OC1B disconnected.
1
0
Clear OCnA/OCnB on Compare Match, set
OCnA/OCnB at TOP
Set OCnA/OCnB on Compare Match, clear
OCnA/OCnB at TOP
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. In
this case the compare match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 116. for more details.
1
Note:
Description
1
Table 15-4 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the phase
correct or the phase and frequency correct, PWM mode.
Table 15-3.
124
Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
0
0
Description
Normal port operation, OCnA/OCnB disconnected.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 15-3.
Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
0
1
WGMn3:0 = 8, 9 10 or 11: Toggle OCnA on Compare
Match, OCnB disconnected (normal port operation).
For all other WGM1 settings, normal port operation,
OC1A/OC1B disconnected.
1
0
Clear OCnA/OCnB on Compare Match when upcounting. Set OCnA/OCnB on Compare Match when
downcounting.
Set OCnA/OCnB on Compare Match when upcounting. Clear OCnA/OCnB on Compare Match
when downcounting.
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. See
“Phase Correct PWM Mode” on page 118. for more details.
1
Note:
Description
1
• Bit 1:0 – WGMn1:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 15-5. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types
of Pulse Width Modulation (PWM) modes. (See “16-bit Timer/Counter1 with PWM” on page
103.).
Waveform Generation Mode Bit Description(1)
Table 15-4.
Mode
WGMn3
WGMn2
(CTCn)
WGMn1
(PWMn1)
WGMn0
(PWMn0)
Timer/Counter Mode of
Operation
TOP
Update of
OCRnx at
TOVn Flag
Set on
0
0
0
0
0
Normal
0xFFFF
Immediate
MAX
1
0
0
0
1
PWM, Phase Correct, 8-bit
0x00FF
TOP
BOTTOM
2
0
0
1
0
PWM, Phase Correct, 9-bit
0x01FF
TOP
BOTTOM
3
0
0
1
1
PWM, Phase Correct, 10-bit
0x03FF
TOP
BOTTOM
4
0
1
0
0
CTC
OCRnA
Immediate
MAX
5
0
1
0
1
Fast PWM, 8-bit
0x00FF
TOP
TOP
6
0
1
1
0
Fast PWM, 9-bit
0x01FF
TOP
TOP
7
0
1
1
1
Fast PWM, 10-bit
0x03FF
TOP
TOP
8
1
0
0
0
PWM, Phase and Frequency
Correct
ICRn
BOTTOM
BOTTOM
9
1
0
0
1
PWM, Phase and Frequency
Correct
OCRnA
BOTTOM
BOTTOM
10
1
0
1
0
PWM, Phase Correct
ICRn
TOP
BOTTOM
11
1
0
1
1
PWM, Phase Correct
OCRnA
TOP
BOTTOM
12
1
1
0
0
CTC
ICRn
Immediate
MAX
13
1
1
0
1
(Reserved)
–
–
–
14
1
1
1
0
Fast PWM
ICRn
TOP
TOP
15
1
1
1
1
Fast PWM
OCRnA
TOP
TOP
125
4317I–AVR–01/08
Note:
15.10.2
1. The CTCn and PWMn1:0 bit definition names are obsolete. Use the WGMn2:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
Timer/Counter1 Control Register B – TCCR1B
Bit
7
6
5
4
3
2
1
0
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
Read/Write
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TCCR1B
• Bit 7 – ICNCn: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is
activated, the input from the Input Capture pin (ICPn) is filtered. The filter function requires four
successive equal valued samples of the ICPn pin for changing its output. The Input Capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICESn: Input Capture Edge Select
This bit selects which edge on the Input Capture pin (ICPn) that is used to trigger a capture
event. When the ICESn bit is written to zero, a falling (negative) edge is used as trigger, and
when the ICESn bit is written to one, a rising (positive) edge will trigger the capture.
When a capture is triggered according to the ICESn setting, the counter value is copied into the
Input Capture Register (ICRn). The event will also set the Input Capture Flag (ICFn), and this
can be used to cause an Input Capture Interrupt, if this interrupt is enabled.
When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the
TCCRnA and the TCCRnB Register), the ICPn is disconnected and consequently the Input Capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCRnB is written.
• Bit 4:3 – WGMn3:2: Waveform Generation Mode
See TCCRnA Register description.
• Bit 2:0 – CSn2:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure
15-10 and Figure 15-11.
Table 15-5.
126
Clock Select Bit Description
CSn2
CSn1
CSn0
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clkI/O/1 (No prescaling)
0
1
0
clkI/O/8 (From prescaler)
0
1
1
clkI/O/64 (From prescaler)
1
0
0
clkI/O/256 (From prescaler)
1
0
1
clkI/O/1024 (From prescaler)
1
1
0
External clock source on Tn pin. Clock on falling edge.
1
1
1
External clock source on Tn pin. Clock on rising edge.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
If external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
15.10.3
Timer/Counter1 Control Register C – TCCR1C
Bit
7
6
5
4
3
2
1
FOC1A
FOC1B
–
–
–
–
–
0
–
Read/Write
R/W
R/W
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
TCCR1C
• Bit 7 – FOCnA: Force Output Compare for Channel A
• Bit 6 – FOCnB: Force Output Compare for Channel B
The FOCnA/FOCnB bits are only active when the WGMn3:0 bits specifies a non-PWM mode.
However, for ensuring compatibility with future devices, these bits must be set to zero when
TCCRnA is written when operating in a PWM mode. When writing a logical one to the
FOCnA/FOCnB bit, an immediate compare match is forced on the Waveform Generation unit.
The OCnA/OCnB output is changed according to its COMnx1:0 bits setting. Note that the
FOCnA/FOCnB bits are implemented as strobes. Therefore it is the value present in the
COMnx1:0 bits that determine the effect of the forced compare.
A FOCnA/FOCnB strobe will not generate any interrupt nor will it clear the timer in Clear Timer
on Compare match (CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB bits are always read as zero.
15.10.4
Timer/Counter1 – TCNT1H and TCNT1L
Bit
7
6
5
4
3
2
1
0
TCNT1[15:8]
TCNT1H
TCNT1[7:0]
TCNT1L
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The two Timer/Counter I/O locations (TCNTnH and TCNTnL, combined TCNTn) give direct
access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To
ensure that both the high and low bytes are read and written simultaneously when the CPU
accesses these registers, the access is performed using an 8-bit temporary High Byte Register
(TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit
Registers” on page 105.
Modifying the counter (TCNTn) while the counter is running introduces a risk of missing a compare match between TCNTn and one of the OCRnx Registers.
Writing to the TCNTn Register blocks (removes) the compare match on the following timer clock
for all compare units.
15.10.5
Output Compare Register 1 A – OCR1AH and OCR1AL
Bit
7
6
5
4
3
2
1
0
OCR1A[15:8]
OCR1AH
OCR1A[7:0]
15.10.6
OCR1AL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
4
3
2
1
0
Output Compare Register 1 B – OCR1BH and OCR1BL
Bit
7
6
5
OCR1B[15:8]
OCR1BH
127
4317I–AVR–01/08
OCR1B[7:0]
OCR1BL
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Output Compare Registers contain a 16-bit value that is continuously compared with the
counter value (TCNTn). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OCnx pin.
The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are
written simultaneously when the CPU writes to these registers, the access is performed using an
8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other
16-bit registers. See “Accessing 16-bit Registers” on page 105.
15.10.7
Input Capture Register 1 – ICR1H and ICR1L
Bit
7
6
5
4
3
2
1
0
ICR1[15:8]
ICR1H
ICR1[7:0]
ICR1L
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
The Input Capture is updated with the counter (TCNTn) value each time an event occurs on the
ICPn pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture
can be used for defining the counter TOP value.
The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit
temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 105.
15.10.8
Timer/Counter1 Interrupt Mask Register – TIMSK1
Bit
7
6
5
4
3
2
1
0
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIMSK1
• Bit 7, 6 – Res: Reserved Bits
These bits are unused bits in the AT90PWM2/2B/3/3B, and will always read as zero.
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (see “Reset and Interrupt Vectors Placement in AT90PWM2/2B/3/3B(1)” on page 58) is
executed when the ICF1 Flag, located in TIFR1, is set.
• Bit 4, 3 – Res: Reserved Bits
These bits are unused bits in the AT90PWM2/2B/3/3B, and will always read as zero.
• Bit 2 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare B Match interrupt is enabled. The corresponding
Interrupt Vector (see “Reset and Interrupt Vectors Placement in AT90PWM2/2B/3/3B(1)” on
page 58) is executed when the OCF1B Flag, located in TIFR1, is set.
• Bit 1 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare A Match interrupt is enabled. The corresponding
128
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Interrupt Vector (see “Reset and Interrupt Vectors Placement in AT90PWM2/2B/3/3B(1)” on
page 58) is executed when the OCF1A Flag, located in TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Overflow interrupt is enabled. The corresponding Interrupt Vector
(see “Reset and Interrupt Vectors Placement in AT90PWM2/2B/3/3B(1)” on page 58) is executed when the TOV1 Flag, located in TIFR1, is set.
15.10.9
Timer/Counter1 Interrupt Flag Register – TIFR1
Bit
7
6
5
4
3
2
1
0
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
Read/Write
R
R
R/W
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
TIFR1
• Bit 7, 6 – Res: Reserved Bits
These bits are unused bits in the AT90PWM2/2B/3/3B, and will always read as zero.
• Bit 5 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register
(ICR1) is set by the WGMn3:0 to be used as the TOP value, the ICF1 Flag is set when the
counter reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF1 can be cleared by writing a logic one to its bit location.
• Bit 4, 3 – Res: Reserved Bits
These bits are unused bits in the AT90PWM2/2B/3/3B, and will always read as zero.
• Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register B (OCR1B).
Note that a Forced Output Compare (FOC1B) strobe will not set the OCF1B Flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is executed. Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
• Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register A (OCR1A).
Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is executed. Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In Normal and CTC modes,
the TOV1 Flag is set when the timer overflows. Refer to Table 15-5 on page 125 for the TOV1
Flag behavior when using another WGMn3:0 bit setting.
TOV1 is automatically cleared when the Timer/Counter1 Overflow Interrupt Vector is executed.
Alternatively, TOV1 can be cleared by writing a logic one to its bit location.
129
4317I–AVR–01/08
16. Power Stage Controller – (PSC0, PSC1 & PSC2)
The Power Stage Controller is a high performance waveform controller.
16.1
Features
•
•
•
•
•
•
•
•
•
•
PWM waveform generation function (2 complementary programmable outputs)
Dead time control
Standard mode up to 12 bit resolution
Frequency Resolution Enhancement Mode (12 + 4 bits)
Frequency up to 64 Mhz
Conditional Waveform on External Events (Zero Crossing, Current Sensing ...)
All on chip PSC synchronization
ADC synchronization
Overload protection function
Abnormality protection function, emergency input to force all outputs to high impedance or in
inactive state (fuse configurable)
• Center aligned and edge aligned modes synchronization
• Fast emergency stop by hardware
16.2
Overview
Many register and bit references in this section are written in general form.
•
A lower case “n” replaces the PSC number, in this case 0, 1 or 2. However, when using the
register or bit defines in a program, the precise form must be used, i.e., PSOC1 for
accessing PSC 0 Synchro and Output Configuration register and so on.
•
A lower case “x” replaces the PSC part , in this case A or B. However, when using the
register or bit defines in a program, the precise form must be used, i.e., PFRCnA for
accessing PSC n Fault/Retrigger n A Control register and so on.
The purpose of a Power Stage Controller (PSC) is to control power modules on a board. It has
two outputs on PSC0 and PSC1 and four outputs on PSC2.
These outputs can be used in various ways:
•
“Two Ouputs” to drive a half bridge (lighting, DC motor ...)
•
“One Output” to drive single power transistor (DC/DC converter, PFC, DC motor ...)
•
“Four Outputs” in the case of PSC2 to drive a full bridge (lighting, DC motor ...)
Each PSC has two inputs the purpose of which is to provide means to act directly on the generated waveforms:
•
Current sensing regulation
•
Zero crossing retriggering
•
Demagnetization retriggering
•
Fault input
The PSC can be chained and synchronized to provide a configuration to drive three half bridges.
Thanks to this feature it is possible to generate a three phase waveforms for applications such
as Asynchronous or BLDC motor drive.
130
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
16.3
PSC Description
Figure 16-1. Power Stage Controller 0 or 1 Block Diagram
PSC Counter
Waveform
Generator B
=
PSCOUTn1
( From Analog
Comparator n Ouput )
OCRnRB
PSC Input
Module B
DATABUS
=
PSCn Input B
OCRnSB
PISELnB
Part B
PSC Input
Module A
=
PSCn Input A
PSCINn
OCRnRA
PISELnA
PSCOUTn0
Waveform
Generator A
=
OCRnSA
Part A
PICRn
PCNFn
PCTLn
Note:
PFRCnB
PFRCnA
POM2(PSC2 only)
PSOCn
n = 0, 1
The principle of the PSC is based on the use of a counter (PSC counter). This counter is able to
count up and count down from and to values stored in registers according to the selected running mode.
The PSC is seen as two symetrical entities. One part named part A which generates the output
PSCOUTn0 and the second one named part B which generates the PSCOUTn1 output.
Each part A or B has its own PSC Input Module to manage selected input.
131
4317I–AVR–01/08
16.3.1
PSC2 Distinctive Feature
Figure 16-2. PSC2 versus PSC1&PSC0 Block Diagram
PSC Counter
PSCOUTn3
=
POS23
Waveform
Generator B
PSCOUTn1
( From Analog
Comparator n Ouput )
OCRnRB
DATABUS
=
PSC Input
Module B
OCRnSB
Part A
=
PSC Input
Module A
PSCn Input B
Output
Matrix
PISELnB
PSCn Input A
PSCINn
OCRnRA
=
PISELnA
POS22
Waveform
Generator A
PSCOUTn2
PSCOUTn0
OCRnSA
Part B
PICRn
PCNFn
PCTLn
Note:
PFRCnB
PFRCnA
POM2(PSC2 only)
PSOCn
n=2
PSC2 has two supplementary outputs PSCOUT22 and PSCOUT23. Thanks to a first selector
PSCOUT22 can duplicate PSCOUT20 or PSCOUT21. Thanks to a second selector PSCOUT23
can duplicate PSCOUT20 or PSCOUT21.
The Output Matrix is a kind of 2*2 look up table which gives the possibility to program the output
values according to a PSC sequence (See “Output Matrix” on page 158.)
16.3.2
Output Polarity
The polarity “active high” or “active low” of the PSC outputs is programmable. All the timing diagrams in the following examples are given in the “active high” polarity.
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16.4
Signal Description
Figure 16-3. PSC External Block View
CLK PLL
CLK I/O
SYnIn
StopOut
OCRnRB[11:0]
OCRnSB[11:0]
OCRnRA[11:0]
OCRnSA[11:0]
OCRnRB[15:12]
(Flank Width
Modulation)
12
PSCOUTn0
12
PSCOUTn1
12
(1)
PSCOUTn2
12
(1)
PSCOUTn3
4
PICRn[11:0]
12
PSCINn
IRQ PSCn
Analog
Comparator
n Output
StopIn SYnOut PSCnASY
Note:
1. available only for PSC2
2. n = 0, 1 or 2
16.4.1
Input Description
Table 16-1.
Name
Internal Inputs
Description
Type
Width
OCRnRB[1
1:0]
Compare Value which Reset Signal on Part B (PSCOUTn1)
Register
12 bits
OCRnSB[1
1:0]
Compare Value which Set Signal on Part B (PSCOUTn1)
Register
12 bits
OCRnRA[1
1:0]
Compare Value which Reset Signal on Part A (PSCOUTn0)
Register
12 bits
OCRnSA[1
1:0]
Compare Value which Set Signal on Part A (PSCOUTn0)
Register
12 bits
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Name
OCRnRB[1
5:12]
Frequency Resolution Enhancement value
(Flank Width Modulation)
Register
4 bits
CLK I/O
Clock Input from I/O clock
Signal
CLK PLL
Clock Input from PLL
Signal
(1)
SYnIn
Synchronization In (from adjacent PSC)
Signal
StopIn
Stop Input (for synchronized mode)
Signal
Note:
1. See Figure 16-38 on page 159
Table 16-2.
Name
16.4.2
Type
Width
Description
Block Inputs
Description
Type
Width
PSCINn
Input 0 used for Retrigger or Fault functions
Signal
from A C
Input 1 used for Retrigger or Fault functions
Signal
Output Description
Table 16-3.
Name
Block Outputs
Description
Type
Width
PSCOUTn0
PSC n Output 0 (from part A of PSC)
Signal
PSCOUTn1
PSC n Output 1 (from part B of PSC)
Signal
PSCOUTn2
(PSC2 only)
PSC n Output 2 (from part A or part B of PSC)
Signal
PSCOUTn3(
PSC2 only)
PSC n Output 3 (from part A or part B of PSC)
Signal
Table 16-4.
Name
Internal Outputs
Description
Type
Width
SYnOut
Synchronization Output(1)
Signal
PICRn
[11:0]
PSC n Input Capture Register
Counter value at retriggering event
Register
12 bits
IRQPSCn
PSC Interrupt Request : three souces, overflow, fault, and input
capture
Signal
PSCnASY
ADC Synchronization (+ Amplifier Syncho. )(2)
Signal
StopOut
Stop Output (for synchronized mode)
Note:
1. See Figure 16-38 on page 159
2. See “Analog Synchronization” on page 158.
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16.5
16.5.1
Functional Description
Waveform Cycles
The waveform generated by PSC can be described as a sequence of two waveforms.
The first waveform is relative to PSCOUTn0 output and part A of PSC. The part of this waveform
is sub-cycle A in the following figure.
The second waveform is relative to PSCOUTn1 output and part B of PSC. The part of this waveform is sub-cycle B in the following figure.
The complete waveform is ended with the end of sub-cycle B. It means at the end of waveform
B.
Figure 16-4. Cycle Presentation in 1, 2 & 4 Ramp Mode
PSC Cycle
Sub-Cycle A
Sub-Cycle B
4 Ramp Mode
Ramp A0
Ramp A1
Ramp B0
Ramp B1
2 Ramp Mode
Ramp A
Ramp B
1 Ramp Mode
UPDATE
Figure 16-5. Cycle Presentation in Centered Mode
PSC Cycle
Centered Mode
UPDATE
Ramps illustrate the output of the PSC counter included in the waveform generators. Centered
Mode is like a one ramp mode which count down up and down.
Notice that the update of a new set of values is done regardless of ramp Mode at the top of the
last ramp.
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16.5.2
Running Mode Description
Waveforms and length of output signals are determined by Time Parameters (DT0, OT0, DT1,
OT1) and by the running mode. Four modes are possible :
16.5.2.1
–
Four Ramp mode
–
Two Ramp mode
–
One Ramp mode
–
Center Aligned mode
Four Ramp Mode
In Four Ramp mode, each time in a cycle has its own definition
Figure 16-6. PSCn0 & PSCn1 Basic Waveforms in Four Ramp mode
PSC Counter
OCRnSA
OCRnRA
OCRnRB
OCRnSB
0
0
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
Dead-Time 1
Dead-Time 0
PSC Cycle
The input clock of PSC is given by CLKPSC.
PSCOUTn0 and PSCOUTn1 signals are defined by On-Time 0, Dead-Time 0, On-Time 1 and
Dead-Time 1 values with :
On-Time 0 = OCRnRAH/L * 1/Fclkpsc
On-Time 1 = OCRnRBH/L * 1/Fclkpsc
Dead-Time 0 = (OCRnSAH/L + 2) * 1/Fclkpsc
Dead-Time 1 = (OCRnSBH/L + 2) * 1/Fclkpsc
Note:
16.5.2.2
Minimal value for Dead-Time 0 and Dead-Time 1 = 2 * 1/Fclkpsc
Two Ramp Mode
In Two Ramp mode, the whole cycle is divided in two moments
One moment for PSCn0 description with OT0 which gives the time of the whole moment
One moment for PSCn1 description with OT1 which gives the time of the whole moment
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Figure 16-7. PSCn0 & PSCn1 Basic Waveforms in Two Ramp mode
OCRnRA
PSC Counter
OCRnSA
OCRnRB
OCRnSB
0
0
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
Dead-Time 1
Dead-Time 0
PSC Cycle
PSCOUTn0 and PSCOUTn1 signals are defined by On-Time 0, Dead-Time 0, On-Time 1 and
Dead-Time 1 values with :
On-Time 0 = (OCRnRAH/L - OCRnSAH/L) * 1/Fclkpsc
On-Time 1 = (OCRnRBH/L - OCRnSBH/L) * 1/Fclkpsc
Dead-Time 0 = (OCRnSAH/L + 1) * 1/Fclkpsc
Dead-Time 1 = (OCRnSBH/L + 1) * 1/Fclkpsc
Note:
16.5.2.3
Minimal value for Dead-Time 0 and Dead-Time 1 = 1/Fclkpsc
One Ramp Mode
In One Ramp mode, PSCOUTn0 and PSCOUTn1 outputs can overlap each other.
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Figure 16-8. PSCn0 & PSCn1 Basic Waveforms in One Ramp mode
OCRnRB
OCRnSB
OCRnRA
PSC Counter
OCRnSA
0
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
Dead-Time 1
Dead-Time 0
PSC Cycle
On-Time 0 = (OCRnRAH/L - OCRnSAH/L) * 1/Fclkpsc
On-Time 1 = (OCRnRBH/L - OCRnSBH/L) * 1/Fclkpsc
Dead-Time 0 = (OCRnSAH/L + 1) * 1/Fclkpsc
Dead-Time 1 = (OCRnSBH/L - OCRnRAH/L) * 1/Fclkpsc
Note:
16.5.2.4
Minimal value for Dead-Time 0 = 1/Fclkpsc
Center Aligned Mode
In center aligned mode, the center of PSCn00 and PSCn01 signals are centered.
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Figure 16-9. PSCn0 & PSCn1 Basic Waveforms in Center Aligned Mode
OCRnRB
OCRnSB
PSC Counter
OCRnSA
0
On-Time 0
On-Time 1
On-Time 1
PSCOUTn0
PSCOUTn1
(AT90PWM2/3)
PSCOUTn1
(AT90PWM2B/3B)
Dead-Time
Dead-Time
PSC Cycle
On-Time 0 = 2 * OCRnSAH/L * 1/Fclkpsc
On-Time 1 = 2 * (OCRnRBH/L - OCRnSBH/L + 1) * 1/Fclkpsc
Dead-Time = (OCRnSBH/L - OCRnSAH/L) * 1/Fclkpsc
PSC Cycle = 2 * (OCRnRBH/L + 1) * 1/Fclkpsc
Note:
Minimal value for PSC Cycle = 2 * 1/Fclkpsc
OCRnRAH/L is not used to control PSC Output waveform timing. Nevertheless, it can be useful
to adjust ADC synchronization (See “Analog Synchronization” on page 158.).
Figure 16-10. Run and Stop Mechanism in Centered Mode
OCRnRB
OCRnSB
OCRnSA
PSC Counter
0
Run
PSCOUTn0
PSCOUTn1
(AT90PWM2/3)
PSCOUTn1
(AT90PWM2B/3B)
Note:
See “PSC 0 Control Register – PCTL0” on page 165.(or PCTL1 or PCTL2)
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16.5.3
Fifty Percent Waveform Configuration
When PSCOUTn0 and PSCOUTn1 have the same characteristics, it’s possible to configure the
PSC in a Fifty Percent mode. When the PSC is in this configuration, it duplicates the
OCRnSBH/L and OCRnRBH/L registers in OCRnSAH/L and OCRnRAH/L registers. So it is not
necessary to program OCRnSAH/L and OCRnRAH/L registers.
16.6
Update of Values
To avoid unasynchronous and incoherent values in a cycle, if an update of one of several values
is necessary, all values are updated at the same time at the end of the cycle by the PSC. The
new set of values is calculated by sofware and the update is initiated by software.
Figure 16-11. Update at the end of complete PSC cycle.
Regulation Loop
Calculation
Writting in
PSC Registers
Software
Cycle
With Set i
Cycle
With Set i
Cycle
With Set i
Request for
an Update
Cycle
With Set i
PSC
Cycle
With Set j
End of Cycle
The software can stop the cycle before the end to update the values and restart a new PSC
cycle.
16.6.1
Value Update Synchronization
New timing values or PSC output configuration can be written during the PSC cycle. Thanks to
LOCK and AUTOLOCK configuration bits, the new whole set of values can be taken into
account after the end of the PSC cycle.
When AUTOLOCK configuration is selected, the update of the PSC internal registers will be
done at the end of the PSC cycle if the Output Compare Register RB has been the last written.
The AUTOLOCK configuration bit is taken into account at the end of the first PSC cycle.
When LOCK configuration bit is set, there is no update. The update of the PSC internal registers
will be done at the end of the PSC cycle if the LOCK bit is released to zero.
The registers which update is synchronized thanks to LOCK and AUTOLOCK are PSOCn,
POM2, OCRnSAH/L, OCRnRAH/L, OCRnSBH/L and OCRnRBH/L.
See these register’s description starting on page 163.
When set, AUTOLOCK configuration bit prevails over LOCK configuration bit.
See “PSC 0 Configuration Register – PCNF0” on page 164.
16.7
Enhanced Resolution
Lamp Ballast applications need an enhanced resolution down to 50Hz. The method to improve
the normal resolution is based on Flank Width Modulation (also called Fractional Divider).
Cycles are grouped into frames of 16 cycles. Cycles are modulated by a sequence given by the
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fractional divider number. The resulting output frequency is the average of the frequencies in the
frame. The fractional divider (d) is given by OCRnRB[15:12].
The PSC output period is directly equal to the PSCOUTn0 On Time + Dead Time (OT0+DT0)
and PSCOUTn1 On Time + DeadTime (OT1+DT1) values. These values are 12 bits numbers.
The frequency adjustment can only be done in steps like the dedicated counters. The step width
is defined as the frequency difference between two neighboring PSC frequencies:
f PLL f PLL
1
Δf = f1 – f2 = ---------- – ------------ = fPSC × -------------------k(k + 1 )
k
k+1
with k is the number of CLKPSC period in a PSC cycle and is given by the following formula:
fPSC
n = ---------fOP
with fOP is the output operating frequency.
Exemple, in normal mode, with maximum operating frequency 160 kHz and fPLL = 64 Mhz, k
equals 400. The resulting resolution is Delta F equals 64MHz / 400 / 401 = 400 Hz.
In enhanced mode, the output frequency is the average of the frame formed by the 16 consecutive cycles.
16 – d
d
f AVERAGE = --------------- × fb1 + ------ × f b2
16
16
fb1 and fb2 are two neightboring base frequencies.
f PLL
16 – d f PLL d
f AVERAGE = --------------- × ---------- + ------ × -----------n
16
16 n + 1
Then the frequency resolution is divided by 16. In the example above, the resolution equals 25
Hz.
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16.7.1
Frequency distribution
The frequency modulation is done by switching two frequencies in a 16 consecutive cycle frame.
These two frequencies are fb1 and fb2 where fb1 is the nearest base frequency above the wanted
frequency and fb2 is the nearest base frequency below the wanted frequency. The number of fb1
in the frame is (d-16) and the number of fb2 is d. The fb1 and fb2 frequencies are evenly distributed in the frame according to a predefined pattern. This pattern can be as given in the following
table or by any other implementation which give an equivallent evenly distribution.
Table 16-5.
Distribution of fb2 in the modulated frame
Distribution of fb2 in the modulated frame
PWM - cycle
Fraction
al
Divider
(d)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
1
X
2
X
3
X
X
X
4
X
X
X
X
5
X
X
X
X
X
6
X
X
X
X
X
X
7
X
X
X
X
X
X
X
8
X
X
X
X
X
X
X
X
9
X
X
X
X
X
X
X
X
X
10
X
X
X
X
X
X
X
X
X
X
11
X
X
X
X
X
X
X
X
X
X
X
12
X
X
X
X
X
X
X
X
X
X
X
X
13
X
X
X
X
X
X
X
X
X
X
X
X
X
14
X
X
X
X
X
X
X
X
X
X
X
X
X
X
15
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
While ‘X’ in the table, fb2 prime to fb1 in cycle corresponding cycle.
So for each row, a number of fb2 take place of fb1.
Figure 16-12. Resulting Frequency versus d.
fb1
fb2
fOP
d:
142
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
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16.7.2
Modes of Operation
16.7.2.1
Normal Mode
The simplest mode of operation is the normal mode. See Figure 16-6.
The active time of PSCOUTn0 is given by the OT0 value. The active time of PSCOUTn1 is given
by the OT1 value. Both of them are 12 bit values. Thanks to DT0 & DT1 to ajust the dead time
between PSCOUTn0 and PSCOUTn1 active signals.
The waveform frequency is defined by the following equation:
f CLK_PSCn
1
f PSCn = ------------------------------ = ---------------------------------------------------------------------- =
PSCnCycle
( OT0 + OT1 + DT0 + DT1 )
16.7.2.2
= 1
Enhanced Mode
The Enhanced Mode uses the previously described method to generate a high resolution
frequency.
Figure 16-13. Enhanced Mode, Timing Diagram
DT0
OT0
DT1
DT0
OT1
DT1
OT0
OT1+1
DT0
PSCOUTn0
PSCOUTn1
Period
T2
T1
The supplementary step in counting to generate fb2 is added on the PSCn0 signal while needed
in the frame according to the fractional divider. SeeTable 16-5, “Distribution of fb2 in the modulated frame,” on page 142.
The waveform frequency is defined by the following equations:
f CLK_PSCn
1
f1 PSCn = ------ = ---------------------------------------------------------------------T1
( OT0 + OT1 + DT0 + DT1 )
f CLK_PSCn
1
f2 PSCn = ------ = -------------------------------------------------------------------------------T2
( OT0 + OT1 + DT0 + DT1 + 1 )
d
16 – d
fAVERAGE = ------ × f1 PSCn + --------------- × f2 PSCn
16
16
d is the fractionel divider factor.
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16.8
PSC Inputs
Each part A or B of PSC has its own system to take into account one PSC input. According to
PSC n Input A/B Control Register (see description 16.25.14page 168), PSCnIN0/1 input can act
has a Retrigger or Fault input.
This system A or B is also configured by this PSC n Input A/B Control Register (PFRCnA/B).
Figure 16-14. PSC Input Module
PAOCnA
(PAOCnB)
0
PSCINn
Analog
Comparator
n Output
0
Digital
Filter
1
1
CLK PSC
PFLTEnA
(PFLTEnB)
PISELnA
(PISELnB)
PELEVnA / PCAEnA
(PELEVnB) (PCAEnB)
PRFMnA3:0
(PRFMnB3:0)
2
4
Input
Processing
(retriggering ...)
CLK PSC
PSC Core
(Counter,
Waveform
Generator, ...)
CLK PSC
16.8.1
Output
Control
PSCOUTn0
(PSCOUTn1)
(PSCOUT22)
(PSCOUT23)
PSC Retrigger Behaviour versus PSC running modes
In centered mode, Retrigger Inputs have no effect.
In two ramp or four ramp mode, Retrigger Inputs A or B cause the end of the corresponding
cycle A or B and the beginning of the following cycle B or A.
In one ramp mode, Retrigger Inputs A or B reset the current PSC counting to zero.
16.8.2
Retrigger PSCOUTn0 On External Event
PSCOUTn0 ouput can be resetted before end of On-Time 0 on the change on PSCn Input A.
PSCn Input A can be configured to do not act or to act on level or edge modes. The polarity of
PSCn Input A is configurable thanks to a sense control block. PSCn Input A can be the Output of
the analog comparator or the PSCINn input.
As the period of the cycle decreases, the instantaneous frequency of the two outputs increases.
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Figure 16-15. PSCOUTn0 retriggered by PSCn Input A (Edge Retriggering)
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
PSCn Input A
(falling edge)
PSCn Input A
(rising edge)
Dead-Time 0
Note:
Dead-Time 1
This exemple is given in “Input Mode 8” in “2 or 4 ramp mode” See Figure 16-31. for details.
Figure 16-16. PSCOUTn0 retriggered by PSCn Input A (Level Acting)
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
PSCn Input A
(high level)
PSCn Input A
(low level)
Dead-Time 0
Note:
16.8.3
Dead-Time 1
This exemple is given in “Input Mode 1” in “2 or 4 ramp mode” See Figure 16-20. for details.
Retrigger PSCOUTn1 On External Event
PSCOUTn1 ouput can be resetted before end of On-Time 1 on the change on PSCn Input B.
The polarity of PSCn Input B is configurable thanks to a sense control block. PSCn Input B can
be configured to do not act or to act on level or edge modes. PSCn Input B can be the Output of
the analog comparator or the PSCINn input.
As the period of the cycle decreases, the instantaneous frequency of the two outputs increases.
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Figure 16-17. PSCOUTn1 retriggered by PSCn Input B (Edge Retriggering)
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
PSCn Input B
(falling edge)
PSCn Input B
(rising edge)
Dead-Time 0
Note:
Dead-Time 1
Dead-Time 0
This exemple is given in “Input Mode 8” in “2 or 4 ramp mode” See Figure 16-31. for details.
Figure 16-18. PSCOUTn1 retriggered by PSCn Input B (Level Acting)
On-Time 0
On-Time 1
PSCOUTn0
PSCOUTn1
PSCn Input B
(high level)
PSCn Input B
(low level)
Dead-Time 0
Note:
16.8.3.1
Dead-Time 0
This exemple is given in “Input Mode 1” in “2 or 4 ramp mode” See Figure 16-20. for details.
Burst Generation
Note:
146
Dead-Time 1
On level mode, it’s possible to use PSC to generate burst by using Input Mode 3 or
Mode 4 (See Figure 16-24. and Figure 16-25. for details.)
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Figure 16-19. Burst Generation
OFF
BURST
PSCOUTn0
PSCOUTn1
PSCn Input A
(high level)
PSCn Input A
(low level)
16.8.4
PSC Input Configuration
The PSC Input Configuration is done by programming bits in configuration registers.
16.8.4.1
Filter Enable
If the “Filter Enable” bit is set, a digital filter of 4 cycles is inserted before evaluation of the signal.
The disable of this function is mainly needed for prescaled PSC clock sources, where the noise
cancellation gives too high latency.
Important: If the digital filter is active, the level sensitivity is true also with a disturbed PSC clock
to deactivate the outputs (emergency protection of external component). Likewise when used as
fault input, PSCn Input A or Input B have to go through PSC to act on PSCOUTn0/1/2/3 output.
This way needs that CLK PSC is running. So thanks to PSC Asynchronous Output Control bit
(PAOCnA/B), PSCnIN0/1 input can desactivate directly the PSC output. Notice that in this case,
input is still taken into account as usually by Input Module System as soon as CLKPSC is running.
PSC Input Filterring
CLKPSC
Digital
Filter
4 x CLK PSC
PSC Input
Module X
16.8.4.2
PSCn Input A or B
Ouput
Stage
PSCOUTnX
PIN
Signal Polarity
One can select the active edge (edge modes) or the active level (level modes) See PELEVnx bit
description in Section “PSC n Input A Control Register – PFRCnA”, page 16816.25.14.
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If PELEVnx bit set, the significant edge of PSCn Input A or B is rising (edge modes) or the active
level is high (level modes) and vice versa for unset/falling/low
- In 2- or 4-ramp mode, PSCn Input A is taken into account only during Dead-Time0 and OnTime0 period (respectively Dead-Time1 and On-Time1 for PSCn Input B).
- In 1-ramp-mode PSC Input A or PSC Input B act on the whole ramp.
16.8.4.3
Input Mode Operation
Thanks to 4 configuration bits (PRFM3:0), it’s possible to define the mode of the PSC input. All
Table 16-6.
PSC Input Mode Operation
PRFM3:0
Description
0
0000b
PSCn Input has no action on PSC output
1
0001b
2
0010b
3
0011b
4
0100b
5
0101b
6
0110b
7
0111b
8
1000b
9
1001b
10
1010b
11
1011b
12
1100b
13
1101b
14
1110b
15
1111b
16.9See “PSC Input Mode 1: Stop signal, Jump to Opposite Dead-Time
and Wait” on page 149.
See “PSC Input Mode 2: Stop signal, Execute Opposite Dead-Time and
Wait” on page 150.
See “PSC Input Mode 3: Stop signal, Execute Opposite while Fault
active” on page 151.
See “PSC Input Mode 4: Deactivate outputs without changing timing.” on
page 151.
See “PSC Input Mode 5: Stop signal and Insert Dead-Time” on page 152.
See “PSC Input Mode 6: Stop signal, Jump to Opposite Dead-Time and
Wait.” on page 153.
See “PSC Input Mode 7: Halt PSC and Wait for Software Action” on page
153.
See “PSC Input Mode 8: Edge Retrigger PSC” on page 153.
See “PSC Input Mode 9: Fixed Frequency Edge Retrigger PSC” on page
154.
Reserved : Do not use
See “PSC Input Mode 14: Fixed Frequency Edge Retrigger PSC and Disactivate Output” on page 155.
Reserved : Do not use
Notice: All following examples are given with rising edge or high level active inputs.
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16.9
PSC Input Mode 1: Stop signal, Jump to Opposite Dead-Time and Wait
Figure 16-20. PSCn behaviour versus PSCn Input A in Fault Mode 1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input A is taken into account during DT0 and OT0 only. It has no effect during DT1 and
OT1.
When PSC Input A event occurs, PSC releases PSCOUTn0, waits for PSC Input A inactive state
and then jumps and executes DT1 plus OT1.
Figure 16-21. PSCn behaviour versus PSCn Input B in Fault Mode 1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input B is take into account during DT1 and OT1 only. It has no effect during DT0 and OT0.
When PSC Input B event occurs, PSC releases PSCOUTn1, waits for PSC Input B inactive state
and then jumps and executes DT0 plus OT0.
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16.10 PSC Input Mode 2: Stop signal, Execute Opposite Dead-Time and Wait
Figure 16-22. PSCn behaviour versus PSCn Input A in Fault Mode 2
DT0
OT0
DT1
OT1
DT0 OT0 DT1 OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input A is take into account during DT0 and OT0 only. It has no effect during DT1 and OT1.
When PSCn Input A event occurs, PSC releases PSCOUTn0, jumps and executes DT1 plus
OT1 and then waits for PSC Input A inactive state.
Even if PSC Input A is released during DT1 or OT1, DT1 plus OT1 sub-cycle is always completely executed.
Figure 16-23. PSCn behaviour versus PSCn Input B in Fault Mode 2
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1 DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input B is take into account during DT1 and OT1 only. It has no effect during DT0 and OT0.
When PSC Input B event occurs, PSC releases PSCOUTn1, jumps and executes DT0 plus OT0
and then waits for PSC Input B inactive state.
Even if PSC Input B is released during DT0 or OT0, DT0 plus OT0 sub-cycle is always completely executed.
150
AT90PWM2/3/2B/3B
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AT90PWM2/3/2B/3B
16.11 PSC Input Mode 3: Stop signal, Execute Opposite while Fault active
Figure 16-24. PSCn behaviour versus PSCn Input A in Mode 3
DT0
OT0
DT1
OT1
DT0 OT0 DT1 OT1
DT1 OT1
DT1 OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input A is taken into account during DT0 and OT0 only. It has no effect during DT1 and
OT1.
When PSC Input A event occurs, PSC releases PSCOUTn0, jumps and executes DT1 plus OT1
plus DT0 while PSC Input A is in active state.
Even if PSC Input A is released during DT1 or OT1, DT1 plus OT1 sub-cycle is always completely executed.
Figure 16-25. PSCn behaviour versus PSCn Input B in Mode 3
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1 DT0
OT0
DT0
OT0
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSC Input A
PSC Input B
PSC Input B is taken into account during DT1 and OT1 only. It has no effect during DT0 and
OT0.
When PSC Input B event occurs, PSC releases PSCnOUT1, jumps and executes DT0 plus OT0
plus DT1 while PSC Input B is in active state.
Even if PSC Input B is released during DT0 or OT0, DT0 plus OT0 sub-cycle is always completely executed.
16.12 PSC Input Mode 4: Deactivate outputs without changing timing.
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Figure 16-26. PSC behaviour versus PSCn Input A or Input B in Mode 4
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
or
PSCn Input B
Figure 16-27. PSC behaviour versus PSCn Input A or Input B in Fault Mode 4
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
or
PSCn Input B
PSCn Input A or PSCn Input B act indifferently on On-Time0/Dead-Time0 or on OnTime1/Dead-Time1.
16.13 PSC Input Mode 5: Stop signal and Insert Dead-Time
PSCOUTn0
OT1
DT0 OT0
DT0
DT1
DT1
DT0
DT1
OT0
DT1
DT0
DT0
Figure 16-28. PSC behaviour versus PSCn Input A in Fault Mode 5
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn1
PSCn Input A
or
PSCn Input B
Used in Fault mode 5, PSCn Input A or PSCn Input B act indifferently on On-Time0/Dead-Time0
or on On-Time1/Dead-Time1.
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16.14 PSC Input Mode 6: Stop signal, Jump to Opposite Dead-Time and Wait.
Figure 16-29. PSC behaviour versus PSCn Input A in Fault Mode 6
DT0
OT0
DT1 OT1
DT0 OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
or
PSCn Input B
Used in Fault mode 6, PSCn Input A or PSCn Input B act indifferently on On-Time0/Dead-Time0
or on On-Time1/Dead-Time1.
16.15 PSC Input Mode 7: Halt PSC and Wait for Software Action
Figure 16-30. PSC behaviour versus PSCn Input A in Fault Mode 7
DT0
OT0
DT1
OT1
DT0 OT0
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
or
PSCn Input B
Software Action (1)
Note:
1. Software action is the setting of the PRUNn bit in PCTLn register.
Used in Fault mode 7, PSCn Input A or PSCn Input B act indifferently on On-Time0/Dead-Time0
or on On-Time1/Dead-Time1.
16.16 PSC Input Mode 8: Edge Retrigger PSC
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Figure 16-31. PSC behaviour versus PSCn Input A in Mode 8
DT0
OT0
DT1
DT0 OT0
OT1
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
The output frequency is modulated by the occurence of significative edge of retriggering input.
Figure 16-32. PSC behaviour versus PSCn Input B in Mode 8
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input B
or
PSCn Input B
The output frequency is modulated by the occurrence of significative edge of retriggering input.
The retrigger event is taken into account only if it occurs during the corresponding On-Time.
Note: In one ramp mode, the retrigger event on input A resets the whole ramp. So the PSC
doesn’t jump to the opposite dead-time.
16.17 PSC Input Mode 9: Fixed Frequency Edge Retrigger PSC
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Figure 16-33. PSC behaviour versus PSCn Input A in Mode 9
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
The output frequency is not modified by the occurence of significative edge of retriggering input.
Only the output is disactivated when significative edge on retriggering input occurs.
Note: In this mode the output of the PSC becomes active during the next ramp even if the Retrigger/Fault input is actve. Only the significative edge of Retrigger/Fault input is taken into account.
Figure 16-34. PSC behaviour versus PSCn Input B in Mode 9
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input B
The retrigger event is taken into account only if it occurs during the corresponding On-Time.
16.18 PSC Input Mode 14: Fixed Frequency Edge Retrigger PSC and Disactivate Output
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Figure 16-35. PSC behaviour versus PSCn Input A in Mode 14
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input A
The output frequency is not modified by the occurence of significative edge of retriggering input.
Figure 16-36. PSC behaviour versus PSCn Input B in Mode 14
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
DT0
OT0
DT1
OT1
PSCOUTn0
PSCOUTn1
PSCn Input B
The output is disactivated while retriggering input is active.
The output of the PSC is set to an inactive state and the corresponding ramp is not aborted. The
output stays in an inactive state while the Retrigger/Fault input is actve. The PSC runs at constant frequency.
AT90PWM2/3 : The retrigger event is taken into account only if it occurs during the corresponding On-Time. In the case of the retrigger event is not taken into account, the following active
outputs remains active, they are not desactivated.
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16.18.1
Available Input Mode according to Running Mode
Some Input Modes are not consistent with some Running Modes. So the table below gives the
input modes which are valid according to running modes..
Table 16-7.
Available Input Modes according to Running Modes
Input Mode
Number :
1 Ramp Mode
2 Ramp Mode
4 Ramp Mode
Centered Mode
1
Valid
Valid
Valid
Do not use
2
Do not use
Valid
Valid
Do not use
3
Do not use
Valid
Valid
Do not use
4
Valid
Valid
Valid
Valid
5
Do not use
Valid
Valid
Do not use
6
Do not use
Valid
Valid
Do not use
7
Valid
Valid
Valid
Valid
8
Valid
Valid
Valid
Do not use
9
Valid
Valid
Valid
Do not use
Valid
Valid
Do not use
10
11
Do not use
12
13
16.18.2
14
Valid
15
Do not use
Event Capture
The PSC can capture the value of time (PSC counter) when a retrigger event or fault event
occurs on PSC inputs. This value can be read by sofware in PICRnH/L register.
16.18.3
Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the PICRn Register before the next event occurs, the PICRn will
be overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the PICRn Register should be read as early in the interrupt handler routine as possible. Even though the Input Capture interrupt has relatively high
priority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.
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16.19 PSC2 Outputs
16.19.1
Output Matrix
PSC2 has an output matrix which allow in 4 ramp mode to program a value of PSCOUT20 and
PSCOUT21 binary value for each ramp.
Table 16-8.
Output Matrix versus ramp number
Ramp 0
Ramp 1
Ramp 2
Ramp 3
PSCOUT20
POMV2A0
POMV2A1
POMV2A2
POMV2A3
PSCOUT21
POMV2B0
POMV2B1
POMV2B2
POMV2B3
PSCOUT2m takes the value given in Table 16-8. during all corresponding ramp. Thanks to the
Output Matrix it is possible to generate all kind of PSCOUT20/PSCOUT21 combination.
When Output Matrix is used, the PSC n Output Polarity POPn has no action on the outputs.
16.19.2
PSCOUT22 & PSCOUT23 Selectors
PSC 2 has two supplementary outputs PSCOUT22 and PSCOUT23.
According to POS22 and POS23 bits in PSOC2 register, PSCOUT22 and PSCOUT23 duplicate
PSCOUT20 and PSCOU21.
If POS22 bit in PSOC2 register is clear, PSCOUT22 duplicates PSCOUT20.
If POS22 bit in PSOC2 register is set, PSCOUT22 duplicates PSCOUT21.
If POS23 bit in PSOC2 register is clear, PSCOUT23 duplicates PSCOUT21.
If POS23 bit in PSOC2 register is set, PSCOUT23 duplicates PSCOUT20.
Figure 16-37. PSCOUT22 and PSCOUT23 Outptuts
PSCOUT20
Waveform
Generator A
0
PSCOUT22
1
POS22
POS23
Output
Matrix
1
PSCOUT23
0
Waveform
Generator B
PSCOUT21
16.20 Analog Synchronization
PSC generates a signal to synchronize the sample and hold; synchronisation is mandatory for
measurements.
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This signal can be selected between all falling or rising edge of PSCn0 or PSCn1 outputs.
In center aligned mode, OCRnRAH/L is not used, so it can be used to specified the synchronization of the ADC. It this case, it’s minimum value is 1.
16.21 Interrupt Handling
As each PSC can be dedicated for one function, each PSC has its own interrupt system (vector
...)
List of interrupt sources:
•
Counter reload (end of On Time 1)
•
PSC Input event (active edge or at the beginning of level configured event)
•
PSC Mutual Synchronization Error
16.22 PSC Synchronization
2 or 3 PSC can be synchronized together. In this case, two waveform alignments are possible:
•
The waveforms are center aligned in the Center Aligned mode if master and slaves are all
with the same PSC period (which is the natural use).
•
The waveforms are edge aligned in the 1, 2 or 4 ramp mode
Figure 16-38. PSC Run Synchronization
SY0In
PRUN0
Run PSC0
PARUN0
SY0Out
PSC0
SY1In
PRUN1
Run PSC1
PARUN1
SY1Out
PSC1
SY2In
PRUN2
Run PSC2
PARUN2
SY2Out
PSC2
If the PSCm has its PARUNn bit set, then it can start at the same time than PSCn-1.
PRUNn and PARUNn bits are located in PCTLn register. See “PSC 0 Control Register – PCTL0”
on page 165. See “PSC 1 Control Register – PCTL1” on page 166. See “PSC 2 Control Register
– PCTL2” on page 167.
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Note : Do not set the PARUNn bits on the three PSC at the same time.
Thanks to this feature, we can for example configure two PSC in slave mode (PARUNn = 1 /
PRUNn = 0) and one PSC in master mode (PARUNm = 0 / PRUNm = 0). This PSC master can
start all PSC at the same moment ( PRUNm = 1).
16.22.1
Fault events in Autorun mode
To complete this master/slave mechanism, fault event (input mode 7) is propagated from PSCn1 to PSCn and from PSCn to PSCn-1.
A PSC which propagate a Run signal to the following PSC stops this PSC when the Run signal
is deactivate.
According to the architecture of the PSC synchronization which build a “daisy-chain on the PSC
run signal” beetwen the three PSC, only the fault event (mode 7) which is able to “stop” the PSC
through the PRUN bits is transmited along this daisy-chain.
A PSC which receive its Run signal from the previous PSC transmits its fault signal (if enabled)
to this previous PSC. So a slave PSC propagates its fault events when they are configured and
enabled.
16.23 PSC Clock Sources
PSC must be able to generate high frequency with enhanced resolution.
Each PSC has two clock inputs:
•
CLK PLL from the PLL
•
CLK I/O
Figure 16-39. Clock selection
1
CK
(1) : CK/16 for AT90PWM2/3
(2) : CK/64 for AT90PWM2/3
CK/256 (2)
CK/4
01
PCLKSELn
11
CK
0
I/O
00
CLK
PRESCALER
CK/32 (1)
PLL
10
CLK
PPREn1/0
CLK PSCn
PCLKSELn bit in PSC n Configuration register (PCNFn) is used to select the clock source.
PPREn1/0 bits in PSC n Control Register (PCTLn) are used to select the divide factor of the
clock.
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Table 16-9.
Output Clock versus Selection and Prescaler
PCLKSELn
PPREn1
PPREn0
CLKPSCn output
AT90PWM2/3
CLKPSCn output
AT90PWM2B/3B
0
0
0
CLK I/O
CLK I/O
0
0
1
CLK I/O / 4
CLK I/O / 4
0
1
0
CLK I/O / 16
CLK I/O / 32
0
1
1
CLK I/O / 64
CLK I/O / 256
1
0
0
CLK PLL
CLK PLL
1
0
1
CLK PLL / 4
CLK PLL / 4
1
1
0
CLK PLL / 16
CLK PLL / 32
1
1
1
CLK PLL / 64
CLK PLL / 256
16.24 Interrupts
This section describes the specifics of the interrupt handling as performed in
AT90PWM2/2B/3/3B.
16.24.1
List of Interrupt Vector
Each PSC provides 2 interrupt vectors
•
PSCn EC (End of Cycle): When enabled and when a match with OCRnRB occurs
•
PSCn CAPT (Capture Event): When enabled and one of the two following events occurs :
retrigger, capture of the PSC counter or Synchro Error.
16.26.216.26.2See PSCn Interrupt Mask Register page 171 and PSCn Interrupt Flag Register
page 172.
16.24.2
PSC Interrupt Vectors in AT90PWM2/2B/3/3B
Table 16-10. PSC Interrupt Vectors
Vector
No.
Program
Address
-
-
2
0x0001
PSC2 CAPT
PSC2 Capture Event or Synchronization Error
3
0x0002
PSC2 EC
PSC2 End Cycle
4
0x0003
PSC1 CAPT
PSC1 Capture Event or Synchronization Error
5
0x0004
PSC1 EC
PSC1 End Cycle
6
0x0005
PSC0 CAPT
PSC0 Capture Event or Synchronization Error
7
0x0006
PSC0 EC
PSC0 End Cycle
-
-
Source
Interrupt Definition
-
-
-
-
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16.25 PSC Register Definition
Registers are explained for PSC0. They are identical for PSC1. For PSC2 only different registers
are described.
16.25.1
PSC 0 Synchro and Output Configuration – PSOC0
Bit
16.25.2
7
6
5
4
3
2
1
0
-
-
PSYNC01
PSYNC00
-
POEN0B
-
POEN0A
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
PSC 1 Synchro and Output Configuration – PSOC1
Bit
16.25.3
PSOC0
7
6
5
4
3
2
1
0
-
-
PSYNC11
PSYNC10
-
POEN1B
-
POEN1A
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
PSOC1
PSC 2 Synchro and Output Configuration – PSOC2
Bit
7
6
5
4
3
2
1
0
POS23
POS22
PSYNC21
PSYNC20
POEN2D
POEN2B
POEN2C
POEN2A
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
PSOC2
• Bit 7 – POS23 : PSCOUT23 Selection (PSC2 only)
When this bit is clear, PSCOUT23 outputs the waveform generated by Waveform Generator B.
When this bit is set, PSCOUT23 outputs the waveform generated by Waveform Generator A.
• Bit 6 – POS22 : PSCOUT22 Selection (PSC2 only)
When this bit is clear, PSCOUT22 outputs the waveform generated by Waveform Generator A.
When this bit is set, PSCOUT22 outputs the waveform generated by Waveform Generator B.
• Bit 5:4 – PSYNCn1:0: Synchronization Out for ADC Selection
Select the polarity and signal source for generating a signal which will be sent to the ADC for
synchronization.
Table 16-11. Synchronization Source Description in One/Two/Four Ramp Modes
162
PSYNCn1
PSYNCn0
Description
0
0
Send signal on leading edge of PSCOUTn0 (match with OCRnSA)
0
1
Send signal on trailing edge of PSCOUTn0 (match with OCRnRA or
fault/retrigger on part A)
1
0
Send signal on leading edge of PSCOUTn1 (match with OCRnSB)
1
1
Send signal on trailing edge of PSCOUTn1 (match with OCRnRB or
fault/retrigger on part B)
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 16-12. Synchronization Source Description in Centered Mode
PSYNCn1
PSYNCn0
Description
0
0
Send signal on match with OCRnRA (during counting down of PSC). The
min value of OCRnRA must be 1.
0
1
Send signal on match with OCRnRA (during counting up of PSC). The
min value of OCRnRA must be 1.
1
0
no synchronization signal
1
1
no synchronization signal
• Bit 3 – POEN2D : PSCOUT23 Output Enable (PSC2 only)
When this bit is clear, second I/O pin affected to PSCOUT23 acts as a standard port.
When this bit is set, second I/O pin affected to PSCOUT23 is connected to the PSC waveform
generator B output and is set and clear according to the PSC operation.
• Bit 2 – POENnB: PSC n OUT Part B Output Enable
When this bit is clear, I/O pin affected to PSCOUTn1 acts as a standard port.
When this bit is set, I/O pin affected to PSCOUTn1 is connected to the PSC waveform generator
B output and is set and clear according to the PSC operation.
• Bit 1 – POEN2C : PSCOUT22 Output Enable (PSC2 only)
When this bit is clear, second I/O pin affected to PSCOUT22 acts as a standard port.
When this bit is set, second I/O pin affected to PSCOUT22 is connected to the PSC waveform
generator A output and is set and clear according to the PSC operation.
• Bit 0 – POENnA: PSC n OUT Part A Output Enable
When this bit is clear, I/O pin affected to PSCOUTn0 acts as a standard port.
When this bit is set, I/O pin affected to PSCOUTn0 is connected to the PSC waveform generator
A output and is set and clear according to the PSC operation.
16.25.4
Output Compare SA Register – OCRnSAH and OCRnSAL
Bit
7
6
5
4
–
–
–
–
3
2
1
0
OCRnSA[11:8]
OCRnSAH
OCRnSA[7:0]
16.25.5
OCRnSAL
Read/Write
W
W
W
W
W
W
W
W
Initial Value
0
0
0
0
0
0
0
0
2
1
0
Output Compare RA Register – OCRnRAH and OCRnRAL
Bit
7
6
5
4
–
–
–
–
3
OCRnRA[11:8]
OCRnRAH
OCRnRA[7:0]
16.25.6
OCRnRAL
Read/Write
W
W
W
W
W
W
W
W
Initial Value
0
0
0
0
0
0
0
0
2
1
0
Output Compare SB Register – OCRnSBH and OCRnSBL
Bit
7
6
5
4
–
–
–
–
3
OCRnSB[7:0]
OCRnSB[11:8]
OCRnSBH
OCRnSBL
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16.25.7
Read/Write
W
W
W
W
W
W
W
W
Initial Value
0
0
0
0
0
0
0
0
2
1
0
Output Compare RB Register – OCRnRBH and OCRnRBL
Bit
7
6
5
4
3
OCRnRB[15:12]
OCRnRB[11:8]
OCRnRBH
OCRnRB[7:0]
OCRnRBL
Read/Write
W
W
W
W
W
W
W
W
Initial Value
0
0
0
0
0
0
0
0
Note : n = 0 to 2 according to PSC number.
The Output Compare Registers RA, RB, SA and SB contain a 12-bit value that is continuously
compared with the PSC counter value. A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the associated pin.
The Output Compare Registers RB contains also a 4-bit value that is used for the flank width
modulation.
The Output Compare Registers are 16bit and 12-bit in size. To ensure that both the high and low
bytes are written simultaneously when the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary register is shared by
all the other 16-bit registers.
16.25.8
PSC 0 Configuration Register – PCNF0
Bit
16.25.9
7
6
5
4
3
2
1
PFIFTY0
PALOCK0
PLOCK0
PMODE01
PMODE00
POP0
PCLKSEL0
0
-
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
0
PCNF0
PSC 1 Configuration Register – PCNF1
Bit
7
6
5
4
3
2
1
PFIFTY1
PALOCK1
PLOCK1
PMODE11
PMODE10
POP1
PCLKSEL1
-
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
PCNF1
16.25.10 PSC 2 Configuration Register – PCNF2
Bit
7
6
5
4
3
2
1
0
PFIFTY2
PALOCK2
PLOCK2
PMODE21
PMODE20
POP2
PCLKSEL2
POME2
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
PCNF2
The PSC n Configuration Register is used to configure the running mode of the PSC.
• Bit 7 - PFIFTYn: PSC n Fifty
Writing this bit to one, set the PSC in a fifty percent mode where only OCRnRBH/L and
OCRnSBH/L are used. They are duplicated in OCRnRAH/L and OCRnSAH/L during the update
of OCRnRBH/L. This feature is useful to perform fifty percent waveforms.
• Bit 6 - PALOCKn: PSC n Autolock
When this bit is set, the Output Compare Registers RA, SA, SB, the Output Matrix POM2 and
the PSC Output Configuration PSOCn can be written without disturbing the PSC cycles. The
164
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
update of the PSC internal registers will be done at the end of the PSC cycle if the Output Compare Register RB has been the last written.
When set, this bit prevails over LOCK (bit 5)
• Bit 5 – PLOCKn: PSC n Lock
When this bit is set, the Output Compare Registers RA, RB, SA, SB, the Output Matrix POM2
and the PSC Output Configuration PSOCn can be written without disturbing the PSC cycles.
The update of the PSC internal registers will be done if the LOCK bit is released to zero.
• Bit 4:3 – PMODEn1: 0: PSC n Mode
Select the mode of PSC.
Table 16-13. PSC n Mode Selection
PMODEn1
PMODEn0
Description
0
0
One Ramp Mode
0
1
Two Ramp Mode
1
0
Four Ramp Mode
1
1
Center Aligned Mode
• Bit 2 – POPn: PSC n Output Polarity
If this bit is cleared, the PSC outputs are active Low.
If this bit is set, the PSC outputs are active High.
• Bit 1 – PCLKSELn: PSC n Input Clock Select
This bit is used to select between CLKPF or CLKPS clocks.
Set this bit to select the fast clock input (CLKPF).
Clear this bit to select the slow clock input (CLKPS).
• Bit 0 – POME2: PSC 2 Output Matrix Enable (PSC2 only)
Set this bit to enable the Output Matrix feature on PSC2 outputs. See “PSC2 Outputs” on page
158.
When Output Matrix is used, the PSC n Output Polarity POPn has no action on the outputs.
16.25.11 PSC 0 Control Register – PCTL0
Bit
7
6
5
4
3
2
1
0
PPRE01
PPRE00
PBFM0
PAOC0B
PAOC0A
PARUN0
PCCYC0
PRUN0
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
PCTL0
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4317I–AVR–01/08
• Bit 7:6 – PPRE01:0 : PSC 0 Prescaler Select
This two bits select the PSC input clock division factor. All generated waveform will be modified
by this factor.
Table 16-14. PSC 0 Prescaler Selection
PPRE01
PPRE00
Description PWM2/3
Description PWM2B/3B
0
0
No divider on PSC input clock
No divider on PSC input clock
0
1
Divide the PSC input clock by 4
Divide the PSC input clock by 4
1
0
Divide the PSC input clock by 16
Divide the PSC input clock by 32
1
1
Divide the PSC clock by 64
Divide the PSC clock by 256
• Bit 5 – PBFM0 : Balance Flank Width Modulation
When this bit is clear, Flank Width Modulation operates on On-Time 1 only.
When this bit is set, Flank Width Modulation operates on On-Time 0 and On-Time 1.
• Bit 4 – PAOC0B : PSC 0 Asynchronous Output Control B
When this bit is set, Fault input selected to block B can act directly to PSCOUT01 output. See
Section “PSC Input Configuration”, page 147.
• Bit 3 – PAOC0A : PSC 0 Asynchronous Output Control A
When this bit is set, Fault input selected to block A can act directly to PSCOUT00 output. See
Section “PSC Input Configuration”, page 147.
• Bit 2 – PARUN0 : PSC 0 Autorun
When this bit is set, the PSC 0 starts with PSC2. That means that PSC 0 starts :
•
when PRUN2 bit in PCTL2 is set,
•
or when PARUN2 bit in PCTL2 is set and PRUN1 bit in PCTL1 register is set.
Thanks to this bit, 2 or 3 PSCs can be synchronized (motor control for example)
• Bit 1 – PCCYC0 : PSC 0 Complete Cycle
When this bit is set, the PSC 0 completes the entire waveform cycle before halt operation
requested by clearing PRUN0. This bit is not relevant in slave mode (PARUN0 = 1).
• Bit 0 – PRUN0 : PSC 0 Run
Writing this bit to one starts the PSC 0.
When set, this bit prevails over PARUN0 bit.
16.25.12 PSC 1 Control Register – PCTL1
Bit
166
7
6
5
4
3
2
1
0
PPRE11
PPRE10
PBFM1
PAOC1B
PAOC1A
PARUN1
PCCYC1
PRUN1
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
PCTL1
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
• Bit 7:6 – PPRE11:0 : PSC 1 Prescaler Select
This two bits select the PSC input clock division factor.All generated waveform will be modified
by this factor.
Table 16-15. PSC 1 Prescaler Selection
PPRE11
PPRE10
Description PWM2/3
Description PWM2B/3B
0
0
No divider on PSC input clock
No divider on PSC input clock
0
1
Divide the PSC input clock by 4
Divide the PSC input clock by 4
1
0
Divide the PSC input clock by 16
Divide the PSC input clock by 32
1
1
Divide the PSC clock by 64
Divide the PSC clock by 256
• Bit 5 – PBFM1 : Balance Flank Width Modulation
When this bit is clear, Flank Width Modulation operates on On-Time 1 only.
When this bit is set, Flank Width Modulation operates on On-Time 0 and On-Time 1.
• Bit 4 – PAOC1B : PSC 1 Asynchronous Output Control B
When this bit is set, Fault input selected to block B can act directly to PSCOUT11 output. See
Section “PSC Clock Sources”, page 160
• Bit 3 – PAOC1A : PSC 1 Asynchronous Output Control A
When this bit is set, Fault input selected to block A can act directly to PSCOUT10 output. See
Section “PSC Clock Sources”, page 160
• Bit 2 – PARUN1 : PSC 1 Autorun
When this bit is set, the PSC 1 starts with PSC0. That means that PSC 1 starts :
•
when PRUN0 bit in PCTL0 register is set,
•
or when PARUN0 bit in PCTL0 is set and PRUN2 bit in PCTL2 register is set.
Thanks to this bit, 2 or 3 PSCs can be synchronized (motor control for example)
• Bit 1 – PCCYC1 : PSC 1 Complete Cycle
When this bit is set, the PSC 1 completes the entire waveform cycle before halt operation
requested by clearing PRUN1. This bit is not relevant in slave mode (PARUN1 = 1).
• Bit 0 – PRUN1 : PSC 1 Run
Writing this bit to one starts the PSC 1.
When set, this bit prevails over PARUN1 bit.
16.25.13 PSC 2 Control Register – PCTL2
Bit
7
6
5
4
3
2
1
0
PPRE21
PPRE20
PBFM2
PAOC2B
PAOC2A
PARUN2
PCCYC2
PRUN2
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
PCTL2
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4317I–AVR–01/08
• Bit 7:6 – PPRE21:0 : PSC 2 Prescaler Select
This two bits select the PSC input clock division factor.All generated waveform will be modified
by this factor.
Table 16-16. PSC 2 Prescaler Selection
PPRE21
PPRE20
Description PWM2/3
Description PWM2B/3B
0
0
No divider on PSC input clock
No divider on PSC input clock
0
1
Divide the PSC input clock by 4
Divide the PSC input clock by 4
1
0
Divide the PSC input clock by 16
Divide the PSC input clock by 32
1
1
Divide the PSC clock by 64
Divide the PSC clock by 256
• Bit 5 – PBFM2 : Balance Flank Width Modulation
When this bit is clear, Flank Width Modulation operates on On-Time 1 only.
When this bit is set, Flank Width Modulation operates on On-Time 0 and On-Time 1.
• Bit 4 – PAOC2B : PSC 2 Asynchronous Output Control B
When this bit is set, Fault input selected to block B can act directly to PSCOUT21 and
PSCOUT23 outputs. See Section “PSC Clock Sources”, page 160.
• Bit 3 – PAOC2A : PSC 2 Asynchronous Output Control A
When this bit is set, Fault input selected to block A can act directly to PSCOUT20 and
PSCOUT22 outputs. See Section “PSC Clock Sources”, page 160.
• Bit 2 – PARUN2 : PSC 2 Autorun
When this bit is set, the PSC 2 starts with PSC1. That means that PSC 2 starts :
•
when PRUN1 bit in PCTL1 register is set,
•
or when PARUN1 bit in PCTL1 is set and PRUN0 bit in PCTL0 register is set.
• Bit 1 – PCCYC2 : PSC 2 Complete Cycle
When this bit is set, the PSC 2 completes the entire waveform cycle before halt operation
requested by clearing PRUN2. This bit is not relevant in slave mode (PARUN2 = 1).
• Bit 0 – PRUN2 : PSC 2 Run
Writing this bit to one starts the PSC 2.
When set, this bit prevails over PARUN2 bit.
16.25.14 PSC n Input A Control Register – PFRCnA
Bit
168
7
6
5
4
PCAEnA
PISELnA
PELEVnA
PFLTEnA
3
2
1
0
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
PRFMnA3 PRFMnA2 PRFMnA1 PRFMnA0
PFRCnA
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
16.25.15 PSC n Input B Control Register – PFRCnB
Bit
7
6
5
4
PCAEnB
PISELnB
PELEVnB
PFLTEnB
3
2
1
0
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
PRFMnB3 PRFMnB2 PRFMnB1 PRFMnB0
PFRCnB
The Input Control Registers are used to configure the 2 PSC’s Retrigger/Fault block A & B. The
2 blocks are identical, so they are configured on the same way.
• Bit 7 – PCAEnx : PSC n Capture Enable Input Part x
Writing this bit to one enables the capture function when external event occurs on input selected
as input for Part x (see PISELnx bit in the same register).
• Bit 6 – PISELnx : PSC n Input Select for Part x
Clear this bit to select PSCINn as input of Fault/Retrigger block x.
Set this bit to select Comparator n Output as input of Fault/Retrigger block x.
• Bit 5 –PELEVnx : PSC n Edge Level Selector of Input Part x
When this bit is clear, the falling edge or low level of selected input generates the significative
event for retrigger or fault function .
When this bit is set, the rising edge or high level of selected input generates the significative
event for retrigger or fault function.
• Bit 4 – PFLTEnx : PSC n Filter Enable on Input Part x
Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is
activated, the input from the retrigger pin is filtered. The filter function requires four successive
equal valued samples of the retrigger pin for changing its output. The Input Capture is therefore
delayed by four oscillator cycles when the noise canceler is enabled.
• Bit 3:0 – PRFMnx3:0: PSC n Fault Mode
These four bits define the mode of operation of the Fault or Retrigger functions.
(see PSC Functional Specification for more explanations)
Table 16-17. Level Sensitivity and Fault Mode Operation
PRFMnx3:0
Description
0000b
No action, PSC Input is ignored
0001b
PSC Input Mode 1: Stop signal, Jump to Opposite Dead-Time and Wait
0010b
PSC Input Mode 2: Stop signal, Execute Opposite Dead-Time and Wait
0011b
PSC Input Mode 3: Stop signal, Execute Opposite while Fault active
0100b
PSC Input Mode 4: Deactivate outputs without changing timing.
0101b
PSC Input Mode 5: Stop signal and Insert Dead-Time
0110b
PSC Input Mode 6: Stop signal, Jump to Opposite Dead-Time and Wait.
0111b
PSC Input Mode 7: Halt PSC and Wait for Software Action
1000b
PSC Input Mode 8: Edge Retrigger PSC
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PRFMnx3:0
Description
1001b
PSC Input Mode 9: Fixed Frequency Edge Retrigger PSC
1010b
Reserved (do not use)
1011b
1100b
1101b
1110b
1111b
PSC Input Mode 14: Fixed Frequency Edge Retrigger PSC and Disactivate
Output
Reserved (do not use)
16.25.16 PSC 0 Input Capture Register – PICR0H and PICR0L
Bit
7
6
5
4
PCST0
–
–
–
3
2
1
0
PICR0[11:8]
PICR0H
PICR0[7:0]
PICR0L
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
3
2
1
0
16.25.17 PSC 1 Input Capture Register – PICR1H and PICR1L
Bit
7
6
5
4
PCST1
–
–
–
PICR1[11:8]
PICR1H
PICR1[7:0]
PICR1L
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
3
2
1
0
16.25.18 PSC 2 Input Capture Register – PICR2H and PICR2L
Bit
7
6
5
4
PCST2
–
–
–
PICR2[11:8]
PICR2H
PICR2[7:0]
PICR2L
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
• Bit 7 – PCSTn : PSC Capture Software Trig bit (not implemented on AT90PWM2/3)
Set this bit to trigger off a capture of the PSC counter. When reading, if this bit is set it means
that the capture operation was triggered by PCSTn setting otherwise it means that the capture
operation was triggered by a PSC input.
The Input Capture is updated with the PSC counter value each time an event occurs on the
enabled PSC input pin (or optionally on the Analog Comparator output) if the capture function is
enabled (bit PCAEnx in PFRCnx register is set).
The Input Capture Register is 12-bit in size. To ensure that both the high and low bytes are read
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit
temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit or
12-bit registers.
Note for AT90PWM2/3 : This register is read only and a write to this register is not allowed.
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16.26 PSC2 Specific Register
16.26.1
PSC 2 Output Matrix – POM2
Bit
7
6
5
4
3
2
1
0
POMV2B3
POMV2B2
POMV2B1
POMV2B0
POMV2A3
POMV2A2
POMV2A1
POMV2A0
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
POM2
• Bit 7 – POMV2B3: Output Matrix Output B Ramp 3
This bit gives the state of the PSCOUT21 (and/or PSCOUT23) during ramp 3
• Bit 6 – POMV2B2: Output Matrix Output B Ramp 2
This bit gives the state of the PSCOUT21 (and/or PSCOUT23) during ramp 2
• Bit 5 – POMV2B1: Output Matrix Output B Ramp 1
This bit gives the state of the PSCOUT21 (and/or PSCOUT23) during ramp 1
• Bit 4 – POMV2B0: Output Matrix Output B Ramp 0
This bit gives the state of the PSCOUT21 (and/or PSCOUT23) during ramp 0
• Bit 3 – POMV2A3: Output Matrix Output A Ramp 3
This bit gives the state of the PSCOUT20 (and/or PSCOUT22) during ramp 3
• Bit 2 – POMV2A2: Output Matrix Output A Ramp 2
This bit gives the state of the PSCOUT20 (and/or PSCOUT22) during ramp 2
• Bit 1 – POMV2A1: Output Matrix Output A Ramp 1
This bit gives the state of the PSCOUT20 (and/or PSCOUT22) during ramp 1
• Bit 0 – POMV2A0: Output Matrix Output A Ramp 0
This bit gives the state of the PSCOUT20 (and/or PSCOUT22) during ramp 0
16.26.2
PSC0 Interrupt Mask Register – PIM0
Bit
16.26.3
7
6
5
4
3
2
1
0
-
-
PSEIE0
PEVE0B
PEVE0A
-
-
PEOPE0
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PIM0
PSC1 Interrupt Mask Register – PIM1
Bit
7
6
5
4
3
2
1
0
-
-
PSEIE1
PEVE1B
PEVE1A
-
-
PEOPE1
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PIM1
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4317I–AVR–01/08
16.26.4
PSC2 Interrupt Mask Register – PIM2
Bit
7
6
5
4
3
2
1
0
-
-
PSEIE2
PEVE2B
PEVE2A
-
-
PEOPE2
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PIM2
• Bit 5 – PSEIEn : PSC n Synchro Error Interrupt Enable
When this bit is set, the PSEIn bit (if set) generate an interrupt.
• Bit 4 – PEVEnB : PSC n External Event B Interrupt Enable
When this bit is set, an external event which can generates a capture from Retrigger/Fault block
B generates also an interrupt.
• Bit 3 – PEVEnA : PSC n External Event A Interrupt Enable
When this bit is set, an external event which can generates a capture from Retrigger/Fault block
A generates also an interrupt.
• Bit 0 – PEOPEn : PSC n End Of Cycle Interrupt Enable
When this bit is set, an interrupt is generated when PSC reaches the end of the whole cycle.
16.26.5
PSC0 Interrupt Flag Register – PIFR0
Bit
16.26.6
7
6
5
4
3
2
1
0
POAC0B
POAC0A
PSEI0
PEV0B
PEV0A
PRN01
PRN00
PEOP2
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PSC1 Interrupt Flag Register – PIFR1
Bit
16.26.7
PIFR0
7
6
5
4
3
2
1
0
POAC1B
POAC1A
PSEI1
PEV1B
PEV1A
PRN11
PRN10
PEOP1
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PIFR1
PSC2 Interrupt Flag Register – PIFR2
Bit
7
6
5
4
3
2
1
0
POAC2B
POAC2A
PSEI2
PEV2B
PEV2A
PRN21
PRN20
PEOP2
Read/Write
R
R
R/W
R/W
R/W
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
PIFR2
• Bit 7 – POACnB : PSC n Output B Activity (not implemented on AT90PWM2/3)
This bit is set by hardware each time the output PSCOUTn1 changes from 0 to 1 or from 1 to 0.
Must be cleared by software by writing a one to its location.
This feature is useful to detect that a PSC output doesn’t change due to a freezen external input
signal.
• Bit 6 – POACnA : PSC n Output A Activity (not implemented on AT90PWM2/3)
This bit is set by hardware each time the output PSCOUTn0 changes from 0 to 1 or from 1 to 0.
Must be cleared by software by writing a one to its location.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
This feature is useful to detect that a PSC output doesn’t change due to a freezen external input
signal.
• Bit 5 – PSEIn : PSC n Synchro Error Interrupt
This bit is set by hardware when the update (or end of PSC cycle) of the PSCn configured in
auto run (PARUNn = 1) does not occur at the same time than the PSCn-1 which has generated
the input run signal. (For PSC0, PSCn-1 is PSC2).
Must be cleared by software by writing a one to its location.
This feature is useful to detect that a PSC doesn’t run at the same speed or with the same phase
than the PSC master.
• Bit 4 – PEVnB : PSC n External Event B Interrupt
This bit is set by hardware when an external event which can generates a capture or a retrigger
from Retrigger/Fault block B occurs.
Must be cleared by software by writing a one to its location.
This bit can be read even if the corresponding interrupt is not enabled (PEVEnB bit = 0).
• Bit 3 – PEVnA : PSC n External Event A Interrupt
This bit is set by hardware when an external event which can generates a capture or a retrigger
from Retrigger/Fault block A occurs.
Must be cleared by software by writing a one to its location.
This bit can be read even if the corresponding interrupt is not enabled (PEVEnA bit = 0).
• Bit 2:1 – PRNn1:0 : PSC n Ramp Number
Memorization of the ramp number when the last PEVnA or PEVnB occured.
Table 16-18. PSC n Ramp Number Description
PRNn1
PRNn0
Description
0
0
The last event which has generated an interrupt occured during ramp 1
0
1
The last event which has generated an interrupt occured during ramp 2
1
0
The last event which has generated an interrupt occured during ramp 3
1
1
The last event which has generated an interrupt occured during ramp 4
• Bit 0 – PEOPn: End Of PSC n Interrupt
This bit is set by hardware when PSC n achieves its whole cycle.
Must be cleared by software by writing a one to its location.
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17. Serial Peripheral Interface – SPI
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the
AT90PWM2/2B/3/3B and peripheral devices or between several AVR devices.
The AT90PWM2/2B/3/3B SPI includes the following features:
17.1
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 17-1. SPI Block Diagram(1)
SPIPS
MISO
MISO
_A
clk IO
MOSI
MOSI
_A
DIVIDER
/2/4/8/16/32/64/128
SCK
SCK
_A
SPI2X
SS
SPI2X
SS_A
Note:
1. Refer to Figure 3-1 on page 3, and Table 15 on page 69 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 17-2. The system consists of two shift Registers, and a Master clock generator. The SPI Master initiates the
communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and
Slave prepare the data to be sent in their respective shift Registers, and the Master generates
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the required clock pulses on the SCK line to interchange data. Data is always shifted from Master to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In
– Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pulling
high the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing a
byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight
bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of
transmission flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, an
interrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or
signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be
kept in the Buffer Register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as long
as the SS pin is driven high. In this state, software may update the contents of the SPI Data
Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin
until the SS pin is driven low. As one byte has been completely shifted, the end of transmission
flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an interrupt is
requested. The Slave may continue to place new data to be sent into SPDR before reading the
incoming data. The last incoming byte will be kept in the Buffer Register for later use.
Figure 17-2. SPI Master-slave Interconnection
SHIFT
ENABLE
The system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must be
read from the SPI Data Register before the next character has been completely shifted in. Otherwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the frequency of the SPI clock should never exceed fclkio/4.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 17-1. For more details on automatic port overrides, refer to “Alternate Port
Functions” on page 67.
Table 17-1.
Pin
MOSI
SPI Pin Overrides(1)
Direction, Master SPI
Direction, Slave SPI
User Defined
Input
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Table 17-1.
Pin
SPI Pin Overrides(1)
Direction, Master SPI
Direction, Slave SPI
MISO
Input
User Defined
SCK
User Defined
Input
SS
User Defined
Input
Note:
1. See “Alternate Functions of Port B” on page 69 for a detailed description of how to define the
direction of the user defined SPI pins.
The following code examples show how to initialize the SPI as a Master and how to perform a
simple transmission.
DDR_SPI in the examples must be replaced by the actual Data Direction Register controlling the
SPI pins. DD_MOSI, DD_MISO and DD_SCK must be replaced by the actual data direction bits
for these pins. E.g. if MOSI is placed on pin PB2, replace DD_MOSI with DDB2 and DDR_SPI
with DDRB.
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Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi
r17,(1<<DD_MOSI)|(1<<DD_SCK)
out
DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi
r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out
SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out
SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}
Note:
1. The example code assumes that the part specific header file is included.
The following code examples show how to initialize the SPI as a Slave and how to perform a
simple reception.
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Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi
r17,(1<<DD_MISO)
out
DDR_SPI,r17
; Enable SPI
ldi
r17,(1<<SPE)
out
SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in
r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return data register */
return SPDR;
}
Note:
17.2
17.2.1
1. The example code assumes that the part specific header file is included.
SS Pin Functionality
Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When SS is
held low, the SPI is activated, and MISO becomes an output if configured so by the user. All
other pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which
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means that it will not receive incoming data. Note that the SPI logic will be reset once the SS pin
is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous
with the master clock generator. When the SS pin is driven high, the SPI slave will immediately
reset the send and receive logic, and drop any partially received data in the Shift Register.
17.2.2
Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the
direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If the SS pin
is driven low by peripheral circuitry when the SPI is configured as a Master with the SS pin
defined as an input, the SPI system interprets this as another master selecting the SPI as a
slave and starting to send data to it. To avoid bus contention, the SPI system takes the following
actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result of
the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is
set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possibility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If the
MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI Master
mode.
17.2.3
MCU Control Register – MCUCR
Bit
7
6
5
4
3
2
1
0
SPIPS
–
–
PUD
–
–
IVSEL
IVCE
Read/Write
R/W
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
MCUCR
• Bit 7– SPIPS: SPI Pin Redirection
Thanks to SPIPS (SPI Pin Select) in MCUCR Sfr, SPI pins can be redirected.
On 32 pins packages, SPIPS has the following action:
–
When the SPIPS bit is written to zero, the SPI signals are directed on pins
MISO,MOSI, SCK and SS.
–
When the SPIPS bit is written to one,the SPI signals are directed on alternate SPI
pins, MISO_A, MOSI_A, SCK_A and SS_A.
On 24 pins package, SPIPS has the following action:
–
When the SPIPS bit is written to zero, the SPI signals are directed on alternate SPI
pins, MISO_A, MOSI_A, SCK_A and SS_A.
–
When the SPIPS bit is written to one,the SPI signals are directed on pins
MISO,MOSI, SCK and SS.
Note that programming port are always located on alternate SPI port.
17.2.4
SPI Control Register – SPCR
Bit
7
6
5
4
3
2
1
0
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
SPCR
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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 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and the if
the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared,
and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low
when idle. Refer to Figure 17-3 and Figure 17-4 for an example. The CPOL functionality is summarized below:
Table 17-2.
CPOL Functionality
CPOL
Leading Edge
Trailing Edge
0
Rising
Falling
1
Falling
Rising
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or
trailing (last) edge of SCK. Refer to Figure 17-3 and Figure 17-4 for an example. The CPOL
functionality is summarized below:
Table 17-3.
CPHA Functionality
CPHA
Leading Edge
Trailing Edge
0
Sample
Setup
1
Setup
Sample
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
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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 clkIO frequency fclkio is shown in
the following table:
Table 17-4.
17.2.5
Relationship Between SCK and the Oscillator Frequency
SPI2X
SPR1
SPR0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
SCK Frequency
fclkio/4
fclkio/16
fclkio/64
fclkio/128
fclkio/2
fclkio/8
fclkio/32
fclkio/64
SPI Status Register – SPSR
Bit
7
6
5
4
3
2
1
0
SPIF
WCOL
–
–
–
–
–
SPI2X
Read/Write
R
R
R
R
R
R
R
R/W
Initial Value
0
0
0
0
0
0
0
0
SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is
in Master mode, this will also set the SPIF flag. SPIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set,
and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see Table 17-4). This means that the minimum SCK period will be two CPU
clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fclkio/4
or lower.
The SPI interface on the AT90PWM2/2B/3/3B is also used for program memory and EEPROM
downloading or uploading. See Serial Programming Algorithm295 for serial programming and
verification.
17.2.6
SPI Data Register – SPDR
Bit
7
6
5
4
3
2
1
0
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
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
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• Bits 7:0 - SPD7:0: SPI Data
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.
17.3
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
17-3 and Figure 17-4. Data bits are shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing
Table 17-2 and Table 17-3, as done below:
Table 17-5.
CPOL Functionality
Leading Edge
Trailing eDge
SPI Mode
CPOL=0, CPHA=0
Sample (Rising)
Setup (Falling)
0
CPOL=0, CPHA=1
Setup (Rising)
Sample (Falling)
1
CPOL=1, CPHA=0
Sample (Falling)
Setup (Rising)
2
CPOL=1, CPHA=1
Setup (Falling)
Sample (Rising)
3
Figure 17-3. SPI Transfer Format with CPHA = 0
SCK (CPOL = 0)
mode 0
SCK (CPOL = 1)
mode 2
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0) MSB
LSB first (DORD = 1) LSB
182
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
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Figure 17-4. SPI Transfer Format with CPHA = 1
SCK (CPOL = 0)
mode 1
SCK (CPOL = 1)
mode 3
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SS
MSB first (DORD = 0)
LSB first (DORD = 1)
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
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18. USART
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a
highly flexible serial communication device. The main features are:
18.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
18.2
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
USART Extended mode (EUSART) with:
– Independant bit number configuration for transmit and receive
– Supports Serial Frames with 5, 6, 7, 8, 9 or 13, 14, 15, 16, 17 Data Bits and 1 or 2 Stop Bits
– Biphase Manchester encode/decoder (for DALI Communications)
– Manchester framing error detection
– Bit ordering configuration (MSB or LSB first)
– Sleep mode exit under reception of EUSART frame
Overview
A simplified block diagram of the USART Transmitter is shown in Figure 18-1. CPU accessible
I/O Registers and I/O pins are shown in bold.
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Figure 18-1. USART Block Diagram(1)
Clock Generator
UBRR[H:L]
CLKio
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCK
Transmitter
TX
CONTROL
UDR (Transmit)
DATA BUS
PARITY
GENERATOR
TxD
Receiver
RECEIVE SHIFT REGISTER
UDR
UCSRA
Note:
PIN
CONTROL
TRANSMIT SHIFT REGISTER
CLOCK
RECOVERY
RX
CONTROL
DATA
RECOVERY
PIN
CONTROL
RxD
PARITY
CHECKER
(Receive)
UCSRB
UCSRC
1. Refer to Pin Configurations3, Table 21 on page 74, and Table 19 on page 73 for USART pin
placement.
The dashed boxes in the block diagram separate the three main parts of the USART (listed from
the top): Clock Generator, Transmitter and Receiver. Control registers are shared by all units.
The Clock Generation logic consists of synchronization logic for external clock input used by
synchronous slave operation, and the baud rate generator. The XCK (Transfer Clock) pin is only
used by synchronous transfer mode. The Transmitter consists of a single write buffer, a serial
Shift Register, Parity Generator and Control logic for handling different serial frame formats. The
write buffer allows a continuous transfer of data without any delay between frames. The
Receiver is the most complex part of the USART module due to its clock and data recovery
units. The recovery units are used for asynchronous data reception. In addition to the recovery
units, the Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDR). The Receiver supports the same frame formats as the Transmitter, and
can detect Frame Error, Data OverRun and Parity Errors.
18.3
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 asyn185
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chronous, 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 18-2 shows a block diagram of the clock generation logic.
Figure 18-2. USART Clock Generation Logic, Block Diagram
UBRRn
U2Xn
fclk io
Prescaling
Down-Counter
UBRRn+1
/2
/4
/2
0
1
0
clk io
1
DDR_XCKn
xn cki
XCKn
Pin
Sync
Register
Edge
Detector
DDR_XCKn
0
UMSELn
1
xn cko
txn clk
1
UCPOLn
0
rxn clk
Signal description:
txn clk Transmitter clock (Internal Signal).
rxn clk Receiver base clock (Internal Signal).
xn cki Input from XCK pin (internal Signal). Used for synchronous slave operation.
xn cko Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
fclkio
18.3.1
System I/O Clock frequency.
Internal Clock Generation – Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes of
operation. The description in this section refers to Figure 18-2.
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
(fclkio), is loaded with the UBRR value each time the counter has counted down to zero or when
the UBRRL Register is written. A clock is generated each time the counter reaches zero. This
clock is the baud rate generator clock output (= fclkio/(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 18-1 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 18-1.
Equations for Calculating Baud Rate Register Setting
Equation for Calculating Baud
Rate(1)
Equation for Calculating UBRR
Value
Asynchronous Normal mode
(U2X = 0)
f CLKio
BAUD = -----------------------------------------16 ( UBRRn + 1 )
f CLKio
UBRRn = ------------------------ – 1
16BAUD
Asynchronous Double Speed
mode (U2X = 1)
f CLKio
BAUD = --------------------------------------8 ( UBRRn + 1 )
f CLKio
UBRRn = -------------------- – 1
8BAUD
Synchronous Master mode
f CLKio
BAUD = --------------------------------------2 ( UBRRn + 1 )
f CLKio
UBRRn = -------------------- – 1
2BAUD
Operating Mode
Note:
1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD Baud rate (in bits per second, bps).
fclkio
System I/O Clock frequency.
UBRR Contents of the UBRRH and UBRRL Registers, (0-4095).
Some examples of UBRR values for some system clock frequencies are found in Table 18-9
(see page 208).
18.3.2
Double Speed Operation (U2X)
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.
18.3.3
External Clock
External clocking is used by the synchronous slave modes of operation. The description in this
section refers to Figure 18-2 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 CLKio
f XCKn < ---------------4
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Note that fclkio 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.
18.3.4
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 (TxDn) is changed.
Figure 18-3. Synchronous Mode XCK Timing.
UCPOLn = 1
XCKn
RxDn / TxDn
Sample
UCPOLn = 0
XCKn
RxDn / TxDn
Sample
The UCPOL bit UCRSnC selects which XCK clock edge is used for data sampling and which is
used for data change. As Figure 18-3 shows, when UCPOL is zero the data will be changed at
rising XCK edge and sampled at falling XCK edge. If UCPOL is set, the data will be changed at
falling XCK edge and sampled at rising XCK edge.
18.4
Serial Frame
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.
18.4.1
Frame Formats
The USART accepts all 30 combinations of the following as valid frame formats:
•
1 start bit
•
5, 6, 7, 8, or 9 data bits
•
no, even or odd parity bit
•
1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits,
up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit
is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can
be directly followed by a new frame, or the communication line can be set to an idle (high) state.
Figure 18-4 illustrates the possible combinations of the frame formats. Bits inside brackets are
optional.
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Figure 18-4. Frame Formats
FRAME
(IDLE)
St
0
1
2
3
4
[5]
[6]
[7]
[8]
[P]
Sp1 [Sp2]
(St / IDLE)
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.
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 use the same setting. Note that changing the setting
of any of these bits will corrupt all ongoing communication for both the Receiver and Transmitter.
The USART Character SiZe (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.
18.4.2
Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the
result of the exclusive or is inverted. The relation between the parity bit and data bits is as
follows:
P even = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 0
P odd = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 1
Peven
P
odd
dn
Parity bit using even parity
Parity bit using odd parity
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.
18.5
USART Initialization
The USART has to be initialized before any communication can take place.
The configuration between the USART or EUSART mode should be done before any other
configuration.
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
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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 are 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.
Assembly Code Example(1)
USART_Init:
; Set baud rate
sts
UBRRH, r17
sts
UBRRL, r16
; Set frame format: 8data, no parity & 2 stop bits
ldi
r16, (0<<UMSEL)|(0<<UPM0)|(1<<USBS)|(3<<UCSZ0)
sts
UCSRC,r16
; Enable receiver and transmitter
ldi
r16, (1<<RXEN0)|(1<<TXEN0)
sts
UCSRB,r16
ret
C Code Example(1)
void USART_Init( unsigned int baud )
{
/* Set baud rate */
UBRRH = (unsigned char)(baud>>8);
UBRRL = (unsigned char)baud;
/* Set frame format: 8data, no parity & 2 stop bits */
UCSRC = (0<<UMSEL)|(0<<UPM0)|(1<<USBS)|(3<<UCSZ0);
/* Enable receiver and transmitter */
UCSRB = (1<<RXEN0)|(1<<TXEN0);
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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.
18.6
Data Transmission – 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 TxDn 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 syn-
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chronous operation is used, the clock on the XCK pin will be overridden and used as
transmission clock.
18.6.1
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 bits, 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
sts UDR,r16
ret
C Code Example(1)
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.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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.
18.6.2
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 is 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.
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Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB80
cbi
UCSRB,TXB80
sbrc r17,0
sbi
UCSRB,TXB80
; Put LSB data (r16) into buffer, sends the data
sts
UDR,r16
ret
C Code Example(1)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) )
;
/* Copy 9th bit to TXB8 */
UCSRB &= ~(1<<TXB80);
if ( data & 0x0100 )
UCSRB |= (1<<TXB80);
/* Put data into buffer, sends the data */
UDR = data;
}
Notes:
1. These transmit functions are written to be general functions. They can be optimized if the contents of the UCSRB is static. For example, only the TXB80 bit of the UCSRB0 Register is used
after initialization.
2. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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.
18.6.3
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 write this bit to zero when writing the UCSRA Register.
When the Data Register Empty Interrupt Enable (UDRIE) bit in UCSRB is written to one, 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
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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 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 Complete 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.
18.6.4
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.
18.6.5
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 do not contain data to be transmitted. When disabled, the Transmitter
will no longer override the TxD pin.
18.7
Data Reception – USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXEN) bit in the UCSRB Register to one. When the Receiver is enabled, the normal pin operation of the RxD pin is overridden
by the USART and given the function as the Receiver’s serial input. The baud rate, mode of
operation and frame format must be set up once before any serial reception can be done. If synchronous operation is used, the clock on the XCK pin will be used as transfer clock.
18.7.1
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.
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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
lds
r16, UDR
ret
C Code Example(1)
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.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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.
18.7.2
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 UPE 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 UPE 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.
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Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSRA, RXC0
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
lds
r18, UCSRA
lds r17, UCSRB
lds r16, UDR
; If error, return -1
andi r18,(1<<FE0)|(1<<DOR0)|(1<<UPE0)
breq USART_ReceiveNoError
ldi
r17, HIGH(-1)
ldi
r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr
r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSRA & (1<<RXC0)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSRA;
resh = UCSRB;
resl = UDR;
/* If error, return -1 */
if ( status & (1<<FE0)|(1<<DOR0)|(1<<UPE0) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
Note:
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The receive function example reads all the I/O Registers into the Register File before any computation is done. This gives an optimal receive buffer utilization since the buffer location read will
be free to accept new data as early as possible.
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18.7.3
Receive Complete 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.
18.7.4
Receiver Error Flags
The USART Receiver has three error flags: Frame Error (FE), Data OverRun (DOR) and Parity
Error (UPE). 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 write 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 following example (See Figure 18-5.) represents a Data OverRun condition. As the receive
buffer is full with CH1 and CH2, CH3 is lost. When a Data OverRun condition is detected, the
OverRun error is memorized. When the two characters CH1 and CH2 are read from the receive
buffer, the DOR bit is set (and not before) and RxC remains set to warn the application about the
overrun error.
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Figure 18-5. Data OverRun example
RxD
CH1
CH2
CH3
DOR
RxC
t
Software Access
to Receive buffer
RxC=1
UDR=CH1
DOR=0
RxC=1
UDR=CH2
DOR=0
RxC=1
UDR=XX
DOR=1
The Parity Error (UPE) Flag indicates that the next frame in the receive buffer had a Parity Error
when received. If Parity Check is not enabled the UPE 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 189 and “Parity Checker” on page 197.
18.7.5
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 (UPE) flag can then be read by software to
check if the frame had a Parity Error.
The UPE 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.
18.7.6
Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing
receptions will therefore be lost. When disabled (i.e., the 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
18.7.7
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.
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Assembly Code Example(1)
USART_Flush:
sbis UCSRA, RXC0
ret
lds
r16, UDR
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSRA & (1<<RXC0) ) dummy = UDR;
}
Note:
18.8
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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.
18.8.1
Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 18-6
illustrates the sampling process of the start bit of an incoming frame. The sample rate is 16 times
the baud rate for Normal mode, and eight times the baud rate for Double Speed mode. The horizontal arrows illustrate the synchronization variation due to the sampling process. Note the
larger time variation when using the Double Speed mode (U2X = 1) of operation. Samples
denoted zero are samples done when the RxD line is idle (i.e., no communication activity).
Figure 18-6. Start Bit Sampling
RxDn
IDLE
START
BIT 0
Sample
(U2Xn = 0)
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
Sample
(U2Xn = 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
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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.
18.8.2
Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data
recovery unit uses a state machine that has 16 states for each bit in Normal mode and eight
states for each bit in Double Speed mode. Figure 18-7 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 18-7. Sampling of Data and Parity Bit
RxDn
BIT x
Sample
(U2Xn = 0)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
Sample
(U2Xn = 1)
1
2
3
4
5
6
7
8
1
The decision of the logic level of the received bit is taken by doing a majority voting of the logic
value to the three samples in the center of the received bit. The center samples are emphasized
on the figure by having the sample number inside boxes. The majority voting process is done as
follows: If two or all three samples have high levels, the received bit is registered to be a logic 1.
If two or all three samples have low levels, the received bit is registered to be a logic 0. This
majority voting process acts as a low pass filter for the incoming signal on the RxD pin. The
recovery process is then repeated until a complete frame is received. Including the first stop bit.
Note that the Receiver only uses the first stop bit of a frame.
Figure 18-8 shows the sampling of the stop bit and the earliest possible beginning of the start bit
of the next frame.
Figure 18-8. Stop Bit Sampling and Next Start Bit Sampling
RxDn
STOP 1
(A)
(B)
(C)
Sample
(U2Xn = 0)
1
2
3
4
5
6
7
8
9
10
0/1
0/1
0/1
Sample
(U2Xn = 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 18-8. 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.
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18.8.3
Asynchronous Operational Range
The operational range of the Receiver is dependent on the mismatch between the received bit
rate and the internally generated baud rate. If the Transmitter is sending frames at too fast or too
slow bit rates, or the internally generated baud rate of the Receiver does not have a similar (see
Table 18-2) 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 + 2 )S
R fast = ----------------------------------( D + 1 )S + S M
( D + 1 )S
R slow = ------------------------------------------S – 1 + D ⋅ S + SF
D
Sum of character size and parity size (D = 5 to 10 bit)
S
Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
SF
First sample number used for majority voting. SF = 8 for normal speed and SF = 4
for Double Speed mode.
SM
Middle sample number used for majority voting. SM = 9 for normal speed and
SM = 5 for Double Speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate.
Rfast is the ratio of the fastest incoming data rate that can be accepted in relation to the
receiver baud rate.
Table 18-2 and Table 18-3 list the maximum receiver baud rate error that can be tolerated. Note
that Normal Speed mode has higher toleration of baud rate variations.
Table 18-2.
200
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
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 18-3.
Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2X = 1)
D
# (Data+Parity Bit)
Rslow (%)
Rfast (%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
94.12
105.66
+5.66/-5.88
± 2.5
6
94.92
104.92
+4.92/-5.08
± 2.0
7
95.52
104,35
+4.35/-4.48
± 1.5
8
96.00
103.90
+3.90/-4.00
± 1.5
9
96.39
103.53
+3.53/-3.61
± 1.5
10
96.70
103.23
+3.23/-3.30
± 1.0
The recommendations of the maximum receiver baud rate error was made under the assumption that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The Receiver’s system clock
(XTAL) will always have some minor instability over the supply voltage range and the temperature range. When using a crystal to generate the system clock, this is rarely a problem, but for a
resonator the system clock may differ more than 2% depending of the resonators tolerance. The
second source for the error is more controllable. The baud rate generator can not always do an
exact division of the system frequency to get the baud rate wanted. In this case an UBRR value
that gives an acceptable low error can be used if possible.
18.9
Multi-processor Communication Mode
This mode is available only in USART mode, not in EUSART.
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.
18.9.1
MPCM Protocol
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indicates if the frame contains data or address information. If the Receiver is set up for frames with
nine data bits, then the ninth bit (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.
18.9.2
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
201
4317I–AVR–01/08
(TXBn = 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 fullduplex operation difficult since the Transmitter and Receiver use 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.
18.10 USART Register Description
18.10.1
USART I/O Data Register – UDR
Bit
7
6
5
4
3
2
1
0
RXB[7:0]
UDR (Read)
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
• Bit 7:0 – RxB7:0: Receive Data Buffer (read access)
• Bit 7:0 – TxB7:0: Transmit Data Buffer (write access)
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 (TXBn) 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 (RXBn).
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 TxDn pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the
receive buffer is accessed.
This register is available in both USART and EUSART modes.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
18.10.2
USART Control and Status Register A – UCSRA
Bit
Read/Write
Initial Value
0
7
6
5
4
3
2
1
0
RXC
TXC
UDRE
FE
DOR
UPE
U2X
MPCM
R
R/W
R
R
R
R
R/W
R/W
0
1
0
0
0
0
UCSRA
0
• Bit 7 – RXC: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive
buffer will be flushed and consequently the RXC bit will become zero. The RXC flag can be used
to generate a Receive Complete interrupt (see description of the RXCIE bit).
This bit is available in both USART and EUSART modes.
• Bit 6 – TXC: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and
there are no new data currently present in the transmit buffer (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).
This bit is available in both USART and EUSART modes.
• 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 to be written. The UDRE flag can generate a Data
Register Empty interrupt (see description of the UDRIE bit).
UDRE is set after a reset to indicate that the Transmitter is ready.
This bit is available in both USART and EUSART modes.
• 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.
This bit is also valid in EUSART mode only when data bits are level encoded (in Manchester
mode the FEM bit allows to detect a framing error).
• Bit 3 – DOR: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the receive
buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a
new start bit is detected. This bit is valid until the receive buffer (UDR) is read. Always set this bit
to zero when writing to UCSRA.
This bit is available in both USART and EUSART modes.
• Bit 2 – UPE: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and the
Parity Checking was enabled at that point (UPM1 = 1). This bit is valid until the receive buffer
(UDR) is read. Always set this bit to zero when writing to UCSRA.
This bit is also valid in EUSART mode only when data bits are level encoded (there is no parity
in Manchester mode).
• Bit 1 – U2X: Double the USART Transmission Speed
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This bit only has effect for the asynchronous operation. Write this bit to zero when using synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for asynchronous communication.
This bit is available in both USART and EUSART modes.
• Bit 0 – MPCM: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCM bit is written to
one, all the incoming frames received by the USART Receiver that do not contain address information will be ignored. The Transmitter is unaffected by the MPCM setting. For more detailed
information see “Multi-processor Communication Mode” on page 201.
This mode is unavailable when the EUSART mode is set.
18.10.3
USART Control and Status Register B – UCSRB
Bit
7
6
5
4
3
2
1
0
RXCIE
TXCIE
UDRIE
RXEN
TXEN
UCSZ2
RXB8
TXB8
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
R/W
Initial Value
0
0
0
0
0
0
0
0
UCSRB
• Bit 7 – RXCIE: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXC flag. A USART Receive Complete interrupt
will be generated only if the RXCIE bit is written to one, the Global Interrupt Flag in SREG is written to one and the RXC bit in UCSRA is set.
This bit is available for both USART and EUSART modes.
• Bit 6 – TXCIE: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXC flag. A USART Transmit Complete interrupt
will be generated only if the TXCIE bit is written to one, the Global Interrupt Flag in SREG is written to one and the TXC bit in UCSRA is set.
This bit is available for both USART and EUSART mode.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDRE flag. A Data Register Empty interrupt will
be generated only if the UDRIE bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDRE bit in UCSRA is set.
This bit is available for both USART and EUSART mode.
• Bit 4 – RXEN: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal port operation for the RxD pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FE, DOR, and UPE Flags.
This bit is available for both USART and EUSART mode.
• Bit 3 – TXEN: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxDn pin when enabled. The disabling of the Transmitter (writing 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 do not contain data to be transmitted. When disabled, the Transmitter will no longer override the TxDn port.
204
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
This bit is available for both USART and EUSART mode.
• 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.
This bit have no effect when the EUSART mode is enabled.
• 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.
When the EUSART mode is enable and configured in 17 bits receive mode, this bit contains the
seventeenth bit (see EUSART section).
• 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.
When the EUSART mode is enable and configured in 17 bits transmit mode, this bit contains the
seventeenth bit (See EUSART section).
18.10.4
USART Control and Status Register C – UCSRC
Bit
7
6
5
4
3
2
1
0
-
UMSEL0
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
0
0
0
0
0
1
1
0
UCSRC
• Bit 7 – Reserved Bit
This bit is reserved for future use. For compatibilty with future devices, this bit must be written to
zero when USCRC is written.
• Bit 6 – UMSEL: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
Table 18-4.
UMSEL Bit Settings
UMSEL
Mode
0
Asynchronous Operation
1
Synchronous Operation
When configured in EUSART mode, the synchronous mode should not be set with Manchester
mode (See EUSART section).
• Bit 5:4 – UPM1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter will
automatically generate and send the parity of the transmitted data bits within each frame. The
205
4317I–AVR–01/08
Receiver will generate a parity value for the incoming data and compare it to the UPM setting. If
a mismatch is detected, the UPE Flag in UCSRA will be set.
Table 18-5.
UPM Bits Settings
UPM1
UPM0
Parity Mode
0
0
Disabled
0
1
Reserved
1
0
Enabled, Even Parity
1
1
Enabled, Odd Parity
This setting is available in EUSART mode only when data bits are level encoded (in Manchester
the parity checker and generator are not available).
• Bit 3 – USBS: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores
this setting.
In EUSART mode, the USBS bit has the same behavior and the EUSB bit of the EUSART allows
to configure the number of stop bit for the receiver in this mode.
Table 18-6.
USBS Bit Settings
USBS
Stop Bit(s)
0
1-bit
1
2-bit
• 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 use.
Table 18-7.
UCSZ Bits Settings
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
When the EUSART mode is set, these bits have no effect.
• Bit 0 – UCPOL: Clock Polarity
206
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
This bit is used for synchronous mode only. Write 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).
Table 18-8.
Transmitted Data Changed
(Output of TxDn Pin)
Received Data Sampled
(Input on RxD Pin)
0
Rising XCK Edge
Falling XCK Edge
1
Falling XCK Edge
Rising XCK Edge
UCPOL
18.10.5
UCPOL Bit Settings
USART Baud Rate Registers – UBRRL and UBRRH
Bit
15
14
13
12
–
–
–
–
11
10
9
8
UBRR[11:8]
UBRRH
UBRR[7:0]
7
Read/Write
Initial Value
6
5
4
UBRRL
3
2
1
0
R
R
R
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the four
most significant bits, and the UBRRL contains the eight least significant bits of the USART baud
rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate is
changed. Writing UBRRL will trigger an immediate update of the baud rate prescaler.
18.11 Examples of Baud Rate Setting
For standard crystal, resonator and external oscillator frequencies, the most commonly used
baud rates for asynchronous operation can be generated by using the UBRR settings in Table
18-9 up to Table 18-12. 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 200). The error values are calculated using the following equation:
BaudRate Closest Match
Error[%] = ⎛⎝ 1 – --------------------------------------------------------⎞⎠ • 100%
BaudRate
207
4317I–AVR–01/08
Table 18-9.
Examples of UBRR Settings for Commonly Frequencies
fclkio = 1.0000 MHz
fclkio = 1.8432 MHz
fclkio = 2.0000 MHz
Baud
Rate
(bps)
UBRR
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
51
0.2%
103
0.2%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
25
0.2%
51
0.2%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
12
0.2%
25
0.2%
14.4k
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
19.2k
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
28.8k
1
8.5%
3
8.5%
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
38.4k
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
57.6k
0
8.5%
1
8.5%
1
0.0%
3
0.0%
1
8.5%
3
8.5%
76.8k
–
–
1
-18.6%
1
-25.0%
2
0.0%
1
-18.6%
2
8.5%
115.2k
–
–
0
8.5%
0
0.0%
1
0.0%
0
8.5%
1
8.5%
230.4k
–
–
–
–
–
–
0
0.0%
–
–
–
–
250k
–
–
–
–
–
–
–
–
–
–
–
–
500k
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1M
Max.
(1)
1.
U2X = 0
U2X = 1
Error
UBRR
62.5 kbps
U2X = 0
Error
125 kbps
UBRR
U2X = 1
Error
115.2 kbps
UBRR
U2X = 0
Error
UBRR
230.4 Kbps
U2X = 1
Error
UBRR
125 kpbs
Error
250 kbps
UBRR = 0, Error = 0.0%
Table 18-10. Examples of UBRR Settings for Commonly Frequencies (Continued)
fclkio = 3.6864 MHz
Baud
Rate
(bps)
U2X = 0
UBRR
fclkio = 4.0000 MHz
U2X = 1
Error
UBRR
U2X = 0
Error
UBRR
fclkio = 7.3728 MHz
U2X = 1
Error
UBRR
U2X = 0
Error
UBRR
U2X = 1
Error
UBRR
Error
2400
95
0.0%
191
0.0%
103
0.2%
207
0.2%
191
0.0%
383
0.0%
4800
47
0.0%
95
0.0%
51
0.2%
103
0.2%
95
0.0%
191
0.0%
9600
23
0.0%
47
0.0%
25
0.2%
51
0.2%
47
0.0%
95
0.0%
14.4k
15
0.0%
31
0.0%
16
2.1%
34
-0.8%
31
0.0%
63
0.0%
19.2k
11
0.0%
23
0.0%
12
0.2%
25
0.2%
23
0.0%
47
0.0%
28.8k
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
15
0.0%
31
0.0%
38.4k
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
57.6k
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
76.8k
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
115.2k
1
0.0%
3
0.0%
1
8.5%
3
8.5%
3
0.0%
7
0.0%
230.4k
0
0.0%
1
0.0%
0
8.5%
1
8.5%
1
0.0%
3
0.0%
250k
0
-7.8%
1
-7.8%
0
0.0%
1
0.0%
1
-7.8%
3
-7.8%
208
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 18-10. Examples of UBRR Settings for Commonly Frequencies (Continued)
fclkio = 3.6864 MHz
Baud
Rate
(bps)
U2X = 0
UBRR
500k
1M
Max.
1.
(1)
fclkio = 4.0000 MHz
U2X = 1
Error
UBRR
U2X = 0
Error
UBRR
fclkio = 7.3728 MHz
U2X = 1
Error
UBRR
U2X = 0
Error
UBRR
U2X = 1
Error
UBRR
Error
–
–
0
-7.8%
–
–
0
0.0%
0
-7.8%
1
-7.8%
–
–
–
–
–
–
–
–
–
–
0
-7.8%
230.4 kbps
460.8 kbps
250 kbps
0.5 Mbps
460.8 kpbs
921.6 kbps
UBRR = 0, Error = 0.0%
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Table 18-11. Examples of UBRR Settings for Commonly Frequencies (Continued)
fclkio = 8.0000 MHz
fclkio = 10.000 MHz
fclkio = 11.0592 MHz
Baud
Rate
(bps)
UBRR
2400
207
0.2%
416
-0.1%
259
0.2%
520
0.0%
287
0.0%
575
0.0%
4800
103
0.2%
207
0.2%
129
0.2%
259
0.2%
143
0.0%
287
0.0%
9600
51
0.2%
103
0.2%
64
0.2%
129
0.2%
71
0.0%
143
0.0%
14.4k
34
-0.8%
68
0.6%
42
0.9%
86
0.2%
47
0.0%
95
0.0%
19.2k
25
0.2%
51
0.2%
32
-1.4%
64
0.2%
35
0.0%
71
0.0%
28.8k
16
2.1%
34
-0.8%
21
-1.4%
42
0.9%
23
0.0%
47
0.0%
38.4k
12
0.2%
25
0.2%
15
1.8%
32
-1.4%
17
0.0%
35
0.0%
57.6k
8
-3.5%
16
2.1%
10
-1.5%
21
-1.4%
11
0.0%
23
0.0%
76.8k
6
-7.0%
12
0.2%
7
1.9%
15
1.8%
8
0.0%
17
0.0%
115.2k
3
8.5%
8
-3.5%
4
9.6%
10
-1.5%
5
0.0%
11
0.0%
230.4k
1
8.5%
3
8.5%
2
-16.8%
4
9.6%
2
0.0%
5
0.0%
250k
1
0.0%
3
0.0%
2
-33.3%
4
0.0%
2
-7.8%
5
-7.8%
500k
0
0.0%
1
0.0%
–
–
2
-33.3%
–
–
2
-7.8%
–
–
0
0.0%
–
–
–
–
–
–
–
–
1M
Max.
1.
210
(1)
U2X = 0
U2X = 1
Error
UBRR
0.5 Mbps
Error
1 Mbps
U2X = 0
UBRR
U2X = 1
Error
625 kbps
UBRR
U2X = 0
Error
1.25 Mbps
UBRR
U2X = 1
Error
691.2 kbps
UBRR
Error
1.3824 Mbps
UBRR = 0, Error = 0.0%
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 18-12. Examples of UBRR Settings for Commonly Frequencies (Continued)
fclkio = 12.0000 MHz
fclkio = 14.7456 MHz
fclkio = 16.0000 MHz
Baud
Rate
(bps)
UBRR
2400
312
-0.2%
624
0.0%
383
0.0%
767
0.0%
416
-0.1%
832
0.0%
4800
155
0.2%
312
-0.2%
191
0.0%
383
0.0%
207
0.2%
416
-0.1%
9600
77
0.2%
155
0.2%
95
0.0%
191
0.0%
103
0.2%
207
0.2%
14.4k
51
0.2%
103
0.2%
63
0.0%
127
0.0%
68
0.6%
138
-0.1%
19.2k
38
0.2%
77
0.2%
47
0.0%
95
0.0%
51
0.2%
103
0.2%
28.8k
25
0.2%
51
0.2%
31
0.0%
63
0.0%
34
-0.8%
68
0.6%
38.4k
19
-2.5%
38
0.2%
23
0.0%
47
0.0%
25
0.2%
51
0.2%
57.6k
12
0.2%
25
0.2%
15
0.0%
31
0.0%
16
2.1%
34
-0.8%
76.8k
9
-2.7%
19
-2.5%
11
0.0%
23
0.0%
12
0.2%
25
0.2%
115.2k
6
-8.9%
12
0.2%
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
230.4k
2
11.3%
6
-8.9%
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
250k
2
0.0%
5
0.0%
3
-7.8%
6
5.3%
3
0.0%
7
0.0%
500k
–
–
2
0.0%
1
-7.8%
3
-7.8%
1
0.0%
3
0.0%
–
–
–
–
0
-7.8%
1
-7.8%
0
0.0%
1
0.0%
U2X = 0
1M
Max.
1.
(1)
U2X = 1
Error
UBRR
750 kbps
U2X = 0
Error
1.5 Mbps
UBRR
Error
921.6 kbps
U2X = 1
UBRR
Error
1.8432 Mbps
U2X = 0
UBRR
Error
1 Mbps
U2X = 1
UBRR
Error
2 Mbps
UBRR = 0, Error = 0.0%
19. EUSART (Extended USART)
The Extended Universal Synchronous and Asynchronous serial Receiver and Transmitter
(EUSART) provides functionnal extensions to the USART.
19.1
Features
•
•
•
•
•
19.2
Independant bit number configuration for transmit and receive
Supports Serial Frames with 5, 6, 7, 8, 9 or 13, 14, 15, 16, 17 Data Bits and 1 or 2 Stop Bits
Biphase Manchester encoder/decoder (for DALI Communications)
Manchester framing error detection
Bit ordering (MSB first or LSB first)
Overview
A simplified block diagram of the EUSART Transmitter is shown in Figure 19-1. CPU accessible
I/O Registers and I/O pins are shown in bold.
Figure 19-1. EUSART Block Diagram
The EUSART is activated with the EUSART bit of EUCSRB register. Until this bit is not set, the
USART will behave as standard USART, all the functionnalities of the EUSART are not
accessible.
The EUSART supports more serial frame formats than the standard USART interface:
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4317I–AVR–01/08
Clock Generator
UBRR[H:L]
CLKio
BAUD RATE GENERATOR
SYNC LOGIC
PIN
CONTROL
XCK
Transmitter
DATA BUS
EUDR
(Transmit)
TX
CONTROL
UDR
(Transmit)
PARITY
GENERATOR
MANCHESTER
ENCODER
PIN
CONTROL
TRANSMIT SHIFT REGISTER
Receiver
CLOCK
RECOVERY
RECEIVE SHIFT REGISTER
EUDR
(Receive)
•
•
UDR
(Receive)
RX
CONTROL
MANCHESTER
DECODER
DATA
RECOVERY
PIN
CONTROL
RxD
PARITY
CHECKER
UCSRA
UCSRB
UCSRC
EUCSRA
EUCSRB
EUCSRC
Asynchonous frames
–
Standard bit level encoded
–
Manchester bit encoded
Synchronous frames
–
19.3
TxD
In this mode only the Standard bit level encoded is available
Serial Frames
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.
19.3.1
Frame Formats
The EUSART allows to receive and transmit serial frame with the following format:
212
•
1 start bit
•
5, 6, 7, 8, 9, 13, 14,15,16,17 data bits
•
data bits and start bit level encoded or Manchester encoded
•
data transmition MSB or LSB first (bit ordering)
•
no, even or odd parity bit
•
1 or 2 stop bits:
–
Stop bits insertion for transmition
–
Stop bits value read access in reception
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
The fr ame format used by the EUSART can be configur ed thr ough the following
USART/EUSART registers:
•
UTxS3:0 and URxS3:0 (EUCSRA of EUSART register) select the number of data bits per
frame
•
UPM1:0 bits enable and set the type of parity bit (when configured in Manchester mode, the
parity should be fixed to none).
USBS (UCSRC register of USART) and EUSBS (EUCSRB register of EUSART) select the number of stop bits to be processed respectively by the transmiter and the receiver. The receiver
stores the two stop bit values when configured in Manchester mode. When configured in level
encoded mode, the second stop bit is ignored (behavior similar as the USART).
19.3.2
Parity Bit Calculation
The parity bit behavior is similar to the USART mode, except for the Manchester encoded mode,
where no parity bit can be inserted or detected (should be configured to none with the UPM1:0
bits. The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used,
the result of the exclusive or is inverted. The relation between the parity bit and data bits is as
follows:
P even = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 0
P odd = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 1
Peven
P
odd
dn
Parity bit using even parity
Parity bit using odd parity
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.
19.3.3
Manchester encoding
Manchester encoding (also know as Biphase Code) is a synchronous clock encoding technique
used to encode the clock and data of a synchronous bit stream. In this technique, the actual
binary data to be transmitted are not sent as a sequence of logic 1's and 0's as in level encoded
way as in standard USART (known technically as Non Return to Zero (NRZ)). Instead, the bits
are translated into a slightly different format that has a number of advantages over using straight
binary encoding (i.e. NRZ).
Manchester encoding follows the rules:
•
If the original data is a Logic 1, the Manchester code is: 0 to 1 (upward transition at bit
center)
•
If the original data is a Logic 0, the Manchester code is: 1 to 0 (downward transition at bit
center)
Figure 19-2. Manchester Bi-phase levels
Logical 0
Logical 1
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19.3.3.1
Manchester frame
The USART supports Manchester encoded frames with the following characteristics:
•
One start bit Manchester encoded (logical ‘1’)
•
5, 6, 7, 8, 9, 13, 14,15,16,17 data bits in transmission or reception (MSB or LSB first)
•
The number of data bit in a frame is independently configurable in reception and
transmission mode.
•
One or Two stop bits (level encoded)
Figure 19-3. Manchester Frame example
Encoder Clock
Manchester Data
Binary Data
1 0 0 1 1 1 1 0 1 0 0 1 0 1 0 1 0
Start
Bit
19.3.3.2
Data Bits
(up to 17 data bit)
Stop
Bits
Manchester decoder
When configured in Manchester mode, the EUSART receiver is able to receive serial frame
using a 17-bit shift register, an edge detector and several data/control registers. The Manchester
decoder receives a frame from the RxD pin of the EUSART interface and loads the received
data in the EUSART data register (UDR and EUDR).
The bit order of the data bits in the frame is configurable to handle MSB or LSB first.
The polarity of the bi-phase start is not configurable. The start bit a logical ‘1’ (rising edge at bit
center).
The polarity of the stop bits is not configurable, the interface allows to read the 2 stops bits value
by software.
The Manchester decoder is enable when the EUSART is configured in Manchester mode and
the RXEN of USCRB set (global USART receive enable).
The number of data bits to be received can be configured with the URxS bits of EUCSRA
register.
The Manchester decoder provides a special mode where 16 or 17 data bits can be received. In
this mode the Manchester decoder can automatically detects if the seventeenth bit is Manchester encoded or not (seventeenth data bit or first stop bit). If the receiver detects a valid data bit
(Manchester transition) during the seventeenth bit time of the frame, the receiver will process the
frame as a 17-bit frame lenght and set the F1617 bit of EUCSRC register.
In Manchester mode, the clock used for sampling the EUSART input signal is programmed by
the baudrate generator.
The edge detector of the Manchester decoder is based upon a 16 bits up/down counter which
maximum value can be configured through the MUBRRH and MUBRRL registers.
214
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
The maximum counter value is given by the following formula:
MUBRR[H:L]=FCLKIO / (baud rate frequency)
MBURR[H:L] is used to calibrate the detect window of the start bit and to detect time overflow of
the other bits.
19.3.4
Double Speed Operation (U2X)
Double Speed Operation is controlled by U2X bit in UCSRA. See “Double Speed Operation
(U2X)” on page 187.
This mode of operation is not allowed in manchester bit coding.
Each ‘bit time’ in the Manchester serial frame is divided into two phases (See Figure 19-4). The
counter counts during the first phase and counts down during the second one. When the data bit
transition is detected, the counter memorises the N1 counter value and start counting down.
When the counter reaches the zero value, it starts counting up again and the N1/2 value allows
to open the next detection window. This detection window defines the time zone where the next
data bit edge is sampled.
215
4317I–AVR–01/08
Figure 19-4. Manchester Decoder operation
Data Clock
Start Bit
Bit 3
Bit 2
Bit 1
Delayed edge
Manchester
Data
N4
N1/2
Manchester
Decoder
Counter
N3
N2
N1
N2/4
N2/2
N3/4
N3/2
N4/4
Detection
Window
Internal
Manchester
Clock
Decoded
Data
Note:
19.3.4.1
Start Bit
N1 = MBURR[H:L]/2
Manchester Framing error detection
When configured in Manchester mode, the framing error (FE) of the USCRA register is not used,
the EUSART generates a dedicated Frame Error Manchester (FEM) when a data data bit is not
detected during the detection window (See Figure 19-5).
216
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 19-5. Manchester Frame error detection
Internal
Manchester
Clock
Resynchronize
Internal
Manchester
Clock
Start Bit
Bit 1
Bit 2
Start Bit
Bit 1
Bit 2
Manchester
Data
front shift
back shift
Framing Error
Counter
Overflow
Start Bit
Start Bit
N3
N3
N2
N1
Manchester
Decoder
Counter
N1
N2
N2/2
N1/2
N2/4
Transition outside
the detect window
Edge Detection
Space
Internal
Manchester
Clock
The counter reaches the counter overflow
value without reaching a manchester edge
Note:
Counter Overflow = MBURR[H:L]
When a Manchester framing error is detected the FEM bit and RxC bit are set at the same time.
This allows the application to execute the reception complete interrupt subroute when this error
conditon is detected.
When a Manchester framing error is detected, the EUSART receiver immediately enters in a
new start bit detection phase. Thus when a Manchester framing error is detected within a frame,
the receiver will process the rest of the frame as a new incomming frame and generate other
FEM errors.
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4317I–AVR–01/08
19.4
19.4.1
Configuring the EUSART
Data Transmission – EUSART Transmitter
The EUSART Transmitter is enabled in the same way as standard USART, by setting the Transmit Enable (TXEN) bit in the UCSRB Register. When the Transmitter is enabled, the normal port
operation of the TxDn pin is overridden by the EUSART 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.
19.4.2
Sending Frames with 5 to 8 Data Bit
In this mode the behavior is the same as the standard USART (See “Sending Frames with 5 to 8
Data Bit” in USART section).
19.4.3
Sending Frames with 9, 13, 14, 15 or 16 Data Bit
In these configurations the most significant bits (9, 13, 14, 15 or 16) should be loaded in the
EUDR register before the low byte of the character is written to UDR. The write operation in the
UDR register allows to start the transmission.
Assembly Code Example(1)
EUSART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp EUSART_Transmit
; Put LSB data (r16) and MSN data (r15) into buffer, sends the data
sts
EUDR,r15
sts
UDR,r16
ret
C Code Example(1)
void EUSART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) )
/* Put data into buffer, sends the data */
EUDR = data>>8;
UDR = data;
}
Note:
218
The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS”
and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
19.4.4
Sending 17 Data Bit Frames
In this configuration the seventeenth bit shoud be loaded in the RXB8 bit register, the rest of the
most significant bits (9, 10, 11, 12, 13, 14, 15 and 16) should be loaded in the EUDR register,
before the low byte of the character is written to UDR.
19.4.5
Transmitter Flags and Interrupts
The behavior of the EUSART is the same as in USART mode (See “Receive Complete Flag and
Interrupt”).
The interrupts generation and handling for transmission in EUSART mode are the same as in
USART mode.
19.4.6
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 do not contain data to be transmitted.
19.4.7
19.5
Data Reception – EUSART Receiver
Data Reception – EUSART Receiver
The EUSART Receiver is enabled by writing the Receive Enable (RXEN) bit in the UCSRB Register to one (same as USART). When the Receiver is enabled, the normal pin operation of the
RxD pin is overridden by the EUSART 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.
19.5.1
Receiving Frames with 5 to 8 Data Bits
In this mode the behavior is the same as the standard USART (See “Receiving Frames with 5 to
8 Data Bits” in USART section).
19.5.2
Receiving Frames with 9, 13, 14, 15 or 16 Data Bits
In these configurations the most significant bits (9, 13, 14, 15 or 16) should be read in the EUDR
register before reading the of the character in the UDR register.
Read status from EUCSRC, then data from UDR.
219
4317I–AVR–01/08
The following code example shows a simple EUSART receive function.
Assembly Code Example(1)
EUSART_Receive:
; Wait for data to be received
sbis UCSRA, RXC
rjmp EUSART_Receive
; Get MSB (r15), LSB (r16)
lds
r15, EUDR
lds
r16, UDR
ret
C Code Example(1)
unsigned int EUSART_Receive( void )
{
unsigneg int rx_data
/* Wait for data to be received */
while ( !(UCSRA & (1<<RXC)) )
;
/* Get and return received data from buffer */
rx_data=EUDR;
rx_data=rx_data<<8+UDR;
return rx_data;
}
Note:
19.5.3
The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS”
and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
Receiving 17 Data Bit Frames
In this configuration the seventeenth bit shoud be read from the RXB8 bit register, the rest of the
most significant bits (9, 10, 11, 12, 13, 14, 15 and 16) should be read from the EUDR register,
before the low byte of the character is read from UDR.
19.5.4
Receive Complete Flag and Interrupt
The EUSART Receiver has the same USART flag that indicates the Receiver state.
See “Receive Complete Flag and Interrupt” in USART section.
19.5.5
Receiver Error Flags
When the EUSART is not configured in Manchester mode, the EUSART has the three same
errors flags as standard mode: Frame Error (FE), Data OverRun (DOR) and Parity Error (UPE).
All can be accessed by reading UCSRA. (See “Receiver Error Flags” in USART section).
When the EUSART is configured in Machester mode, the EUSART has two errors flags: Data
OverRun (DOR), and Manchester framing error (FEM bit of EUCSRC).
220
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
All the receiver error flags are valid only when the RxC bit is set and until the UDR register is
read.
19.5.5.1
Parity Checker
The parity checker of the EUSART is available only when data bits are level encoded and
behaves as is USART mode (See Parity checker of the USART).
19.5.5.2
OverRun
The Data OverRun (DOR bit of USCRA) flag indicates data loss due to a receiver buffer full condition. This flag operates as in USART mode (See USART section).
19.6
EUSART Registers Description
19.6.1
USART I/O Data Register – UDR
Bit
7
6
5
4
3
2
1
0
RXB[7:0]
UDR (Read)
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
• Bit 7:0 – RxB7:0: Receive Data Buffer (read access)
• Bit 7:0 – TxB7:0: Transmit Data Buffer (write access)
This register is common to the USART and EUSART interfaces for Transmit Data Buffer Register and Receive Data Buffer Register. See description for UDR register in USART.
19.6.2
EUSART I/O Data Register – EUDR
Bit
7
6
5
4
3
2
1
0
RXB[15:8]
EUDR (Read)
TXB[15:8]
EUDR (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
1
0
0
• Bit 7:0 – RxB15:8: Receive Data Buffer (read access)
• Bit 7:0 – TxB15:8: Transmit Data Buffer (write access)
This register provide an extension to the UDR register when EUSART is used with more than 8
bits.
19.6.2.1
UDR/EUDR data access with character size up to 8 bits
When the EUSART is used with 8 or less bits, only the UDR register is used for dta access.
19.6.2.2
UDR/EUDR data access with 9 bits per character
When the EUSART is used with 9 bits character, the behavior is different of the standart USART
mode, the UDR register is used in combinaison with the first bit of EUDR (EUDR:0) for data
access, the RxB8/TxB8 bit is not used.
221
4317I–AVR–01/08
Figure 19-6. 9 bits communication data access
Data 8:0
8 7
EUDR
19.6.2.3
0
UDR
UDR/EUDR data access from 13 to 17 bits per character
When the EUSART is used in 13, 14, 15, 16 or 17 bits per character mode, the EUDR/UDR registers are used in combinaison with the RxB8/TxB8 bit for data access.
For 13, 14, 15 or 16 bit character the upper unused bits in EUDR will be ignored by the Transmitter and set to zero by the Receiver. In transmitter mode, the data should be written MSB first.
The data transmission starts when the UDR register is written.
In these modes, the RxB8/TxB8 registers are not used.
Figure 19-7. 13, 14, 15 and 16 bits communication data access
Data 15:0
15
8 7
EUDR
0
UDR
For 17 bit character the seventeenth bit is locate in RxB8 or TXB8 register. In transmitter mode,
the data should be written MSB first. The data transmission starts when the UDR register is
written.
Figure 19-8. 17 bits communication data access
Data 16:0
16 15
RxB8 (receive)
or TxB8 (transmit)
222
8 7
EUDR
0
UDR
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
19.6.3
EUSART Control and Status Register A – EUCSRA
Bit
7
6
5
4
3
2
1
0
UTxS3
UTxS2
UTxS1
UTxS0
URxS3
URxS2
URxS1
URxS0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
1
1
0
0
1
1
EUCSRA
• Bit 7:4 – EUSART Transmit Character Size
The UTxS3:0 bits sets the number of data bits (Character Size) in a frame the Transmitter use.
Table 19-1.
UTxS Bits Settings
UTxS3
UTxS2
UTxS1
UTxS0
Transmit Character Size
0
0
0
0
5-bit
0
0
0
1
6-bit
0
0
1
0
7-bit
0
0
1
1
8-bit
0
1
0
0
Reserved
0
1
0
1
Reserved
0
1
1
0
Reserved
0
1
1
1
9-bit
1
0
0
0
13-bit
1
0
0
1
14-bit
1
0
1
0
15-bit
1
0
1
1
16-bit
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
17-bit
• Bit 3:0 – EUSART Receive Character Size
The UTxS3:0 bits sets the number of data bits (Character Size) in a frame the Receiver use.
Table 19-2.
URxS Bits Settings
URxS3
URxS2
URxS1
URxS0
Receive Character Size
0
0
0
0
5-bit
0
0
0
1
6-bit
0
0
1
0
7-bit
0
0
1
1
8-bit
0
1
0
0
Reserved
0
1
0
1
Reserved
0
1
1
0
Reserved
0
1
1
1
9-bit
1
0
0
0
13-bit
223
4317I–AVR–01/08
Table 19-2.
19.6.4
URxS Bits Settings
URxS3
URxS2
URxS1
URxS0
Receive Character Size
1
0
0
1
14-bit
1
0
1
0
15-bit
1
0
1
1
16-bit
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
16 OR 17 bit (for Manchester
encoded only mode)
1
1
1
1
17-bit
EUSART Control Register B – EUCSRB
Bit
7
6
5
4
3
2
1
0
-
-
-
EUSART
EUSBS
-
EMCH
BODR
Read/Write
R
R
R
R/W
R/W
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
EUCSRB
• Bit 7:5 –Reserved Bits
These bits are reserved for future use. For compatibilty with future devices, these bits must be
written to zero when EUSCRB is written.
• Bit 4 – EUSART Enable Bit
Set to enable the EUSART mode, clear to operate as standard USART.
• Bit 3– EUSBS Enable Bit
This bit selects the number of stop bits detected by the receiver.
Table 19-3.
EUSBS Bit Settings
EUSBS
Note:
Receiver Stop Bit(s)
0
1-bit
1
2-bit
The number of stop bit inserted by the Transmitter in EUSART mode is configurable throught the
USBS bit of in the of the USART.
• Bit 2–Reserved Bit
This bit is reserved for future use. For compatibilty with future devices, this bit must be written to
zero when EUSCRB is written.
• Bit 1 – Manchester mode
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
When set the EUSART operates in manchester encoder/decoder mode (Manchester encoded
frames). When cleared the EUSART detected and transmit level encoded frames.
Table 19-4.
USART/EUSART modes selection summary
UMSEL
EMCH
EUSART
Mode
0
X
0
Asynchronous up to 9 bits level encoded (standard
asynchronous USART mode)
1
X
0
Synchronous up to 9 bits level encoded (standard
synchronous USART mode)
0
0
1
Asynchronous up to 17 bits level encoded
0
1
1
Asynchronous up to 17 bits Manchester encoded
1
0
1
Synchronous up to 17 bits level encoded
1
1
1
Reserved
As in Manchester mode the parity checker and generator are unavailable, the parity
should be configured to none ( write UPM1:0 to 00 in UCSRC), see Table 18-5.
• Bit 0 –Bit Order
This bit allows to change the bit ordering in the transmit and received frames.
Clear to transmit and receive LSB first (standard USART mode)
Set to transmit and receive MSB first.
19.6.5
EUSART Status Register C – EUCSRC
Bit
7
6
5
4
3
2
1
0
-
-
-
-
FEM
F1617
STP1
STP0
Read/Write
R
R
R
R
R
R
R
R
Initial Value
0
0
0
0
0
0
0
0
EUCSRC
• Bit 7:4 –Reserved Bits
These bits are reserved for future use. For compatibilty with future devices, these bits must be
written to zero when EUSCRC is written.
• Bit 3 –Frame Error Manchester
This bit is set by hardware when a framing error is detected in manchester mode. This bit is valid
when the RxC bit is set and until the receive buffer (UDR) is read.
• Bit 2 –F1617
When the receiver is configured for 16 or 17 bits in Manchester encoded mode, this bit indicates
if the received frame is 16 or 17 bits lenght.
Cleared: indicates that the received frame is 16 bits lenght.
Set: Indicates that the received frame is 17 bits lenght.
This bit is valid when the RxC bit is set and until the receive buffer (UDR) is read.
• Bit 1:0 –Stop bits values
When Manchester mode is activated, these bits contains the stop bits value of the previous
received frame.
When the data bits in the serial frame are standard level encoded, these bits are not updated.
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4317I–AVR–01/08
19.6.6
Manchester receiver Baud Rate Registers – MUBRRL and MUBRRH
Bit
15
14
13
12
11
10
9
8
MUBRR[15:8]
MUBRRH
MUBRR[7:0]
7
Read/Write
Initial Value
6
5
4
3
MUBRRL
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
• Bit 15:0 – MUBRR15:0: Manchester Receiver Baud Rate Register
This is a 16-bit register which contains the maximum value for the Machester receiver counter.
The MUBRRH contains the eight most significant bits, and the MUBRRL contains the eight least
significant bits. Ongoing transmissions by the Receiver will be corrupted if the baud rate is
changed.
MUBRR[H:L]=FCLKIO / (baud rate frequency)
Table 19-5.
226
Examples of MUBRR Settings for Commonly Frequencies
Baud
Rate
(bps)
fclkio =
fclkio =
fclkio =
4.0000
MHz
8.0000
MHz
fclkio =
11.0592
MHz
fclkio =
1.8432
MHz
fclkio =
2.0000
MHz
fclkio =
1
MHz
1200
833
1536
1667
3333
6667
9216
13333
2400
417
768
833
1667
3333
4608
6667
4800
208
384
417
833
1667
2304
3333
9600
104
192
208
417
833
1152
1667
16.000
MHz
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
20. Analog Comparator
The Analog Comparator compares the input values on the positive pin ACMPx and negative pin
ACMPM.
20.1
Overview
The AT90PWM2/2B/3/3B features three fast analog comparators.
Each comparator has a dedicated input on the positive input, and the negative input can be configured as:
•
a steady value among the 4 internal reference levels defined by the Vref selected thanks to
the REFS1:0 bits in ADMUX register.
•
a value generated from the internal DAC
•
an external analog input ACMPM.
When the voltage on the positive ACMPn pin is higher than the voltage selected by the ACnM
multiplexer on the negative input, the Analog Comparator output, ACnO, is set.
The comparator is a clocked comparator. A new comparison is done on the falling edge of
CLKI/O or CLKI/O/2 ( Depending on ACCKDIV fit of ACSR register, See “Analog Comparator Status Register – ACSR” on page 231.).
Each comparator can trigger a separate interrupt, exclusive to the Analog Comparator. In addition, the user can select Interrupt triggering on comparator output rise, fall or toggle.
The interrupt flags can also be used to synchronize ADC or DAC conversions.
Moreover, the comparator’s output of the comparator 1 can be set to trigger the Timer/Counter1
Input Capture function.
A block diagram of the three comparators and their surrounding logic is shown in Figure 20-1.
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4317I–AVR–01/08
Figure 20-1. Analog Comparator Block Diagram(1)(2)
AC0O
CLK I/O (/2)
AC0IF
+
ACMP0
Interrupt Sensitivity Control
Analog Comparator 0 Interrupt
AC0IE
AC0IS1
AC0EN
AC0M
2 1 0
AC0IS0
AC1O
CLK I/O (/2)
AC1IF
+
ACMP1
Interrupt Sensitivity Control
Analog Comparator 1 Interrupt
AC1IE
AC1IS1
AC1EN
AC1IS0
T1 Capture Trigger
AC1ICE
AC2O
AC1M
2 1 0
ACMP2
CLK I/O (/2)
AC2IF
+
Interrupt Sensitivity Control
Analog Comparator 2 Interrupt
AC0IE
AC2EN
AC2IS1
AC2IS0
ACMPM
Vref
DAC
DAC
Result
AC2M
2 1 0
DACEN
Aref
AVcc
Internal 2.56V
Reference
REFS0
Notes:
20.2
/1.60
/2.13
/3.20
REFS1
/6.40
1. ADC multiplexer output: see Table 27 on page 248.
2. Refer to Figure 3-1 on page 3 and for Analog Comparator pin placement.
3. The voltage on Vref is defined in 26 “ADC Voltage Reference Selection” on page 247
Analog Comparator Register Description
Each analog comparator has its own control register.
A dedicated register has been designed to consign the outputs and the flags of the 3 analog
comparators.
20.2.1
Analog Comparator 0 Control Register – AC0CON
Bit
7
6
5
4
3
2
1
0
AC0EN
AC0IE
AC0IS1
AC0IS0
-
AC0M2
AC0M1
AC0M0
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
AC0CON
• Bit 7– AC0EN: Analog Comparator 0 Enable Bit
Set this bit to enable the analog comparator 0.
Clear this bit to disable the analog comparator 0.
• Bit 6– AC0IE: Analog Comparator 0 Interrupt Enable bit
Set this bit to enable the analog comparator 0 interrupt.
Clear this bit to disable the analog comparator 0 interrupt.
• Bit 5, 4– AC0IS1, AC0IS0: Analog Comparator 0 Interrupt Select bit
228
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
These 2 bits determine the sensitivity of the interrupt trigger.
The different setting are shown in Table 20-1.
Table 20-1.
Interrupt sensitivity selection
AC0IS1
AC0IS0
Description
0
0
Comparator Interrupt on output toggle
0
1
Reserved
1
0
Comparator interrupt on output falling edge
1
1
Comparator interrupt on output rising edge
• Bit 2, 1, 0– AC0M2, AC0M1, AC0M0: Analog Comparator 0 Multiplexer register
These 3 bits determine the input of the negative input of the analog comparator.
The different setting are shown in Table 20-2.
Table 20-2.
20.2.2
Analog Comparator 0 negative input selection
AC0M2
AC0M1
AC0M0
Description
0
0
0
“Vref”/6.40
0
0
1
“Vref”/3.20
0
1
0
“Vref”/2.13
0
1
1
“Vref”/1.60
1
0
0
Analog Comparator Negative Input (ACMPM pin)
1
0
1
DAC result
1
1
0
Reserved
1
1
1
Reserved
Analog Comparator 1Control Register – AC1CON
Bit
7
6
5
4
3
2
1
0
AC1EN
AC1IE
AC1IS1
AC1IS0
AC1ICE
AC1M2
AC1M1
AC1M0
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
AC1CON
• Bit 7– AC1EN: Analog Comparator 1 Enable Bit
Set this bit to enable the analog comparator 1.
Clear this bit to disable the analog comparator 1.
• Bit 6– AC1IE: Analog Comparator 1 Interrupt Enable bit
Set this bit to enable the analog comparator 1 interrupt.
Clear this bit to disable the analog comparator 1 interrupt.
• Bit 5, 4– AC1IS1, AC1IS0: Analog Comparator 1 Interrupt Select bit
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4317I–AVR–01/08
These 2 bits determine the sensitivity of the interrupt trigger.
The different setting are shown in Table 20-1.
Table 20-3.
Interrupt sensitivity selection
AC1IS1
AC1IS0
Description
0
0
Comparator Interrupt on output toggle
0
1
Reserved
1
0
Comparator interrupt on output falling edge
1
1
Comparator interrupt on output rising edge
• Bit 3– AC1ICE: Analog Comparator 1 Interrupt Capture Enable bit
Set this bit to enable the input capture of the Timer/Counter1 on the analog comparator event.
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. To make the comparator trigger the Timer/Counter1
Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask Register (TIMSK1) must be set.
In case ICES1 bit (“Timer/Counter1 Control Register B – TCCR1B” on page 125) is set high, the
rising edge of AC1O is the capture/trigger event of the Timer/Counter1, in case ICES1 is set to
zero, it is the falling edge which is taken into account.
Clear this bit to disable this function. In this case, no connection between the Analog Comparator and the input capture function exists.
• Bit 2, 1, 0– AC1M2, AC1M1, AC1M0: Analog Comparator 1 Multiplexer register
These 3 bits determine the input of the negative input of the analog comparator.
The different setting are shown in Table 20-4.
Table 20-4.
20.2.3
Analog Comparator 1 negative input selection
AC1M2
AC1M1
AC1M0
Description
0
0
0
“Vref”/6.40
0
0
1
“Vref”/3.20
0
1
0
“Vref”/2.13
0
1
1
“Vref”/1.60
1
0
0
Analog Comparator Negative Input (ACMPM pin)
1
0
1
DAC result
1
1
0
Reserved
1
1
1
Reserved
Analog Comparator 2 Control Register – AC2CON
Bit
7
6
5
4
AC2EN
AC2IE
AC2IS1
AC2IS0
Read/Write
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
3
2
1
0
AC2M2
AC2M1
AC2M0
-
R/W
R/W
R/W
0
0
0
0
AC2CON
• Bit 7– AC2EN: Analog Comparator 2 Enable Bit
Set this bit to enable the analog comparator 2.
Clear this bit to disable the analog comparator 2.
230
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
• Bit 6– AC2IE: Analog Comparator 2 Interrupt Enable bit
Set this bit to enable the analog comparator 2 interrupt.
Clear this bit to disable the analog comparator 2 interrupt.
• Bit 5, 4– AC2IS1, AC2IS0: Analog Comparator 2 Interrupt Select bit
These 2 bits determine the sensitivity of the interrupt trigger.
The different setting are shown in Table 20-1.
Table 20-5.
Interrupt sensitivity selection
AC2IS1
AC2IS0
Description
0
0
Comparator Interrupt on output toggle
0
1
Reserved
1
0
Comparator interrupt on output falling edge
1
1
Comparator interrupt on output rising edge
• Bit 2, 1, 0– AC2M2, AC2M1, AC2M0: Analog Comparator 2 Multiplexer register
These 3 bits determine the input of the negative input of the analog comparator.
The different setting are shown in Table 20-6.
Table 20-6.
20.2.4
Analog Comparator 2 negative input selection
AC2M2
AC2M1
AC2M0
Description
0
0
0
“Vref”/6.40
0
0
1
“Vref”/3.20
0
1
0
“Vref”/2.13
0
1
1
“Vref”/1.60
1
0
0
Analog Comparator Negative Input (ACMPM pin)
1
0
1
DAC result
1
1
0
Reserved
1
1
1
Reserved
Analog Comparator Status Register – ACSR
Bit
7
6
5
4
3
2
1
0
ACCKDIV
AC2IF
AC1IF
AC0IF
-
AC2O
AC1O
AC0O
Read/Write
R/W
R/W
R/W
R/W
-
R
R
R
Initial Value
0
0
0
0
0
0
0
0
ACSR
• Bit 7– ACCKDIV: Analog Comparator Clock Divider
The analog comparators can work with a clock up to 8MHz@3V and 16MHz@5V.
Set this bit in case the clock frequency of the microcontroller is higher than 8 MHz to insert a
divider by 2 between the clock of the microcontroller and the clock of the analog comparators.
Clear this bit to have the same clock frequency for the microcontroller and the analog
comparators.
• Bit 6– AC2IF: Analog Comparator 2 Interrupt Flag Bit
This bit is set by hardware when comparator 2 output event triggers off the interrupt mode
defined by AC2IS1 and AC2IS0 bits in AC2CON register.
This bit is cleared by hardware when the corresponding interrupt vector is executed in case the
231
4317I–AVR–01/08
AC2IE in AC2CON register is set. Anyway, this bit is cleared by writing a logical one on it.
This bit can also be used to synchronize ADC or DAC conversions.
• Bit 5– AC1IF: Analog Comparator 1 Interrupt Flag Bit
This bit is set by hardware when comparator 1 output event triggers off the interrupt mode
defined by AC1IS1 and AC1IS0 bits in AC1CON register.
This bit is cleared by hardware when the corresponding interrupt vector is executed in case the
AC1IE in AC1CON register is set. Anyway, this bit is cleared by writing a logical one on it.
This bit can also be used to synchronize ADC or DAC conversions.
• Bit 5– AC0IF: Analog Comparator 0 Interrupt Flag Bit
This bit is set by hardware when comparator 0 output event triggers off the interrupt mode
defined by AC0IS1 and AC0IS0 bits in AC0CON register.
This bit is cleared by hardware when the corresponding interrupt vector is executed in case the
AC0IE in AC0CON register is set. Anyway, this bit is cleared by writing a logical one on it.
This bit can also be used to synchronize ADC or DAC conversions.
• Bit 2– AC2O: Analog Comparator 2 Output Bit
AC2O bit is directly the output of the Analog comparator 2.
Set when the output of the comparator is high.
Cleared when the output comparator is low.
• Bit 1– AC1O: Analog Comparator 1 Output Bit
AC1O bit is directly the output of the Analog comparator 1.
Set when the output of the comparator is high.
Cleared when the output comparator is low.
• Bit 0– AC0O: Analog Comparator 0 Output Bit
AC0O bit is directly the output of the Analog comparator 0.
Set when the output of the comparator is high.
Cleared when the output comparator is low.
20.2.5
Digital Input Disable Register 0 – DIDR0
Bit
7
6
5
4
3
2
1
0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ACMPM
ADC2D
ACMP2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR0
• Bit 3:2 – ACMPM and ACMP2D: ACMPM and ACMP2 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding Analog pin is disabled. The corresponding PIN Register bit will always read as zero when this bit is set. When an
analog signal is applied to one of these pins and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
20.2.6
Digital Input Disable Register 1– DIDR1
Bit
7
6
5
4
3
2
1
0
-
-
ACMP0D
AMP0PD
AMP0ND
ADC10D
ACMP1D
ADC9D
AMP1PD
ADC8D
AMP1ND
Read/Write
-
-
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR1
• Bit 5, 2: ACMP0D and ACMP1 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding analog pin is disabled. The corresponding PIN Register bit will always read as zero when this bit is set. When an
232
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
analog signal is applied to one of these pins and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
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21. Analog to Digital Converter - ADC
21.1
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
10-bit Resolution
0.5 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
8- 320 µs Conversion Time
Up to 125 kSPS at Maximum Resolution
11 Multiplexed Single Ended Input Channels
Two Differential input channels with accurate programmable gain 5, 10, 20 and 40
Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
Selectable 2.56 V ADC Reference Voltage
Free Running or Single Conversion Mode
ADC Start Conversion by Auto Triggering on Interrupt Sources
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler
The AT90PWM2/2B/3/3B features a 10-bit successive approximation ADC. The ADC is connected to an 15-channel Analog Multiplexer which allows eleven single-ended input. The singleended voltage inputs refer to 0V (GND).
The device also supports 2 differential voltage input combinations which are equipped with a
programmable gain stage, providing amplification steps of 14dB (5x), 20 dB (10x), 26 dB (20x),
or 32dB (40x) on the differential input voltage before the A/D conversion. On the amplified channels, 8-bit resolution can be expected.
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is
held at a constant level during conversion. A block diagram of the ADC is shown in Figure 21-1.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±
0.3V from VCC. See the paragraph “ADC Noise Canceler” on page 241 on how to connect this
pin.
Internal reference voltages of nominally 2.56V or AVCC are provided On-chip. The voltage reference may be externally decoupled at the AREF pin by a capacitor for better noise performance.
234
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 21-1. Analog to Digital Converter Block Schematic
AREF
AVCC
Internal 2.56V
Reference
REFS0
ADC0
ADC1
ADC2
ADC3
ADC4
ADC5
ADC6
ADC7
AMP1-/ADC8
AMP1+/ADC9
ADC10
AMP0AMP0+
REFS1
Coarse/Fine DAC
10
+
-
CONTROL
ADCL
ADC CONVERSION
COMPLETE IRQ
GND
Bandgap
REFS0
10
CKADC CKADC
+
REFS1
ADCH
SAR
+
AMP0CSR
10
CK
AMP1CSR
ADLAR
-
MUX3
MUX2
MUX1
MUX0
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
ADCSRA
ADMUX
Sources
ADEN
PRESCALER
Edge
Detector
ADATE
Only on AT90PWM2/3
-
-
-
ADASCR
ADTS3
ADTS2
ADTS1
ADTS0
ADCSRB
235
4317I–AVR–01/08
21.2
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value represents GND and the maximum value represents the voltage on
the AREF pin minus 1 LSB. Optionally, AVCC or an internal 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 are selected by writing to the MUX bits in ADMUX. Any of the ADC
input pins, as well as GND and a fixed bandgap voltage reference, can be selected as single
ended inputs to the ADC.
The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage reference is set
by the REFS1 and REFS0 bits in ADMUX register, whatever the ADC is enabled or not. The
ADC does not consume power when ADEN is cleared, so it is recommended to switch off the
ADC before entering power saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and
ADCL. By default, the result is presented right adjusted, but can optionally be presented left
adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read
ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the Data
Registers belongs to the same conversion. Once ADCL is read, ADC access to Data Registers
is blocked. This means that if ADCL has been read, and a conversion completed 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. The ADC
access to the Data Registers is prohibited between reading of ADCH and ADCL, the interrupt
will trigger even if the result is lost.
21.3
Starting a Conversion
A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC.
This bit stays high as long as the conversion is in progress and will be cleared by hardware
when the conversion is completed. If a different data channel is selected while a conversion is in
progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is
enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is
selected by setting the ADC Trigger Select bits, ADTS in ADCSRB (See description of the ADTS
bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal,
the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions at fixed intervals. If the trigger signal is still set when the conversion completes, a new
conversion will not be started. If another positive edge occurs on the trigger signal during conversion, the edge will be ignored. Note that an interrupt flag will be set even if the specific
interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus
be triggered without causing an interrupt. However, the interrupt flag must be cleared in order to
trigger a new conversion at the next interrupt event.
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Figure 21-2. ADC Auto Trigger Logic
ADTS[2:0]
PRESCALER
START
CLKADC
ADATE
ADIF
SOURCE 1
.
.
.
.
CONVERSION
LOGIC
EDGE
DETECTOR
SOURCE n
ADSC
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon
as the ongoing conversion has finished. The ADC then operates in Free Running mode, constantly sampling and updating the ADC Data Register. The first conversion must be started by
writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive
conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not. The free
running mode is not allowed on the amplified channels.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to
one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be
read as one during a conversion, independently of how the conversion was started.
21.4
Prescaling and Conversion Timing
Figure 21-3. ADC Prescaler
ADEN
START
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
By default, the successive approximation circuitry requires an input clock frequency between 50
kHz and 2 MHz to get maximum resolution. If a lower resolution than 10 bits is needed, the input
clock frequency to the ADC can be higher than 2 MHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit
in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously
reset when ADEN is low.
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When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion
starts at the following rising edge of the ADC clock cycle. See “Changing Channel or Reference
Selection” on page 239 for details on differential conversion timing.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched
on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry.
The actual sample-and-hold takes place 3.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures
a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold
takes place two ADC clock cycles after the rising edge on the trigger source signal. Three additional CPU clock cycles are used for synchronization logic.
In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. For a summary of conversion times, see Table 21-1.
Figure 21-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Next
Conversion
First Conversion
Cycle Number
1
2
12
13
14
16
15
17
18
19
20
21
22
24
23
25
1
2
3
ADC Clock
ADEN
ADSC
ADIF
Sign and MSB of Result
ADCH
LSB of Result
ADCL
MUX and REFS
Update
MUX
and REFS
Update
Conversion
Complete
Sample & Hold
Figure 21-5. ADC Timing Diagram, Single Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
9
10
11
12
Next Conversion
13
14
15
16
1
2
3
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
MUX and REFS
Update
238
Conversion
Complete
MUX and REFS
Update
AT90PWM2/3/2B/3B
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AT90PWM2/3/2B/3B
Figure 21-6. ADC Timing Diagram, Auto Triggered Conversion
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
Next Conversion
13
14
15
16
1
2
ADC Clock
Trigger
Source
ADATE
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Prescaler
Reset
Sample &
Hold
Conversion
Complete
Prescaler
Reset
MUX and REFS
Update
Figure 21-7. ADC Timing Diagram, Free Running Conversion
One Conversion
Cycle Number
14
15
Next Conversion
16
1
2
3
4
5
ADC Clock
ADSC
ADIF
ADCH
Sign and MSB of Result
ADCL
LSB of Result
Sample & Hold
Conversion
Complete
Table 21-1.
ADC Conversion Time
Condition
Sample & Hold
(Cycles from Start of Conversion)
Conversion Time
(Cycles)
21.5
MUX and REFS
Update
First Conversion
Normal
Conversion,
Single Ended
Auto Triggered
Conversion
13.5
3.5
4
25
15.5
16
Changing Channel or Reference Selection
The MUXn and REFS1:0 bits in the ADMUX Register are single buffered through a temporary
register to which the CPU has random access. This ensures that the channels and reference
selection only takes place at a safe point during the conversion. The channel and reference
selection is continuously updated until a conversion is started. Once the conversion starts, the
channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in
ADCSRA is set). Note that the conversion starts on the following rising ADC clock edge after
ADSC is written. The user is thus advised not to write new channel or reference selection values
to ADMUX until one ADC clock cycle after ADSC is written.
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If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
1. When ADATE or ADEN is cleared.
2. During conversion, minimum one ADC clock cycle after the trigger event.
3. After a conversion, before the interrupt flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
In order to start a conversion on an amplified channel, there is a dedicated ADASCR bit in ADCSRB register which wait for the next amplifier trigger event before really starting the conversion
by an hardware setting of the ADSC bit in ADCSRA register.
21.5.1
ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
21.5.2
•
In Single Conversion mode, always select the channel before starting the conversion. The
channel selection may be changed one ADC clock cycle after writing one to ADSC.
However, the simplest method is to wait for the conversion to complete before changing the
channel selection.
•
In Free Running mode, always select the channel before starting the first conversion. The
channel selection may be changed one ADC clock cycle after writing one to ADSC.
However, the simplest method is to wait for the first conversion to complete, and then
change the channel selection. Since the next conversion has already started automatically,
the next result will reflect the previous channel selection. Subsequent conversions will
reflect the new channel selection.
•
In Free Running mode, because the amplifier clear the ADSC bit at the end of an amplified
conversion, it is not possible to use the free running mode, unless ADSC bit is set again by
soft at the end of each conversion.
ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either AVCC, internal 2.56V reference, or external AREF pin.
AVCC is connected to the ADC through a passive switch. The internal 2.56V reference is generated from the internal bandgap reference (VBG) through an internal amplifier. In either case, the
external AREF pin is directly connected to the ADC, and the reference voltage can be made
more immune to noise by connecting a capacitor between the AREF pin and ground. VREF can
also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high
impedant source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no
external voltage is applied to the AREF pin, the user may switch between AVCC and 2.56V as
reference selection. The first ADC conversion result after switching reference voltage source
may be inaccurate, and the user is advised to discard this result.
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If differential channels are used, the selected reference should not be closer to AVCC than indicated in Table 26-3 on page 306.
21.6
ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise
induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC
Noise Reduction and Idle mode. To make use of this feature, the following procedure should be
used:
a. Make sure that the ADATE bit is reset.
b. 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.
c.
Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion
once the CPU has been halted.
d. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt
routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt
request will be generated when the ADC conversion completes. The CPU will
remain in active mode until a new sleep command is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle
mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power consumption.
If the ADC is enabled in such sleep modes and the user wants to perform differential conversions, the user is advised to switch the ADC off and on after waking up from sleep to prompt an
extended conversion to get a valid result.
21.6.1
Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 21-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the ADC. When the channel is selected, the
source must drive the S/H capacitor through the series resistance (combined resistance in the
input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long time the source needs to charge the
S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources
with slowly varying signals, since this minimizes the required charge transfer to the S/H
capacitor.
If differential gain channels are used, the input circuitry looks somewhat different, although
source impedances of a few hundred kΩ or less is recommended.
Signal components higher than the Nyquist frequency (fADC/2) should not be present for either
kind of channels, to avoid distortion from unpredictable signal convolution. The user is advised
to remove high frequency components with a low-pass filter before applying the signals as
inputs to the ADC.
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Figure 21-8. Analog Input Circuitry
IIH
ADCn
1..100 kΩ
CS/H= 14 pF
IIL
VCC/2
21.6.2
Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. If conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
1. Keep analog signal paths as short as possible. Make sure analog tracks run over the
analog ground plane, and keep them well away from high-speed switching digital
tracks.
2. The AVCC pin on the device should be connected to the digital VCC supply voltage via
an LC network as shown in Figure 21-9.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC port pins are used as digital outputs, it is essential that these do not
switch while a conversion is in progress.
Figure 21-9. ADC Power Connections
VCC
GND
(ADC0) PE2
(ADC1) PD4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
PB7(ADC4)
PB6 (ADC7)
PB5 (ADC6)
PC7 (D2A)
PB4 (AMP0+)
PB3 (AMP0-)
PC6 (ADC10/ACMP1)
AREF
AGND
AVCC
PC5 (ADC9/AMP1+)
PC4 (ADC8/AMP1-)
PB2 (ADC5)
PD7 (ACMP0)
PD6 (ADC3/ACMPM)
PD5 (ADC2/ACMP2)
10μH
100nF
Analog Ground Plane
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21.6.3
Offset Compensation Schemes
The gain stage has a built-in offset cancellation circuitry that nulls the offset of differential measurements as much as possible. The remaining offset in the analog path can be measured
directly by shortening both differential inputs using the AMPxIS bit with both inputs unconnected.
(See “Amplifier 0 Control and Status register – AMP0CSR” on page 256. and See “Amplifier
1Control and Status register – AMP1CSR” on page 257.). This offset residue can be then subtracted in software from the measurement results. Using this kind of software based offset
correction, offset on any channel can be reduced below one LSB.
21.6.4
ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior:
•
Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Ideal value: 0 LSB.
Figure 21-10. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
•
VREF Input Voltage
Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last
transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum).
Ideal value: 0 LSB
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Figure 21-11. Gain Error
Gain
Error
Output Code
Ideal ADC
Actual ADC
VREF Input Voltage
•
Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0
LSB.
Figure 21-12. Integral Non-linearity (INL)
Output Code
INL
Ideal ADC
Actual ADC
VREF
•
244
Input Voltage
Differential Non-linearity (DNL): The maximum deviation of the actual code width (the
interval between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0
LSB.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 21-13. Differential Non-linearity (DNL)
Output Code
0x3FF
1 LSB
DNL
0x000
0
21.7
VREF Input Voltage
•
Quantization Error: Due to the quantization of the input voltage into a finite number of codes,
a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
•
Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared
to an ideal transition for any code. This is the compound effect of offset, gain error,
differential error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH).
For single ended conversion, the result is:
V IN ⋅ 1023
ADC = -------------------------V REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 21-3 on page 247 and Table 21-4 on page 248). 0x000 represents analog ground, and
0x3FF represents the selected reference voltage.
If differential channels are used, the result is:
( V POS – V NEG ) ⋅ GAIN ⋅ 512
ADC = -----------------------------------------------------------------------V REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
GAIN the selected gain factor and VREF the selected voltage reference. The result is presented
in two’s complement form, from 0x200 (-512d) through 0x1FF (+511d). Note that if the user
wants to perform a quick polarity check of the result, it is sufficient to read the MSB of the result
(ADC9 in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is positive. Figure 21-14 shows the decoding of the differential input range.
Table 82 shows the resulting output codes if the differential input channel pair (ADCn - ADCm) is
selected with a reference voltage of VREF.
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Figure 21-14. Differential Measurement Range
Output Code
0x1FF
0x000
- VREF /Gain
0x3FF
0
VREF/Gain Differential Input
Voltage (Volts)
0x200
Table 21-2.
Correlation Between Input Voltage and Output Codes
VADCn
Read code
Corresponding decimal value
VADCm + VREF /GAIN
0x1FF
511
VADCm + 0.999 VREF /GAIN
0x1FF
511
VADCm + 0.998 VREF /GAIN
0x1FE
510
...
...
...
VADCm + 0.001 VREF /GAIN
0x001
1
VADCm
0x000
0
VADCm - 0.001 VREF /GAIN
0x3FF
-1
...
...
...
VADCm - 0.999 VREF /GAIN
0x201
-511
VADCm - VREF /GAIN
0x200
-512
Example 1:
246
–
ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result)
–
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
–
ADCR = 512 * 10 * (300 - 500) / 2560 = -400 = 0x270
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
–
ADCL will thus read 0x00, and ADCH will read 0x9C.
Writing zero to ADLAR right adjusts the result: ADCL = 0x70, ADCH = 0x02.
Example 2:
21.8
–
ADMUX = 0xFB (ADC3 - ADC2, 1x gain, 2.56V reference, left adjusted result)
–
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
–
ADCR = 512 * 1 * (300 - 500) / 2560 = -41 = 0x029.
–
ADCL will thus read 0x40, and ADCH will read 0x0A.
Writing zero to ADLAR right adjusts the result: ADCL = 0x00, ADCH = 0x29.
ADC Register Description
The ADC of the AT90PWM2/2B/3/3B is controlled through 3 different registers. The ADCSRA
and The ADCSRB registers which are the ADC Control and Status registers, and the ADMUX
which allows to select the Vref source and the channel to be converted.
The conversion result is stored on ADCH and ADCL register which contain respectively the most
significant bits and the less significant bits.
21.8.1
ADC Multiplexer Register – ADMUX
Bit
7
6
5
4
3
2
1
0
REFS1
REFS0
ADLAR
-
MUX3
MUX2
MUX1
MUX0
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
ADMUX
• Bit 7, 6 – REFS1, 0: ADC Vref Selection Bits
These 2 bits determine the voltage reference for the ADC.
The different setting are shown in Table 21-3.
Table 21-3.
ADC Voltage Reference Selection
REFS1
REFS0
Description
0
0
External Vref on AREF pin, Internal Vref is switched off
0
1
AVcc with external capacitor connected on the AREF pin
1
0
Reserved
1
1
Internal 2.56V Reference voltage with external capacitor connected on
the AREF pin
If these bits are changed during a conversion, the change will not take effect until this conversion
is complete (it means while the ADIF bit in ADCSRA register is set).
In case the internal Vref is selected, it is turned ON as soon as an analog feature needed it is
set.
• Bit 5 – ADLAR: ADC Left Adjust Result
Set this bit to left adjust the ADC result.
Clear it to right adjust the ADC result.
The ADLAR bit affects the configuration of the ADC result data registers. Changing this bit
affects the ADC data registers immediately regardless of any on going conversion. For a complete description of this bit, see Section “ADC Result Data Registers – ADCH and ADCL”,
page 251.
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• Bit 3, 2, 1, 0 – MUX3, MUX2, MUX1, MUX0: ADC Channel Selection Bits
These 4 bits determine which analog inputs are connected to the ADC input. The different setting are shown in Table 21-4.
Table 21-4.
ADC Input Channel Selection
MUX3
MUX2
MUX1
MUX0
Description
0
0
0
0
ADC0
0
0
0
1
ADC1
0
0
1
0
ADC2
0
0
1
1
ADC3
0
1
0
0
ADC4
0
1
0
1
ADC5
0
1
1
0
ADC6
0
1
1
1
ADC7
1
0
0
0
ADC8
1
0
0
1
ADC9
1
0
1
0
ADC10
1
0
1
1
AMP0
1
1
0
0
AMP1 (- is ADC8, + is ADC9)
1
1
0
1
Reserved
1
1
1
0
Bandgap
1
1
1
1
GND
If these bits are changed during a conversion, the change will not take effect until this conversion
is complete (it means while the ADIF bit in ADCSRA register is set).
21.8.2
ADC Control and Status Register A – ADCSRA
Bit
7
6
5
4
3
2
1
0
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
Read/Write
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRA
• Bit 7 – ADEN: ADC Enable Bit
Set this bit to enable the ADC.
Clear this bit to disable the ADC.
Clearing this bit while a conversion is running will take effect at the end of the conversion.
• Bit 6– ADSC: ADC Start Conversion Bit
Set this bit to start a conversion in single conversion mode or to start the first conversion in free
running mode.
Cleared by hardware when the conversion is complete. Writing this bit to zero has no effect.
The first conversion performs the initialization of the ADC.
• Bit 5 – ADATE: ADC Auto trigger Enable Bit
Set this bit to enable the auto triggering mode of the ADC.
Clear it to return in single conversion mode.
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In auto trigger mode the trigger source is selected by the ADTS bits in the ADCSRB register.
See Table 21-6 on page 250.
• Bit 4– ADIF: ADC Interrupt Flag
Set by hardware as soon as a conversion is complete and the Data register are updated with the
conversion result.
Cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, ADIF can be cleared by writing it to logical one.
• Bit 3– ADIE: ADC Interrupt Enable Bit
Set this bit to activate the ADC end of conversion interrupt.
Clear it to disable the ADC end of conversion interrupt.
• Bit 2, 1, 0– ADPS2, ADPS1, ADPS0: ADC Prescaler Selection Bits
These 3 bits determine the division factor between the system clock frequency and input clock of
the ADC.
The different setting are shown in Table 21-5.
Table 21-5.
21.8.3
ADC Prescaler Selection
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
ADC Control and Status Register B– ADCSRB
Bit
7
6
5
4
3
2
1
0
ADHSM
-
-
ADASCR
ADTS3
ADTS2
ADTS1
ADTS0
Read/Write
-
-
-
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
ADCSRB
• Bit 7 – ADHSM: ADC High Speed Mode
Writing this bit to one enables the ADC High Speed mode. Set this bit if you wish to convert with
an ADC clock frequency higher than 200KHz.
• Bit 4– ADASCR: Analog to Digital Conversion on Amplified Channel Start Conversion
Request Bit (AT90PWM2/3 only - NA on AT90PWM2B/3B)
Set this to request a conversion on an amplified channel.
Cleared by hardware as soon as the Analog to Digital Conversion is started.
Alternatively, this bit can be cleared by writing it to logical zero.
In order to start a conversion on an amplified channel with the AT90PWM2B/3B, use the ADCS
bit in ADCSRA register.
• Bit 3, 2, 1, 0– ADTS3:ADTS0: ADC Auto Trigger Source Selection Bits
These bits are only necessary in case the ADC works in auto trigger mode. It means if ADATE
bit in ADCSRA register is set.
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4317I–AVR–01/08
In accordance with the Table 21-6, these 3 bits select the interrupt event which will generate the
trigger of the start of conversion. The start of conversion will be generated by the rising edge of
the selected interrupt flag whether the interrupt is enabled or not. In case of trig on PSCnASY
event, there is no flag. So in this case a conversion will start each time the trig event appears
and the previous conversion is completed
Table 21-6.
ADTS3
ADTS2
ADTS1
ADTS0
Description
0
0
0
0
Free Running Mode
0
0
0
1
Analog Comparator 0
0
0
1
0
External Interrupt Request 0
0
0
1
1
Timer/Counter0 Compare Match
0
1
0
0
Timer/Counter0 Overflow
0
1
0
1
Timer/Counter1 Compare Match B
0
1
1
0
Timer/Counter1 Overflow
0
1
1
1
Timer/Counter1 Capture Event
1
0
0
0
PSC0ASY Event (1)
1
0
0
1
PSC1ASY Event(1)
1
0
1
0
PSC2ASY Event(1)
1
0
1
1
Analog comparator 1
1
1
0
0
Analog comparator 2
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
1.
For trigger on any PSC event, if the PSC uses the PLL clock, the core must use PLL/4 clock
source.
Table 21-7.
250
ADC Auto Trigger Source Selection for non amplified conversions
ADC Auto Trigger Source Selection for amplified conversions
ADTS3
ADTS2
ADTS1
ADTS0
Description
0
0
0
0
Free Running Mode
0
0
0
1
Reserved
0
0
1
0
Reserved
0
0
1
1
Reserved
0
1
0
0
Reserved
0
1
0
1
Reserved
0
1
1
0
Reserved
0
1
1
1
Reserved
1
0
0
0
PSC0ASY Event (1)
1
0
0
1
PSC1ASY Event(1)
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 21-7.
ADTS3
ADTS2
ADTS1
ADTS0
Description
1
0
1
0
PSC2ASY Event(1)
1
0
1
1
Reserved
1
1
0
0
Reserved
1
1
0
1
Reserved
1
1
1
0
Reserved
1
1
1
1
Reserved
1.
21.8.4
ADC Auto Trigger Source Selection for amplified conversions
For trigger on any PSC event, if the PSC uses the PLL clock, the core must use PLL/4 clock
source.
ADC Result Data Registers – ADCH and ADCL
When an ADC conversion is complete, the conversion results are stored in these two result data
registers.
When the ADCL register is read, the two ADC result data registers can’t be updated until the
ADCH register has also been read.
Consequently, in 10-bit configuration, the ADCL register must be read first before the ADCH.
Nevertheless, to work easily with only 8-bit precision, there is the possibility to left adjust the
result thanks to the ADLAR bit in the ADCSRA register. Like this, it is sufficient to only read
ADCH to have the conversion result.
21.8.4.1
ADLAR = 0
Bit
Read/Write
Initial Value
21.8.4.2
6
5
4
3
2
1
0
-
-
-
-
-
-
ADC9
ADC8
ADCH
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
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
ADLAR = 1
Bit
Read/Write
Initial Value
21.8.5
7
7
6
5
4
3
2
1
0
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
ADC1
ADC0
-
-
-
-
-
-
ADCL
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
Digital Input Disable Register 0 – DIDR0
Bit
7
6
5
4
3
2
1
0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D
ACMPM
ADC2D
ACMP2D
ADC1D
ADC0D
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR0
• Bit 7:0 – ADC7D..ADC0D: ACMP2:1 and ADC7:0 Digital Input Disable
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4317I–AVR–01/08
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN Register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC7..0 pin and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
21.8.6
Digital Input Disable Register 1– DIDR1
Bit
7
6
5
4
3
2
1
0
-
-
ACMP0D
AMP0PD
AMP0ND
ADC10D
ACMP1D
ADC9D
AMP1PD
ADC8D
AMP1ND
Read/Write
-
-
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
DIDR1
• Bit 5:0 – ACMP0D, AMP0+D, AMP0-D, ADC10D..ADC8D: ACMP0, AMP1:0 and ADC10:8
Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN Register bit will always read as zero when this bit is set. When an
analog signal is applied to an analog pin and the digital input from this pin is not needed, this bit
should be written logic one to reduce power consumption in the digital input buffer.
21.9
Amplifier
The AT90PWM2/2B/3/3B features two differential amplified channels with programmable 5, 10,
20, and 40 gain stage. Despite the result is given by the 10 bit ADC, the amplifier has been sized
to give a 8bits resolution.
Because the amplifier is a switching capacitor amplifier, it needs to be clocked by a synchronization signal called in this document the amplifier synchronization clock. The maximum clock for
the amplifier is 250kHz.
To ensure an accurate result, the amplifier input needs to have a quite stable input value at the
sampling point during at least 4 Amplifier synchronization clock periods.
Amplified conversions can be synchronized to PSC events (See “Synchronization Source
Description in One/Two/Four Ramp Modes” on page 162 and “Synchronization Source Description in Centered Mode” on page 163) or to the internal clock CKADC equal to eighth the ADC
clock frequency. In case the synchronization is done by the ADC clock divided by 8, this synchronization is done automatically by the ADC interface in such a way that the sample-and-hold
occurs at a specific phase of CKADC2. A conversion initiated by the user (i.e., all single conversions, and the first free running conversion) when CKADC2 is low will take the same amount of
time as a single ended conversion (13 ADC clock cycles from the next prescaled clock cycle). A
conversion initiated by the user when CKADC2 is high will take 14 ADC clock cycles due to the
synchronization mechanism.
The normal way to use the amplifier is to select a synchronization clock via the AMPxTS1:0 bits
in the AMPxCSR register. Then the amplifier can be switched on, and the amplification is done
on each synchronization event. The amplification is done independently of the ADC.
In order to start an amplified Analog to Digital Conversion on the amplified channel, the ADMUX
must be configured as specified on Table 21-4 on page 248.
Depending on AT90PWM2/2B/3/3B revision the ADC starting is done:
- By setting the ADASCR (Analog to Digital Conversion on Amplified Channel Start Conversion
Request) bit in the ADCSRB register on AT90PWM2/3. Then, the ADSC bit of the ADCSRA
Register is automatically set on the next amplifier clock event, and a conversion is started.
- By setting the ADSC (ADC Start conversion) bit in the ADCSRB register on AT90PWM2B/3B.
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AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Until the conversion is not achieved, it is not possible to start a conversion on another channel.
In order to have a better understanding of the functioning of the amplifier synchronization, a timing diagram example is shown Figure 21-15 for AT90PWM2/3.
Figure 21-15. Amplifier synchronization timing diagram for AT90PWM2/3.
Delta V
4th stable sample
Signal to be
measured
PSC
Block
PSCn_ASY
AMPLI_clk
(Sync Clock)
CK ADC
Amplifier
Block
Amplifier Sample
Enable
Amplifier Hold
Value
Valid sample
ADASCR
ADC
ADSC
ADC
Sampling
ADC Result Ready
It is also possible to auto trigger conversion on the amplified channel. In this case, the conversion is started at the next amplifier clock event following the last auto trigger event selected
thanks to the ADTS bits in the ADCSRB register. In auto trigger conversion, the free running
mode is not possible unless the ADSC bit in ADCSRA is set by soft after each conversion.
Only PSC sources can auto trigger the amplified conversion. In this case, the core must have a
clock synchronous with the PSC. If the PSC uses the PLL clock, the core must use the PLL/4
clock source.
AT90PWM2B/3B:
On PWM2B/3B, the amplifier has been improved in order to speed-up the conversion time.The
proposed improvement takes advantage of the amplifier characteristics to ensure a conversion
in less time.
In order to have a better understanding of the functioning of the amplifier synchronization, a timing diagram example is shown Figure for AT90PWM2B/3B.
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4317I–AVR–01/08
As soon as a conversion is requested thanks to the ADSC bit, the Analog to Digital Conversion
is started. In case the amplifier output is modified during the sample phase of the ADC, the ongoing conversion is aborted and restarted as soon as the output of the amplifier is stable. This
ensure a fast response time. The only precaution to take is to be sure that the trig signal (PSC)
frequency is lower than ADCclk/4.
Figure 21-16. Amplifier synchronization timing diagram for AT90PWM2B/3B
With change on analog input signal
Delta V
4th stable sample
Signal to be
measured
PSC
Block
PSCn_ASY
AMPLI_clk
(Sync Clock)
CK ADC
Valid sample
ADSC
ADC
ADC
Activity
ADC
Conv
ADC
Sampling
ADC
Conv
ADC
Sampling
ADCResult
Ready
ADCResult
Ready
Figure 21-17. Amplifier synchronization timing diagram for AT90PWM2B/3B
ADSC is set when the amplifier output is changing due to the amplifier clock
switch.
254
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Signal to be
measured
PSC
Block
PSCn_ASY
AMPLI_clk
(Sync Clock)
CK ADC
Valid sample
ADSC
ADC
ADC
Activity
ADC
Conv
ADC
Sampling
ADC
Sampling
Aborted
ADC
Conv
ADC
Sampling
ADCResult
Ready
ADCResult
Ready
255
4317I–AVR–01/08
The block diagram of the two amplifiers is shown on Figure 21-18.
Figure 21-18. Amplifiers block diagram
+
SAMPLING
AMP0+
AMP0-
Toward ADC MUX
(AMP0)
ADCK/8
ASY0
ASY1
ASY2
00
01
10
01
Sampling
Clock
AMP0EN AMP0IS AMP0G1 AMP0G0
-
-
AMP0TS1AMP0TS0
AMP0CSR
+
SAMPLING
AMP1+
AMP1-
Toward ADC MU
(AMP1)
ADCK/8
ASY0
ASY1
ASY2
00
01
10
01
Sampling
Clock
AMP1EN AMP1IS AMP1G1 AMP1G0
-
AMP1TS1AMP1TS0
-
AMP1CSR
21.10 Amplifier Control Registers
The configuration of the amplifiers are controlled via two dedicated registers AMP0CSR and
AMP1CSR. Then the start of conversion is done via the ADC control and status registers.
The conversion result is stored on ADCH and ADCL register which contain respectively the most
significant bits and the less significant bits.
21.10.1
Amplifier 0 Control and Status register – AMP0CSR
Bit
256
7
6
5
4
3
2
1
0
AMP0EN
AMP0IS
AMP0G1
AMP0G0
-
-
AMP0TS1
AMP0TS0
Read/Write
R/W
R/W
R/W
R/W
-
-
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
AMP0CSR
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
• Bit 7 – AMP0EN: Amplifier 0 Enable Bit
Set this bit to enable the Amplifier 0.
Clear this bit to disable the Amplifier 0.
Clearing this bit while a conversion is running will take effect at the end of the conversion.
Warning: Always clear AMP0TS1:0 when clearing AMP0EN.
• Bit 6– AMP0IS: Amplifier 0 Input Shunt
Set this bit to short-circuit the Amplifier 0 input.
Clear this bit to normally use the Amplifier 0.
• Bit 5, 4– AMP0G1, 0: Amplifier 0 Gain Selection Bits
These 2 bits determine the gain of the amplifier 0.
The different setting are shown in Table 21-8.
Table 21-8.
Amplifier 0 Gain Selection
AMP0G1
AMP0G0
Description
0
0
Gain 5
0
1
Gain 10
1
0
Gain 20
1
1
Gain 40
To ensure an accurate result, after the gain value has been changed, the amplifier input needs
to have a quite stable input value during at least 4 Amplifier synchronization clock periods.
• Bit 1, 0– AMP0TS1, AMP0TS0: Amplifier 0 Trigger Source Selection Bits
In accordance with the Table 21-9, these 2 bits select the event which will generate the trigger
for the amplifier 0. This trigger source is necessary to start the conversion on the amplified
channel.
Table 21-9.
21.10.2
AMP0 Auto Trigger Source Selection
AMP0TS1
AMP0TS0
Description
0
0
Auto synchronization on ADC Clock/8
0
1
Trig on PSC0ASY
1
0
Trig on PSC1ASY
1
1
Trig on PSC2ASY
Amplifier 1Control and Status register – AMP1CSR
Bit
7
6
5
4
3
2
1
0
AMP1EN
AMP1IS
AMP1G1
AMP1G0
-
-
AMP1TS1
AMP1TS0
Read/Write
R/W
R/W
R/W
R/W
-
-
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
AMP1CSR
• Bit 7 – AMP1EN: Amplifier 1 Enable Bit
Set this bit to enable the Amplifier 1.
Clear this bit to disable the Amplifier 1.
Clearing this bit while a conversion is running will take effect at the end of the conversion.
Warning: Always clear AMP1TS1:0 when clearing AMP1EN.
• Bit 6– AMP1IS: Amplifier 1 Input Shunt
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4317I–AVR–01/08
Set this bit to short-circuit the Amplifier 1 input.
Clear this bit to normally use the Amplifier 1.
• Bit 5, 4– AMP1G1, 0: Amplifier 1 Gain Selection Bits
These 2 bits determine the gain of the amplifier 0.
The different setting are shown in Table 21-10.
Table 21-10. Amplifier 1 Gain Selection
AMP1G1
AMP1G0
Description
0
0
Gain 5
0
1
Gain 10
1
0
Gain 20
1
1
Gain 40
To ensure an accurate result, after the gain value has been changed, the amplifier input needs
to have a quite stable input value during at least 4 Amplifier synchronization clock periods.
• Bit 1, 0– AMP1TS1, AMP1TS0: Amplifier 1 Trigger Source Selection Bits
In accordance with the Table 21-11, these 2 bits select the event which will generate the trigger
for the amplifier 1. This trigger source is necessary to start the conversion on the amplified
channel.
Table 21-11. AMP1 Auto Trigger source selection
258
AMP1TS1
AMP1TS0
Description
0
0
Auto synchronization on ADC Clock/8
0
1
Trig on PSC0ASY
1
0
Trig on PSC1ASY
1
1
Trig on PSC2ASY
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
22. Digital to Analog Converter - DAC
22.1
Features
•
•
•
•
•
10 bits resolution
8 bits linearity
+/- 0.5 LSB accuracy between 150mV and AVcc-150mV
Vout = DAC*Vref/1023
The DAC could be connected to the negative inputs of the analog comparators and/or to a
dedicated output driver.
• Output impedance around 100 Ohm.
The AT90PWM2/2B/3/3B features a 10-bit Digital to Analog Converter. This DAC can be used
for the analog comparators and/or can be output on the D2A pin of the microcontroller via a dedicated driver.
This allows to drive (worst case) a 1nF capacitance in parallel with a resistor higher than 33K
load with a time constant around 1us. Response time and power consumption are improved by
reducing the load (reducing the capacitor value and increasing the load resistor value (The best
case is a high impedance)).
The DAC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±
0.3V from VCC. See the paragraph “ADC Noise Canceler” on page 241 on how to connect this
pin.
The reference voltage is the same as the one used for the ADC, See “ADC Multiplexer Register
– ADMUX” on page 247.. These nominally 2.56V Vref or AVCC are provided On-chip. The voltage reference may be externally decoupled at the AREF pin by a capacitor for better noise
performance.
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4317I–AVR–01/08
Figure 22-1. Digital to Analog Converter Block Schematic
DAC
Result
D2A pin
VRef
DAC
Output
Driver
10
1
0
10
10
DAC High bits
DAC Low bits
Sources
DACH
Update DAC
Trigger
Edge
Detector
DAATE
DACL
DATS2
DATS1
DATS0
-
DALA
DAOE
DAEN
DACON
22.2
Operation
The Digital to Analog Converter generates an analog signal proportional to the value of the DAC
registers value.
In order to have an accurate sampling frequency control, there is the possibility to update the
DAC input values through different trigger events.
22.3
Starting a Conversion
The DAC is configured thanks to the DACON register. As soon as the DAEN bit in DACON register is set, the DAC converts the value present on the DACH and DACL registers in accordance
with the register DACON setting.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is
enabled by setting the DAC Auto Trigger Enable bit, DAATE in DACON. The trigger source is
selected by setting the DAC Trigger Select bits, DATS in DACON (See description of the DATS
bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal,
the DAC converts the value present on the DACH and DACL registers in accordance with the
register DACON setting. This provides a method of starting conversions at fixed intervals. If the
trigger signal is still set when the conversion completes, a new conversion will not be started. If
another positive edge occurs on the trigger signal during conversion, the edge will be ignored.
Note that an interrupt flag will be set even if the specific interrupt is disabled or the Global Inter-
260
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
rupt Enable bit in SREG is cleared. A conversion can thus be triggered without causing an
interrupt. However, the interrupt flag must be cleared in order to trigger a new conversion at the
next interrupt event.
22.3.1
DAC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the DAC. VREF can
be selected as either AVCC, internal 2.56V reference, or external AREF pin.
AVCC is connected to the DAC through a passive switch. The internal 2.56V reference is generated from the internal bandgap reference (VBG) through an internal amplifier. In either case, the
external AREF pin is directly connected to the DAC, and the reference voltage can be made
more immune to noise by connecting a capacitor between the AREF pin and ground. VREF can
also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high
impedant source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no
external voltage is applied to the AREF pin, the user may switch between AVCC and 2.56V as
reference selection. The first DAC conversion result after switching reference voltage source
may be inaccurate, and the user is advised to discard this result.
22.4
DAC Register Description
The DAC is controlled via three dedicated registers:
22.4.1
•
The DACON register which is used for DAC configuration
•
DACH and DACL which are used to set the value to be converted.
Digital to Analog Conversion Control Register – DACON
Bit
7
6
5
4
3
2
1
0
DAATE
DATS2
DATS1
DATS0
-
DALA
DAOE
DAEN
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
DACON
• Bit 7 – DAATE: DAC Auto Trigger Enable bit
Set this bit to update the DAC input value on the positive edge of the trigger signal selected with
the DACTS2-0 bit in DACON register.
Clear it to automatically update the DAC input when a value is written on DACH register.
• Bit 6:4 – DATS2, DATS1, DATS0: DAC Trigger Selection bits
These bits are only necessary in case the DAC works in auto trigger mode. It means if DAATE
bit is set.
In accordance with the Table 22-1, these 3 bits select the interrupt event which will generate the
update of the DAC input values. The update will be generated by the rising edge of the selected
interrupt flag whether the interrupt is enabled or not.
Table 22-1.
DAC Auto Trigger source selection
DATS2
DATS1
DATS0
Description
0
0
0
Analog comparator 0
0
0
1
Analog comparator 1
0
1
0
External Interrupt Request 0
0
1
1
Timer/Counter0 Compare Match
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4317I–AVR–01/08
Table 22-1.
DAC Auto Trigger source selection (Continued)
DATS2
DATS1
DATS0
Description
1
0
0
Timer/Counter0 Overflow
1
0
1
Timer/Counter1 Compare Match B
1
1
0
Timer/Counter1 Overflow
1
1
1
Timer/Counter1 Capture Event
• Bit 2 – DALA: Digital to Analog Left Adjust
Set this bit to left adjust the DAC input data.
Clear it to right adjust the DAC input data.
The DALA bit affects the configuration of the DAC data registers. Changing this bit affects the
DAC output on the next DACH writing.
• Bit 1 – DAOE: Digital to Analog Output Enable bit
Set this bit to output the conversion result on D2A,
Clear it to use the DAC internally.
• Bit 0 – DAEN: Digital to Analog Enable bit
Set this bit to enable the DAC,
Clear it to disable the DAC.
22.4.2
Digital to Analog Converter input Register – DACH and DACL
DACH and DACL registers contain the value to be converted into analog voltage.
Writing the DACL register forbid the update of the input value until DACH has not been written
too. So the normal way to write a 10-bit value in the DAC register is firstly to write DACL the
DACH.
In order to work easily with only 8 bits, there is the possibility to left adjust the input value. Like
this it is sufficient to write DACH to update the DAC value.
22.4.2.1
DALA = 0
Bit
Read/Write
Initial Value
22.4.2.2
6
5
4
3
2
1
0
-
-
-
-
-
-
DAC9
DAC8
DACH
DAC7
DAC6
DAC5
DAC4
DAC3
DAC2
DAC1
DAC0
DACL
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
DALA = 1
Bit
Read/Write
Initial Value
262
7
7
6
5
4
3
2
1
0
DAC9
DAC8
DAC7
DAC6
DAC5
DAC4
DAC3
DAC2
DACH
DAC1
DAC0
-
-
-
-
-
-
DACL
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
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
To work with the 10-bit DAC, two registers have to be updated. In order to avoid intermediate
value, the DAC input values which are really converted into analog signal are buffering into
unreachable registers. In normal mode, the update of the shadow register is done when the register DACH is written.
In case DAATE bit is set, the DAC input values will be updated on the trigger event selected
through DATS bits.
In order to avoid wrong DAC input values, the update can only be done after having written
respectively DACL and DACH registers. It is possible to work on 8-bit configuration by only writing the DACH value. In this case, update is done each trigger event.
In case DAATE bit is cleared, the DAC is in an automatic update mode. Writing the DACH register automatically update the DAC input values with the DACH and DACL register values.
It means that whatever is the configuration of the DAATE bit, changing the DACL register has no
effect on the DAC output until the DACH register has also been updated. So, to work with 10
bits, DACL must be written first before DACH. To work with 8-bit configuration, writing DACH
allows the update of the DAC.
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23. debugWIRE On-chip Debug System
23.1
Features
•
•
•
•
•
•
•
•
•
•
23.2
Complete Program Flow Control
Emulates All On-chip Functions, Both Digital and Analog, except RESET Pin
Real-time Operation
Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)
Unlimited Number of Program Break Points (Using Software Break Points)
Non-intrusive Operation
Electrical Characteristics Identical to Real Device
Automatic Configuration System
High-Speed Operation
Programming of Non-volatile Memories
Overview
The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatile
memories.
23.3
Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed,
the debugWIRE system within the target device is activated. The RESET port pin is configured
as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway between target and emulator.
Figure 23-1. The debugWIRE Setup
1.8 - 5.5V
VCC
dW
dW(RESET)
GND
Figure 23-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.
When designing a system where debugWIRE will be used, the following observations must be
made for correct operation:
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AT90PWM2/3/2B/3B
23.4
•
Pull-up resistors on the dW/(RESET) line must not be smaller than 10kΩ. The pull-up
resistor is not required for debugWIRE functionality.
•
Connecting the RESET pin directly to VCC will not work.
•
Capacitors connected to the RESET pin must be disconnected when using debugWire.
•
All external reset sources must be disconnected.
Software Break Points
debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a
Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruction replaced by the BREAK instruction will be stored. When program execution is continued, the
stored instruction will be executed before continuing from the Program memory. A break can be
inserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a Break Point is changed. This is automatically
handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore
reduce the Flash Data retention. Devices used for debugging purposes should not be shipped to
end customers.
23.5
Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is
enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken while
accessing some of the I/O Registers via the debugger (AVR Studio).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should
be disabled when debugWire is not used.
23.6
debugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.
23.6.1
debugWire Data Register – DWDR
Bit
7
6
5
4
3
2
1
0
DWDR[7:0]
DWDR
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 DWDR Register provides a communication channel from the running program in the MCU
to the debugger. This register is only accessible by the debugWIRE and can therefore not be
used as a general purpose register in the normal operations.
24. Boot Loader Support – Read-While-Write Self-Programming
In AT90PWM2/2B/3/3B, the Boot Loader Support provides a real Read-While-Write Self-Programming mechanism for downloading and uploading program code by the MCU itself. This
feature allows flexible application software updates controlled by the MCU using a Flash-resident Boot Loader program. The Boot Loader program can use any available data interface and
associated protocol to read code and write (program) that code into the Flash memory, or read
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the code from the program memory. The program code within the Boot Loader section has the
capability to write into the entire Flash, including the Boot Loader memory. The Boot Loader can
thus even modify itself, and it can also erase itself from the code if the feature is not needed anymore. The size of the Boot Loader memory is configurable with fuses and the Boot Loader has
two separate sets of Boot Lock bits which can be set independently. This gives the user a
unique flexibility to select different levels of protection.
24.1
Boot Loader Features
•
•
•
•
•
•
•
Read-While-Write Self-Programming
Flexible Boot Memory Size
High Security (Separate Boot Lock Bits for a Flexible Protection)
Separate Fuse to Select Reset Vector
Optimized Page(1) Size
Code Efficient Algorithm
Efficient Read-Modify-Write Support
Note:
24.2
1. A page is a section in the Flash consisting of several bytes (see Table 25-11 on page 285)
used during programming. The page organization does not affect normal operation.
Application and Boot Loader Flash Sections
The Flash memory is organized in two main sections, the Application section and the Boot
Loader section (see Figure 24-2). The size of the different sections is configured by the
BOOTSZ Fuses as shown in Table 24-6 on page 278 and Figure 24-2. These two sections can
have different level of protection since they have different sets of Lock bits.
24.2.1
Application Section
The Application section is the section of the Flash that is used for storing the application code.
The protection level for the Application section can be selected by the application Boot Lock bits
(Boot Lock bits 0), see Table 24-2 on page 270. The Application section can never store any
Boot Loader code since the SPM instruction is disabled when executed from the Application
section.
24.2.2
BLS – Boot Loader Section
While the Application section is used for storing the application code, the The Boot Loader software must be located in the BLS since the SPM instruction can initiate a programming when
executing from the BLS only. The SPM instruction can access the entire Flash, including the
BLS itself. The protection level for the Boot Loader section can be selected by the Boot Loader
Lock bits (Boot Lock bits 1), see Table 24-3 on page 270.
24.3
Read-While-Write and No Read-While-Write Flash Sections
Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader software update is dependent on which address that is being programmed. In addition to the two
sections that are configurable by the BOOTSZ Fuses as described above, the Flash is also
divided into two fixed sections, the Read-While-Write (RWW) section and the No Read-WhileWrite (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 247 on page 278 and Figure 24-2 on page 269. The main difference between the two sections is:
266
•
When erasing or writing a page located inside the RWW section, the NRWW section can be
read during the operation.
•
When erasing or writing a page located inside the NRWW section, the CPU is halted during
the entire operation.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
Note that the user software can never read any code that is located inside the RWW section during a Boot Loader software operation. The syntax “Read-While-Write section” refers to which
section that is being programmed (erased or written), not which section that actually is being
read during a Boot Loader software update.
24.3.1
RWW – Read-While-Write Section
If a Boot Loader software update is programming a page inside the RWW section, it is possible
to read code from the Flash, but only code that is located in the NRWW section. During an ongoing programming, the software must ensure that the RWW section never is being read. If the
user software is trying to read code that is located inside the RWW section (i.e., by a
call/jmp/lpm or an interrupt) during programming, the software might end up in an unknown
state. To avoid this, the interrupts should either be disabled or moved to the Boot Loader section. The Boot Loader section is always located in the NRWW section. The RWW Section Busy
bit (RWWSB) in the Store Program Memory Control and Status Register (SPMCSR) will be read
as logical one as long as the RWW section is blocked for reading. After a programming is completed, the RWWSB must be cleared by software before reading code located in the RWW
section. See “Store Program Memory Control and Status Register – SPMCSR” on page 271. for
details on how to clear RWWSB.
24.3.2
NRWW – No Read-While-Write Section
The code located in the NRWW section can be read when the Boot Loader software is updating
a page in the RWW section. When the Boot Loader code updates the NRWW section, the CPU
is halted during the entire Page Erase or Page Write operation.
Table 24-1.
Read-While-Write Features
Which Section does the Z-pointer
Address During the Programming?
Which Section Can
be Read During
Programming?
Is the CPU
Halted?
Read-While-Write
Supported?
RWW Section
NRWW Section
No
Yes
NRWW Section
None
Yes
No
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Figure 24-1. Read-While-Write vs. No Read-While-Write
Read-While-Write
(RWW) Section
Z-pointer
Addresses RWW
Section
Z-pointer
Addresses NRWW
Section
No Read-While-Write
(NRWW) Section
CPU is Halted
During the Operation
Code Located in
NRWW Section
Can be Read During
the Operation
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AT90PWM2/3/2B/3B
Figure 24-2. Memory Sections
Program Memory
BOOTSZ = '10'
Program Memory
BOOTSZ = '11'
0x0000
No Read-While-Write Section
Read-While-Write Section
Application Flash Section
End RWW
Start NRWW
Application Flash Section
Boot Loader Flash Section
End Application
Start Boot Loader
Flashend
No Read-While-Write Section
Read-While-Write Section
0x0000
Program Memory
BOOTSZ = '01'
Application Flash Section
End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '00'
24.4
Read-While-Write Section
Application Flash Section
No Read-While-Write Section
Note:
0x0000
End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
No Read-While-Write Section
Read-While-Write Section
0x0000
Application Flash Section
End RWW, End Application
Start NRWW, Start Boot Loader
Boot Loader Flash Section
Flashend
1. The parameters in the figure above are given in Table 24-6 on page 278.
Boot Loader Lock Bits
If no Boot Loader capability is needed, the entire Flash is available for application code. The
Boot Loader has two separate sets of Boot Lock bits which can be set independently. This gives
the user a unique flexibility to select different levels of protection.
The user can select:
•
To protect the entire Flash from a software update by the MCU.
•
To protect only the Boot Loader Flash section from a software update by the MCU.
•
To protect only the Application Flash section from a software update by the MCU.
•
Allow software update in the entire Flash.
See Table 24-2 and Table 24-3 for further details. The Boot Lock bits can be set in software and
in Serial or Parallel Programming mode, but they can be cleared by a Chip Erase command
only. The general Write Lock (Lock Bit mode 2) does not control the programming of the Flash
memory by SPM instruction. Similarly, the general Read/Write Lock (Lock Bit mode 1) does not
control reading nor writing by LPM/SPM, if it is attempted.
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Table 24-2.
BLB0 Mode
BLB02
BLB01
1
1
1
No restrictions for SPM or LPM accessing the Application
section.
2
1
0
SPM is not allowed to write to the Application section.
0
SPM is not allowed to write to the Application section, and LPM
executing from the Boot Loader section is not allowed to read
from the Application section. If Interrupt Vectors are placed in
the Boot Loader section, interrupts are disabled while executing
from the Application section.
3
Note:
0
Protection
LPM executing from the Boot Loader section is not allowed to
read from the Application section. If Interrupt Vectors are placed
4
0
1
in the Boot Loader section, interrupts are disabled while
executing from the Application section.
1. “1” means unprogrammed, “0” means programmed
Table 24-3.
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.
0
SPM is not allowed to write to the Boot Loader section, and LPM
executing from the Application section is not allowed to read
from the Boot Loader section. If Interrupt Vectors are placed in
the Application section, interrupts are disabled while executing
from the Boot Loader section.
1
LPM executing from the Application section is not allowed to
read from the Boot Loader section. If Interrupt Vectors are
placed in the Application section, interrupts are disabled while
executing from the Boot Loader section.
3
4
Note:
24.5
Boot Lock Bit0 Protection Modes (Application Section)(1)
0
0
Protection
1. “1” means unprogrammed, “0” means programmed
Entering the Boot Loader Program
Entering the Boot Loader takes place by a jump or call from the application program. This may
be initiated by a trigger such as a command received via USART, or SPI interface. 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 24-4.
BOOTRST
Note:
270
Boot Reset Fuse(1)
Reset Address
1
Reset Vector = Application Reset (address 0x0000)
0
Reset Vector = Boot Loader Reset (see Table 24-6 on page 278)
1. “1” means unprogrammed, “0” means programmed
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AT90PWM2/3/2B/3B
24.5.1
Store Program Memory Control and Status Register – SPMCSR
The Store Program Memory Control and Status Register contains the control bits needed to control the Boot Loader operations.
Bit
7
6
5
4
3
2
1
0
SPMIE
RWWSB
–
RWWSRE
BLBSET
PGWRT
PGERS
SPMEN
Read/Write
R/W
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
SPMCSR
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SPMEN
bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is initiated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-Programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the AT90PWM2/2B/3/3B and always read as zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section is
blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, the
user software must wait until the programming is completed (SPMEN will be cleared). Then, if
the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while
the Flash is busy with a Page Erase or a Page Write (SPMEN is set). If the RWWSRE bit is written while the Flash is being loaded, the Flash load operation will abort and the data loaded will
be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles sets Boot Lock bits and Memory Lock bits, according to the data in R0. The data in R1
and the address in the Z-pointer are ignored. The BLBSET bit will automatically be cleared upon
completion of the Lock bit set, or if no SPM instruction is executed within four clock cycles.
An LPM instruction within three cycles after BLBSET and SPMEN are set in the SPMCSR Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the
destination register. See “Reading the Fuse and Lock Bits from Software” on page 275 for
details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address is
taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four
clock cycles. The CPU is halted during the entire Page Write operation if the NRWW section is
addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
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data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation if the NRWW section is addressed.
• Bit 0 – SPMEN: Self Programming Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with
either RWWSRE, BLBSET, PGWRT or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN is written, the following SPM instruction will
store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of
the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction,
or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write,
the SPMEN bit remains high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower
five bits will have no effect.
24.6
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
Since the Flash is organized in pages (see Table 25-11 on page 285), the Program Counter can
be treated as having two different sections. One section, consisting of the least significant bits, is
addressing the words within a page, while the most significant bits are addressing the pages.
This is1 shown in Figure 24-3. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the Boot Loader software
addresses the same page in both the Page Erase and Page Write operation. Once a programming operation is initiated, the address is latched and the Z-pointer can be used for other
operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits.
The content of the Z-pointer is ignored and will have no effect on the operation. The LPM
instruction does also use the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
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Figure 24-3. Addressing the Flash During SPM(1)
BIT
15
ZPCMSB
ZPAGEMSB
Z - REGISTER
1 0
0
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
24.7
1. The different variables used in Figure 24-3 are listed in Table 24-8 on page 279.
Self-Programming the Flash
The program memory is updated in a page by page fashion. Before programming a page with
the data stored in the temporary page buffer, the page must be erased. The temporary page
buffer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase
•
Fill temporary page buffer
•
Perform a Page Erase
•
Perform a Page Write
Alternative 2, fill the buffer after Page Erase
•
Perform a Page Erase
•
Fill temporary page buffer
•
Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be rewritten. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page address used in both the Page Erase and Page Write operation is addressing the
same page. See “Simple Assembly Code Example for a Boot Loader” on page 276 for an
assembly code example.
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24.7.1
Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will
be ignored during this operation.
24.7.2
•
Page Erase to the RWW section: The NRWW section can be read during the Page Erase.
•
Page Erase to the NRWW section: The CPU is halted during the operation.
Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the RWWSRE bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
24.7.3
Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “X0000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
24.7.4
•
Page Write to the RWW section: The NRWW section can be read during the Page Write.
•
Page Write to the NRWW section: The CPU is halted during the operation.
Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the
SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used instead of polling
the SPMCSR Register in software. When using the SPM interrupt, the Interrupt Vectors should
be moved to the BLS section to avoid that an interrupt is accessing the RWW section when it is
blocked for reading. How to move the interrupts is described in XXXXXXXX.
24.7.5
Consideration While Updating BLS
Special care must be taken if the user allows the Boot Loader section to be updated by leaving
Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can corrupt the
entire Boot Loader, and further software updates might be impossible. If it is not necessary to
change the Boot Loader software itself, it is recommended to program the Boot Lock bit11 to
protect the Boot Loader software from any internal software changes.
24.7.6
Prevent Reading the RWW Section During Self-Programming
During Self-Programming (either Page Erase or Page Write), the RWW section is always
blocked for reading. The user software itself must prevent that this section is addressed during
the self programming operation. The RWWSB in the SPMCSR will be set as long as the RWW
section is busy. During Self-Programming the Interrupt Vector table should be moved to the BLS
as described in XXXXXXX, or the interrupts must be disabled. Before addressing the RWW section after the programming is completed, the user software must clear the RWWSB by writing
the RWWSRE. See “Simple Assembly Code Example for a Boot Loader” on page 276 for an
example.
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24.7.7
Setting the Boot Loader Lock Bits by SPM
To set the Boot Loader Lock bits, write the desired data to R0, write “X0001001” to SPMCSR
and execute SPM within four clock cycles after writing SPMCSR. 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
See Table 24-2 and Table 24-3 for how the different settings of the Boot Loader bits affect the
Flash access.
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 SPMCSR.
The Z-pointer is don’t care during this operation, but for future compatibility it is recommended to
load the Z-pointer with 0x0001 (same as used for reading the lOck bits). For future compatibility it
is also recommended to set bits 7, 6, 1, and 0 in R0 to “1” when writing the Lock bits. When programming the Lock bits the entire Flash can be read during the operation.
24.7.8
EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
24.7.9
Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the BLBSET and SPMEN bits are set in SPMCSR,
the value of the Lock bits will be loaded in the destination register. The BLBSET and SPMEN
bits will auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When BLBSET and SPMEN are cleared, LPM will work as described in the Instruction set Manual.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
BLB12
BLB11
BLB02
BLB01
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the BLBSET
and SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the
BLBSET and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will be
loaded in the destination register as shown below. Refer to Table 25-4 on page 281 for a
detailed description and mapping of the Fuse Low byte.
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruction is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR,
the value of the Fuse High byte (FHB) will be loaded in the destination register as shown below.
Refer to Table 25-5 on page 282 for detailed description and mapping of the Fuse High byte.
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an LPM instruction
is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the
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4317I–AVR–01/08
value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown below.
Refer to Table 25-4 on page 281 for detailed description and mapping of the Extended Fuse
byte.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
–
EFB3
EFB2
EFB1
EFB0
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
24.7.10
Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot Loader
Lock bits to prevent any Boot Loader software updates.
2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating voltage matches the detection level. If not, an external low VCC reset protection circuit can be
used. If a reset occurs while a write operation is in progress, the write operation will be
completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will prevent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
24.7.11
Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 24-5 shows the typical programming time for Flash accesses from the CPU.
Table 24-5.
24.7.12
SPM Programming Time
Symbol
Min Programming Time
Max Programming Time
Flash write (Page Erase, Page Write, and
write Lock bits by SPM)
3.7 ms
4.5 ms
Simple Assembly Code Example for a Boot Loader
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
276
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
;-It is assumed that either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2
;PAGESIZEB is page size in BYTES, not words
.org SMALLBOOTSTART
Write_page:
; Page Erase
ldi spmcrval, (1<<PGERS) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB)
;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:
ld
r0, Y+
ld
r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2
;use subi for PAGESIZEB<=256
brne Wrloop
; execute Page Write
subi ZL, low(PAGESIZEB)
;restore pointer
sbci ZH, high(PAGESIZEB)
;not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; read back and check, optional
ldi looplo, low(PAGESIZEB)
;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB)
;restore pointer
sbci YH, high(PAGESIZEB)
Rdloop:
lpm r0, Z+
ld
r1, Y+
cpse r0, r1
jmp Error
sbiw loophi:looplo, 1
;use subi for PAGESIZEB<=256
brne Rdloop
; return to RWW section
; verify that RWW section is safe to read
Return:
in
temp1, SPMCSR
sbrs temp1, RWWSB
; If RWWSB is set, the RWW section is not ready yet
ret
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
rjmp Return
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4317I–AVR–01/08
Do_spm:
; check for previous SPM complete
Wait_spm:
in
temp1, SPMCSR
sbrc temp1, SPMEN
rjmp Wait_spm
; input: spmcrval determines SPM action
; disable interrupts if enabled, store status
in
temp2, SREG
cli
; check that no EEPROM write access is present
Wait_ee:
sbic EECR, EEPE
rjmp Wait_ee
; SPM timed sequence
out SPMCSR, spmcrval
spm
; restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret
24.7.13
Boot Loader Parameters
In Table 24-6 through Table 24-8, the parameters used in the description of the self programming are given.
Table 24-6.
Boot Size Configuration
Boot
Size
BOOTSZ0
1
1
128
words
4
0x000 0xF7F
0xF80 0xFFF
0xF7F
0xF80
1
0
256
words
8
0x000 0xEFF
0xF00 0xFFF
0xEFF
0xF00
0
1
512
words
16
0x000 0xDFF
0xE00 0xFFF
0xDFF
0xE00
0
0
1024
words
32
0x000 0xBFF
0xC00 0xFFF
0xBFF
0xC00
The different BOOTSZ Fuse configurations are shown in Figure 24-2.
Table 24-7.
Read-While-Write Limit
Section
278
End
Application
Section
Boot Reset
Address
(Start Boot
Loader
Section)
BOOTSZ1
Note:
Pages
Application
Flash
Section
Boot
Loader
Flash
Section
Pages
Address
Read-While-Write section (RWW)
96
0x000 - 0xBFF
No Read-While-Write section (NRWW)
32
0xC00 - 0xFFF
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
For details about these two section, see “NRWW – No Read-While-Write Section” on page 267
and “RWW – Read-While-Write Section” on page 267
Table 24-8.
Explanation of Different Variables used in Figure 24-3 and the Mapping to the Zpointer
Corresponding
Z-value(1)
Variable
Description
PCMSB
11
Most significant bit in the Program Counter. (The
Program Counter is 12 bits PC[11:0])
PAGEMSB
4
Most significant bit which is used to address the
words within one page (32 words in a page requires
5 bits PC [4:0]).
ZPCMSB
Z12
Bit in Z-register that is mapped to PCMSB. Because
Z0 is not used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB
Z5
Bit in Z-register that is mapped to PAGEMSB.
Because Z0 is not used, the ZPAGEMSB equals
PAGEMSB + 1.
PCPAGE
PC[11:5]
Z12:Z6
Program counter page address: Page select, for
page erase and page write
PCWORD
PC[4:0]
Z5:Z1
Program counter word address: Word select, for
filling temporary buffer (must be zero during page
write operation)
Note:
1. Z15:Z13: always ignored
Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See “Addressing the Flash During Self-Programming” on page 272 for details about the use of
Z-pointer during Self-Programming.
25. Memory Programming
25.1
Program And Data Memory Lock Bits
The AT90PWM2/2B/3/3B provides six Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 25-2. The Lock bits can only be
erased to “1” with the Chip Erase command.
Table 25-1.
Lock Bit Byte(1)
Lock Bit Byte
Bit No
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
BLB12
5
Boot Lock bit
1 (unprogrammed)
BLB11
4
Boot Lock bit
1 (unprogrammed)
BLB02
3
Boot Lock bit
1 (unprogrammed)
BLB01
2
Boot Lock bit
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)
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4317I–AVR–01/08
Notes:
1. “1” means unprogrammed, “0” means programmed.
Table 25-2.
Lock Bit Protection Modes(1)(2)
Memory Lock Bits
Protection Type
LB Mode
LB2
LB1
1
1
1
No memory lock features enabled.
2
1
0
Further programming of the Flash and EEPROM is disabled in
Parallel and Serial Programming mode. The Fuse bits are
locked in both Serial and Parallel Programming mode.(1)
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming mode.
3
0
0
The Boot Lock bits and Fuse bits are locked in both Serial and
Parallel Programming mode.(1)
Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Table 25-3.
BLB0 Mode
BLB02
BLB01
1
1
1
No restrictions for SPM or LPM accessing the Application
section.
2
1
0
SPM is not allowed to write to the Application section.
0
SPM is not allowed to write to the Application section, and LPM
executing from the Boot Loader section is not allowed to read
from the Application section. If Interrupt Vectors are placed in
the Boot Loader section, interrupts are disabled while executing
from the Application section.
LPM executing from the Boot Loader section is not allowed to
read from the Application section. If Interrupt Vectors are placed
in the Boot Loader section, interrupts are disabled while
executing from the Application section.
3
0
4
0
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.
0
SPM is not allowed to write to the Boot Loader section, and LPM
executing from the Application section is not allowed to read
from the Boot Loader section. If Interrupt Vectors are placed in
the Application section, interrupts are disabled while executing
from the Boot Loader section.
1
LPM executing from the Application section is not allowed to
read from the Boot Loader section. If Interrupt Vectors are
placed in the Application section, interrupts are disabled while
executing from the Boot Loader section.
3
4
Notes:
280
Lock Bit Protection Modes(1)(2).
0
0
1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
25.2
Fuse Bits
The AT90PWM2/2B/3/3B has three Fuse bytes. Table 25-4 - Table 25-6 describe briefly the
functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses
are read as logical zero, “0”, if they are programmed.
Table 25-4.
Extended Fuse Byte
Extended Fuse Byte
Bit No
Description
Default Value
PSC2RB
7
PSC2 Reset Behaviour
1
PSC1RB
6
PSC1 Reset Behaviour
1
PSC0RB
5
PSC0 Reset Behaviour
1
PSCRV
4
PSCOUT Reset Value
1
–
3
–
1
BOOTSZ1
2
Select Boot Size
(see Table 113 for details)
0 (programmed)(1)
BOOTSZ0
1
Select Boot Size
(see Table 113 for details)
0 (programmed)(1)
BOOTRST
0
Select Reset Vector
1 (unprogrammed)
Note:
1. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 25-7 on page 284
for details.
25.3
PSC Output Behaviour During Reset
For external component safety reason, the state of PSC outputs during Reset can be programmed by fuses PSCRV, PSC0RB, PSC1RB & PSC2RB.
These fuses are located in the Extended Fuse Byte ( see Table 25-4)
PSCRV gives the state low or high which will be forced on PSC outputs selected by PSC0RB,
PSC1RB & PSC2RB fuses.
If PSCRV fuse equals 0 (programmed), the selected PSC outputs will be forced to low state. If
PSCRV fuse equals 1 (unprogrammed), the selected PSC outputs will be forced to high state.
If PSC0RB fuse equals 1 (unprogrammed), PSCOUT00 & PSCOUT01 keep a standard port
behaviour. If PSC0RB fuse equals 0 (programmed), PSCOUT00 & PSCOUT01 are forced at
reset to low level or high level according to PSCRV fuse bit. In this second case, PSCOUT00 &
PSCOUT01 keep the forced state until PSOC0 register is written..
If PSC1RB fuse equals 1 (unprogrammed), PSCOUT10 & PSCOUT11 keep a standard port
behaviour. If PSC1RB fuse equals 0 (programmed), PSCOUT10 & PSCOUT11 are forced at
reset to low level or high level according to PSCRV fuse bit. In this second case, PSCOUT10 &
PSCOUT11 keep the forced state until PSOC1 register is written.
If PSC2RB fuse equals 1 (unprogrammed), PSCOUT20, PSCOUT21, PSCOUT22 &
PSCOUT23 keep a standard port behaviour. If PSC1RB fuse equals 0 (programmed),
PSCOUT20, PSCOUT21, PSCOUT22 & PSCOUT23 are forced at reset to low level or high
level according to PSCRV fuse bit. In this second case, PSCOUT20, PSCOUT21, PSCOUT22 &
PSCOUT23 keep the forced state until PSOC2 register is written.
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4317I–AVR–01/08
Table 25-5.
Fuse High Byte
High Fuse Byte
Description
Default Value
7
External Reset Disable
1 (unprogrammed)
DWEN
6
debugWIRE Enable
1 (unprogrammed)
SPIEN(2)
5
Enable Serial Program and
Data Downloading
0 (programmed, SPI
programming enabled)
WDTON(3)
4
Watchdog Timer Always On
1 (unprogrammed)
EESAVE
3
EEPROM memory is
preserved through the Chip
Erase
1 (unprogrammed), EEPROM
not reserved
BODLEVEL2(4)
2
Brown-out Detector trigger
level
1 (unprogrammed)
BODLEVEL1(4)
1
Brown-out Detector trigger
level
1 (unprogrammed)
RSTDISBL
Bit No
(1)
Brown-out Detector trigger
1 (unprogrammed)
level
See “Alternate Functions of Port C” on page 72 for description of RSTDISBL Fuse.
The SPIEN Fuse is not accessible in serial programming mode.
See “Watchdog Timer Configuration” on page 55 for details.
See Table 9-2 on page 49 for BODLEVEL Fuse decoding.
BODLEVEL0(4)
Notes:
1.
2.
3.
4.
Table 25-6.
0
Fuse Low Byte
Low Fuse Byte
Description
Default Value
7
Divide clock by 8
0 (programmed)
6
Clock output
1 (unprogrammed)
SUT1
5
Select start-up time
1 (unprogrammed)(1)
SUT0
4
Select start-up time
0 (programmed)(1)
CKSEL3
3
Select Clock source
0 (programmed)(2)
CKSEL2
2
Select Clock source
0 (programmed)(2)
CKSEL1
1
Select Clock source
1 (unprogrammed)(2)
CKSEL0
0
Select Clock source
0 (programmed)(2)
(4)
(3)
CKDIV8
CKOUT
Note:
Bit No
1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 7 on page 38 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See Table 7 on
page 38 for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. See “Clock Output
Buffer” on page 38 for details.
4. See “System Clock Prescaler” on page 38 for details.
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.
25.3.1
Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the
fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.
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4317I–AVR–01/08
AT90PWM2/3/2B/3B
25.4
Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and parallel mode, also when the device is locked. The three
bytes reside in a separate address space.
25.4.1
Signature Bytes
For the AT90PWM2/3 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8KB Flash memory).
3. 0x002: 0x81 (indicates AT90PWM2/3 device when 0x001 is 0x93).
For the AT90PWM2B/3B the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8KB Flash memory).
3. 0x002: 0x83 (indicates AT90PWM2B/3B device when 0x001 is 0x93).
25.5
Calibration Byte
The AT90PWM2/2B/3/3B has a byte calibration value for the internal RC Oscillator. This byte
resides in the high byte of address 0x000 in the signature address space. During reset, this byte
is automatically written into the OSCCAL Register to ensure correct frequency of the calibrated
RC Oscillator.
25.6
Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the AT90PWM2/2B/3/3B. Pulses are
assumed to be at least 250 ns unless otherwise noted.
25.6.1
Signal Names
In this section, some pins of the AT90PWM2/2B/3/3B are referenced by signal names describing
their functionality during parallel programming, see Figure 25-1 and Table 25-7. Pins not
described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.
The bit coding is shown in Table 25-9.
When pulsing WR or OE, the command loaded determines the action executed. The different
Commands are shown in Table 25-10.
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4317I–AVR–01/08
Figure 25-1. Parallel Programming
+ 5V
RDY/BSY
PD1
OE
PD2
WR
PD3
BS1
PD4
XA0
PD5
VCC
XA1
PAGEL
+ 12 V
+ 5V
AVCC
PB[7:0]
PD6
DATA
PD7
RESET
BS2
PE2
XTAL1
GND
Table 25-7.
Pin Name Mapping
Signal Name in
Programming Mode
Pin Name
I/O
Function
RDY/BSY
PD1
O
0: Device is busy programming, 1: Device is
ready for new command
OE
PD2
I
Output Enable (Active low)
WR
PD3
I
Write Pulse (Active low)
BS1
PD4
I
Byte Select 1 (“0” selects Low byte, “1” selects
High byte)
XA0
PD5
I
XTAL Action Bit 0
XA1
PD6
I
XTAL Action Bit 1
PAGEL
PD7
I
Program memory and EEPROM Data Page
Load
BS2
PE2
I
Byte Select 2 (“0” selects Low byte, “1” selects
2’nd High byte)
PB[7:0]
I/O
DATA
Table 25-8.
284
Bi-directional Data bus (Output when OE is
low)
Pin Values Used to Enter Programming Mode
Pin
Symbol
Value
PAGEL
Prog_enable[3]
0
XA1
Prog_enable[2]
0
XA0
Prog_enable[1]
0
BS1
Prog_enable[0]
0
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 25-9.
XA1 and XA0 Coding
XA1
XA0
Action when XTAL1 is Pulsed
0
0
Load Flash or EEPROM Address (High or low address byte determined by
BS1).
0
1
Load Data (High or Low data byte for Flash determined by BS1).
1
0
Load Command
1
1
No Action, Idle
Table 25-10. Command Byte Bit Coding
Command Byte
Command Executed
1000 0000
Chip Erase
0100 0000
Write Fuse bits
0010 0000
Write Lock bits
0001 0000
Write Flash
0001 0001
Write EEPROM
0000 1000
Read Signature Bytes and Calibration byte
0000 0100
Read Fuse and Lock bits
0000 0010
Read Flash
0000 0011
Read EEPROM
Table 25-11. No. of Words in a Page and No. of Pages in the Flash
Device
Flash Size
Page Size
PCWORD
No. of
Pages
PCPAGE
PCMSB
AT90PWM2/2B/3/
3B
4K words
(8K bytes)
32 words
PC[4:0]
128
PC[11:5]
11
Table 25-12. No. of Words in a Page and No. of Pages in the EEPROM
Device
AT90PWM2/2B/3/
3B
25.7
EEPROM
Size
Page
Size
PCWORD
No. of
Pages
PCPAGE
EEAMSB
512 bytes
4 bytes
EEA[1:0]
128
EEA[8:2]
8
Serial Programming Pin Mapping
Table 25-13. Pin Mapping Serial Programming
Symbol
Pins
I/O
Description
MOSI_A
PD3
I
Serial Data in
MISO_A
PD2
O
Serial Data out
SCK_A
PD4
I
Serial Clock
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4317I–AVR–01/08
25.8
25.8.1
Parallel Programming
Enter Programming Mode
The following algorithm puts the device in Parallel (High-voltage) > Programming mode:
1. Set Prog_enable pins listed in Table 25-8. to “0000”, RESET pin to “0” and Vcc to 0V.
2. Apply 4.5 - 5.5V between VCC and GND. Ensure that Vcc reaches at least 1.8V within
the next 20µs.
3. Wait 20 - 60µs, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Wait at least 300µs before giving any parallel programming commands.
6. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
If the rise time of the Vcc is unable to fulfill the requirements listed above, the following alternative algorithm can be used.
1. Set Prog_enable pins listed in Table 25-8. to “0000”, RESET pin to “0” and Vcc to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Monitor Vcc, and as soon as Vcc reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Wait until Vcc actually reaches 4.5 -5.5V before giving any parallel programming
commands.
6. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
25.8.2
Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
25.8.3
•
The command needs only be loaded once when writing or reading multiple memory
locations.
•
Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
•
Address high byte needs only be loaded before programming or reading a new 256 word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.
Chip Erase
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the program memory has been completely erased. The Fuse bits are not
changed. A Chip Erase must be performed before the Flash and/or EEPROM are
reprogrammed.
Note:
1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
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AT90PWM2/3/2B/3B
6. Wait until RDY/BSY goes high before loading a new command.
25.8.4
Programming the Flash
The Flash is organized in pages, see Table 25-11 on page 285. When programming the Flash,
the program data is latched into a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes how to program the entire Flash
memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 25-3 for signal
waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
While the lower bits in the address are mapped to words within the page, the higher bits address
the pages within the FLASH. This is illustrated in Figure 25-2 on page 288. Note that if less than
eight bits are required to address words in the page (pagesize < 256), the most significant bit(s)
in the address low byte are used to address the page when performing a Page Write.
G. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program Page
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1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY
goes low.
2. Wait until RDY/BSY goes high (See Figure 25-3 for signal waveforms).
I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are
reset.
Figure 25-2. Addressing the Flash Which is Organized in Pages(1)
PCMSB
PROGRAM
COUNTER
PAGEMSB
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
PCWORD[PAGEMSB:0]:
00
INSTRUCTION WORD
01
02
PAGEEND
Note:
1. PCPAGE and PCWORD are listed in Table 25-11 on page 285.
Figure 25-3. Programming the Flash Waveforms(1)
F
DATA
A
B
0x10
ADDR. LOW
C
DATA LOW
D
E
DATA HIGH
XX
B
ADDR. LOW
C
D
DATA LOW
DATA HIGH
E
XX
G
ADDR. HIGH
H
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
Note:
288
1. “XX” is don’t care. The letters refer to the programming description above.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
25.8.5
Programming the EEPROM
The EEPROM is organized in pages, see Table 25-12 on page 285. When programming the
EEPROM, the program data is latched into a page buffer. This allows one page of data to be
programmed simultaneously. The programming algorithm for the EEPROM data memory is as
follows (refer to “Programming the Flash” on page 287 for details on Command, Address and
Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 25-4 for
signal waveforms).
Figure 25-4. Programming the EEPROM Waveforms
K
DATA
A
G
0x11
ADDR. HIGH
B
ADDR. LOW
C
DATA
E
XX
B
ADDR. LOW
C
DATA
E
L
XX
XA1
XA0
BS1
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
BS2
25.8.6
Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” on
page 287 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS1 to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
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25.8.7
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the Flash”
on page 287 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.
25.8.8
Programming the Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the Flash”
on page 287 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
25.8.9
Programming the Fuse High Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming the
Flash” on page 287 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
25.8.10
Programming the Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the
Flash” on page 287 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
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Figure 25-5. Programming the FUSES Waveforms
Write Fuse Low byte
DATA
A
C
0x40
DATA
XX
Write Fuse high byte
A
C
0x40
DATA
XX
Write Extended Fuse byte
A
C
0x40
DATA
XX
XA1
XA0
BS1
BS2
XTAL1
WR
RDY/BSY
RESET +12V
OE
PAGEL
25.8.11
Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on
page 287 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed
(LB1 and LB2 is programmed), it is not possible to program the Boot Lock bits by any
External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
25.8.12
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 287 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can now be
read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can now be
read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the Extended Fuse bits can now
be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be read at
DATA (“0” means programmed).
6. Set OE to “1”.
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Figure 25-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
0
Fuse Low Byte
0
Extended Fuse Byte
1
DATA
BS2
0
Lock Bits
1
Fuse High Byte
BS1
1
BS2
25.8.13
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash” on
page 287 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS1 to “0”. The selected Signature byte can now be read at DATA.
4. Set OE to “1”.
25.8.14
Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the Flash” on
page 287 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
25.8.15
Parallel Programming Characteristics
Figure 25-7. Parallel Programming Timing, Including some General Timing Requirements
tXLWL
tXHXL
XTAL1
tDVXH
tXLDX
Data & Contol
(DATA, XA0/1, BS1, BS2)
tPLBX t BVWL
tBVPH
PAGEL
tWLBX
tPHPL
tWLWH
WR
tPLWL
WLRL
RDY/BSY
tWLRH
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Figure 25-8. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA LOAD DATA
(HIGH BYTE)
LOAD DATA
(LOW BYTE)
tXLPH
t XLXH
LOAD ADDRESS
(LOW BYTE)
tPLXH
XTAL1
BS1
PAGEL
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
1. The timing requirements shown in Figure 25-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading operation.
Figure 25-9. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
tXLOL
XTAL1
tBVDV
BS1
tOLDV
OE
DATA
tOHDZ
ADDR0 (Low Byte)
DATA (Low Byte)
ADDR1 (Low Byte)
DATA (High Byte)
XA0
XA1
Note:
1. The timing requirements shown in Figure 25-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading operation.
Table 25-14. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol
Parameter
Min
Typ
Max
Units
VPP
Programming Enable Voltage
11.5
12.5
V
IPP
Programming Enable Current
250
μA
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXLXH
XTAL1 Low to XTAL1 High
200
ns
tXHXL
XTAL1 Pulse Width High
150
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
0
ns
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Table 25-14. Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
Symbol
Parameter
Min
tXLPH
XTAL1 Low to PAGEL high
0
ns
tPLXH
PAGEL low to XTAL1 high
150
ns
tBVPH
BS1 Valid before PAGEL High
67
ns
tPHPL
PAGEL Pulse Width High
150
ns
tPLBX
BS1 Hold after PAGEL Low
67
ns
tWLBX
BS2/1 Hold after WR Low
67
ns
tPLWL
PAGEL Low to WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tWLWH
WR Pulse Width Low
150
ns
tWLRL
WR Low to RDY/BSY Low
(1)
Typ
Max
Units
0
1
μs
3.7
4.5
ms
7.5
9
ms
tWLRH
WR Low to RDY/BSY High
tWLRH_CE
WR Low to RDY/BSY High for Chip Erase(2)
tXLOL
XTAL1 Low to OE Low
0
tBVDV
BS1 Valid to DATA valid
0
tOLDV
OE Low to DATA Valid
ns
250
ns
250
ns
tOHDZ
Notes: 1.
OE High to DATA Tri-stated
250
ns
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.
2. tWLRH_CE is valid for the Chip Erase command.
25.9
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. NOTE, in Table 25-13 on page 285, the pin
mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal
SPI interface.
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AT90PWM2/3/2B/3B
Figure 25-10. Serial Programming and Verify(1)
+1.8 - 5.5V
VCC
+1.8 - 5.5V(2)
MOSI_A
AVCC
MISO_A
SCK_A
XTAL1
RESET
GND
Notes:
1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
XTAL1 pin.
2. VCC - 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8 - 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
Low:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
High:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
25.9.1
Serial Programming Algorithm
When writing serial data to the AT90PWM2/2B/3/3B, data is clocked on the rising edge of SCK.
When reading data from the AT90PWM2/2B/3/3B, data is clocked on the falling edge of SCK.
See Figure 25-11 for timing details.
To program and verify the AT90PWM2/2B/3/3B in the serial programming mode, the following
sequence is recommended (See four byte instruction formats in Table 25-16):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization. When in sync. the second byte (0x53), will echo back when issuing the third
byte of the Programming Enable instruction. Whether the echo is correct or not, all four
bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte at a
time by supplying the 6 LSB of the address and data together with the Load Program
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Memory Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program Memory
Page is stored by loading the Write Program Memory Page instruction with the 8 MSB of
the address. If polling is not used, the user must wait at least tWD_FLASH before issuing the
next page. (See Table 25-15.) Accessing the serial programming interface before the
Flash write operation completes can result in incorrect programming.
5. 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. (See Table 25-15.) In a chip erased
device, no 0xFFs in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns the content at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
25.9.2
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 0xFF. 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 0xFF, 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 0xFF in all locations, programming of addresses that are meant to
contain 0xFF, can be skipped. See Table 25-15 for tWD_FLASH value.
25.9.3
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 0xFF. 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 0xFF, but the user should have the following
in mind: As a chip-erased device contains 0xFF in all locations, programming of addresses that
are meant to contain 0xFF, 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
0xFF, and the user will have to wait at least tWD_EEPROM before programming the next byte. See
Table 25-15 for tWD_EEPROM value.
Table 25-15. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
296
Symbol
Minimum Wait Delay
tWD_FLASH
4.5 ms
tWD_EEPROM
3.6 ms
tWD_ERASE
9.0 ms
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 25-11. Serial Programming Waveforms
SERIAL DATA INPUT
(MOSI)
MSB
LSB
SERIAL DATA OUTPUT
(MISO)
MSB
LSB
SERIAL CLOCK INPUT
(SCK)
SAMPLE
Table 25-16. Serial Programming Instruction Set
Instruction Format
Instruction
Programming Enable
Chip Erase
Read Program Memory
Byte 1
Byte 2
Byte 3
Byte4
1010 1100
0101 0011
xxxx xxxx
xxxx xxxx
Enable Serial Programming after
RESET goes low.
1010 1100
100x xxxx
xxxx xxxx
xxxx xxxx
Chip Erase EEPROM and Flash.
0010 H000
000a aaaa
bbbb bbbb
oooo oooo
Read H (high or low) data o from
Program memory at word address a:b.
0100 H000
000x xxxx
xxbb bbbb
iiii iiii
Write H (high or low) data i to Program
Memory page at word address b. Data
low byte must be loaded before Data
high byte is applied within the same
address.
0100 1100
000a aaaa
bbxx xxxx
xxxx xxxx
Write Program Memory Page at
address a:b.
1010 0000
000x xxaa
bbbb bbbb
oooo oooo
Read data o from EEPROM memory at
address a:b.
1100 0000
000x xxaa
bbbb bbbb
iiii iiii
Write data i to EEPROM memory at
address a:b.
1100 0001
0000 0000
0000 00bb
iiii iiii
Load data i to EEPROM memory page
buffer. After data is loaded, program
EEPROM page.
1100 0010
00xx xxaa
bbbb bb00
xxxx xxxx
0101 1000
0000 0000
xxxx xxxx
xxoo oooo
Read Lock bits. “0” = programmed, “1”
= unprogrammed. See Table 25-1 on
page 279 for details.
1010 1100
111x xxxx
xxxx xxxx
11ii iiii
Write Lock bits. Set bits = “0” to
program Lock bits. See Table 25-1 on
page 279 for details.
0011 0000
000x xxxx
xxxx xxbb
oooo oooo
Read Signature Byte o at address b.
1010 1100
1010 0000
xxxx xxxx
iiii iiii
Set bits = “0” to program, “1” to
unprogram. See Table XXX on page
XXX for details.
Load Program Memory Page
Write Program Memory Page
Read EEPROM Memory
Write EEPROM Memory
Load EEPROM Memory
Page (page access)
Write EEPROM Memory
Page (page access)
Read Lock bits
Write Lock bits
Read Signature Byte
Write Fuse bits
Operation
Write EEPROM page at address a:b.
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Table 25-16. Serial Programming Instruction Set (Continued)
Instruction Format
Instruction
Byte 1
Byte 2
Byte 3
Byte4
1010 1100
1010 1000
xxxx xxxx
iiii iiii
Set bits = “0” to program, “1” to
unprogram. See Table 25-5 on page
282 for details.
1010 1100
1010 0100
xxxx xxxx
xxxx xxii
Set bits = “0” to program, “1” to
unprogram. See Table 25-4 on page
281 for details.
0101 0000
0000 0000
xxxx xxxx
oooo oooo
Read Fuse bits. “0” = programmed, “1”
= unprogrammed. See Table XXX on
page XXX for details.
0101 1000
0000 1000
xxxx xxxx
oooo oooo
Read Fuse High bits. “0” = programmed, “1” = unprogrammed. See
Table 25-5 on page 282 for details.
0101 0000
0000 1000
xxxx xxxx
oooo oooo
Read Extended Fuse bits. “0” = programmed, “1” = unprogrammed. See
Table 25-4 on page 281 for details.
0011 1000
000x xxxx
0000 0000
oooo oooo
Read Calibration Byte
1111 0000
0000 0000
xxxx xxxx
xxxx xxxo
If o = “1”, a programming operation is
still busy. Wait until this bit returns to
“0” before applying another command.
Write Fuse High bits
Write Extended Fuse Bits
Read Fuse bits
Read Fuse High bits
Read Extended Fuse Bits
Read Calibration Byte
Poll RDY/BSY
Note:
25.9.4
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
SPI Serial Programming Characteristics
For characteristics of the SPI module see “SPI Serial Programming Characteristics” on page
298.
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26. Electrical Characteristics(1)
26.1
Absolute Maximum Ratings*
Operating Temperature.................................. -40°C to +105°C
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-1.0V to VCC+0.5V
Voltage on RESET with respect to Ground......-1.0V to +13.0V
*NOTICE:
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
Note:
1. Electrical Characteristics for this product have not yet been finalized. Please consider all values listed herein as preliminary and non-contractual.
299
4317I–AVR–01/08
26.2
DC Characteristics
TA = -40°C to +105°C, VCC = 2.7V to 5.5V (unless otherwise noted)
Symbol
Parameter
Condition
Min.
VIL
Input Low Voltage
Port B, C & D and XTAL1,
XTAL2 pins as I/O
VIH
Input High Voltage
Port B, C & D and XTAL1,
XTAL2 pins as I/O
VIL1
Input Low Voltage
VIH1
VIL2
VIH2
Max.
Units
-0.5
0.2VCC(1)
V
0.6VCC(2)
VCC+0.5
V
XTAL1 pin , External
Clock Selected
-0.5
0.1VCC(1)
V
Input High Voltage
XTAL1 pin , External
Clock Selected
0.7VCC(2)
VCC+0.5
V
Input Low Voltage
RESET pin
-0.5
0.2VCC(1)
V
VCC+0.5
V
(1)
V
VCC+0.5
V
0.7
0.5
V
V
Input High Voltage
RESET pin
0.9VCC
Typ.
(2)
VIL3
Input Low Voltage
RESET pin as I/O
-0.5
VIH3
Input High Voltage
RESET pin as I/O
0.8VCC(2)
0.2VCC
(3)
VOL
Output Low Voltage
(Port B, C & D and
XTAL1, XTAL2 pins as
I/O)
IOL = 20 mA, VCC = 5V
IOL = 10 mA, VCC = 3V
VOH
Output High Voltage(4)
(Port B, C & D and
XTAL1, XTAL2 pins as
I/O)
IOH = -20 mA, VCC = 5V
IOH = -10 mA, VCC = 3V
VOL3
Output Low Voltage(3)
(RESET pin as I/O)
IOL = 2.1 mA, VCC = 5V
IOL = 0.8 mA, VCC = 3V
VOH3
Output High Voltage(4)
(RESET pin as I/O)
IOH = -0.6 mA, VCC = 5V
IOH = -0.4 mA, VCC = 3V
IIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value)
1
µA
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value)
1
µA
RRST
Reset Pull-up Resistor
30
200
kΩ
Rpu
I/O Pin Pull-up Resistor
20
50
kΩ
300
4.2
2.4
V
V
0.7
0.5
3.8
2.2
V
V
V
V
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
TA = -40°C to +105°C, VCC = 2.7V to 5.5V (unless otherwise noted) (Continued)
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
Active 8 MHz, VCC = 3V,
RC osc, PRR = 0xFF
3.8
7
mA
Active 16 MHz, VCC = 5V,
Ext Clock, PRR = 0xFF
14
24
mA
Idle 8 MHz, VCC = 3V, RC
Osc
1.5
3
mA
Idle 16 MHz, VCC = 5V,
Ext Clock
5.5
10
mA
WDT enabled, VCC = 3V
t0 < 90°C
5
15
µA
WDT enabled, VCC = 3V
t0 < 105°C
9
20
µA
WDT disabled, VCC = 3V
t0 < 90°C
2
3
µA
WDT disabled, VCC = 3V
t0 < 105°C
5
10
µA
20
50
mV
46
62
71
110
mV
mV
50
nA
Power Supply Current
ICC
Power-down mode
(5)
VACIO
Analog Comparator
Input Offset Voltage
AT90PWM2/3
VCC = 5V, Vin = 3V
Vhysr
Analog Comparator
Hysteresis Voltage
AT90PWM2B/3B
VCC = 5V, Vin = 3V
Rising Edge
Falling Edge
IACLK
Analog Comparator
Input Leakage Current
VCC = 5V
Vin = VCC/2
tACID
Note:
33
34
-50
Analog Comparator
VCC = 2.7V
Propagation Delay
VCC = 5.0V
1. “Max” means the highest value where the pin is guaranteed to be read as low
(6)
(6)
ns
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
SO32, SO24 and TQFN Package:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for ports B6 - B7, C0 - C1, D0 - D3, E0 should not exceed 100 mA.
3] The sum of all IOL, for ports B0 - B1, C2 - C3, D4, E1 - E2 should not exceed 100 mA.
4] The sum of all IOL, for ports B3 - B5, C6 - C7 should not exceed 100 mA.
5] The sum of all IOL, for ports B2, C4 - C5, D5 - 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 (20 mA at Vcc = 5V, 10 mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed:
SO32, SO24 and TQFN Package:
1] The sum of all IOH, for all ports, should not exceed 400 mA.
2] The sum of all IOH, for ports B6 - B7, C0 - C1, D0 - D3, E0 should not exceed 150 mA.
3] The sum of all IOH, for ports B0 - B1, C2 - C3, D4, E1 - E2 should not exceed 150 mA.
4] The sum of all IOH, for ports B3 - B5, C6 - C7 should not exceed 150 mA.
5] The sum of all IOH, for ports B2, C4 - C5, D5 - D7 should not exceed 150 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.
301
4317I–AVR–01/08
5. Minimum VCC for Power-down is 2.5V.
6. The Analog Comparator Propogation Delay equals 1 comparator clock plus 30 nS. See “Analog Comparator” on page 227.
for comparator clock definition.
26.3
26.3.1
External Clock Drive Characteristics
Calibrated Internal RC Oscillator Accuracy
Table 26-1.
Calibration Accuracy of Internal RC Oscillator
Frequency
VCC
Temperature
Calibration Accuracy
Factory
Calibration
8.0 MHz
3V
25°C
±10%
User
Calibration
7.3 - 8.1 MHz
2.7V - 5.5V
-40°C - 85°C
±1%
26.3.2
External Clock Drive Waveforms
Figure 26-1. External Clock Drive Waveforms
V IH1
V IL1
26.3.3
External Clock Drive
Table 26-2.
302
External Clock Drive
VCC=1.8-5.5V
VCC=2.7-5.5V
VCC=4.5-5.5V
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Max.
Units
1/tCLCL
Oscillator
Frequency
0
4
0
10
0
20
MHz
tCLCL
Clock Period
250
100
50
ns
tCHCX
High Time
100
40
20
ns
tCLCX
Low Time
100
40
20
ns
tCLCH
Rise Time
2.0
1.6
0.5
μs
tCHCL
Fall Time
2.0
1.6
0.5
μs
ΔtCLCL
Change in period
from one clock
cycle to the next
2
2
2
%
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
26.4
Maximum Speed vs. VCC
Maximum frequency is depending on VCC. As shown in Figure 26-2 , the Maximum Frequency
equals 8Mhz when VCC is contained between 2.7V and 4.5V and equals 16Mhz when VCC is
contained between 4.5V and 5.5V.
Figure 26-2. Maximum Frequency vs. VCC, AT90PWM2/2B/3/3B
16Mhz
8Mhz
Safe Operating Area
2.7V
26.5
4.5V
5.5V
PLL Characteristics
.
Table 26-3.
PLL Characteristics - VCC = 2.7V to 5.5V (unless otherwise noted)
Symbol
Parameter
PLLIF
Input Frequency
PLLF
PLL Factor
PLLLT
Lock-in Time
Note:
Min.
Typ.
Max.
Units
0.5
1
2
MHz
64
µS
64
While connected to external clock or external oscillator, PLL Input Frequency must be selected to
provide outputs with frequency in accordance with driven parts of the circuit (CPU core, PSC...)
303
4317I–AVR–01/08
26.6
SPI Timing Characteristics
See Figure 26-3 and Figure 26-4 for details.
Table 26-4.
SPI Timing Parameters
Description
Mode
1
SCK period
Master
See Table 64
2
SCK high/low
Master
50% duty cycle
3
Rise/Fall time
Master
3.6
4
Setup
Master
10
5
Hold
Master
10
6
Out to SCK
Master
0.5 • tsck
7
SCK to out
Master
10
8
SCK to out high
Master
10
9
SS low to out
Slave
15
10
SCK period
Slave
4 • tck
11
SCK high/low (1)
Slave
2 • tck
12
Rise/Fall time
Slave
13
Setup
Slave
10
14
Hold
Slave
tck
15
SCK to out
Slave
16
SCK to SS high
Slave
17
SS high to tri-state
Slave
18
SS low to SCK
Slave
Note:
Min.
Typ.
Max.
ns
1.6
15
20
10
2 • tck
In SPI Programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12 MHz
- 3 tCLCL for fCK >12 MHz
Figure 26-3. SPI Interface Timing Requirements (Master Mode)
SS
6
1
SCK
(CPOL = 0)
2
2
SCK
(CPOL = 1)
4
MISO
(Data Input)
5
3
MSB
...
LSB
7
MOSI
(Data Output)
304
MSB
8
...
LSB
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 26-4. SPI Interface Timing Requirements (Slave Mode)
SS
10
9
16
SCK
(CPOL = 0)
11
11
SCK
(CPOL = 1)
13
MOSI
(Data Input)
14
12
MSB
...
LSB
15
MISO
(Data Output)
MSB
17
...
LSB
X
305
4317I–AVR–01/08
26.7
ADC Characteristics
Table 26-5.
Symbol
ADC Characteristics - TA = -40°C to +105°C, VCC = 2.7V to 5.5V (unless otherwise noted)
Parameter
Condition
Min
Typ
Max
Units
Single Ended Conversion
10
Bits
Differential Conversion
8
Bits
Resolution
Absolute accuracy
Single Ended Conversion
VREF = 2.56V
ADC clock = 500 kHz
2.5
3
LSB
Single Ended Conversion
VREF = 2.56V
ADC clock = 1MHz
6 (*)
7
LSB
20
LSB
Single Ended Conversion
VREF = 2.56V
ADC clock = 2MHz
Differential Conversion
VREF = 2.56V
ADC clock = 500 kHz
2
3
LSB
Differential Conversion
VREF = 2.56V
ADC clock = 1MHz
3 (1)
4
LSB
Single Ended Conversion
VCC = 4.5V, VREF = 2.56V
ADC clock = 1MHz
1.1
1.5
LSB
Single Ended Conversion
VCC = 4.5V, VREF = 2.56V
ADC clock = 500 kHz
0.6
1
LSB
Differential Conversion
VCC = 4.5V, VREF = 2.56V
ADC clock = 1MHz
1.5
2
LSB
Differential Conversion
VCC = 4.5V, VREF = 2.56V
ADC clock = 500 kHz
1
1.5
LSB
Single Ended Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 1MHz
0.4
0.6
LSB
Single Ended Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 500 kHz
0.3
0.5
LSB
Differential Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 1MHz
0.5
0.8
LSB
Differential Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 500 kHz
0.4
0.8
LSB
Integral Non-linearity
Differential Non-linearity
306
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Table 26-5.
Symbol
ADC Characteristics - TA = -40°C to +105°C, VCC = 2.7V to 5.5V (unless otherwise noted) (Continued)
Parameter
Condition
Min
Typ
Max
Units
Single Ended Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 1MHz
-4
0
LSB
Single Ended Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 500 kHz
-2
2.5
LSB
Differential Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 1MHz
-0.5
-0.5
LSB
Differential Conversion
VCC = 4.5V, VREF = 4V
ADC clock = 500 kHz
-0.5
-0.5
LSB
8
320
µs
50
2000
kHz
VCC - 0.3
VCC + 0.3
V
Single Ended Conversion
2.0
AVCC
V
Differential Conversion
2.0
AVCC - 0.2
V
GND
VREF
-VREF/Gain
+VREF/Gain
Zero Error (Offset)
Conversion Time
Single Conversion
Clock Frequency
AVCC
Analog Supply Voltage
VREF
Reference Voltage
VIN
Single Ended Conversion
Input voltage
Differential Conversion
Single Ended Conversion
Input bandwidth
Differential Conversion
38.5
kHz
(2)
4
kHz
VINT
Internal Voltage Reference
2.56
V
RREF
Reference Input Resistance
30
kΩ
RAIN
Analog Input Resistance
100
MΩ
IHSM
Increased Current
Consumption
Notes:
High Speed Mode
Single Ended Conversion
380
µA
1. On AT90PWM2B/3B, this value will be close to the value at 500kHz.
2. 125KHz when input signal is synchronous with amplifier clock.
307
4317I–AVR–01/08
26.8
Parallel Programming Characteristics
Figure 26-5. Parallel Programming Timing, Including some General Timing Requirements
tXLWL
tXHXL
XTAL1
tDVXH
tXLDX
Data & Contol
(DATA, XA0/1, BS1, BS2)
tPLBX t BVWL
tBVPH
PAGEL
tWLBX
tPHPL
tWLWH
WR
tPLWL
WLRL
RDY/BSY
tWLRH
Figure 26-6. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
LOAD DATA LOAD DATA
(HIGH BYTE)
LOAD DATA
(LOW BYTE)
t XLXH
tXLPH
LOAD ADDRESS
(LOW BYTE)
tPLXH
XTAL1
BS1
PAGEL
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
DATA (High Byte)
ADDR1 (Low Byte)
XA0
XA1
Note:
308
1. The timing requirements shown in Figure 26-5 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading operation.
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 26-7. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
tXLOL
XTAL1
tBVDV
BS1
tOLDV
OE
tOHDZ
DATA
ADDR0 (Low Byte)
DATA (Low Byte)
ADDR1 (Low Byte)
DATA (High Byte)
XA0
XA1
Note:
1. ggThe timing requirements shown in Figure 26-5 (i.e., tDVXH, tXHXL, and tXLDX) also apply to
reading operation.
Table 26-6.
Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol
Parameter
Min.
VPP
Programming Enable Voltage
11.5
IPP
Programming Enable Current
tDVXH
Data and Control Valid before XTAL1 High
67
ns
tXLXH
XTAL1 Low to XTAL1 High
200
ns
tXHXL
XTAL1 Pulse Width High
150
ns
tXLDX
Data and Control Hold after XTAL1 Low
67
ns
tXLWL
XTAL1 Low to WR Low
0
ns
tXLPH
XTAL1 Low to PAGEL high
0
ns
tPLXH
PAGEL low to XTAL1 high
150
ns
tBVPH
BS1 Valid before PAGEL High
67
ns
tPHPL
PAGEL Pulse Width High
150
ns
tPLBX
BS1 Hold after PAGEL Low
67
ns
tWLBX
BS2/1 Hold after WR Low
67
ns
tPLWL
PAGEL Low to WR Low
67
ns
tBVWL
BS1 Valid to WR Low
67
ns
tWLWH
WR Pulse Width Low
150
ns
tWLRL
WR Low to RDY/BSY Low
(1)
tWLRH
WR Low to RDY/BSY High
tWLRH_CE
WR Low to RDY/BSY High for Chip Erase(2)
Typ.
Max.
Units
12.5
V
250
μA
0
1
μs
3.7
5
ms
7.5
10
ms
309
4317I–AVR–01/08
Table 26-6.
Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
Symbol
Parameter
Min.
tXLOL
XTAL1 Low to OE Low
0
tBVDV
BS1 Valid to DATA valid
0
tOLDV
OE Low to DATA Valid
Typ.
Max.
Units
ns
250
ns
250
ns
tOHDZ
Notes: 1.
OE High to DATA Tri-stated
250
ns
tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.
2. tWLRH_CE is valid for the Chip Erase command.
27. AT90PWM2/2B/3/3B Typical Characteristics
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 rail-to-rail output is used as clock
source.
All Active- and Idle current consumption measurements are done with all bits in the PRR register
set and thus, the corresponding I/O modules are turned off. Also the Analog Comparator is disabled during these measurements. Table 27-1 on page 315 and Table 27-2 on page 315 show
the additional current consumption compared to ICC Active and ICC Idle for every I/O module controlled by the Power Reduction Register. See “Power Reduction Register” on page 37 for details.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.
310
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
27.1
Active Supply Current
Figure 27-1. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. LOW FREQUENCY
ICC (mA)
1,6
1,4
5.5 V
1,2
5.0 V
1
4.5 V
4.0 V
0,8
3.3 V
3.0 V
2.7 V
0,6
0,4
0,2
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Frequency (MHz)
Figure 27-2. Active Supply Current vs. Frequency (1 - 24 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
30
25
5.5 V
5.0 V
20
ICC (mA)
4.5 V
15
4.0 V
10
3.3 V
3.0 V
5
2.7 V
0
0
5
10
15
20
25
Frequency (MHz)
311
4317I–AVR–01/08
Figure 27-3. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. V CC
INTERNAL RC OSCILLATOR, 8 MHz
105 °C
85 °C
25 °C
-40 °C
9
8
7
ICC (mA)
6
5
4
3
2
1
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-4. Active Supply Current vs. VCC (Internal PLL Oscillator, 16 MHz)
ACTIVE SUPPLY CURRENT vs. VCC
INTERNAL PLL OSCILLATOR, 16 MHz
20
105 °C
85 °C
25 °C
-40 °C
18
16
14
ICC (mA)
12
10
8
6
4
2
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
312
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
27.2
Idle Supply Current
Figure 27-5. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
IDLE SUPPLY CURRENT vs. LOW FREQUENCY
0,45
0,4
5.5 V
ICC (mA)
0,35
5.0 V
0,3
4.5 V
0,25
4.0 V
0,2
3.3 V
3.0 V
2.7 V
0,15
0,1
0,05
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Frequency (MHz)
Figure 27-6. Idle Supply Current vs. Frequency (1 - 24 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
12
10
5.5 V
5.0 V
8
ICC (mA)
4.5 V
6
4.0 V
4
3.3 V
3.0 V
2
2.7 V
0
-1
1
3
5
7
9
11
13
15
17
19
21
23
25
Frequency (MHz)
313
4317I–AVR–01/08
Figure 27-7. IIdle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL RC OSCILLATOR, 8 MHz
4
3,5
105 °C
85 °C
25 °C
-40 °C
3
ICC (mA)
2,5
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-8. Idle Supply Current vs. VCC (Internal PLL Oscillator, 16 MHz)
IDLE SUPPLY CURRENT vs. VCC
INTERNAL PLL OSCILLATOR, 16 MHz
9
105 °C
85 °C
25 °C
-40 °C
8
7
ICC (mA)
6
5
4
3
2
1
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
27.2.1
Using the Power Reduction Register
The tables and formulas below can be used to calculate the additional current consumption for
the different I/O modules in Active and Idle mode. The enabling or disabling of the I/O modules
314
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
are controlled by the Power Reduction Register. See “Power Reduction Register” on page 43 for
details.
Table 27-1.
PRR bit
Additional Current Consumption for the different I/O modules (absolute values)
Typical numbers
VCC = 3V, F = 8MHz
VCC = 5V, F = 16MHz
PRPSC2
350 uA
1.3 mA
PRPSC1
350 uA
1.3 mA
PRPSC0
350 uA
1.3 mA
PRTIM1
300 uA
1.15 mA
PRTIM0
200 uA
0.75 mA
PRSPI
250 uA
0.9 mA
PRUSART
550 uA
2 mA
PRADC
350 uA
1.3 mA
Table 27-2.
Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external
clock
(see Figure 27-1 and Figure 27-2)
Additional Current consumption
compared to Idle with external clock
(see Figure 27-5 and Figure 27-6)
PRPSC2
10%
25%
PRPSC1
10%
25%
PRPSC0
10%
25%
PRTIM1
8.5%
22%
PRTIM0
4.3%
11%
PRSPI
5.3%
14%
PRUSART
15.6
36
PRADC
10.5%
25%
It is possible to calculate the typical current consumption based on the numbers from Table 27-2
for other VCC and frequency settings than listed in Table 27-1.
27.2.1.1
Example 1
Calculate the expected current consumption in idle mode with USART, TIMER1, and SPI
enabled at VCC = 3.0V and F = 1MHz. From Table 27-2, third column, we see that we need to
add 18% for the USART, 26% for the SPI, and 11% for the TIMER1 module. Reading from Figure 27-5, we find that the idle current consumption is ~0,17mA at VCC = 3.0V and F = 1MHz. The
total current consumption in idle mode with USART0, TIMER1, and SPI enabled, gives:
I CC total ≈ 0.17mA • ( 1 + 0.36 + 0.22 + 0.14 ) ≈ 0.29mA
27.2.1.2
Example 2
Same conditions as in example 1, but in active mode instead. From Table 27-2, second column
we see that we need to add 3.3% for the USART, 4.8% for the SPI, and 2.0% for the TIMER1
module. Reading from Figure 27-1, we find that the active current consumption is ~0,6mA at VCC
315
4317I–AVR–01/08
= 3.0V and F = 1MHz. The total current consumption in idle mode with USART, TIMER1, and
SPI enabled, gives:
I CC total ≈ 0.6mA • ( 1 + 0.156 + 0.085 + 0.053 ) ≈ 0.77mA
27.2.1.3
Example 3
All I/O modules should be enabled. Calculate the expected current consumption in active mode
at VCC = 3.6V and F = 10MHz. We find the active current consumption without the I/O modules
to be ~ 7.0mA (from Figure 27-2). Then, by using the numbers from Table 27-2 - second column,
we find the total current consumption:
I CC total ≈ 7.0mA • ( 1 + 0.1 + 0.1 + 0.1 + 0.085 + 0.043 + 0.053 + 0.156 + 0.105 ) ≈ 12.2mA
27.3
Power-Down Supply Current
Figure 27-9. Power-Down Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. V CC
WATCHDOG TIMER DISABLED
7
105 °C
6
ICC (uA)
5
4
3
85 °C
2
-40 °C
25 °C
1
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
316
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-10. Power-Down Supply Current vs. VCC (Watchdog Timer Enabled)
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER ENABLED
14
105 °C
12
ICC (uA)
10
85 °C
-40 °C
25 °C
8
6
4
2
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
27.4
Pin Pull-up
Figure 27-11. I/O Pin Pull-Up Resistor Current vs. Input Voltage (VCC = 5V)
I/O PIN (including PE1 & PE2) PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5.0 V
-40 °C
160
25 °C
85 °C 140
105 °C
120
IOP (uA)
100
80
60
40
20
0
0
1
2
3
4
5
6
-20
V OP (V)
317
4317I–AVR–01/08
Figure 27-12. I/O Pin Pull-Up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O PIN (including PE1 & PE2) PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7 V
-40 °C 90
25 °C 80
85 °C
105 °C 70
60
IOP (uA)
50
40
30
20
10
0
-10
0
0,5
1
1,5
2
2,5
3
V OP (V)
Figure 27-13. Reset Pull-Up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
PE0 and RESET PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5.0 V
25 °C 120
-40 °C
85 °C
105 °C 100
IOP (uA)
80
60
40
20
0
0
1
2
3
4
5
6
V OP (V)
318
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-14. Reset Pull-Up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
PE0 and RESET PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7 V
70
25 °C
-40 °C 60
85 °C
105 °C 50
IOP (uA)
40
30
20
10
0
0
0,5
1
1,5
2
2,5
3
V OP (V)
27.5
Pin Driver Strength
Figure 27-15. I/O Pin Source Current vs. Output Voltage (VCC = 5V)
I/O PIN (including PE1 & PE2) SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5.0 V
25
85 °C 25 °C -40 °C
20
IOH (mA)
105 °C
15
10
5
0
4
4,2
4,4
4,6
4,8
5
5,2
V OH (V)
319
4317I–AVR–01/08
Figure 27-16. I/O Pin Source Current vs. Output Voltage (VCC = 2.7V)
I/O PIN (including PE1 & PE2) SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7 V
25
105 °C 85 °C
IOH (mA)
20
25 °C -40 °C
15
10
5
0
0
0,5
1
1,5
2
2,5
3
V OH (V)
Figure 27-17. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)
I/O PIN (including PE1 & PE2) SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5.0 V
25
-40 °C25 °C 85 °C105 °C
20
IOL (mA)
15
10
5
0
0
0,2
0,4
0,6
0,8
1
-5
V OL (V)
320
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-18. I/O Pin Sink Current vs. Output Voltage (VCC = 2.7V)
I/O PIN (including PE1 & PE2) SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7 V
25
-40 °C 25 °C
85 °C
105 °C
20
IOL (mA)
15
10
5
0
0
0,5
1
1,5
2
2,5
3
-5
V OL (V)
27.6
Pin Thresholds and Hysteresis
Figure 27-19. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read As '1')
I/O PIN (including PE1 & PE2) INPUT THRESHOLD VOLTAGE vs. VCC
VIH, IO PIN READ AS '1'
2,5
-40 °C
25 °C
85 °C
105 °C
Threshold (V)
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
321
4317I–AVR–01/08
Figure 27-20. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read As '0')
I/O PIN (including PE1 & PE2) INPUT THRESHOLD VOLTAGE vs. V CC
VIL, IO PIN READ AS '0'
2,5
Threshold (V)
2
-40 °C
25 °C
85 °C
105 °C
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-21. I/O Pin Input HysteresisVoltage vs. VCC
I/O PIN INPUT HYSTERESIS vs. VCC
0.6
-40 C
0.5
25 C
Input Hysteresis ( V)
0.4
85 C
0.3
0.2
0.1
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
322
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-22. Reset Input Threshold Voltage vs. VCC (VIH, Reset Pin Read As '1')
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIH, RESET PIN READ AS '1'
2,5
Threshold (V)
2
-40
25
85
105
1,5
1
°C
°C
°C
°C
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-23. Reset Input Threshold Voltage vs. VCC (VIL, Reset Pin Read As '0')
RESET INPUT THRESHOLD VOLTAGE vs. VCC
VIL, RESET PIN READ AS '0'
105 °C
85 °C
25 °C
-40 °C
2,5
Threshold (V)
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
323
4317I–AVR–01/08
Figure 27-24. Reset Input Pin Hysteresis vs. VCC
RESET PIN INPUT HYSTERESIS vs. VCC
0,6
-40 °C
Input Hysteresis (V)
0,5
0,4
25 °C
0,3
0,2
85 °C
105 °C
0,1
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-25. XTAL1 Input Threshold Voltage vs. VCC (XTAL1 Pin Read As '1')
XTAL1 INPUT THRESHOLD VOLTAGE vs. VCC
XTAL1 PIN READ AS "1"
4
3,5
-40 °C
25 °C
85 °C
105 °C
Threshold (V)
3
2,5
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
324
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-26. XTAL1 Input Threshold Voltage vs. VCC (XTAL1 Pin Read As '0')
XTAL1 INPUT THRESHOLD VOLTAGE vs. V CC
XTAL1 PIN READ AS "0"
4
3,5
Threshold (V)
3
2,5
-40 °C
25 °C
85 °C
105 °C
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-27. PE0 Input Threshold Voltage vs. VCC (PE0 Pin Read As '1')
PE0 INPUT THRESHOLD VOLTAGE vs. VCC
VIH, PE0 PIN READ AS '1'
-40 °C
25 °C
85 °C
105 °C
4
3,5
Threshold (V)
3
2,5
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
325
4317I–AVR–01/08
Figure 27-28. PE0 Input Threshold Voltage vs. VCC (PE0 Pin Read As '0')
PE0 INPUT THRESHOLD VOLTAGE vs. VCC
VIL, PE0 PIN READ AS '0'
2,5
105 °C
85 °C
25 °C
-40 °C
Threshold (V)
2
1,5
1
0,5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
27.7
BOD Thresholds and Analog Comparator Offset
Figure 27-29. BOD Thresholds vs. Temperature (BODLEVEL Is 4.3V)
BOD THRESHOLDS vs. TEMPERATURE
BODLV IS 4.3 V
4,42
Rising Vcc
4,4
Threshold (V)
4,38
4,36
4,34
Falling Vcc
4,32
4,3
4,28
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
Temperature (C)
326
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-30. BOD Thresholds vs. Temperature (BODLEVEL Is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLV IS 2.7 V
2,82
2,8
Rising Vcc
Threshold (V)
2,78
2,76
2,74
Falling Vcc
2,72
2,7
2,68
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
Temperature (C)
Figure 27-31. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC=5V)
ANALOG COMPARATOR TYPICAL OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
Vcc = 5.0 V
Analog comparator offset voltage (V)
0,14
0,12
0,1
0,08
0,06
0,04
0,02
0
0
1
2
3
4
5
6
Common Mode Voltage (V)
Note:
corrected on AT90PWM2B/3B to allow almost full scale use.
327
4317I–AVR–01/08
Figure 27-32. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC=3V)
ANALOG COMPARATOR TYPICAL OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
Vcc = 3.0 V
0,045
Analog comparator offset voltage (V)
0,04
0,035
0,03
0,025
0,02
0,015
0,01
0,005
0
0
0,5
1
1,5
2
2,5
3
3,5
Common Mode Voltage (V)
Note:
27.8
corrected on AT90PWM2B/3B to allow almost full scale use.
Analog Reference
Figure 27-33. AREF Voltage vs. VCC
AREF VOLTAGE vs. VCC
2,6
105 °C
85 °C
25 °C
2,55
-40 °C
Aref (V)
2,5
2,45
2,4
2,35
2,3
2
2,5
3
3,5
4
4,5
5
5,5
Vcc (V)
328
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-34. AREF Voltage vs. Temperature
AREF VOLTAGE vs. TEMPERATURE
2.59
2.58
5.5
5
4.5
3
Aref (V)
2.57
2.56
2.55
2.54
2.53
2.52
-60
-40
-20
0
20
40
60
80
100
120
Temperature
27.9
Internal Oscillator Speed
Figure 27-35. Watchdog Oscillator Frequency vs. VCC
110
108
106
FRC (kHz)
-40 °C
104
25 °C
102
100
85 °C
98
105 °C
96
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
329
4317I–AVR–01/08
Figure 27-36. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
10000 Cycles sampled w ith 250nS
8.4
8.3
8.2
OSCCAL (MHz)
8.1
8
2.7
7.9
5
7.8
7.7
7.6
7.5
7.4
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
Temperature
Figure 27-37. Calibrated 8 MHz RC Oscillator Frequency vs. VCC
INT RC OSCILLATOR FREQUENCY vs. OPERATING VOLTAGE
10000 Cycles sampled w ith 250nS
8.5
8.4
8.3
FRC (MHz)
8.2
105
8.1
85
8
25
7.9
-40
7.8
7.7
7.6
7.5
2
2.5
3
3.5
4
4.5
5
5.5
V CC (V)
330
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-38. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
18
16
14
FRC (MHz)
12
10
8
6
4
2
0
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
OSCCAL
27.10 Current Consumption of Peripheral Units
Figure 27-39. Brownout Detector Current vs. VCC
BROWNOUT DETECTOR CURRENT vs. VCC
45
40
35
ICC (uA)
30
105 °C
85 °C
25 °C
-40 °C
25
20
15
10
5
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
331
4317I–AVR–01/08
Figure 27-40. ADC Current vs. VCC (ADC at 50 kHz)
AREF vs. VCC
ADC AT 50 KHz
500
450
-40 °C
ICC (uA)
400
350
TE
300
250
TO
200
B
L
MP
E
AT
AR
H
EC
T
AC
ED
Z
I
ER
25 °C
85 °C
150
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
Figure 27-41. Aref Current vs. VCC (ADC at 1 MHz)
AREF vs. VCC
ADC AT 1 MHz
180
85 ˚C
25 ˚C
-40 ˚C
160
140
ICC (uA)
120
100
80
60
40
20
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
332
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-42. Analog Comparator Current vs. VCC
ANALOG COMPARATOR CURRENT vs. VCC
80
-40 °C
105 °C
85 °C
25 °C
70
60
ICC (uA)
50
40
30
20
10
0
2
2,5
3
3,5
4
4,5
5
5,5
V CC (V)
Figure 27-43. Programming Current vs. VCC
PROGRAMMING CURRENT vs. Vcc
14
-40 ˚C
12
ICC (mA)
10
25 ˚C
8
85 ˚C
6
4
2
0
1.5
2
2.5
3
3.5
4
4.5
5
5.5
VCC (V)
333
4317I–AVR–01/08
27.11 Current Consumption in Reset and Reset Pulse width
Figure 27-44. Reset Supply Current vs. VCC (0.1 - 1.0 MHz, Excluding Current through the
Reset Pull-up)
RESET SUPPLY CURRENT vs. VCC
EXCLUDING CURRENT THROUGH THE RESET PULLUP
ICC (mA)
0,18
0,16
5.5 V
0,14
5.0 V
0,12
4.5 V
0,1
4.0 V
0,08
3.3 V
3.0 V
2.7 V
0,06
0,04
0,02
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Frequency (MHz)
Figure 27-45. Reset Supply Current vs. VCC (1 - 24 MHz, Excluding Current through the Reset
Pull-up)
RESET SUPPLY CURRENT vs. VCC
EXCLUDING CURRENT THROUGH THE RESET PULLUP
4
5.5 V
3,5
5.0 V
3
4.5 V
ICC (mA)
2,5
2
4.0 V
1,5
3.3 V
1
3.0 V
2.7 V
0,5
0
0
5
10
15
20
25
Frequency (MHz)
334
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 27-46. Reset Supply Current vs. VCC (Clock Stopped, Excluding Current through the
Reset Pull-up)
RESET CURRENT vs. VCC (CLOCK STOPPED)
EXCLUDING CURRENT THROUGH THE RESET PULLUP
0,05
0,04
ICC (mA)
0,03
0,02
105 °C
-40 °C
85 °C
25 °C
0,01
0
2
2,5
3
3,5
4
4,5
5
5,5
-0,01
V CC (V)
Figure 27-47. Reset Pulse Width vs. VCC
RESET PULSE WIDTH vs. VCC
Ext Clock 1 MHz
1600
1400
Pulsewidth (ns)
1200
1000
800
600
105 °C
85 °C
25 °C
-40 °C
400
200
0
0
1
2
3
4
5
6
V CC (V)
335
4317I–AVR–01/08
AT90PWM2/3/2B/3B
28. Register Summary
Address
Name
(0xFF)
PICR2H
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
page 170
(0xFE)
PICR2L
(0xFD)
PFRC2B
PCAE2B
PISEL2B
PELEV2B
PFLTE2B
PRFM2B3
PRFM2B2
PRFM2B1
PRFM2B0
page 170
page 169
(0xFC)
PFRC2A
PCAE2A
PISEL2A
PELEV2A
PFLTE2A
PRFM2A3
PRFM2A2
PRFM2A1
PRFM2A0
page 169
(0xFB)
PCTL2
PPRE21
PPRE20
PBFM2
PAOC2B
PAOC2A
PARUN2
PCCYC2
PRUN2
page 168
(0xFA)
PCNF2
PFIFTY2
PALOCK2
PLOCK2
PMODE21
PMODE20
POP2
PCLKSEL2
POME2
page 164
(0xF9)
OCR2RBH
page 164
(0xF8)
OCR2RBL
page 164
(0xF7)
OCR2SBH
page 164
(0xF6)
OCR2SBL
page 164
(0xF5)
OCR2RAH
page 163
(0xF4)
OCR2RAL
page 163
(0xF3)
OCR2SAH
page 163
(0xF2)
OCR2SAL
(0xF1)
POM2
POMV2B3
POMV2B2
POMV2B1
POMV2B0
(0xF0)
PSOC2
POS23
POS22
PSYNC21
PSYNC20
(0xEF)
PICR1H
(0xEE)
PICR1L
(0xED)
PFRC1B
PCAE1B
PISEL1B
PELEV1B
PFLTE1B
PRFM1B3
PRFM1B2
PRFM1B1
PRFM1B0
page 169
(0xEC)
PFRC1A
PCAE1A
PISEL1A
PELEV1A
PFLTE1A
PRFM1A3
PRFM1A2
PRFM1A1
PRFM1A0
page 169
(0xEB)
PCTL1
PPRE11
PPRE10
PBFM1
PAOC1B
PAOC1A
PARUN1
PCCYC1
PRUN1
page 167
(0xEA)
PCNF1
PFIFTY1
PALOCK1
PLOCK1
PMODE11
PMODE10
POP1
PCLKSEL1
-
page 164
(0xE9)
OCR1RBH
page 164
(0xE8)
OCR1RBL
page 164
(0xE7)
OCR1SBH
page 164
(0xE6)
OCR1SBL
page 164
(0xE5)
OCR1RAH
page 163
(0xE4)
OCR1RAL
page 163
(0xE3)
OCR1SAH
page 163
(0xE2)
OCR1SAL
(0xE1)
Reserved
–
–
–
–
–
–
–
–
–
–
PSYNC11
PSYNC10
–
POEN1B
–
POEN1A
page 163
POMV2A3
POEN2D
POMV2A2
POEN2B
POMV2A1
POEN2C
POMV2A0
page 171
POEN2A
page 162
page 170
page 170
page 163
(0xE0)
PSOC1
(0xDF)
PICR0H
page 162
(0xDE)
PICR0L
(0xDD)
PFRC0B
PCAE0B
PISEL0B
PELEV0B
PFLTE0B
PRFM0B3
PRFM0B2
PRFM0B1
PRFM0B0
page 169
(0xDC)
PFRC0A
PCAE0A
PISEL0A
PELEV0A
PFLTE0A
PRFM0A3
PRFM0A2
PRFM0A1
PRFM0A0
page 169
(0xDB)
PCTL0
PPRE01
PPRE00
PBFM0
PAOC0B
PAOC0A
PARUN0
PCCYC0
PRUN0
page 165
(0xDA)
PCNF0
PFIFTY0
PALOCK0
PLOCK0
PMODE01
PMODE00
POP0
PCLKSEL0
-
page 164
(0xD9)
OCR0RBH
page 164
(0xD8)
OCR0RBL
page 164
(0xD7)
OCR0SBH
page 164
(0xD6)
OCR0SBL
page 164
(0xD5)
OCR0RAH
page 163
(0xD4)
OCR0RAL
page 163
(0xD3)
OCR0SAH
page 163
(0xD2)
OCR0SAL
(0xD1)
Reserved
–
–
–
–
–
–
–
–
(0xD0)
PSOC0
–
–
PSYNC01
PSYNC00
–
POEN0B
–
POEN0A
(0xCF)
Reserved
–
–
–
–
–
–
–
–
page 170
page 170
page 163
page 162
(0xCE)
EUDR
EUDR7
EUDR6
EUDR5
EUDR4
EUDR3
EUDR2
EUDR1
EUDR0
page 221
(0xCD)
MUBRRH
MUBRR15
MUBRR014
MUBRR13
MUBRR12
MUBRR011
MUBRR010
MUBRR9
MUBRR8
page 226
(0xCC)
MUBRRL
MUBRR7
MUBRR6
MUBRR5
MUBRR4
MUBRR3
MUBRR2
MUBRR1
MUBRR0
page 226
(0xCB)
Reserved
–
–
–
–
–
–
–
–
(0xCA)
EUCSRC
–
–
–
–
FEM
F1617
STP1
STP0
page 225
(0xC9)
EUCSRB
–
–
–
EUSART
EUSBS
–
EMCH
BODR
page 224
(0xC8)
EUCSRA
UTxS3
UTxS2
UTxS1
UTxS0
URxS3
URxS2
URxS1
URxS0
page 223
(0xC7)
Reserved
–
–
–
–
–
–
–
–
(0xC6)
UDR
UDR07
UDR06
UDR05
UDR04
UDR03
UDR02
UDR01
UDR00
page 221 & page 202
(0xC5)
UBRRH
–
–
–
–
UBRR011
UBRR010
UBRR09
UBRR08
page 207
(0xC4)
UBRRL
UBRR07
UBRR06
UBRR05
UBRR04
UBRR03
UBRR02
UBRR01
UBRR00
page 207
(0xC3)
Reserved
–
–
–
–
–
–
–
–
(0xC2)
UCSRC
–
UMSEL0
UPM01
UPM00
USBS0
UCSZ01
UCSZ00
UCPOL0
page 205
(0xC1)
UCSRB
RXCIE0
TXCIE0
UDRIE0
RXEN0
TXEN0
UCSZ02
RXB80
TXB80
page 204
(0xC0)
UCSRA
RXC0
TXC0
UDRE0
FE0
DOR0
UPE0
U2X0
MPCM0
page 203
(0xBF)
Reserved
–
–
–
–
–
–
–
–
337
4317I–AVR–01/08
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(0xBE)
Reserved
–
–
–
–
–
–
–
–
(0xBD)
Reserved
–
–
–
–
–
–
–
–
(0xBC)
Reserved
–
–
–
–
–
–
–
–
(0xBB)
Reserved
–
–
–
–
–
–
–
–
(0xBA)
Reserved
–
–
–
–
–
–
–
–
(0xB9)
Reserved
–
–
–
–
–
–
–
–
(0xB8)
Reserved
–
–
–
–
–
–
–
–
(0xB7)
Reserved
–
–
–
–
–
–
–
–
(0xB6)
Reserved
–
–
–
–
–
–
–
–
(0xB5)
Reserved
–
–
–
–
–
–
–
–
(0xB4)
Reserved
–
–
–
–
–
–
–
–
(0xB3)
Reserved
–
–
–
–
–
–
–
–
(0xB2)
Reserved
–
–
–
–
–
–
–
–
(0xB1)
Reserved
–
–
–
–
–
–
–
–
(0xB0)
Reserved
–
–
–
–
–
–
–
–
(0xAF)
AC2CON
AC2EN
AC2IE
AC2IS1
AC2IS0
AC2SADE-
AC2M2
AC2M1
AC2M0
(0xAE)
AC1CON
AC1EN
AC1IE
AC1IS1
AC1IS0
AC1ICE
AC1M2
AC1M1
AC1M0
page 229
(0xAD)
AC0CON
AC0EN
AC0IE
AC0IS1
AC0IS0
-
AC0M2
AC0M1
AC0M0
page 228
(0xAC)
DACH
- / DAC9
- / DAC8
- / DAC7
- / DAC6
- / DAC5
- / DAC4
DAC9 / DAC3
DAC8 / DAC2
page 262
(0xAB)
DACL
DAC7 / DAC1
DAC6 /DAC0
DAC5 / -
DAC4 / -
DAC3 / -
DAC2 / -
DAC1 / -
DAC0 /
page 262
(0xAA)
DACON
DAATE
DATS2
DATS1
DATS0
-
DALA
DAOE
DAEN
page 261
(0xA9)
Reserved
–
–
–
–
–
–
–
–
(0xA8)
Reserved
–
–
–
–
–
–
–
–
(0xA7)
Reserved
–
–
–
–
–
–
–
–
(0xA6)
Reserved
(0xA5)
PIM2
–
-
–
-
–
PSEIE2
–
PEVE2B
–
PEVE2A
–
-
–
-
–
PEOPE2
page 172
(0xA4)
PIFR2
-
-
PSEI2
PEV2B
PEV2A
PRN21
PRN20
PEOP2
page 172
(0xA3)
PIM1
-
-
PSEIE1
PEVE1B
PEVE1A
-
-
PEOPE1
page 171
(0xA2)
PIFR1
-
-
PSEI1
PEV1B
PEV1A
PRN11
PRN10
PEOP1
page 172
(0xA1)
PIM0
-
-
PSEIE0
PEVE0B
PEVE0A
-
-
PEOPE0
page 171
(0xA0)
PIFR0
-
-
PSEI0
PEV0B
PEV0A
PRN01
PRN00
PEOP0
page 172
(0x9F)
Reserved
–
–
–
–
–
–
–
–
338
Page
page 230
(0x9E)
Reserved
–
–
–
–
–
–
–
–
(0x9D)
Reserved
–
–
–
–
–
–
–
–
(0x9C)
Reserved
–
–
–
–
–
–
–
–
(0x9B)
Reserved
–
–
–
–
–
–
–
–
(0x9A)
Reserved
–
–
–
–
–
–
–
–
(0x99)
Reserved
–
–
–
–
–
–
–
–
(0x98)
Reserved
–
–
–
–
–
–
–
–
(0x97)
Reserved
–
–
–
–
–
–
–
–
(0x96)
Reserved
–
–
–
–
–
–
–
–
(0x95)
Reserved
–
–
–
–
–
–
–
–
(0x94)
Reserved
–
–
–
–
–
–
–
–
(0x93)
Reserved
–
–
–
–
–
–
–
–
(0x92)
Reserved
–
–
–
–
–
–
–
–
(0x91)
Reserved
–
–
–
–
–
–
–
–
(0x90)
Reserved
–
–
–
–
–
–
–
–
(0x8F)
Reserved
–
–
–
–
–
–
–
–
(0x8E)
Reserved
–
–
–
–
–
–
–
–
(0x8D)
Reserved
–
–
–
–
–
–
–
–
(0x8C)
Reserved
–
–
–
–
–
–
–
–
(0x8B)
OCR1BH
OCR1B15
OCR1B14
OCR1B13
OCR1B12
OCR1B11
OCR1B10
OCR1B9
OCR1B8
(0x8A)
OCR1BL
OCR1B7
OCR1B6
OCR1B5
OCR1B4
OCR1B3
OCR1B2
OCR1B1
OCR1B0
page 127
(0x89)
OCR1AH
OCR1A15
OCR1A14
OCR1A13
OCR1A12
OCR1A11
OCR1A10
OCR1A9
OCR1A8
page 127
page 127
(0x88)
OCR1AL
OCR1A7
OCR1A6
OCR1A5
OCR1A4
OCR1A3
OCR1A2
OCR1A1
OCR1A0
page 127
(0x87)
ICR1H
ICR115
ICR114
ICR113
ICR112
ICR111
ICR110
ICR19
ICR18
page 128
(0x86)
ICR1L
ICR17
ICR16
ICR15
ICR14
ICR13
ICR12
ICR11
ICR10
page 128
(0x85)
TCNT1H
TCNT115
TCNT114
TCNT113
TCNT112
TCNT111
TCNT110
TCNT19
TCNT18
page 127
(0x84)
TCNT1L
TCNT17
TCNT16
TCNT15
TCNT14
TCNT13
TCNT12
TCNT11
TCNT10
page 127
(0x83)
Reserved
–
–
–
–
–
–
–
–
(0x82)
TCCR1C
FOC1A
FOC1B
–
–
–
–
–
–
page 126
(0x81)
TCCR1B
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
page 125
(0x80)
TCCR1A
COM1A1
COM1A0
COM1B1
COM1B0
–
–
WGM11
WGM10
page 123
(0x7F)
DIDR1
–
–
ACMP0D
AMP0PD
AMP0ND
ADC10D/ACMP1D
ADC9D/AMP1PD
ADC8D/AMP1ND
page 252
(0x7E)
DIDR0
ADC7D
ADC6D
ADC5D
ADC4D
ADC3D/ACMPMD
ADC2D/ACMP2D
ADC1D
ADC0D
page 252
(0x7D)
Reserved
–
–
–
–
–
–
–
–
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
(0x7C)
ADMUX
REFS1
REFS0
ADLAR
–
MUX3
MUX2
MUX1
MUX0
page 247
(0x7B)
ADCSRB
ADHSM
–
–
ADASCR
ADTS3
ADTS2
ADTS1
ADTS0
page 249
(0x7A)
ADCSRA
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
page 248
(0x79)
ADCH
- / ADC9
- / ADC8
- / ADC7
- / ADC6
- / ADC5
- / ADC4
ADC9 / ADC3
ADC8 / ADC2
page 251
(0x78)
ADCL
ADC7 / ADC1
ADC6 / ADC0
ADC5 / -
ADC4 / -
ADC3 / -
ADC2 / -
ADC1 / -
ADC0 /
page 251
(0x77)
AMP1CSR
AMP1EN
-
AMP1G1
AMP1G0
-
AMP1TS2
AMP1TS1
AMP1TS0
page 257
(0x76)
AMP0CSR
AMP0EN
-
AMP0G1
AMP0G0
-
AMP0TS2
AMP0TS1
AMP0TS0
page 256
(0x75)
Reserved
–
–
–
–
–
–
–
–
(0x74)
Reserved
–
–
–
–
–
–
–
–
(0x73)
Reserved
–
–
–
–
–
–
–
–
(0x72)
Reserved
–
–
–
–
–
–
–
–
(0x71)
Reserved
–
–
–
–
–
–
–
–
(0x70)
Reserved
–
–
–
–
–
–
–
–
(0x6F)
TIMSK1
–
–
ICIE1
–
–
OCIE1B
OCIE1A
TOIE1
page 128
(0x6E)
TIMSK0
–
–
–
–
–
OCIE0B
OCIE0A
TOIE0
page 101
(0x6D)
Reserved
–
–
–
–
–
–
–
–
(0x6C)
Reserved
–
–
–
–
–
–
–
–
(0x6B)
Reserved
–
–
–
–
–
–
–
–
(0x6A)
Reserved
–
–
–
–
–
–
–
–
(0x69)
EICRA
ISC31
ISC30
ISC21
ISC20
ISC11
ISC10
ISC01
ISC00
(0x68)
Reserved
–
–
–
–
–
–
–
–
(0x67)
Reserved
–
–
–
–
–
–
–
–
(0x66)
OSCCAL
–
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0
(0x65)
Reserved
–
–
–
–
–
–
–
–
(0x64)
PRR
PRPSC2
PRPSC1
PRPSC0
PRTIM1
PRTIM0
PRSPI
PRUSART
PRADC
(0x63)
Reserved
–
–
–
–
–
–
–
–
(0x62)
Reserved
–
–
–
–
–
–
–
–
(0x61)
CLKPR
CLKPCE
–
–
–
CLKPS3
CLKPS2
CLKPS1
CLKPS0
page 39
(0x60)
WDTCSR
WDIF
WDIE
WDP3
WDCE
WDE
WDP2
WDP1
WDP0
page 54
0x3F (0x5F)
SREG
I
T
H
S
V
N
Z
C
page 13
0x3E (0x5E)
SPH
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
page 15
0x3D (0x5D)
SPL
SP7
SP6
SP5
SP4
SP3
SP2
SP1
SP0
page 15
0x3C (0x5C)
Reserved
–
–
–
–
–
–
–
–
0x3B (0x5B)
Reserved
–
–
–
–
–
–
–
–
0x3A (0x5A)
Reserved
–
–
–
–
–
–
–
–
0x39 (0x59)
Reserved
–
–
–
–
–
–
–
–
0x38 (0x58)
Reserved
–
–
–
–
–
–
–
–
0x37 (0x57)
SPMCSR
SPMIE
RWWSB
–
RWWSRE
BLBSET
PGWRT
PGERS
SPMEN
0x36 (0x56)
Reserved
–
–
–
–
–
–
–
–
page 81
page 34
page 43
page 271
0x35 (0x55)
MCUCR
SPIPS
–
–
PUD
–
–
IVSEL
IVCE
page 60 & page 69
0x34 (0x54)
MCUSR
–
–
–
–
WDRF
BORF
EXTRF
PORF
page 50
0x33 (0x53)
SMCR
–
–
–
–
SM2
SM1
SM0
SE
0x32 (0x52)
MSMCR
0x31 (0x51)
MONDR
0x30 (0x50)
ACSR
Monitor Stop Mode Control Register
Monitor Data Register
ACCKDIV
AC2IF
AC1IF
AC0IF
–
page 41
reserved
reserved
AC2O
AC1O
AC0O
page 231
0x2F (0x4F)
Reserved
–
–
–
–
–
–
–
–
0x2E (0x4E)
SPDR
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
page 182
0x2D (0x4D)
SPSR
SPIF
WCOL
–
–
–
–
–
SPI2X
page 181
0x2C (0x4C)
SPCR
SPIE
SPE
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
page 180
0x2B (0x4B)
Reserved
–
–
–
–
–
–
–
–
0x2A (0x4A)
Reserved
–
–
–
–
–
–
–
–
0x29 (0x49)
PLLCSR
-
-
-
-
-
PLLF
PLLE
PLOCK
page 37
0x28 (0x48)
OCR0B
OCR0B7
OCR0B6
OCR0B5
OCR0B4
OCR0B3
OCR0B2
OCR0B1
OCR0B0
page 101
0x27 (0x47)
OCR0A
OCR0A7
OCR0A6
OCR0A5
OCR0A4
OCR0A3
OCR0A2
OCR0A1
OCR0A0
page 100
0x26 (0x46)
TCNT0
TCNT07
TCNT06
TCNT05
TCNT04
TCNT03
TCNT02
TCNT01
TCNT00
page 100
0x25 (0x45)
TCCR0B
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
page 99
0x24 (0x44)
TCCR0A
COM0A1
COM0A0
COM0B1
COM0B0
–
–
WGM01
WGM00
page 96
0x23 (0x43)
GTCCR
TSM
ICPSEL1
–
–
–
–
–
PSRSYNC
page 84
0x22 (0x42)
EEARH
–
–
–
–
EEAR11
EEAR10
EEAR9
EEAR8
page 21
0x21 (0x41)
EEARL
EEAR7
EEAR6
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
page 21
0x20 (0x40)
EEDR
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
page 22
0x1F (0x3F)
EECR
–
–
–
–
EERIE
EEMWE
EEWE
EERE
page 22
0x1E (0x3E)
GPIOR0
GPIOR07
GPIOR06
GPIOR05
GPIOR04
GPIOR03
GPIOR02
GPIOR01
GPIOR00
page 27
0x1D (0x3D)
EIMSK
–
–
–
–
INT3
INT2
INT1
INT0
page 82
0x1C (0x3C)
0x1B (0x3B)
EIFR
–
–
–
–
INTF3
INTF2
INTF1
INTF0
page 82
GPIOR3
GPIOR37
GPIOR36
GPIOR35
GPIOR34
GPIOR33
GPIOR32
GPIOR31
GPIOR30
page 28
339
4317I–AVR–01/08
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Page
0x1A (0x3A)
GPIOR2
GPIOR27
GPIOR26
GPIOR25
GPIOR24
GPIOR23
GPIOR22
GPIOR21
GPIOR20
page 27
0x19 (0x39)
GPIOR1
GPIOR17
GPIOR16
GPIOR15
GPIOR14
GPIOR13
GPIOR12
GPIOR11
GPIOR10
page 27
0x18 (0x38)
Reserved
–
–
–
–
–
–
–
–
0x17 (0x37)
Reserved
–
–
–
–
–
–
–
–
0x16 (0x36)
TIFR1
–
–
ICF1
–
–
OCF1B
OCF1A
TOV1
page 129
0x15 (0x35)
TIFR0
–
–
–
–
–
OCF0B
OCF0A
TOV0
page 101
0x14 (0x34)
Reserved
–
–
–
–
–
–
–
–
0x13 (0x33)
Reserved
–
–
–
–
–
–
–
–
0x12 (0x32)
Reserved
–
–
–
–
–
–
–
–
0x11 (0x31)
Reserved
–
–
–
–
–
–
–
–
0x10 (0x30)
Reserved
–
–
–
–
–
–
–
–
0x0F (0x2F)
Reserved
–
–
–
–
–
–
–
–
0x0E (0x2E)
PORTE
–
–
–
–
–
PORTE2
PORTE1
PORTE0
page 79
0x0D (0x2D)
DDRE
–
–
–
–
–
DDE2
DDE1
DDE0
page 80
0x0C (0x2C)
PINE
–
–
–
–
–
PINE2
PINE1
PINE0
page 80
0x0B (0x2B)
PORTD
PORTD7
PORTD6
PORTD5
PORTD4
PORTD3
PORTD2
PORTD1
PORTD0
page 79
0x0A (0x2A)
DDRD
DDD7
DDD6
DDD5
DDD4
DDD3
DDD2
DDD1
DDD0
page 79
0x09 (0x29)
PIND
PIND7
PIND6
PIND5
PIND4
PIND3
PIND2
PIND1
PIND0
page 79
0x08 (0x28)
PORTC
PORTC7
PORTC6
PORTC5
PORTC4
PORTC3
PORTC2
PORTC1
PORTC0
page 79
0x07 (0x27)
DDRC
DDC7
DDC6
DDC5
DDC4
DDC3
DDC2
DDC1
DDC0
page 79
page 79
0x06 (0x26)
PINC
PINC7
PINC6
PINC5
PINC4
PINC3
PINC2
PINC1
PINC0
0x05 (0x25)
PORTB
PORTB7
PORTB6
PORTB5
PORTB4
PORTB3
PORTB2
PORTB1
PORTB0
page 78
0x04 (0x24)
DDRB
DDB7
DDB6
DDB5
DDB4
DDB3
DDB2
DDB1
DDB0
page 78
page 79
0x03 (0x23)
PINB
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
0x02 (0x22)
Reserved
–
–
–
–
–
–
–
–
0x01 (0x21)
Reserved
–
–
–
–
–
–
–
–
0x00 (0x20)
Reserved
–
–
–
–
–
–
–
–
Note:
1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI
instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O
Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The AT90PWM2/2B/3/3B is
a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for
the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and
LD/LDS/LDD instructions can be used.
340
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
29. 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 ← 0xFF − Rd
Z,C,N,V
1
NEG
Rd
Two’s Complement
Rd ← 0x00 − Rd
Z,C,N,V,H
1
SBR
Rd,K
Set Bit(s) in Register
Rd ← Rd v K
Z,N,V
1
CBR
Rd,K
Clear Bit(s) in Register
Rd ← Rd • (0xFF - K)
Z,N,V
1
INC
Rd
Increment
Rd ← Rd + 1
Z,N,V
1
1
DEC
Rd
Decrement
Rd ← Rd − 1
Z,N,V
TST
Rd
Test for Zero or Minus
Rd ← Rd • Rd
Z,N,V
1
CLR
Rd
Clear Register
Rd ← Rd ⊕ Rd
Z,N,V
1
SER
Rd
Set Register
Rd ← 0xFF
None
1
MUL
Rd, Rr
Multiply Unsigned
R1:R0 ← Rd x Rr
Z,C
2
MULS
Rd, Rr
Multiply Signed
R1:R0 ← Rd x Rr
Z,C
2
MULSU
Rd, Rr
Multiply Signed with Unsigned
R1:R0 ← Rd x Rr
Z,C
2
FMUL
Rd, Rr
Fractional Multiply Unsigned
R1:R0 ← (Rd x Rr) << 1
Z,C
2
FMULS
Rd, Rr
Fractional Multiply Signed
R1:R0 ← (Rd x Rr) << 1
Z,C
2
FMULSU
Rd, Rr
Fractional Multiply Signed with Unsigned
R1:R0 ← (Rd x Rr) << 1
Z,C
2
BRANCH INSTRUCTIONS
RJMP
k
IJMP
Relative Jump
PC ← PC + k + 1
None
2
Indirect Jump to (Z)
PC ← Z
None
2
Relative Subroutine Call
PC ← PC + k + 1
None
3
ICALL
Indirect Call to (Z)
PC ← Z
None
3
RET
Subroutine Return
PC ← STACK
None
4
RETI
Interrupt Return
PC ← STACK
I
4
Compare, Skip if Equal
if (Rd = Rr) PC ← PC + 2 or 3
None
1/2/3
RCALL
k
CPSE
Rd,Rr
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
1
SBRC
Rr, b
Skip if Bit in Register Cleared
if (Rr(b)=0) PC ← PC + 2 or 3
None
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
BRIE
k
Branch if Interrupt Enabled
if ( I = 1) then PC ← PC + k + 1
None
1/2
BRID
k
Branch if Interrupt Disabled
if ( I = 0) then PC ← PC + k + 1
None
1/2
341
4317I–AVR–01/08
Mnemonics
Operands
Description
Operation
Flags
#Clocks
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
1
LSL
Rd
Logical Shift Left
Rd(n+1) ← Rd(n), Rd(0) ← 0
Z,C,N,V
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
1
BCLR
s
Flag Clear
SREG(s) ← 0
SREG(s)
BST
Rr, b
Bit Store from Register to T
T ← Rr(b)
T
1
BLD
Rd, b
Bit load from T to Register
Rd(b) ← T
None
1
SEC
Set Carry
C←1
C
1
CLC
Clear Carry
C←0
C
1
SEN
Set Negative Flag
N←1
N
1
CLN
Clear Negative Flag
N←0
N
1
SEZ
Set Zero Flag
Z←1
Z
1
CLZ
Clear Zero Flag
Z←0
Z
1
SEI
Global Interrupt Enable
I←1
I
1
CLI
Global Interrupt Disable
I←0
I
1
SES
Set Signed Test Flag
S←1
S
1
CLS
Clear Signed Test Flag
S←0
S
1
SEV
Set Twos Complement Overflow.
V←1
V
1
CLV
Clear Twos Complement Overflow
V←0
V
1
SET
Set T in SREG
T←1
T
1
CLT
Clear T in SREG
T←0
T
1
SEH
CLH
Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG
H←1
H←0
H
H
1
1
Rd ← Rr
Rd+1:Rd ← Rr+1:Rr
None
1
None
1
1
DATA TRANSFER INSTRUCTIONS
MOV
Rd, Rr
Move Between Registers
MOVW
Rd, Rr
Copy Register Word
LDI
Rd, K
Load Immediate
Rd ← K
None
LD
Rd, X
Load Indirect
Rd ← (X)
None
2
LD
Rd, X+
Load Indirect and Post-Inc.
Rd ← (X), X ← X + 1
None
2
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
ST
- Y, Rr
Store Indirect and Pre-Dec.
Y ← Y - 1, (Y) ← Rr
None
2
STD
Y+q,Rr
Store Indirect with Displacement
(Y + q) ← Rr
None
2
ST
Z, Rr
Store Indirect
(Z) ← Rr
None
2
ST
Z+, Rr
Store Indirect and Post-Inc.
(Z) ← Rr, Z ← Z + 1
None
2
ST
-Z, Rr
Store Indirect and Pre-Dec.
Z ← Z - 1, (Z) ← Rr
None
2
STD
Z+q,Rr
Store Indirect with Displacement
(Z + q) ← Rr
None
2
STS
k, Rr
LPM
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
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
MCU CONTROL INSTRUCTIONS
342
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Mnemonics
Operands
Description
NOP
No Operation
SLEEP
Sleep
WDR
BREAK
Watchdog Reset
Break
Operation
Flags
#Clocks
None
1
(see specific descr. for Sleep function)
None
1
(see specific descr. for WDR/timer)
For On-chip Debug Only
None
None
1
N/A
343
4317I–AVR–01/08
30. Ordering Information
Speed (MHz)
Power Supply
Ordering Code
Package
16
Operation Range
2.7 - 5.5V
AT90PWM3-16SQ
SO32
16
2.7 - 5.5V
AT90PWM3-16MQT
QFN32
16
2.7 - 5.5V
AT90PWM2-16SQ
SO24
16
2.7 - 5.5V
AT90PWM3B-16SE
SO32
Engineering Samples
16
2.7 - 5.5V
AT90PWM3B-16ME
QFN32
Engineering Samples
16
2.7 - 5.5V
AT90PWM2B-16SE
SO24
Engineering Samples
16
2.7 - 5.5V
AT90PWM3B-16SU
SO32
16
2.7 - 5.5V
AT90PWM3B-16MU
QFN32
16
2.7 - 5.5V
AT90PWM2B-16SU
SO24
Extended (-40°C to
105°C)
Extended (-40°C to
105°C)
Extended (-40°C to
105°C)
Extended (-40°C to
105°C)
Extended (-40°C to
105°C)
Extended (-40°C to
105°C)
Note:
All packages are Pb free, fully LHF
Note:
This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information and
minimum quantities.
Note:
Parts numbers are for shipping in sticks (SO) or in trays (QFN). Thes devices can also be supplied in Tape and Reel. Please
contact your local Atmel sales office for detailed ordering information and minimum quantities.
Note:
PWM2 is not recommended for new designs, use PWM2B for your developments
Note:
PWM3 is not recommended for new designs, use PWM3B for your developments
344
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
31. Package Information
Package Type
SO24
24-Lead, Small Outline Package
SO32
32-Lead, Small Outline Package
QFN32
32-Lead, Quad Flat No lead
345
4317I–AVR–01/08
31.1
346
SO24
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
31.2
SO32
347
4317I–AVR–01/08
31.3
348
QFN32
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
349
4317I–AVR–01/08
32. Errata
32.1
AT90PWM2&3 Rev. A (Mask Revision)
•
PGM: PSCxRB Fuse
•
PSC: Prescaler
•
PSC: PAOCnA and PAOCnB Register Bits (Asynchronous output control)
•
PSC: PEVxA/B Flag Bits
•
PSC: Output Polarity in Centered Mode
•
PSC: Output Activity
•
VREF
•
DALI
•
DAC: Register Update
•
DAC: Output spikes
•
DAC driver: Output Voltage linearity
•
ADC: Conversion accuracy
•
Analog comparator: Offset value
•
Analog comparator: Output signal
•
PSC: Autolock modes
•
DALI: 17th bit detection
•
PSC: One ramp mode with PSC input mode 8
1. PGM: PSCnRB Fuse
The use of PSCnRB fuse can make the parallel ISP fail.
Workaround:
When PSCnRB fuses are used, use the serial programming mode to load a new program
version.
2. PSC: Prescaler
The use of PSC's prescaler have the following effects :
It blocks the sample of PSC inputs until the two first cycles following the set of PSC run bit.
A fault is not properly transferred to other (slave) PSC.
Workaround:
Clear the prescaler PPREx bit when stopping the PSC (prun = 0), and set them to appropriate value when starting the PSC (prun = 1), these bits are in the same PCTL register
Do not use the prescaler when a fault on one PSC should affect other PSC’s
3. PSC: PAOCnA and PAOCnB Register Bits (Asynchronous output control)
These register bits are malfunctioning.
Workaround:
Do not use this feature.
4. PSC: PEVnA/B flag bits
These flags are set when a fault arises, but can also be set again during the fault itself.
Workaround:
Don't clear these flags before the fault disappears.
350
AT90PWM2/3/2B/3B
4317I–AVR–01/08
AT90PWM2/3/2B/3B
5. PSC: Output Polarity in Centered Mode
In centered mode, PSCOUTn1 outputs are not inverted, so they are active at the same time
as PSCOUTn0.
Workaround:
Use an external inverter (or a driver with inverting output) to drive the load on
PSCOUTn1.
6. PSC : POACnA/B Output Activity
These register bits are not implemented in rev A.
Workaround:
Do not use this feature.
7. VREF
Remark: To have Internal Vref on AREF pin select an internal analog feature such as DAC
or ADC.
Some stand by power consuption may be observed if Vref equals AVcc
8. DALI
Some troubles on Dali extension when edges are not symmetric.
Workaround:
Use an optocoupler providing symmetric edges on Rx and Tx DALI lines (only recommanded for software validation purpose).
9. DAC: Register Update
Registers DACL & DACH are not written when the DAC is not enabled.
Workaround:
Enable DAC with DAEN before writing in DACL & DACH. To prevent an unwanted zero output on DAC pin, enable DAC output, with DAOE afterwards.
10. DAC : Output spikes
During transition between two codes, a spike may appears
Work around:
Filter spike or wait for steady state
No spike appears if the 4 last signifiant bits remain zero.
11. DAC driver: Output Voltage linearity
The voltage linearity of the DAC driver is limited when the DAC output goes above Vcc - 1V.
Work around:
Do not use AVcc as Vref ; internal Vref gives good results
12. ADC : Conversion accuracy
The conversion accuracy degrades when the ADC clock is 1 & 2 MHz.
Work around:
When a 10 bit conversion accuracy is required, use an ADC clock of 500 kHz or below.
13. Analog comparator: Offset value
The offset value increases when the common mode voltage is above Vcc - 1.5V.
Work around:
Limit common mode voltage
14. Analog comparator: Output signal
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4317I–AVR–01/08
The comparator output toggles at the comparator clock frequency when the voltage difference between both inputs is lower than the offset. This may occur when comparing signal
with small slew rate.
Work around:
This effect normally do not impact the PSC, as the transition is sampled once per PSC cycle
Be carefull when using the comparator as an interrupt source.
15. PSC : Autolock mode
This mode is not properly handled when CLKPSC is different from CLK IO.
Work around:
With CLKPSC equals 64/32 MHz (CLKPLL), use LOCK mode
16. DALI : 17th bit detection
17th bit detection do not occurs if the signal arrives after the sampling point.
Workaround:
Use this feature only for sofware development and not in field conditions
17. PSC : One ramp mode with PSC input mode 8
The retriggering is not properly handled in this case.
Work around:
Do not program this case.
18. PSC : Desactivation of outputs in mode 14
See “PSC Input Mode 14: Fixed Frequency Edge Retrigger PSC and Disactivate Output” on
page 156.
Work around:
Do not use this mode to desactivate output if retrigger event do not occurs during On-Time.
32.2
AT90PWM2B/3B
•
PSC : Double End-Of-Cycle Interrupt Request in Centered Mode
•
ADC : Conversion accuracy
1. PSC : Double End-Of-Cycle Interrupt Request in Centered Mode
In centered mode, after the “expected” End-Of-Cycle Interrupt, a second unexpected Interrupt occurs 1 PSC cycle after the previous interrupt.
Work around:
While CPU cycle is lower than PSC clock, the CPU sees only one interrupt request. For PSC
clock period greater than CPU cycle, the second interrupt request must be cleared by
software.
2. ADC : Conversion accuracy
The conversion accuracy degrades when the ADC clock is 2 MHz.
Work around:
When a 10 bit conversion accuracy is required, use an ADC clock of 1 MHz or below.
At 2 Mhz the ADC can be used as a 7 bits ADC.
3. DAC Driver linearity above 3.6V
With 5V Vcc, the DAC driver linearity is poor when DAC output level is above Vcc-1V. At 5V,
DAC output for 1023 will be around 5V - 40mV.
Work around: .
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AT90PWM2/3/2B/3B
Use, when Vcc=5V, Vref below Vcc-1V.
Or, when Vref=Vcc=5V, do not uses codes above 800.
4. DAC Update in Autotrig mode
If the cpu writes in DACH register at the same instant that the selected trigger source occurs
and DAC Auto Trigger is enabled, the DACH register is not updated by the new value.
Work around: .
When using the autotrig mode, write twice in the DACH register. The time between the two
CPU writes, must be different than the trigger source frequency.
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33. Datasheet Revision History for AT90PWM2/2B/3/3B
Please note that the referring page numbers in this section are referred to this document. The
referring revision in this section are referring to the document revision.
33.1
Changes from 4317A- to 4317B
1. PSC section has been rewritten.
2. Suppression of description of RAMPZ which does not exist.
33.2
Changes from 4317B- to 4317C
1. Added AT90PWM2B/3B Advance Information.
2. Various updates throughout the document.
33.3
Changes from 4317C- to 4317D
1. Update of Electrical and Typical Characteristics.
33.4
Changes from 4317D to 4317E
1. Changed product status from “Advanced Information” to “Preliminary”.
33.5
Changes from 4317E to 4317F
1. Remove JMP and CALL instruction in the Instruction Set Summary
2. Daisy chain of PSC input is only done in mode 7 - See “Fault events in Autorun mode”
on page 160.
3. Updated “Output Compare SA Register – OCRnSAH and OCRnSAL” on page 163
4. Updated “Output Compare RA Register – OCRnRAH and OCRnRAL” on page 163
5. Updated “Output Compare SB Register – OCRnSBH and OCRnSBL” on page 164
6. Updated “Output Compare RB Register – OCRnRBH and OCRnRBL” on page 164
7. Specify the “Analog Comparator Propagation Delay” - See “DC Characteristics” on
page 300.
8. Specify the “Reset Characteristics” - See “Reset Characteristics(1)” on page 47.
9. Specify the “Brown-out Characteristics” - See “Brown-out Characteristics(1)” on page
49.
10. Specify the “Internal Voltage Reference Characteristics - See “Internal Voltage Reference Characteristics(1)” on page 51.
33.6
Changes from 4317F to 4317G
1. Describe the amplifier operation for Rev B.
2. Clarify the fact that the DAC load given is the worst case.
3. Specify the ADC Min and Max clock frequency.
4. Describe the retrigger mode 8 in one ramp mode.
5. Specify that the amplifier only provides a 8 bits accuracy.
33.7
Changes from 4317G to 4317H
1. Updated “History” on page 2
2. Specify the “AREF Voltage vs. Temperature” on page 329
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AT90PWM2/3/2B/3B
3. PSC : the Balance Flank Width Modulation is done On-Time 1 rather than On-Time 0
(correction of figures)
4. Updated “Maximum Speed vs. VCC” on page 303 (formulas are removed)
5. Update of the “Errata” on page 350
33.8
Changes from 4317H to 4317I
1. Updated “History” on page 2
2. Updated “Device Clocking Options Select AT90PWM2B/3B” on page 31
3. Updated “Start-up Times when the PLL is selected as system clock” on page 35
4. Updated “ADC Noise Canceler” on page 241
5. Updated “ADC Auto Trigger Source Selection for non amplified conversions” on page
250.
6. Added “ADC Auto Trigger Source Selection for amplified conversions” on page 250
7. Updated “Amplifier” on page 252
8. Updated “Amplifier 0 Control and Status register – AMP0CSR” on page 256
9. Updated “AMP0 Auto Trigger Source Selection” on page 257
10. Updated “Amplifier 1Control and Status register – AMP1CSR” on page 257
11. Updated “AMP1 Auto Trigger source selection” on page 258
12. Updated DAC “Features” on page 259 (Output Impedance)
13. Updated temperature range in “DC Characteristics” on page 300
14. Updated Vhysr in “DC Characteristics” on page 300
15. Updated “ADC Characteristics” on page 306
16. Updated “Example 1” on page 315
17. Updated “Example 2” on page 315
18. Updated “Example 3” on page 316
19. Added “I/O Pin Input HysteresisVoltage vs. VCC” on page 323
20. Updated “Ordering Information” on page 344
21. Added Errata for “AT90PWM2B/3B” on page 352
22. Updated Package Drawings “Package Information” on page 345.
23. Updated table on page 2.
24. Updated “Calibrated Internal RC Oscillator” on page 33.
25. Added “Calibrated Internal RC Oscillator Accuracy” on page 302.
26. Updated Figure 27-36 on page 330.
27. Updated Figure 27-37 on page 330.
28. Updated Figure 27-38 on page 331.
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Table of Contents
1
History ....................................................................................................... 2
2
Disclaimer ................................................................................................. 2
3
Pin Configurations ................................................................................... 3
3.1
4
5
6
7
356
Pin Descriptions .................................................................................................5
Overview ................................................................................................... 7
4.1
Block Diagram ...................................................................................................8
4.2
Pin Descriptions .................................................................................................9
4.3
About Code Examples .....................................................................................10
AVR CPU Core .........................................................................................11
5.1
Introduction ......................................................................................................11
5.2
Architectural Overview .....................................................................................11
5.3
ALU – Arithmetic Logic Unit .............................................................................12
5.4
Status Register ................................................................................................13
5.5
General Purpose Register File ........................................................................14
5.6
Stack Pointer ...................................................................................................15
5.7
Instruction Execution Timing ...........................................................................15
5.8
Reset and Interrupt Handling ...........................................................................16
Memories ................................................................................................ 19
6.1
In-System Reprogrammable Flash Program Memory .....................................19
6.2
SRAM Data Memory ........................................................................................19
6.3
EEPROM Data Memory ..................................................................................21
6.4
I/O Memory ......................................................................................................27
6.5
General Purpose I/O Registers .......................................................................27
System Clock ......................................................................................... 29
7.1
Clock Systems and their Distribution ...............................................................29
7.2
Clock Sources .................................................................................................31
7.3
Default Clock Source .......................................................................................32
7.4
Low Power Crystal Oscillator ...........................................................................32
7.5
Calibrated Internal RC Oscillator .....................................................................33
7.6
PLL ..................................................................................................................35
7.7
128 kHz Internal Oscillator ..............................................................................37
7.8
External Clock .................................................................................................37
AT90PWM2/3/2B/3B
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AT90PWM2/3/2B/3B
8
9
7.9
Clock Output Buffer .........................................................................................38
7.10
System Clock Prescaler ..................................................................................38
Power Management and Sleep Modes ................................................. 41
8.1
Idle Mode .........................................................................................................42
8.2
ADC Noise Reduction Mode ............................................................................42
8.3
Power-down Mode ...........................................................................................42
8.4
Standby Mode .................................................................................................42
8.5
Power Reduction Register ...............................................................................43
8.6
Minimizing Power Consumption ......................................................................44
System Control and Reset .................................................................... 46
9.1
Internal Voltage Reference ..............................................................................51
9.2
Watchdog Timer ..............................................................................................52
10 Interrupts ................................................................................................ 57
10.1
Interrupt Vectors in AT90PWM2/2B/3/3B ........................................................57
11 I/O-Ports .................................................................................................. 62
11.1
Introduction ......................................................................................................62
11.2
Ports as General Digital I/O .............................................................................63
11.3
Alternate Port Functions ..................................................................................67
11.4
Register Description for I/O-Ports ....................................................................78
12 External Interrupts ................................................................................. 81
13 Timer/Counter0 and Timer/Counter1 Prescalers ................................ 83
14 8-bit Timer/Counter0 with PWM ............................................................ 86
14.1
Overview ..........................................................................................................86
14.2
Timer/Counter Clock Sources .........................................................................87
14.3
Counter Unit ....................................................................................................87
14.4
Output Compare Unit .......................................................................................88
14.5
Compare Match Output Unit ............................................................................90
14.6
Modes of Operation .........................................................................................91
14.7
Timer/Counter Timing Diagrams .....................................................................95
14.8
8-bit Timer/Counter Register Description ........................................................96
15 16-bit Timer/Counter1 with PWM ........................................................ 103
15.1
Overview ........................................................................................................103
15.2
Accessing 16-bit Registers ............................................................................105
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15.3
Timer/Counter Clock Sources .......................................................................108
15.4
Counter Unit ..................................................................................................109
15.5
Input Capture Unit .........................................................................................110
15.6
Output Compare Units ...................................................................................111
15.7
Compare Match Output Unit ..........................................................................113
15.8
Modes of Operation .......................................................................................114
15.9
Timer/Counter Timing Diagrams ...................................................................122
15.10
16-bit Timer/Counter Register Description ....................................................123
16 Power Stage Controller – (PSC0, PSC1 & PSC2) .............................. 130
358
16.1
Features ........................................................................................................130
16.2
Overview ........................................................................................................130
16.3
PSC Description ............................................................................................131
16.4
Signal Description ..........................................................................................133
16.5
Functional Description ...................................................................................135
16.6
Update of Values ...........................................................................................140
16.7
Enhanced Resolution ....................................................................................140
16.8
PSC Inputs ....................................................................................................144
16.9
PSC Input Mode 1: Stop signal, Jump to Opposite Dead-Time and Wait .....149
16.10
PSC Input Mode 2: Stop signal, Execute Opposite Dead-Time and Wait .....150
16.11
PSC Input Mode 3: Stop signal, Execute Opposite while Fault active ..........151
16.12
PSC Input Mode 4: Deactivate outputs without changing timing. ..................151
16.13
PSC Input Mode 5: Stop signal and Insert Dead-Time ..................................152
16.14
PSC Input Mode 6: Stop signal, Jump to Opposite Dead-Time and Wait. ....153
16.15
PSC Input Mode 7: Halt PSC and Wait for Software Action ..........................153
16.16
PSC Input Mode 8: Edge Retrigger PSC .......................................................154
16.17
PSC Input Mode 9: Fixed Frequency Edge Retrigger PSC ...........................155
16.18
PSC Input Mode 14: Fixed Frequency Edge Retrigger PSC and Disactivate Output 156
16.19
PSC2 Outputs ................................................................................................158
16.20
Analog Synchronization .................................................................................159
16.21
Interrupt Handling ..........................................................................................159
16.22
PSC Synchronization .....................................................................................159
16.23
PSC Clock Sources .......................................................................................160
16.24
Interrupts .......................................................................................................161
16.25
PSC Register Definition .................................................................................162
16.26
PSC2 Specific Register .................................................................................171
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AT90PWM2/3/2B/3B
17 Serial Peripheral Interface – SPI ......................................................... 174
17.1
Features ........................................................................................................174
17.2
SS Pin Functionality ......................................................................................179
17.3
Data Modes ...................................................................................................182
18 USART ................................................................................................... 184
18.1
Features ........................................................................................................184
18.2
Overview ........................................................................................................185
18.3
Clock Generation ...........................................................................................186
18.4
Serial Frame ..................................................................................................188
18.5
USART Initialization .......................................................................................189
18.6
Data Transmission – USART Transmitter .....................................................190
18.7
Data Reception – USART Receiver ..............................................................193
18.8
Asynchronous Data Reception ......................................................................198
18.9
Multi-processor Communication Mode ..........................................................201
18.10
USART Register Description .........................................................................202
18.11
Examples of Baud Rate Setting .....................................................................207
19 EUSART (Extended USART) ............................................................... 212
19.1
Features ........................................................................................................212
19.2
Overview ........................................................................................................212
19.3
Serial Frames ................................................................................................213
19.4
Configuring the EUSART ...............................................................................218
19.5
Data Reception – EUSART Receiver ............................................................219
19.6
EUSART Registers Description .....................................................................221
20 Analog Comparator ............................................................................. 227
20.1
Overview ........................................................................................................227
20.2
Analog Comparator Register Description ......................................................228
21 Analog to Digital Converter - ADC ..................................................... 234
21.1
Features ........................................................................................................234
21.2
Operation .......................................................................................................236
21.3
Starting a Conversion ....................................................................................236
21.4
Prescaling and Conversion Timing ................................................................237
21.5
Changing Channel or Reference Selection ...................................................239
21.6
ADC Noise Canceler .....................................................................................241
21.7
ADC Conversion Result .................................................................................245
21.8
ADC Register Description ..............................................................................247
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21.9
Amplifier .........................................................................................................252
21.10
Amplifier Control Registers ............................................................................256
22 Digital to Analog Converter - DAC ..................................................... 259
22.1
Features ........................................................................................................259
22.2
Operation .......................................................................................................260
22.3
Starting a Conversion ....................................................................................260
22.4
DAC Register Description ..............................................................................261
23 debugWIRE On-chip Debug System .................................................. 264
23.1
Features ........................................................................................................264
23.2
Overview ........................................................................................................264
23.3
Physical Interface ..........................................................................................264
23.4
Software Break Points ...................................................................................265
23.5
Limitations of debugWIRE .............................................................................265
23.6
debugWIRE Related Register in I/O Memory ................................................265
24 Boot Loader Support – Read-While-Write Self-Programming ......... 265
24.1
Boot Loader Features ....................................................................................266
24.2
Application and Boot Loader Flash Sections .................................................266
24.3
Read-While-Write and No Read-While-Write Flash Sections ........................266
24.4
Boot Loader Lock Bits ...................................................................................269
24.5
Entering the Boot Loader Program ................................................................270
24.6
Addressing the Flash During Self-Programming ...........................................272
24.7
Self-Programming the Flash ..........................................................................273
25 Memory Programming ......................................................................... 279
25.1
Program And Data Memory Lock Bits ...........................................................279
25.2
Fuse Bits ........................................................................................................281
25.3
PSC Output Behaviour During Reset ............................................................281
25.4
Signature Bytes .............................................................................................283
25.5
Calibration Byte .............................................................................................283
25.6
Parallel Programming Parameters, Pin Mapping, and Commands ...............283
25.7
Serial Programming Pin Mapping ..................................................................285
25.8
Parallel Programming ....................................................................................286
25.9
Serial Downloading ........................................................................................294
26 Electrical Characteristics(1)
26.1
360
................................................................................................ 299
Absolute Maximum Ratings* .........................................................................299
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AT90PWM2/3/2B/3B
26.2
DC Characteristics .........................................................................................300
26.3
External Clock Drive Characteristics .............................................................302
26.4
Maximum Speed vs. VCC .................................................................................................................... 303
26.5
PLL Characteristics .......................................................................................303
26.6
SPI Timing Characteristics ............................................................................304
26.7
ADC Characteristics ......................................................................................306
26.8
Parallel Programming Characteristics ...........................................................307
27 AT90PWM2/2B/3/3B Typical Characteristics ..................................... 310
27.1
Active Supply Current ....................................................................................311
27.2
Idle Supply Current ........................................................................................313
27.3
Power-Down Supply Current .........................................................................316
27.4
Standby Supply Current ................................................................................317
27.5
Pin Pull-up .....................................................................................................318
27.6
Pin Driver Strength ........................................................................................320
27.7
Pin Thresholds and Hysteresis ......................................................................322
27.8
BOD Thresholds and Analog Comparator Offset ..........................................327
27.9
Analog Reference ..........................................................................................329
27.10
Internal Oscillator Speed ...............................................................................330
27.11
Current Consumption of Peripheral Units ......................................................332
27.12
Current Consumption in Reset and Reset Pulse width .................................334
28 Register Summary ............................................................................... 337
29 Instruction Set Summary .................................................................... 341
30 Ordering Information ........................................................................... 344
31 Package Information ............................................................................ 345
31.1
SO24 .............................................................................................................346
31.2
SO32 .............................................................................................................347
31.3
QFN32 ...........................................................................................................348
32 Errata ..................................................................................................... 350
32.1
AT90PWM2&3 Rev. A (Mask Revision) ........................................................350
32.2
AT90PWM2B/3B ...........................................................................................352
33 Datasheet Revision History for AT90PWM2/2B/3/3B ........................ 354
33.1
Changes from 4317A- to 4317B ....................................................................354
33.2
Changes from 4317B- to 4317C ....................................................................354
33.3
Changes from 4317C- to 4317D ....................................................................354
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362
33.4
Changes from 4317D to 4317E .....................................................................354
33.5
Changes from 4317E to 4317F .....................................................................354
33.6
Changes from 4317F to 4317G .....................................................................354
33.7
Changes from 4317G to 4317H .....................................................................354
33.8
Changes from 4317H to 4317I ......................................................................355
AT90PWM2/3/2B/3B
4317I–AVR–01/08
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4317I–AVR–01/08