Datasheet

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100

Table Of Contents

Features
Pin Configurations
Overview
- Block Diagram
- Disclaimer
- Pin Descriptions
Resources
Data Retention
About Code Examples
Atmel AVR CPU Core
- Introduction
- Architectural Overview
- Arithmetic Logic Unit – ALU
- Status Register
- General Purpose Register File
  - The X-register, Y- register and Z-register
- Stack Pointer
- Instruction Execution Timing
- Reset and Interrupt Handling
  - Interrupt Response Time
AVR ATmega8 Memories
- In-System Reprogrammable Flash Program Memory
- SRAM Data Memory
- Data Memory Access Times
- EEPROM Data Memory
- I/O Memory
System Clock and Clock Options
- Clock Systems and their Distribution
- Clock Sources
- Crystal Oscillator
- Low-frequency Crystal Oscillator
- External RC Oscillator
- Calibrated Internal RC Oscillator
  - Oscillator Calibration Register – OSCCAL
- External Clock
- Timer/Counter Oscillator
Power Management and Sleep Modes
- MCU Control Register – MCUCR
- Idle Mode
- ADC Noise Reduction Mode
- Power-down Mode
- Power-save Mode
- Standby Mode
- Minimizing Power Consumption
System Control and Reset
- Resetting the AVR
- Reset Sources
- Power-on Reset
- External Reset
- Brown-out Detection
- Watchdog Reset
- MCU Control and Status Register – MCUCSR
- Internal Voltage Reference
  - Voltage Reference Enable Signals and Start-up Time
- Watchdog Timer
  - Watchdog Timer Control Register – WDTCR
- Timed Sequences for Changing the Configuration of the Watchdog Timer
  - Safety Level 1 (WDTON Fuse Unprogrammed)
  - Safety Level 2 (WDTON Fuse Programmed)
Interrupts
- Interrupt Vectors in ATmega8
  - Moving Interrupts Between Application and Boot Space
  - General Interrupt Control Register – GICR
I/O Ports
- Introduction
- Ports as General Digital I/O
- Alternate Port Functions
- Register Description for I/O Ports
External Interrupts
- MCU Control Register – MCUCR
- General Interrupt Control Register – GICR
- General Interrupt Flag Register – GIFR
8-bit Timer/Counter0
- Overview
  - Registers
  - Definitions
- Timer/Counter Clock Sources
- Counter Unit
- Operation
- Timer/Counter Timing Diagrams
- 8-bit Timer/Counter Register Description
Timer/Counter0 and Timer/Counter1 Prescalers
- Internal Clock Source
- Prescaler Reset
- External Clock Source
- Special Function IO Register – SFIOR
16-bit Timer/Counter1
- Overview
- Accessing 16-bit Registers
  - Reusing the Temporary High Byte Register
- Timer/Counter Clock Sources
- Counter Unit
- Input Capture Unit
- Output Compare Units
- Compare Match Output Unit
  - Compare Output Mode and Waveform Generation
- Modes of Operation
- Timer/Counter Timing Diagrams
- 16-bit Timer/Counter Register Description
8-bit Timer/Counter2 with PWM and Asynchronous Operation
- Overview
  - Registers
  - Definitions
- Timer/Counter Clock Sources
- Counter Unit
- Output Compare Unit
- Compare Match Output Unit
  - Compare Output Mode and Waveform Generation
- Modes of Operation
- Timer/Counter Timing Diagrams
- 8-bit Timer/Counter Register Description
- Asynchronous Operation of the Timer/Counter
- Timer/Counter Prescaler
  - Special Function IO Register – SFIOR
Serial Peripheral Interface – SPI
- SS Pin Functionality
- Data Modes
USART
- Overview
  - AVR USART vs. AVR UART – Compatibility
- Clock Generation
- Frame Formats
  - Parity Bit Calculation
- USART Initialization
- Data Transmission – The USART Transmitter
- Data Reception – The USART Receiver
- Asynchronous Data Reception
- Multi-processor Communication Mode
  - Using MPCM
- Accessing UBRRH/UCSRC Registers
  - Write Access
  - Read Access
- USART Register Description
- Examples of Baud Rate Setting
Two-wire Serial Interface
- Features
- Two-wire Serial Interface Bus Definition
  - TWI Terminology
  - Electrical Interconnection
- Data Transfer and Frame Format
- Multi-master Bus Systems, Arbitration and Synchronization
- Overview of the TWI Module
- TWI Register Description
- Using the TWI
- Transmission Modes
- Multi-master Systems and Arbitration
Analog Comparator
- Special Function IO Register – SFIOR
- Analog Comparator Control and Status Register – ACSR
- Analog Comparator Multiplexed Input
Analog-to- Digital Converter
- Features
- Starting a Conversion
- Prescaling and Conversion Timing
- Changing Channel or Reference Selection
  - ADC Input Channels
  - ADC Voltage Reference
- ADC Noise Canceler
- ADC Conversion Result
Boot Loader Support – Read- While-Write Self- Programming
- Boot Loader Features
- Application and Boot Loader Flash Sections
  - Application Section
  - BLS – Boot Loader Section
- Read-While-Write and No Read- While-Write Flash Sections
  - RWW – Read-While- Write Section
  - NRWW – No Read- While-Write Section
- Boot Loader Lock Bits
- Entering the Boot Loader Program
  - Store Program Memory Control Register – SPMCR
- Addressing the Flash During Self- Programming
- Self-Programming the Flash
Memory Programming
- Program And Data Memory Lock Bits
- Fuse Bits
  - Latching of Fuses
- Signature Bytes
- Calibration Byte
- Page Size
- Parallel Programming Parameters, Pin Mapping, and Commands
  - Signal Names
- Parallel Programming
- Serial Downloading
- Serial Programming Pin Mapping
Electrical Characteristics – TA = -40°C to 85°C
- Absolute Maximum Ratings*
- DC Characteristics
- External Clock Drive Waveforms
- External Clock Drive
- Two-wire Serial Interface Characteristics
- SPI Timing Characteristics
- ADC Characteristics
Electrical Characteristics – TA = -40°C to 105°C
- Absolute Maximum Ratings*
- DC Characteristics TA = -40°C to 105°C, VCC = 2.7V to 5.5V (unless otherwise noted)
ATmega8 Typical Characteristics – TA = -40°C to 85°C
- Active Supply Current
- Idle Supply Current
- Power-down Supply Current
- Power-save Supply Current
- Standby Supply Current
- Pin Pull-up
- Pin Driver Strength
- Pin Thresholds and Hysteresis
- Bod Thresholds and Analog Comparator Offset
- Internal Oscillator Speed
- Current Consumption of Peripheral Units
- Current Consumption in Reset and Reset Pulsewidth
ATmega8 Typical Characteristics – TA = -40°C to 105°C
- Active Supply Current
- Idle Supply Current
- Power-down Supply Current
- Pin Pull-up
- Pin Driver Strength
- Pin Thresholds and Hysteresis
- Bod Thresholds and Analog Comparator Offset
- Internal Oscillator Speed
- Current Consumption of Peripheral Units
- Current Consumption in Reset and Reset Pulsewidth
Register Summary
Instruction Set Summary
Ordering Information
Packaging Information
- 32A
- 28P3
- 32M1-A
Errata
- ATmega8 Rev. D to I, M
Datasheet Revision History
- Changes from Rev. 2486Z- 02/11 to Rev. 2486AA- 02/2013
- Changes from Rev. 2486Y- 10/10 to Rev. 2486Z- 02/11
- Changes from Rev. 2486X- 06/10 to Rev. 2486Y- 10/10
- Changes from Rev. 2486W- 02/10 to Rev. 2486X- 06/10
- Changes from Rev. 2486V- 05/09 to Rev. 2486W- 02/10
- Changes from Rev. 2486U- 08/08 to Rev. 2486V- 05/09
- Changes from Rev. 2486T- 05/08 to Rev. 2486U- 08/08
- Changes from Rev. 2486S- 08/07 to Rev. 2486T- 05/08
- Changes from Rev. 2486R- 07/07 to Rev. 2486S- 08/07
- Changes from Rev. 2486Q- 10/06 to Rev. 2486R- 07/07
- Changes from Rev. 2486P- 02/06 to Rev. 2486Q- 10/06
- Changes from Rev. 2486O-10/04 to Rev. 2486P- 02/06
- Changes from Rev. 2486N-09/04 to Rev. 2486O-10/04
- Changes from Rev. 2486M-12/03 to Rev. 2486N-09/04
- Changes from Rev. 2486L-10/03 to Rev. 2486M-12/03
- Changes from Rev. 2486K-08/03 to Rev. 2486L-10/03
- Changes from Rev. 2486J-02/03 to Rev. 2486K-08/03
- Changes from Rev. 2486I-12/02 to Rev. 2486J-02/03
- Changes from Rev. 2486H-09/02 to Rev. 2486I-12/02
- Changes from Rev. 2486G-09/02 to Rev. 2486H-09/02
- Changes from Rev. 2486F-07/02 to Rev. 2486G-09/02
- Changes from Rev. 2486E-06/02 to Rev. 2486F-07/02
- Changes from Rev. 2486D-03/02 to Rev. 2486E-06/02
- Changes from Rev. 2486C-03/02 to Rev. 2486D-03/02
- Changes from Rev. 2486B-12/01 to Rev. 2486C-03/02
Table of Contents

2486AA–AVR–02/2013

ATmega8(L)

16-bit

Timer/Counter

Description

Timer/Counter 1

Control Register A –

TCCR1A

• Bit 7:6 – COM1A1:0: Compare Output Mode for channel A

• Bit 5:4 – COM1B1:0: Compare Output Mode for channel B

The COM1A1:0 and COM1B1:0 control the Output Compare Pins (OC1A and OC1B respec-

tively) behavior. If one or both of the COM1A1:0 bits are written to one, the OC1A output

overrides the normal port functionality of the I/O pin it is connected to. If one or both of the

COM1B1:0 bit are written to one, the OC1B output overrides the normal port functionality of the

I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit correspond-

ing to the OC1A or OC1B pin must be set in order to enable the output driver.

When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is depen-

dent of the WGM13:0 bits setting. Table 36 shows the COM1x1:0 bit functionality when the

WGM13:0 bits are set to a normal or a CTC mode (non-PWM).

Table 37 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast PWM

mode.

Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In

this case the Compare Match is ignored, but the set or clear is done at BOTTOM. See “Fast

PWM Mode” on page 88 for more details

Bit 76543210

COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B WGM11 WGM10 TCCR1A

Read/Write R/W R/W R/W R/W W W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 36. Compare Output Mode, Non-PWM

COM1A1/

COM1B1

COM1A0/

COM1B0 Description

0 0 Normal port operation, OC1A/OC1B disconnected.

0 1 Toggle OC1A/OC1B on Compare Match

1 0 Clear OC1A/OC1B on Compare Match (Set output to low level)

1 1 Set OC1A/OC1B on Compare Match (Set output to high level)

Table 37. Compare Output Mode, Fast PWM

(1)

COM1A1/

COM1B1

COM1A0/

COM1B0 Description

0 0 Normal port operation, OC1A/OC1B disconnected.

0 1 WGM13:0 = 15: Toggle OC1A on Compare Match, OC1B

disconnected (normal port operation). For all other WGM1

settings, normal port operation, OC1A/OC1B disconnected.

1 0 Clear OC1A/OC1B on Compare Match, set OC1A/OC1B at

BOTTOM, (non-inverting mode)

1 1 Set OC1A/OC1B on Compare Match, clear OC1A/OC1B at

BOTTOM, (inverting mode)