- •Features
- •1. Pin Configurations
- •2. Overview
- •2.1 Block Diagram
- •2.2 Pin Descriptions
- •2.2.3 Port B (PB7:PB0) – XTAL1/XTAL2/TOSC1/TOSC2
- •2.2.4 Port C (PC5:PC0)
- •2.2.5 PC6/RESET
- •2.2.6 Port D (PD7:PD0)
- •2.2.7 RESET
- •2.2.9 AREF
- •2.2.10 ADC7:6 (TQFP and QFN/MLF Package Only)
- •3. Resources
- •4. Data Retention
- •5. About Code Examples
- •6. AVR CPU Core
- •6.1 Overview
- •6.2 Arithmetic Logic Unit – ALU
- •6.3 Status Register
- •6.3.1 SREG – The AVR Status Register
- •6.4 General Purpose Register File
- •6.5 Stack Pointer
- •6.5.1 SPH and SPL – Stack Pointer High and Low Register
- •6.6 Instruction Execution Timing
- •6.7 Reset and Interrupt Handling
- •6.7.1 Interrupt Response Time
- •7. AVR Memories
- •7.1 Overview
- •7.3 SRAM Data Memory
- •7.3.1 Data Memory Access Times
- •7.4 EEPROM Data Memory
- •7.4.1 EEPROM Read/Write Access
- •7.5 I/O Memory
- •7.6 Register Description
- •7.6.1 EEARH and EEARL – The EEPROM Address Register
- •7.6.2 EEDR – The EEPROM Data Register
- •7.6.3 EECR – The EEPROM Control Register
- •7.6.5 Preventing EEPROM Corruption
- •8. System Clock and Clock Options
- •8.1 Clock Systems and their Distribution
- •8.2 Clock Sources
- •8.3 Crystal Oscillator
- •8.5 External RC Oscillator
- •8.6 Calibrated Internal RC Oscillator
- •8.7 External Clock
- •8.8 Timer/Counter Oscillator
- •8.9 Register Description
- •8.9.1 OSCCAL – Oscillator Calibration Register
- •9. Power Management and Sleep Modes
- •9.1 Sleep Modes
- •9.2 Idle Mode
- •9.3 ADC Noise Reduction Mode
- •9.6 Standby Mode
- •9.7 Minimizing Power Consumption
- •9.7.2 Analog Comparator
- •9.7.4 Internal Voltage Reference
- •9.7.5 Watchdog Timer
- •9.7.6 Port Pins
- •9.8 Register Description
- •9.8.1 MCUCR – MCU Control Register
- •10. System Control and Reset
- •10.1 Resetting the AVR
- •10.2 Reset Sources
- •10.2.2 External Reset
- •10.2.4 Watchdog Reset
- •10.3 Internal Voltage Reference
- •10.4 Watchdog Timer
- •10.5 Timed Sequences for Changing the Configuration of the Watchdog Timer
- •10.5.1 Safety Level 1 (WDTON Fuse Unprogrammed)
- •10.5.2 Safety Level 2 (WDTON Fuse Programmed)
- •10.6 Register Description
- •10.6.1 MCUCSR – MCU Control and Status Register
- •10.6.2 WDTCR – Watchdog Timer Control Register
- •11. Interrupts
- •11.1 Interrupt Vectors in ATmega8A
- •11.1.1 Moving Interrupts Between Application and Boot Space
- •11.2 Register Description
- •11.2.1 GICR – General Interrupt Control Register
- •12. I/O Ports
- •12.1 Overview
- •12.2 Ports as General Digital I/O
- •12.2.1 Configuring the Pin
- •12.2.2 Reading the Pin Value
- •12.2.3 Digital Input Enable and Sleep Modes
- •12.2.4 Unconnected pins
- •12.3 Alternate Port Functions
- •12.3.1 SFIOR – Special Function IO Register
- •12.3.2 Alternate Functions of Port B
- •12.3.3 Alternate Functions of Port C
- •12.3.4 Alternate Functions of Port D
- •12.4 Register Description
- •12.4.1 PORTB – The Port B Data Register
- •12.4.2 DDRB – The Port B Data Direction Register
- •12.4.3 PINB – The Port B Input Pins Address
- •12.4.4 PORTC – The Port C Data Register
- •12.4.5 DDRC – The Port C Data Direction Register
- •12.4.6 PINC – The Port C Input Pins Address
- •12.4.7 PORTD – The Port D Data Register
- •12.4.8 DDRD – The Port D Data Direction Register
- •12.4.9 PIND – The Port D Input Pins Address
- •13. External Interrupts
- •13.1 Register Description
- •13.1.1 MCUCR – MCU Control Register
- •13.1.2 GICR – General Interrupt Control Register
- •13.1.3 GIFR – General Interrupt Flag Register
- •14. 8-bit Timer/Counter0
- •14.1 Features
- •14.2 Overview
- •14.2.1 Registers
- •14.2.2 Definitions
- •14.3 Timer/Counter Clock Sources
- •14.4 Counter Unit
- •14.5 Operation
- •14.6 Timer/Counter Timing Diagrams
- •14.7 Register Description
- •14.7.1 TCCR0 – Timer/Counter Control Register
- •14.7.2 TCNT0 – Timer/Counter Register
- •14.7.3 TIMSK – Timer/Counter Interrupt Mask Register
- •14.7.4 TIFR – Timer/Counter Interrupt Flag Register
- •15. Timer/Counter0 and Timer/Counter1 Prescalers
- •15.1 Overview
- •15.2 Internal Clock Source
- •15.3 Prescaler Reset
- •15.4 External Clock Source
- •15.5 Register Description
- •15.5.1 SFIOR – Special Function IO Register
- •16. 16-bit Timer/Counter1
- •16.1 Features
- •16.2 Overview
- •16.2.1 Registers
- •16.2.2 Definitions
- •16.2.3 Compatibility
- •16.3.1 Reusing the Temporary High Byte Register
- •16.4 Timer/Counter Clock Sources
- •16.5 Counter Unit
- •16.6 Input Capture Unit
- •16.6.1 Input Capture Pin Source
- •16.6.2 Noise Canceler
- •16.6.3 Using the Input Capture Unit
- •16.7 Output Compare Units
- •16.7.1 Force Output Compare
- •16.7.2 Compare Match Blocking by TCNT1 Write
- •16.7.3 Using the Output Compare Unit
- •16.8 Compare Match Output Unit
- •16.8.1 Compare Output Mode and Waveform Generation
- •16.9 Modes of Operation
- •16.9.1 Normal Mode
- •16.9.2 Clear Timer on Compare Match (CTC) Mode
- •16.9.3 Fast PWM Mode
- •16.9.4 Phase Correct PWM Mode
- •16.9.5 Phase and Frequency Correct PWM Mode
- •16.10 Timer/Counter Timing Diagrams
- •16.11 Register Description
- •16.11.1 TCCR1A – Timer/Counter 1 Control Register A
- •16.11.2 TCCR1B – Timer/Counter 1 Control Register B
- •16.11.3 TCNT1H and TCNT1L – Timer/Counter 1
- •16.11.4 OCR1AH and OCR1AL– Output Compare Register 1 A
- •16.11.5 OCR1BH and OCR1BL – Output Compare Register 1 B
- •16.11.6 ICR1H and ICR1L – Input Capture Register 1
- •17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation
- •17.1 Features
- •17.2 Overview
- •17.2.1 Registers
- •17.2.2 Definitions
- •17.3 Timer/Counter Clock Sources
- •17.4 Counter Unit
- •17.5 Output Compare Unit
- •17.5.1 Force Output Compare
- •17.5.2 Compare Match Blocking by TCNT2 Write
- •17.5.3 Using the Output Compare Unit
- •17.6 Compare Match Output Unit
- •17.6.1 Compare Output Mode and Waveform Generation
- •17.7 Modes of Operation
- •17.7.1 Normal Mode
- •17.7.2 Clear Timer on Compare Match (CTC) Mode
- •17.7.3 Fast PWM Mode
- •17.7.4 Phase Correct PWM Mode
- •17.8 Timer/Counter Timing Diagrams
- •17.9 Asynchronous Operation of the Timer/Counter
- •17.9.1 Asynchronous Operation of Timer/Counter2
- •17.10 Timer/Counter Prescaler
- •17.11 Register Description
- •17.11.1 TCCR2 – Timer/Counter Control Register
- •17.11.2 TCNT2 – Timer/Counter Register
- •17.11.3 OCR2 – Output Compare Register
- •17.11.4 ASSR – Asynchronous Status Register
- •17.11.5 TIMSK – Timer/Counter Interrupt Mask Register
- •17.11.6 TIFR – Timer/Counter Interrupt Flag Register
- •17.11.7 SFIOR – Special Function IO Register
- •18. Serial Peripheral Interface – SPI
- •18.1 Features
- •18.2 Overview
- •18.3 SS Pin Functionality
- •18.3.1 Slave Mode
- •18.3.2 Master Mode
- •18.4 Data Modes
- •18.5 Register Description
- •18.5.1 SPCR – SPI Control Register
- •18.5.2 SPSR – SPI Status Register
- •18.5.3 SPDR – SPI Data Register
- •19. USART
- •19.1 Features
- •19.2 Overview
- •19.2.1 AVR USART vs. AVR UART – Compatibility
- •19.3 Clock Generation
- •19.3.1 Internal Clock Generation – The Baud Rate Generator
- •19.3.2 Double Speed Operation (U2X)
- •19.3.3 External Clock
- •19.3.4 Synchronous Clock Operation
- •19.4 Frame Formats
- •19.4.1 Parity Bit Calculation
- •19.5 USART Initialization
- •19.6 Data Transmission – The USART Transmitter
- •19.6.1 Sending Frames with 5 to 8 Data Bits
- •19.6.2 Sending Frames with 9 Data Bits
- •19.6.3 Transmitter Flags and Interrupts
- •19.6.4 Parity Generator
- •19.6.5 Disabling the Transmitter
- •19.6.6 Data Reception – The USART Receiver
- •Receiving Frames with 5 to 8 Data Bits
- •19.6.7 Receiving Frames with 9 Data Bits
- •19.6.8 Receive Compete Flag and Interrupt
- •19.6.9 Receiver Error Flags
- •19.6.10 Parity Checker
- •19.6.11 Disabling the Receiver
- •19.7 Asynchronous Data Reception
- •19.7.1 Asynchronous Clock Recovery
- •19.7.2 Asynchronous Data Recovery
- •19.7.3 Asynchronous Operational Range
- •19.8.1 Using MPCM
- •19.9 Accessing UBRRH/UCSRC Registers
- •19.9.1 Write Access
- •19.9.2 Read Access
- •19.10 Register Description
- •19.10.1 UDR– USART I/O Data Register
- •19.10.2 UCSRA – USART Control and Status Register A
- •19.10.3 UCSRB – USART Control and Status Register B
- •19.10.4 UCSRC – USART Control and Status Register C
- •19.10.5 UBRRL and UBRRH – USART Baud Rate Registers
- •19.11 Examples of Baud Rate Setting
- •20. Two-wire Serial Interface
- •20.1 Features
- •20.2 Overview
- •20.2.1 SCL and SDA Pins
- •20.2.2 Bit Rate Generator Unit
- •20.2.3 Bus Interface Unit
- •20.2.4 Address Match Unit
- •20.2.5 Control Unit
- •20.3.1 TWI Terminology
- •20.3.2 Electrical Interconnection
- •20.4 Data Transfer and Frame Format
- •20.4.1 Transferring Bits
- •20.4.2 START and STOP Conditions
- •20.4.3 Address Packet Format
- •20.4.4 Data Packet Format
- •20.4.5 Combining Address and Data Packets into a Transmission
- •20.6 Using the TWI
- •20.6.1 Transmission Modes
- •20.6.2 Master Transmitter Mode
- •20.6.3 Master Receiver Mode
- •20.6.4 Slave Receiver Mode
- •20.6.5 Slave Transmitter Mode
- •20.6.6 Miscellaneous States
- •20.6.7 Combining Several TWI Modes
- •20.8 Register Description
- •20.8.1 TWBR – TWI Bit Rate Register
- •20.8.2 TWCR – TWI Control Register
- •20.8.3 TWI Status Register – TWSR
- •20.8.4 TWDR – TWI Data Register
- •20.8.5 TWAR – TWI (Slave) Address Register
- •21. Analog Comparator
- •21.1 Overview
- •21.2 Analog Comparator Multiplexed Input
- •21.3 Register Description
- •21.3.1 SFIOR – Special Function IO Register
- •21.3.2 ACSR – Analog Comparator Control and Status Register
- •22. Analog-to-Digital Converter
- •22.1 Features
- •22.2 Overview
- •22.3 Starting a Conversion
- •22.4 Prescaling and Conversion Timing
- •22.5 Changing Channel or Reference Selection
- •22.5.1 ADC Input Channels
- •22.5.2 ADC Voltage Reference
- •22.6 ADC Noise Canceler
- •22.6.1 Analog Input Circuitry
- •22.6.2 Analog Noise Canceling Techniques
- •22.6.3 ADC Accuracy Definitions
- •22.7 ADC Conversion Result
- •22.8 Register Description
- •22.8.1 ADMUX – ADC Multiplexer Selection Register – ADMUX
- •22.8.2 ADCSRA – ADC Control and Status Register A
- •22.8.3 ADCL and ADCH – The ADC Data Register
- •23. Boot Loader Support – Read-While-Write Self-Programming
- •23.1 Features
- •23.2 Overview
- •23.3 Application and Boot Loader Flash Sections
- •23.3.1 Application Section
- •23.3.2 BLS – Boot Loader Section
- •23.5 Boot Loader Lock Bits
- •23.6 Entering the Boot Loader Program
- •23.8.1 Performing Page Erase by SPM
- •23.8.2 Filling the Temporary Buffer (Page Loading)
- •23.8.3 Performing a Page Write
- •23.8.4 Using the SPM Interrupt
- •23.8.5 Consideration While Updating BLS
- •23.8.7 Setting the Boot Loader Lock Bits by SPM
- •23.8.8 EEPROM Write Prevents Writing to SPMCR
- •23.8.9 Reading the Fuse and Lock Bits from Software
- •23.8.10 Preventing Flash Corruption
- •23.8.11 Programming Time for Flash when using SPM
- •23.8.12 Simple Assembly Code Example for a Boot Loader
- •23.8.13 Boot Loader Parameters
- •23.9 Register Description
- •23.9.1 Store Program Memory Control Register – SPMCR
- •24. Memory Programming
- •24.1 Program And Data Memory Lock Bits
- •24.2 Fuse Bits
- •24.2.1 Latching of Fuses
- •24.3 Signature Bytes
- •24.4 Calibration Byte
- •24.5 Page Size
- •24.6 Parallel Programming Parameters, Pin Mapping, and Commands
- •24.6.1 Signal Names
- •24.7 Parallel Programming
- •24.7.1 Enter Programming Mode
- •24.7.2 Considerations for Efficient Programming
- •24.7.3 Chip Erase
- •24.7.4 Programming the Flash
- •24.7.5 Programming the EEPROM
- •24.7.6 Reading the Flash
- •24.7.7 Reading the EEPROM
- •24.7.8 Programming the Fuse Low Bits
- •24.7.9 Programming the Fuse High Bits
- •24.7.10 Programming the Lock Bits
- •24.7.11 Reading the Fuse and Lock Bits
- •24.7.12 Reading the Signature Bytes
- •24.7.13 Reading the Calibration Byte
- •24.7.14 Parallel Programming Characteristics
- •24.8 Serial Downloading
- •24.9 Serial Programming Pin Mapping
- •24.9.1 Serial Programming Algorithm
- •24.9.2 Data Polling Flash
- •24.9.3 Data Polling EEPROM
- •24.9.4 SPI Serial Programming Characteristics
- •25. Electrical Characteristics
- •25.1 Absolute Maximum Ratings*
- •25.2 DC Characteristics
- •25.3 Speed Grades
- •25.4 Clock Characteristics
- •25.4.1 External Clock Drive Waveforms
- •25.4.2 External Clock Drive
- •25.5 System and Reset Characteristics
- •25.7 SPI Timing Characteristics
- •25.8 ADC Characteristics
- •26. Typical Characteristics
- •26.1 Active Supply Current
- •26.2 Idle Supply Current
- •26.5 Standby Supply Current
- •26.7 Pin Driver Strength
- •26.8 Pin Thresholds and Hysteresis
- •26.9 Bod Thresholds and Analog Comparator Offset
- •26.10 Internal Oscillator Speed
- •26.11 Current Consumption of Peripheral Units
- •26.12 Current Consumption in Reset and Reset Pulsewidth
- •27. Register Summary
- •28. Instruction Set Summary
- •29. Ordering Information
- •30. Packaging Information
- •31. Errata
- •31.1 ATmega8A, rev. L
- •32. Datasheet Revision History
- •Table of Contents
ATmega8A
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.
22.5.2ADC 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.
22.6ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the following procedure should be used:
1.Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be selected and the ADC conversion complete interrupt must be enabled.
2.Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted.
3.If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt request will be generated when the ADC conversion completes. The CPU will remain in Active mode until a new sleep command is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power consumption.
22.6.1Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 22-6. An analog source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-
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less of whether that channel is selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or less. If such a source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long time the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor.
Signal components higher than the Nyquist frequency (fADC/2) should not be present for either kind of channels, to avoid distortion from unpredictable signal convolution. The user is advised to remove high frequency components with a low-pass filter before applying the signals as inputs to the ADC.
Figure 22-6. Analog Input Circuitry
IIH
ADCn
1..100 kΩ
CS/H= 14 pF
IIL
VCC/2
22.6.2Analog 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 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 22-7.
3.Use the ADC noise canceler function to reduce induced noise from the CPU.
4.If any ADC [3:0] port pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress. However, using the Two-wire Interface (ADC4 and ADC5) will only affect the conversion on ADC4 and ADC5 and not the other ADC channels.
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Figure 22-7. ADC Power Connections
GND |
VCC |
PC5(ADC5/SCL) |
PC4(ADC4/SDA) |
PC3(ADC3) |
PC2(ADC2) |
Analog Ground Plane
PC1 (ADC1)
PC0 (ADC0)
ADC7
GND |
|
|
AREF |
μH |
|
10 |
||
|
||
ADC6 |
100nF |
|
AVCC |
||
|
PB5
22.6.3ADC 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.
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Figure 22-8. 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
Figure 22-9. Gain Error
Output Code |
Gain |
|
|
Error |
|
|
|
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.
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