ATmega8A Atmel Corporation, ATmega8A Datasheet - Page 119

• Manufacturer Part Number: ATmega8A
• Manufacturer: Atmel Corporation

Specifications of ATmega8A

• Flash (kbytes): 8 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 2
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 1
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Pwm Channels: 3
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

8159D–AVR–02/11
• If Timer/Counter2 is used to wake the device up from Power-save mode, precautions must be
1. Write a value to TCCR2, TCNT2, or OCR2.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or Extended Standby mode.
• When the asynchronous operation is selected, the 32.768kHz Oscillator for Timer/Counter2
• Description of wake up from Power-save or Extended Standby mode when the timer is
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an incorrect
1. Write any value to either of the registers OCR2 or TCCR2.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
• During asynchronous operation, the synchronization of the Interrupt Flags for the
the Output Compare function is disabled during writing to OCR2 or TCNT2. If the write cycle
is not finished, and the MCU enters sleep mode before the OCR2UB bit returns to zero, the
device will never receive a Compare Match interrupt, and the MCU will not wake up.
taken if the user wants to re-enter one of these modes: The interrupt logic needs one TOSC1
cycle to be reset. If the time between wake-up and re-entering sleep mode is less than one
TOSC1 cycle, the interrupt will not occur, and the device will fail to wake up. If the user is in
doubt whether the time before re-entering Power-save or Extended Standby mode is
sufficient, the following algorithm can be used to ensure that one TOSC1 cycle has elapsed:
is always running, except in Power-down and Standby modes. After a Power-up Reset or
Wake-up from Power-down or Standby mode, the user should be aware of the fact that this
Oscillator might take as long as one second to stabilize. The user is advised to wait for at
least one second before using Timer/Counter2 after Power-up or Wake-up from Power-down
or Standby mode. The contents of all Timer/Counter2 Registers must be considered lost after
a wake-up from Power-down or Standby mode due to unstable clock signal upon start-up, no
matter whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
cycles, it executes the interrupt routine, and resumes execution from the instruction following
SLEEP.
result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2 must be
done through a register synchronized to the internal I/O clock domain. Synchronization takes
place for every rising TOSC1 edge. When waking up from Power-save mode, and the I/O
clock (clk
sleep) until the next rising TOSC1 edge. The phase of the TOSC clock after waking up from
Power-save mode is essentially unpredictable, as it depends on the wake-up time. The
recommended procedure for reading TCNT2 is thus as follows:
asynchronous timer takes three processor cycles plus one timer cycle. The timer is therefore
advanced by at least one before the processor can read the timer value causing the setting of
the Interrupt Flag. The Output Compare Pin is changed on the timer clock and is not
synchronized to the processor clock.
I/O
) again becomes active, TCNT2 will read as the previous value (before entering
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