ATMEGA163 ATMEL [ATMEL Corporation], ATMEGA163 Datasheet - Page 59

• Manufacturer Part Number: ATMEGA163
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

1142E–AVR–02/03
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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 clock cycles, it executes the interrupt routine, and resumes
execution from the instruction following SLEEP.
During asynchronous operation, the synchronization of the interrupt flags for the
asynchronous timer takes three processor cycles plus one timer cycle. The timer is
therefore advanced by at least one before the processor can read the timer value
causing the setting of the Interrupt Flag. The output compare pin is changed on the
timer clock and is not synchronized to the processor clock.
After waking up from Power-save mode with the asynchronous timer enabled, there
will be a short interval in which TCNT2 will read as the same value as before Power-
save mode was entered. After an edge on the asynchronous clock, TCNT2 will read
correctly (The compare and overflow functions of the Timer are not affected by this
behavior.). Safe procedure to ensure that the correct value is read:
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.
Note that OCR2 and TCCR2 are never modified by hardware, and will always read
correctly.
ATmega163(L)
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