Rainbow Electronics ATmega163L - Manual (Page 50)

ATmega163(L)
50
• When the asynchronous operation is selected, the 32.768 kHZ oscillator for Timer/Counter2 is always running, except in
power down mode. After a power-up reset or wake-up from power down, 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. The contents of all Timer/Counter2 registers must be
considered lost after a wake-up from power down due to unstable clock signal upon startup.
• Description of wake-up from power save mode when the timer is 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 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 3 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.