228
8331B–AVR–03/12
Atmel AVR XMEGA AU
The Peripheral clock must be more than eight times faster than the RTC32 clock (1.024kHz or
1Hz) when any of the Control or the Count register are accessed (read or written), more than 12
times faster when the Count register is written.
19.2.3
Power Domains
For devices where the RTC32 is located in the V
BAT
power domain, the battery backup feature
enables the RTC32 to also function with no main V
CC
available. A dynamic power switch is used
to automatically switch from the V
CC
domain to the V
BAT
domain if V
CC
falls below the operating
voltage level for the device. When the V
CC
voltage is restored, the power is automatically
switched back to V
CC
.
19.2.4
Interrupts and Events
The RTC32 can generate both interrupts and events. The RTC32 will give a compare interrupt
request and/or event at the next count after the counter value equals the compare register value.
The RTC32 will give an overflow interrupt request and/or event at the next count after the coun-
ter value equals the period register value. The overflow will also reset the counter value to zero.
Due to the asynchronous clock domains, events will be generated only for every third overflow or
compare match if the period register is zero. If the period register is one, events will be gener-
ated only for every second overflow or compare match. When the period register is equal to or
above two, events will trigger at every overflow or compare match, just as the interrupt request.
