15.2.2 Alarms and Overflow

The RTC has up to four independent hardware alarms that can be configured by the user application. These alarms will be triggered on match with the current clock value, and can be set up to trigger an interrupt, event, or both. The RTC can also be configured to clear the clock value on alarm match, resetting the clock to the original start time.

If the RTC is operated in clock-only mode (i.e. with calendar disabled), the RTC counter value will instead be cleared on overflow once the maximum count value has been reached:

When the RTC is operated with the calendar enabled and run using a nominal 1Hz input clock frequency, a register overflow will occur after 64 years.