Synchronization

Due to asynchronicity between the main clock domain and the peripheral clock domain, the Control A register (WDT.CTRLA) is synchronized when written. The Synchronization Busy flag (SYNCBUSY) in the STATUS register (WDT.STATUS) indicates if there is an ongoing synchronization.

Writing to WDT.CTRLA while SYNCBUSY=1 is not allowed.

The following registers are synchronized when written:

PERIOD bits in Control A register (WDT.CTRLA)
Window Period bits (WINDOW) in WDT.CTRLA

The WDR instruction will need two to three cycles of the WDT clock in order to be synchronized. Issuing a new WDR instruction while a WDR instruction is being synchronized will be ignored.