1. 1.The WDT is enabled when a non-zero value is written to the Period (PERIOD) bit field in the Control A (WDT.CTRLA) register.
  2. 2.Optional: Write a non-zero value to the Window (WINDOW) bit field in WDT.CTRLA to enable the Window mode operation.

All bits in the Control A register and the Lock (LOCK) bit in the Status (WDT.STATUS) register are write-protected by the Configuration Change Protection (CCP) mechanism.

A fuse (FUSE.WDTCFG) defines the Reset value of the WDT.CTRLA register. If the value of the PERIOD bit field in the FUSE.WDTCFG fuse is different than zero, the WDT is enabled and the LOCK bit in the WDT.STATUS register is set at boot time.