Preventing Unintentional Changes

The WDT provides two security mechanisms to avoid unintentional changes to the WDT settings:

The CCP mechanism, employing a timed write procedure for changing the WDT control registers. Refer to Configuration Change Protection for further details.
Locking the configuration by writing a ‘1’ to the Lock (LOCK) bit in the Status (WDT.STATUS) register. When this bit is ‘1’, the Control A (WDT.CTRLA) register cannot be changed. The LOCK bit can only be written to ‘1’ in software, while the device needs to be in Debug mode to be able to write it to ‘0’. Consequently, the WDT cannot be disabled from software.

Note: The WDT configuration is loaded from fuses after Reset. If the PERIOD bit field is set to a non-zero value, the LOCK bit is automatically set in WDT.STATUS.