The WDT provides two security mechanisms to avoid unintentional changes to the WDT settings.
The first mechanism is the Configuration Change Protection mechanism, employing a timed-write procedure for changing the WDT control registers.
The second mechanism locks the configuration by writing a ‘1’
to the LOCK bit in the STATUS (WDT.STATUS) register. When this bit is ‘1’,
the Control A (WDT.CTRLA) register cannot be changed. Consequently, the WDT cannot be
disabled from the software.
LOCK in WDT.STATUS can only be written to ‘1’. It can only be
cleared in Debug mode.
If the WDT configuration is loaded from fuses, LOCK is automatically set in WDT.STATUS.