In Normal mode operation, a single time-out period is set for the WDT. If the
WDT is not reset from software using the WDR instruction during the
defined time-out period, the WDT will issue a system Reset.
A new WDT time-out period will start each time the WDT resets the
WDR.
There are 11 possible WDT time-out periods (TOWDT), selectable from 8 ms to 8s by writing to the Period (PERIOD) bit field in the Control A (WDT.CTRLA) register.
The figure below shows a typical timing scheme for the WDT operating in Normal mode.
Figure 1. Normal Mode Operation
Normal mode is enabled as long as the Window (WINDOW) bit field in the WDT.CTRLA register is 0x0.