In Window mode operation, the WDT uses two different time-out periods: A closed window
time-out period (TOWDTW) and an open window time-out period
(TOWDT):
- TOWDTW defines a duration from 8 ms to 8s, where the WDT should not be reset. If the WDT is reset during this period, the WDT will issue a system Reset.
- TOWDT, which is also 8 ms to 8s, defines the duration of the open period during which the WDT can (and needs to) be reset. The open period will always follow the closed period, so the total duration of the time-out period is the sum of the closed window and the open window time-out periods.
When enabling the Window mode or going out of the Debug mode, the window is activated
after the first WDR instruction.
The figure below shows a typical timing scheme for the WDT operating in Window mode.
Figure 1. Window Mode Operation
The Window mode is enabled by writing a
non-zero value to the WINDOW bit field in the Control A (WDT.CTRLA) register and
disabled by writing it to 0x0.