Window Mode

In the Window mode operation, the WDT uses two different time-out periods:

The closed window time-out period (TO_WDTW) defines a duration, from 8 ms to 8s, where the WDT cannot be reset. If the WDT is reset during this period, the WDT will issue a system Reset.
The open window time-out period (TO_WDT), 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 when 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 (WINDOW) bit field in the Control A (WDT.CTRLA) register. The Window mode is disabled by writing the WINDOW bit field to ‘0x0’.