19.3.2.2 Window Mode

In window mode operation, the WDT uses two different timeout periods, a "closed" window timeout period (TOWDTW) and the normal timeout period (TOWDT):

The closed window timeout period defines a duration from 8ms to 8s where the WDT cannot be reset. If the WDT is reset during this period, the WDT will issue a System Reset.

The normal WDT timeout period, which is also 8ms to 8s, defines the duration of the "open" period during which the WDT can (and should) be reset. The open period will always follow the closed period, so the total duration of the timeout period is the sum of the closed window and the open window timeout periods.

When enabling window mode or when going out of debug mode, the first closed period is activated after the first WDR instruction.

Figure 19-3. Window Mode Operation

The window mode is enabled by writing a non-zero value to the WINDOW bit field in the Control A register (WDT.CTRLA), and disabled by writing WINDOW=0x0.