10.4 Watchdog Window

The Windowed Watchdog Timer has an optional Windowed mode that is controlled by the WDTCWS bits in Configuration Word 3 and WINDOW bits in the WDTCON1 register. In the Windowed mode, the CLRWDT instruction must occur within the allowed window of the WDT period. Any CLRWDT instruction that occurs outside of this window will trigger a window violation and will cause a WWDT Reset, similar to a WWDT time-out. See Figure 10-2 for an example.

The window size is controlled by the Watchdog Timer Window Select (WINDOW) bits in WDTCON1, if WDTCWS bits in Configuration Word 3 are set to 111.

The WDTTMR bits in the WDTTMR register are used to determine whether the window is open, as defined by the WINDOW bits.

In the event of a window violation, a Reset will be generated and the WDTWV bit of the PCON0 register will be cleared. This bit is set by a POR or can be set in firmware.