35.4.4 Watchdog Timer Window

The Watchdog Timer has an optional Windowed mode that enables the WINDIS = 0 bit (WDTCON[0]). In the Windowed mode (WINDIS= 0), the WDT must be cleared only within the allowed window interval of the Watchdog time-out period, as shown in Figure 35-2. There is also an option to select a WDT window where the WDT should be cleared based on the Watchdog Window Select bits (WINSIZE[1:0]) in the WDTCON register. The bit settings are as follows:

• 11 = WDT Allowed Window is 25% of the WDT period.
• 10 = WDT Allowed Window is 37.5% of the WDT period.
• 01 = WDT Allowed Window is 50% of the WDT period.
• 00 = WDT Allowed Window is 75% of the WDT period.

If the Watchdog Timer is cleared before the allowed window, a system Reset is generated immediately.

The Windowed mode is useful for resetting the device during unexpectedly quick or slow execution of a critical portion of the code.

T_DW = T_WTO - T_AW

T_AW = (N1) x (N2) x (T_CLK) x (WINSIZE[1:0])

Where:

N1 = 32

N2 = Postscaler divider ratio (see Table 35-2)

T_CLK = WDT clock source