WDI is the watchdog timer input that controls the WDO output. The WDI input is triggered by the falling edge of the input signal. To ensure proper functionality of the watchdog timer, always issue the WDI pulse before t_WD(min). If the pulse is issued in this region, then WDO remains unasserted. Otherwise, the device asserts WDO, putting the WDO pin into a low-impedance state.

The watchdog input (WDI) is a digital pin. To ensure there is no increase in I_DD, drive the WDI pin to either VDD or GND at all times. Putting the pin to an intermediate voltage can cause an increase in supply current (I_DD) because of the architecture of the digital logic gates. When RESET is asserted, the watchdog is disabled and all signals input to WDI are ignored. When RESET is no longer asserted, the device resumes normal operation and no longer ignores the signal on WDI. If the watchdog is disabled, drive the WDI pin to either VDD or GND.
Figure 7-2 shows the valid region for a WDI pulse to be issued to prevent WDO from being triggered and pulled low.

Figure 7-2 Watchdog Timing Diagram