WDI is the watchdog timer input that controls the WDO output. The WDI input is triggered by the falling edge of the input signal. For the first pulse, the watchdog acts as a traditional watchdog timer; thus, the first pulse must be issued before t_WDU(min). After the first pulse, to ensure proper functionality of the watchdog timer, always issue the WDI pulse within the window of t_WDL(max) and t_WDU(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 WDO is asserted, the watchdog is disabled and all signals input to WDI are ignored until the WDO reset delay expires. When WDO 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.