There are two ways to configure the watchdog timer window the most flexible is to connect a capacitor to WDT to set the upper boundary of the window watchdog while connecting WDR to either V_DD or GND, thus setting the lower boundary. The other way to configure the timing is by wiring the WDT and WDR pin to either V_DD or GND. By hard-wiring the pins to either V_DD or GND there are four different timings available; these settings are listed in Table 7-2.

To visualize the values named in the table, a timing diagram was prepared. It is used to describe the upper and lower boundary settings. For an application, the important boundaries are the t_boundary,max and t_window,min. Within these values, the watchdog timer must be retriggered to avoid a time-out condition or a boundary violation in the event of a trigger pulse in the lower boundary. The values in the table above are typical and worst-case conditions and are valid over the whole temperature range of –40°C to +85°C.

The shaded areas shown in Figure 7-2 are cases where undefined operation can happen. This device can not detect a violation if a WDI pulse occurs within these three shaded areas. The first shaded area addresses the situation of two consecutive rising edges occur within a quick amount of time. The typical time between rising edges must be more than 500µs. The second and third shaded areas are defined by the min and max variance of the lower boundary (t_boundary) and upper boundary ( t_window). Set the WDI rising edge within the t_boundary,max and t_window,min for correct operation.

Figure 7-2 Upper and Lower Boundary Visualization