The STWD100 watchdog timer circuits are self-contained devices which prevent system

failures that are caused by certain types of hardware errors (non-responding peripherals,

bus contention, etc.) or software errors (bad code jump, code stuck in loop, etc.).

The STWD100 watchdog timer has an input, WDI, and an output, WDO (see Figure 2). The

input is used to clear the internal watchdog timer periodically within the specified timeout

period, twd (see Section 3: Watchdog timing). While the system is operating correctly, it

periodically toggles the watchdog input, WDI. If the system fails, the watchdog timer is not

reset, a system alert is generated and the watchdog output, WDO, is asserted (see

Section 3: Watchdog timing).

The STWD100 circuit also has an enable pin, EN (see Figure 2), which can enable or

disable the watchdog functionality. The EN pin is connected to the internal pull-down

resistor. The device is enabled if the EN pin is left floating.