The watchdog timer contains a counter, IC3, in addition to the usual retriggerable 555 timer, ICl. The counter will so
und an audible alarm if the watchdog timer trys to reset the a certain number of times (8, in the case of the counter). The alarm indicates that despite numerous resets, the system has failed to restart successfully, and the system is truly dead. A second 555 timer, IC2, resets the counter, 1C3, for the duration of the manual system restart. The design could be modified so that system resets the counter.