IMPROVED METHODS AND APPARATUS FOR DISABLING A WATCHDOG FUNCTION

摘要

An apparatus for disabling a watchdog function of a watchdog circuit when a watchdog input pin of the watchdog circuit fails to receive an externally pulsed signal, which has a first predefined period. The watchdog circuit, while the watchdog function is enabled, generates a watchdog fault condition if the externally pulsed signal is not received at the watchdog input pin by the end of a predefined watchdog timeout period. The apparatus includes a pulse generation circuit for generating a pulsed signal having a second predefined period, the second predefined period being shorter than the watchdog timeout period. Further, the apparatus includes a drive circuit coupled to the pulse generation circuit and the watchdog input pin. The drive circuit provides an internally pulsed signal to the watchdog input pin at a predefined current level, responsive to the pulsed signal from the pulse generation circuit. This predefined current level is sufficient to pull the watchdog input pin to a potential level of the internally pulsed signal when the watchdog input pin does not receive the externally pulsed signal. Moreover, this predefined current level is incapable of pulling the conductor to the potential level of the internally pulsed signal when the watchdog input pin receives the externally pulsed signal.