Watchdog timer lock-up prevention circuit

Abstract

A lock-up prevention circuit and method are used with a watchdog timer circuit. The lock-up prevention circuit includes a logic circuit for receiving a first signal for generating an enabling signal, and responds to a first predetermined bit stored in a control register for controlling a loading of an enabling signal to the control register. The watchdog timer circuit responds to the loading of the enabling signal to be enabled to respond to a second predetermined bit of the control register for controlling initiation of a timing cycle of the watchdog timer circuit. In response to a clock signal and a second predetermined bit of the control register, the logic circuit clocks the control register to load the enabling signal. The method prevents lock-up in a watchdog timer circuit, and includes the steps of receiving a first signal; generating an enabling signal using the first signal; controlling a control register to load the enabling signal thereto; enabling the watchdog timer circuit to respond to a predetermined bit of the control register; and controlling initiation of a timing cycle of the watchdog timer circuit. The step of receiving the first signal includes the step of receiving either a watchdog mode select signal or a timer enable signal; and the step of generating the enabling signal includes the step of generating the enabling signal from the received at least one of the watchdog mode select signal and the timer enable signal. Input lines IDB12 and IDB15 are ORed to set a TIMER.