RUNAWAY RESETTING METHOD OF MICROCOMPUTER AND RESET SIGNAL GENERATING CIRCUIT

摘要

PURPOSE:To detect a runaway of a microcomputer and to generate a reset signal by monitoring the period of an inversion output depending upon the number of operation programs which are interposed in a main program and invert the output of an I/O element. CONSTITUTION:Plural operation programs for inverting the output of the I/O element are interposed in the main program, and the output B7 is inverted alternately at some period. A one-shot pulse generating circuit 11 generates a pulse when the output rises and a one-shot pulse generating circuit 12 generates a pulse when the output falls. Those pulses are supplied as reset inputs to a counter IC9 which counts a clock, so if the microcomputer enters a runaway state, none of operation programs is executed, so that the counter is not reset. When the counter goes up to a specific value, an output Q3 is outputted as the reset signal of the CPU through an OR gate IC12 and an open collector buffer IC13, sychronizing with a chock in an AND gate IC10.