PURPOSE:To shorten a return time during run away of a program by inputting an output signal from an unstable oscillating circuit to a non-maskable interruption terminal when no periodic signal is generated from a computer, issuing an interruption command to the computer, and returning the program to an initial state. CONSTITUTION:Since, during run away of a program, a square wave is not generated in the middle from a terminal Out2 and the voltage of a capacitor C7 is not reset, charging is effected by means of the time constants of the capacitor C7 and a resistance R10 until a next square wave pulse is outputted. In this case, since a voltage Vc7 of the capacitor C7 is increased to a value higher than the threshold level of an IC4, an unstable oscillator is operated. At this point of time, a non-maskable interruption terminal NM1 repeats a change between H-L. Thus, the interruption terminal NM1 performs interruption operation, a program under run away is jumped to an initial address, and a CPU is all reset. As a result, correction of an orbit to a normal routine is effected.
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