NOISE MASK CIRCUIT FOR CONTROL DEVICE

PURPOSE:To prevent a noise mask circuit from being reset even if a computing part is reset when there is no need for resetting of the noise mask circuit by a method wherein resetting of the noise mask circuit is preseafed by a logic product of resetting of the computing part and a signal inputted separately therefrom. CONSTITUTION:In a clock 8a used in a noise mask circuit 6, a signal 2a from a fundamental oscillating circuit 2 is selected by a clock switching circuit 8 by means of a switching signal 3b when a microcomputer 1 is operated in a normal state, and a signal 4a from an oscillating circuit 4 is selected thereby by means of the switching signal when the microcomputer 1 is in an abnormal state and control is effected by a CPU backup circuit 3. Thus, resetting of the noise mask circuit 6 can be made controllable through switching of a test signal 10a in such a way that it is practicable or impracticable through synchronism of the microcomputer 1 with a reset signal 5a.