JPH0563879B

PURPOSE:To prevent the malfunction of an input circuit by inserting a capacitor into the front stage of the initial input circuit during a power source noise generating period, and controlling an input voltage. CONSTITUTION:During the period when a noise is generating on a grounding potential (Vss) supplying line, the input edge of an initial input circuit 3 and the Vss supplying line are linked by a capacitor C, and the input signal level of the initial input circuit 3 is controlled according to the potential fluctuation of the Vss supplying line. Consequently, the input signal level is stabilized without being influenced by the power source noise. Further, since the interval between the signal input edge of the input circuit and the Vss supplying line is linked by the capacitor C only during the power source noise generating period, the switching of the level of the input signal is not delayed by the capacitor C. Thus, the malfunction of the input circuit due to the influence of the power source noise can be prevented.