| 摘要 |
PURPOSE:To prevent noise from being generated at a buzzer driving signal output at the application of power supply, by adding a switching circuit of a synchronism reading clock signal to an input signal processing circuit having a chattering preventing function. CONSTITUTION:The 1st frequency-division circuit output F1 and the 2nd frequency-division circuit output F21 are selected with an initializing signal IR formed at the application of power supply and switched to form a synchronism reading clock signal F22 for a chattering prevention circuit. It is not a problem when an input signal terminal IN is not active. When the terminal IN is active (L level), no output waveform is generated at a buzzer driving circuit 8 and a buzzer driving signal output terminal 13, because the reading is finished at the initial time point of the signal F22 and its differentiation pulse signal BC and the output F1 pass through an AND circuit 7. |
