Reset input circuit for an mcu

Abstract

A semiconductor integrated circuit device includes an MCU, reset circuit and reset input circuit. The reset circuit resets the MCU in response to a reset signal input to a reset terminal. The reset input circuit eliminates an electromagnetic disturbance noise input to the reset terminal, permits only a signal having an effective pulse width to pass therethrough, forms an internal reset signal of a pulse width required for the reset operation according to the signal, and supplies the same to the reset circuit. The reset input circuit includes an analog delay circuit, delay latch group, effective pulse width detection circuit and waveform forming circuit. The analog delay circuit eliminates a noise of a period shorter than the effective pulse width from the reset signal. The delay latch group sequentially samples an output signal of the analog delay circuit. The effective pulse width detection circuit determines whether or not the reset signal has an effective pulse width in response to an output signal of the delay latch group. The waveform forming circuit receives an output signal of the effective pulse width detection circuit, and when it is detected that the reset signal has the effective pulse width, it forms an internal reset signal having a necessary pulse width from the reset signal.