| 摘要 |
PURPOSE:To eliminate the fluctuation of a signal to a data bus due to the fluctuation of an input signal and to prevent malfunction due to noise by adopting the constitution such that the impedance of a low voltage signal viewed from a photocoupler receiving a high voltage input signal depending on the input signal. CONSTITUTION:A buffer circuit 12a of a waveform shaping circuit 7 is of output inversion type and also a buffer circuit 14a is off inversion type. Moreover, the connecting point between the circuits 7 and 14 is connected to an emitter of a photo transistor 3b via a series circuit comprising an inverting buffer circuit 16 and a shunt resistor 17. Thus, the impedance of a low voltage signal side viewed from the photocoupler 3 is varied in response to the level of the input signal. Thus, a prescribed hysteresis width is given to the threshold value of the input signal voltage. Then malfunction against the fluctuation of the input signal or noise is reduced by using the simple circuit.
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