| 摘要 |
PURPOSE:To attain inexpensive input processing with high reliability by providing a cut-off circuit of a signal line at the pre-stage of a potential converting circuit of an input signal and providing a storage circuit holding tentatively an output signal of a potential converting circuit. CONSTITUTION:The cut-off circuit 17 consists of a photocoupler 13 provided with an output transistor (TR)13a and a light emitting diode 13b, of a resistor 14 and a low voltage power supply 10, and the anode of the diode 13b is connected to the power supply 10 and the cathode is connected to an output port 12. Further, a storage circuit 37 consists of a delay circuit 35 and a data latch circuit 36, and the circuit 35 gives an output signal 12a of the output port 12 to the input. In the input processing of an external signal, when the circuit 17 is not operated, the output of the circuit 16 is outputted as it is in addition to the output of the potential converting circuit 16 and the output of the circuit 16 just before the cut-off operation is held by the circuit 37 when the circuit 17 is operated. Thus, the inexpensive input processing with high reliability is attained in such a way that plural computer circuits are used in common by using the same external signal and one signal input processing circuit. |
