| 摘要 |
PROBLEM TO BE SOLVED: To provide a communication circuit capable of protecting from wrong connection, long wiring, and high-speed transfer. SOLUTION: On a master station side, a first constant current source capable of varying a current value, a receiving photocoupler and a constant voltage diode are serially connected, a communication line is distributed from between the first constant current source and the receiving photocoupler to a slave station side via an impedance element having high frequency interrupting characteristic, a diode is connected in parallel to the first constant current source in a reverse bias direction, and a diode is connected in parallel to a serial part of the constant voltage diode and the receiving photocoupler in the reverse bias direction. Each slave station comprises a circuit detecting the presence of a negative voltage between a communication terminal and a communication shared line, and a circuit serially connecting a second constant current source and a slave station receiving photocoupler to a reference line via a relay which is not electrified in a case that the negative voltage is detected and an impedance element which interrupts a high frequency is connected in parallel to the secondary side of the slave station transmitting photocoupler arranged so as to short-circuit the relay output and the reference line. COPYRIGHT: (C)2006,JPO&NCIPI |
