| 摘要 |
PURPOSE:To detect exactly whether the response of an opposite party exists or not, by deriving the variation of a circuit in polarity by a current flowing to a pair of photocouplers in anti-parallel connection between circuits. CONSTITUTION:A pair of photocouplers 21, 22 are connected in anti-parallel between a circuit L1 and L2. In case the circuit L1 is + and the circuit L2 is -, a light emitting diode of the photocoupler 22 emits light, a photodetector conducts, and a signal line 33 goes to an H level. The photocoupler 21 does not emit light, and a signal line 34 goes to an L level. An AND circuit 29 is turned on and an FF30 is reset by a signal line 36 and provides the output to an output line 32. In this case, the polarity of L1 and L2 is inverted, the signal line 33 and the signal line 34 are inverted to an L level and an H level, respectively, a gate 28 is turned on, and the FF30 provides an output to a signal line 31. In case of an instantaneous disconnection, both the gates 28, 29 turn off. In such a way, the response of an opposite party is detected without any error by detecting exactly the inversion in polarity of the circuit. |
