LINE DISCONNECTION DETECTING CIRCUIT

摘要

PURPOSE:To detect the line disconnection by detecting the presence of one-way current flowing without fail in the normal state. CONSTITUTION:A photocoupler 5 for detecting line disconnection is connected in anti-parallel with a photocoupler 3 for receiving data and outputs of both the photocouplers are connected to an exclusive OR circuit 6. Since a current flows in either direction at all times in the differential digital transmission system, the level of any of the photocouplers 3 and 5 is logical 1 when no failure exists in the line and the output of the exclusive OR circuit 6 is logical 1 without fail. If the line 2 is opened or a power supply of a tansmission line 1 is disconnected, the output of the photocouplers 3, 5 goes both to 0 and the output of the exclusive OR circuit 6 goes to 0, thereby detecting line disconnection.