| 摘要 |
PROBLEM TO BE SOLVED: To fix the output level of a receiving circuit at a 'HIGH' level even in case of power supply failure on a transmission side and to prevent the output from entering an ambiguous state or oscillation state by providing a means which disconnects a transmitting circuit and a balanced transmission line from each other. SOLUTION: The auxiliary output terminals 4 and 5 of the transmitting circuit 1 and a transmission line 6 are connected by using an n-type MOS transistor switch 14. If a transmission-side power supply failure occurs to this circuit, the n-type MOS transistor switch 14 enters a high impedance state between its input and output terminals, so a situation that the transmission line 6 appears opened is reached, and the voltage between the differential input terminals 10 and 11 of the receiving circuit 12 has a voltage obtained by dividing Vcc with terminating resistors 7 to 9. The resistance values are so selected that the voltage is larger than the affecting voltage of the receiving circuit 12 and then if a transmission-side power supply failure occurs, the output level of the output terminal 13 of the receiving circuit 12 can be fixed at 'HIGH'.
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