Subscriber circuit provided with a circuit for monitoring a subscriber instrument.

摘要

A subscriber circuit comprising a monitor circuit operating with a power supply voltage supplied to a subscriber instrument and monitoring an operation of the subscriber instrument for generating a monitor signal indicative of the result of monitor, and a power supply voltage abnormality detecting circuit receiving the power supply voltage supplied to the subscriber instrument, for generating an active abnormality detection signal when the power supply voltage deviates from a predetermined voltage range. In response to the active abnormality detection signal, the monitor circuit is inhibited from outputting the monitor signal.