| 摘要 |
PURPOSE:To prevent a malfunction due to the indication noise, etc. by using a means which delivers a prescribed signal only when an earth signal having a prescribed width and a prescribed level is supplied to a signal detecting circuit which has an earth signal detection/transmission function of a PCM transmitter. CONSTITUTION:A PCM transmitter 2 receives an earth signal at an M lead from an earth transmission part 4 of an exchange 1 to supply the earth signal to a signal detecting circuit 6 and then transmits the earth signal to a reception part 5 of the exchange 1 from the circuit 6 via an E lead. The circuit 6 detects the earth signal sent through the M lead at a signal detecting part 9 and transmits the earth signal through a delay circuit 12 only when the signal has a prescribed width and a prescribed level. Then the earth signal is sent to the exchange 1 via an OR circuit 10 and an E lead driving circuit 11. While a modulator/demodulator 7 is actuated by the output of the circuit 12 to multiplex the PCM modulated signal through a multiplexing circuit 8 and to deliver it. At the same time, the signal demodulated by the demodulator 7 drives the circuit 11 via the circuit 10. In such a way a malfunction of the exchange 1 as well as the transmitter 2 which is due to the noises induced at a cable 3 is prevented. |
