| 摘要 |
PURPOSE:To prevent a collision between a test signal and a signal during transmission at the start of test by providing a means detecting a carrier to inhibit the transmission of a test signal and preventing the transmission of the test signal from being started when the transmission line is in use. CONSTITUTION:A line receiver 1 connected to a network and a carrier detection circuit 2 always supervises the operating state of the network. When a carrier exists on the network even when a start signal S1 from a switch circuit 4 or a stop signal S2 is inputted, a test signal generation circuit 5 is stopped. When a detection output by the circuit 2 does not exists, however, the circuit 5 is started via a gate circuit 3, a line driver 6 is brought into the transmission mode, the test signal is sent and the reception of the receiver 1 is inhibited. The carrier is detected by the circuit 2 in this way, and when the transmission line is in use, the transmission of the test signal is not started thereby preventing the collision between the test signal and the signal during transmission at the start of test.
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