| 摘要 |
PURPOSE:To attain an accurate loopback test by providing a means turning off a reception circuit when an incoming call comes from a slave station during the loopback test so as to prevent the mixture of an incoming data in the loopback test loop. CONSTITUTION:A transmission circuit 1 and a reception circuit 2 are both turned on when no call comes from a slave station in the time slot subjected to time division (transmission of the communication mode). Then the data signal passes through a master station internal circuit 7, a transmission circuit 1, a transformer section 5 and a reception circuit 2 and sent back to the circuit 7, where the test loop is formed. In said time slot, the loopback test of the data signal by the test loop formed in this way is applied. The reception circuit 2 is turned off with the call from a slave station in the time slot subjected to time division (reception state of communication mode) to stop the incoming data from the slave station and the output to the master station internal circuit 7 is brought into the high impedance state.
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