| 摘要 |
PURPOSE:To prevent a code error from being generated at the time of switching a line, by detecting the phase difference of the output signals of a current in use and a spare U/B conversion circuits, and performing switching by inserting a dummy pulse of one bit in the case of a negative phase. CONSTITUTION:At the time of inputting a line switching instruction C2, when a phase difference detection circuit 25 judges the negative phase of the bipolar signals of the outputs B2 and B3 of the current in use and the spare U/B conversion circuits 22 and 23, a control circuit 27 sends the line switching instruction C2 and the detection signal C1L of negative decision to a dummy bit insertion circuit 27. The insertion circuit 27 generates the dummy pulse of one bit, and inputs it to the U/B conversion circuit 22 or 23. And the control circuit 26, after confirming of the in-phase of both outputs B2 and B3 of the U/B conversion circuits 22 and 23, performs the switching of the line at a reception terminal switch 24.
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