| 摘要 |
PURPOSE:To make a special interface circuit unnecessary and to make the provision of transmission processing function of trunk polarity detection signals to a common controller unnecessary by inserting the trunk polarity detection signal to the least significant digit of a PCM code when a reception signal is encoded to the PCM code by a codec of an office trunk circuit. CONSTITUTION:The trunk polarity detection signal is inputted to the input terminal of a signaling circuit 29 of an office trunk circuit 4, and the trunk polarity detection signal is inserted to the least significant digit of the PCM code when the reception signal is converted to the PCM code by an A/D converter 12. The PCM code to which the trunk polarity detection signal is inserted is transmitted to a line circuit 4 of the other party of service through a time switch 2. Meanwhile, a D/A converter 13 of a line circuit 7 to which the PCM code is inputted from the time switch 2 decodes the PCM code to audio signals, and simultaneously, the converter 13 extracts the trunk polarity detection signal inserted to the least significant digit of the PCM code by the operation of a signaling circuit 30 of the line circuit 7 and outputs this signal to the output terminal of the signaling circuit 30. |
