| 摘要 |
PURPOSE:To save the exchange circuit in the main unit and to reduce the number of pairs of line, by superimposing audio signal on the data line, separating this audio signal from the data line, and providing the transmission and reception circuit for auxiliary communication with the terminal unit. CONSTITUTION:The main unit 200 is provided witht the circuit superimposing audio signal on the data line and separating audio signal from the data line, and the terminal unit is provided with the reception circuits 210...212 for auxiliary communication. The control signal corresponding to the data signal delivered from the main unit 200 is detected, operating the transmission and reception circuit for auxiliary communication in the terminal unit with the control circuit 216. Thus, the exchanging circuit in the main unit is saved, allowing to reduce the number of pairs of line. |
