| 摘要 |
PURPOSE:To attain the stable transmission/reception of a selecting signal by forming a high resistance loop at the sending of a PB signal, and when the high resistance loop is detected by an intra-station equipment, stopping the sending of a sound source and supplying the PB signal to a PB signal receiving circuit. CONSTITUTION:When a key 155 is depressed, a PB oscillator 254 oscillates a PB signal at the frequency corresponding to the key and the PB signal is amplified 153 and sent to the intra-station equipment 14 through contacts 152a, 152b. The sent PB signal is inputted to a PB signal receiving circuit 45 through a detecting circuit 141, held in a register of a selector 144 and one sound source is selected out of sound sources in terminals 461-46n by a selector 144 based on the held contents. When the key 155 is depressed, a relay 156 is driven by a common contact to close a contact 156a and a loop is formed between subscriber's lines 12a and 12b through a resistor 159. The voltage difference between the lines 12a, 12b is changed by the high resistance loop and the change is detected by the circuit 141, so that the sending of the sound source from the intra-station equipment is stopped and an AC signal on the lines 12a, 12b is sent to the circuit 145.
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