| 摘要 |
PURPOSE:To hold a telephone circuit only with the transmission of a pilot signal in a short time when a slave device is started by providing an FF which works on the detection outputs of the reception and pilot signals to a master device together with a relay which holds a gate circuit and a telephone circuit. CONSTITUTION:When a slave device is set under a calling state, a PL (pilot) signal generator 5 produces the PL signals for several seconds and modulates the carrier wave to transmit it to the master device. At the side of the master device, the carrier wave detected by a reception circuit 9 is applied to a signal detecting circuit 17. The circuit 17 produces the 1st control signal, and a diode 23 is turned on via an inverter IV22. Then the electric charge of a capacitor C24 is discharged and an FF 19 is reset. At the same time, the 2nd control signal of an L level is produced from a PL detecting circuit 18 via an LPF 10. Then a capacitor C26 is discharged, and the FF 19 is set to apply the signal supplied from a terminal Q to an NAND circuit 20. When the PL signals are discontinued, the 2nd control signal is changed to an H level. Then a relay 15 is actuated via the circuit 20 and an inverter IV21 for holding a telephone circuit. In a ring-off mode the relay 15 is cut off with cut-off of the carrier wave and the holding state of the telephone circuit is released. |
