| 摘要 |
PURPOSE:To realize a call during a service interruption, by utilizing the supplying cable of the control signal and the power source of a key telephone set for the by- pass purpose during the service interruption, providing a manual changeover switch to the telephone set and thus connecting the trunk line to the by-pass during the service interruption with operation of the switch. CONSTITUTION:A mannual operation switch 14 is connected between a channel switch matrix 8 of a main device 100 connected via a call line 20 and a talking circuit 15 of a key telephone set 200. With operation of the switch 14, the trunk line is connected to the circuit 15 via the line 20 and the matrix 8. Then both the transmission of the control signal and the supply of electric power are carried out with use of a pair of lines 21 between the device 100 and the telephone 200. Thus the switch 14 is operated to perform the changeover when the power supply + is borken due to a service interruption. As a result, the voltage having an opposite polarity to the power source + is supplied to the circuit 15 via a route of diodes 4 and 7, the line 21, a diode 7 and the switch 14 respectively. |
