| 摘要 |
PURPOSE:To simplify the circuit, by providing a voltage detecting circuit corresponding to each key telephone set and a common voltage discriminating circuit to a main device. CONSTITUTION:A gate pulse is transmitted sequentially from output ports R0- R4 of a processor CPU, a terminal voltage VD of control circuits CT1-CT5 is scanned sequentially and given to the voltage discriminating circuit. Further, a selecting pulse is transmitted in synchronizing with the gate pulse from output ports P0-P3, and a reference voltage VS is changed into four kinds with resistors R104-R107. In determining the reference voltage VS in response to the terminal voltage VD when the buttons K1-K3 are turned on, a serial data in 4-bit is obtained at each period of the gate pulse and this is given sequentially to an input port KD of the CPU. Thus, the transmission information of key telephone sets ET1-ET5 is discriminated by reading an output of the voltage discriminating circuit at each gate pulse by the CPU. |
