| 摘要 |
PURPOSE:To attain free use of an extension line by other slave set by providing a control circuit detecting the hook-off of a handset of a standard telephone set installed remotely so as to eliminate surely the occupancy of the extension line because of the hook-off of the standard telephone set. CONSTITUTION:The button telephone set is constituted by connecting it to a main device by a pair of connecting line and connecting a standard telephone set connected normally to an extension by means of a selecting circuit in the main device. A control section CNT comprising a microprocessor, a memory, and an input/output circuit is located at the center of the main device of the telephone set, and signal circuits SRK1-SRK4 of interfaces IF1-IF5 connected to the button telephone set and a control circuit CTC are connected at the surrounding. Further, relays FA-FE, interfaces IF1-IF5 having contacts la-le, a main trunk circuit SLC, an extension line INC, and a door phone circuit DPE are connected, a control data from a control section CNT is decoded by a decoder DEC01 to control the interfaces IF1-IF4, allowing to make the occupancy of the extension line effective. |
