SIGNAL TRANSMISSION SYSTEM IN BUTTON TELEPHONE SET

PURPOSE:To prevent discontinuous signal from flowing to transmission line and to improve the transmission efficiency, by supplying a synchronizing pulse from a master device to each button telephone set via signal line and transmitting control data with the synchronizing pulse through multiplexing in case of transmission between the both. CONSTITUTION:Data lines DL1-DL6 taking two lines as a pair and button telephone sets 2a-2f arranged in parallel via channel lines BL1-BL6 are connected to a master device 1 connected to three main trunks L1-L3. A synchronizing pulse KP generated from the master device 1 is binarized, transmitted to the lines DL1-DL6 and an interface circuit of the master device 1 receives control data from the telephone sets 2a-2f via the lines DL1-DL6. A main control circuit 6 of the master device 1 supply address signal A1-A6 to the telephone sets 2a-2f, the first half of the address is taken as the transmission mode and the latter half is taken as the reception mode, to avoid a discontinuous signal from flowing to the lines DL1-DL6, allowing to improve the transmission efficiency.