ELECTRONIC BUTTON TELEPHONE SET

PURPOSE:To avoid disable calling even at power failure, by transmitting push button dial information to a main device via a data line during power application and transmitting a selection signal to a channel directly during power failure. CONSTITUTION:When a push button dial PAD is depressed at normal state, two sets of contacts corresponded are closed, a data transmission/reception circuit SDTR detects depressed number and transmits the information to data lines DA, DB, then a main device transmits a corresponding multi-frequency signal to a main trunk. At power failure, a button telephone set is connected to the main trunk directly with a relay of the main device. When a push button dial PAD is depressed at this state, a signal transmission circuit ASC is operative and the corresponding multi-frequency signal is transmitted to channels LA, LB. Thus, even at power failure, main trunk transmission is made from a specific button telephone set provided with a signal transmission circuit.