| 摘要 |
PURPOSE:To treat a main device only as a power source device and attain a compactness of size and an economy by providing a control circuit for realizing all functions including incoming, and transmitting functions at the electric breakdown in respective telephones. CONSTITUTION:When from a station line TL, an incoming comes, in any case of a conduction or a breakdown of a power source device PE, telephones having station line receiving ring switches S1 closed of telephones T1-TN ring sounders S from station line incoming detecting circuits RS and display incoming. During incoming an extension, a calling information from a calling telephone is transmitted from a circuit CONT to a power source and control line CL through a telephone control signal transmission and receiving circuit DTRT. A telephone to be called receives a control signal on the control line CL on the circuit CONT through the circuit DTRT and turns on an analog switch TS and from an extension incoming sound source TON, an extension signal sound is inputted to an amplifier AMP to ring from a speaker. |
