PURPOSE: To eliminate the need for a power cable of each peripheral equipment without complicating a signal cable by sending a data and power through a 2-wire cable such as a coaxial cable while using a 3-voltage level signal.

CONSTITUTION: A signal transmitted/received through a cable 24 is an AC signal rectified to drive an input/output equipment to function the system by using a 2-wire coaxial cable and an AC signal split into time slots having a predetermined number between synchronizing pulses. A terminal equipment 10 generates a waveform shown in figure and send through the cables by a master circuit. A change between voltage levels V0 and V is a clock pulse and the change in the voltage levels V0 and '0' is a synchronizing pulse. The location of each time slot in a data block has a predetermined significance as to which key on a keyboard is depressed, for example and is sent to a terminal equipment, where the location is decoded.