Abstract: A communication system for communicating between a central control unit and a plurality of controlled units, all interconnected by a single communication channel, wherein communication is time multiplexed with control words being transmitted in each direction during each time interval allocated to each separate controlled unit. The control words are transmitted during half-cycles of a periodic clock signal of one polarity, while data from the controlled units may be transmitted to the central control unit only during half-cycles of the periodic signal of the opposite polarity.