Communication systems

Claim 1

A communication system for providing communication between a central control unit and a plurality of controlled units over a single communication channel linking all of the units which includes, at the central control unit, clock generator means operable to generate a periodic signal, timing means for generating a repetitive sequence of time intervals each of which is allocated for communication between the central control unit and a different one of the controlled units only during half-cycles of the periodic signal of one polarity, a control word generator operable to generate a number of control words, control means operable to transmit a selected control word to the designated controlled unit during part only of each time interval allocated to that controlled unit, data receiving means for receiving data from a controlled unit during half-cycles of the periodic signal of the opposite polarity, and display means for displaying such received data; and at each controlled unit, a control word generator operable to generate a number of control words different from those generated in the central control unit, control means responsive to a control word received from the central control unit during the time interval allocated to that controlled unit to transmit an appropriate control word to the central control unit during another part of each said time interval, register means for storing data generated at the controlled unit, and data transmitting means for transmitting said data to the central control unit during half-cycles of the periodic signal of said opposite polarity on receipt of an appropriate control word from the cental control unit.