Motorola Corporation

Haim Kashi

Shmuel Katar

A communications system is described having a central station and a number of remote units arranged for communication over a common communications channel. Each remote unit has a predetermined priority parameter and each remote unit has a processor element (30), a receiver (28), a channel monitoring circuit (26) for sensing when the channel is free and a transmitter (29). The processor element is arranged to identify from received data a priority parameter of a unit currently transmitting. A comparison is performed between the priority parameter of that unit and the predetermined priority parameter, to initiate a timer function (108) in response to the channel monitoring circuit when the channel monitoring circuit indicates that the channel has become free, and to reset the timer function if the channel monitor circuit indicates that the channel has become occupied. The timer function times a selectable period which is dependent on the comparison and the timer function causes activation of the transmitter when the timer function times the selectable period. The invention is applicable to, but not limited to use in supervisory control and acquisition-of-data (SCADA) systems.

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Tel Aviv, Israel

Haim Kashi