Communication system capable of broadcast messaging and transponder polling

A communication system in which a controller, which provides timing, is coupled over a communication path with two or more transponders, at least two of which transponders have different addresses, said system comprising:

• means for periodically transmitting a broadcast message simultaneously to all of said transponders;
• means for transmitting an acknowledge message, responsive to receipt of said broadcast message, from one of said transponders;
• to said controller responsive to a new input existing at said one of said transponders;
• means for polling said transponders by sequentially transmitting signals corresponding to their individual addresses using a polling technique which incorporates time periods to allow communication between the controller and a selected transponder, wherein said means for polling is activated to poll all of the transponders only if at least said one of the transponders has acknowledge the broadcast message by transmitting an acknowledge message to said controller;
• and
• means for polling high priority transponders first by starting the polling at address zero, said high priority transponders having addresses, which are the lowest of addresses assigned to transponders.