TDMA communication system having common time slots for system maintenance

Claim 1

A demand assignment time division multiple access communication system having a plurality of terminal stations and a central station, comprising: a pair of first and second time division multiplexed (TDM) transmitting channels for establishing a broadcast channel from said central station to said terminal stations and a pair of first and second TDM receiving channels for establishing individual channels from said terminal stations to said central station on an as needed basis, said first and second TDM receiving channels having inputs coupled together so that when one of the outputs of said receiving channels is coupled to a demultiplexer the other receiving channel is in a hot-standby state; a polling circuit for transmitting a polling signal on a common time slot of the broadcast channel for sequentially polling said terminal stations to permit each of the terminal stations to send an acknowledgement to said central station on a common time slot of the individual channels in response to said polling signal; a fault identification circuit connected to the outputs of said first and second receiving channels for detecting the presence and absence of said acknowledgment at said central station and detecting acknowledgments received through said first and second receiving channels for determining therefrom which one of said first and second receiving channels is faulty; and switch means responsive to the output of said fault identification circuit for selectively coupling the outputs of said first and second receiving channels to said demultiplexer.