Abstract

A deman assignment TDMA communication system includes first and second time division multiplexed (TDM) transmitting channels for establishing a broadcast channel from the central station to the terminal stations and a pair of first and second TDM receiving channels for establishing channels from the terminal stations to the central station on an as needed basis. A polling circuit transmits a polling signal on a common time slot of the broadcast channel for polling the terminal stations and periodically shifting the polled station to the next to permit each of the terminal stations to send an acknowledgment to the central station on a common time slot of the established channels. A fault identification circuit is provided for detecting the presence and absence of the acknowledgment at the central station and determining therefrom the location of a fault. Switches are responsive to the output of the fault identification circuit for selectively coupling the outputs of the transmitting channels to the broadcast channel and selectively coupling the outputs of the receiving channels to a demultiplexer.