POLLING MEANS FOR COMMUNICATION MULTIPLEXER

Polling means for polling a plurality of devices with receive and transmit channel numbers. The channel numbers are held in a register 504 and a recirculatory FIFO memory 500, and circulated through the register and memory, the channel number in register 504 polling the devices via line adapter 66. The channel number sequence defines the priorities of the channels, receive channels first then transmit channels. On a device response, the channel number is held in register 504 while the other channel numbers recirculate, so that on the next polling, a responding receive channel has top priority while a responding transmit channel has bottom priority. A counter 514 determines the mode of operation (initialize, scan, etc.) and a flip-flop 524 provides the receive/transmit bit of each channel number.