Abstract: A communications multiplexer module (CMM) assembles serial by bit data from a plurality of input ports into parallel-by-bit characters before transmitting them to a host computer. On output operations the host computer supplies characters parallel-by-bit to the communications multiplexer module and the module disassembles the characters into serial by bit data for distribution to output ports. The CMM includes a main memory for storing control words, there being one control word for each port. The main memory is scanned in a fixed sequence so that the control words are read out of the main memory in the same sequence that the input and output multiplexers for the ports are scanned. This permits most of the logic circuits of the CMM to be time shared between all ports the logic circuits being controlled in turn by each control word. Any port may be an input or an output port, the designation being determined by bits of the control word associated with the port.