Communication multiplexer module

TL;DR: In this article, 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.

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. The control word also contains bits designating whether the port is to function in association with a synchronous or an asynchronous line adapter connected to the port, the number of bits in each character, and other information necessary for assembling input or disassembling output data and controlling the transfers between the ports and the computer. The control word has a character assembly/disassembly area where characters are assembled a bit at a time during input operations, and are disassembled a bit at a time during output operations. Characters are transferred between the assembly/disassembly area and the host computer through a storage area in the control word. Character detect tables are provided for sensing each input character after assembly, or each output character before disassembly and, if it is a control character, converting it into a standard control word code used within the CMM. The outputs from the character detect table control certain hard wired functions and, in addition, may address a second memory containing a plurality of control interpretation tables. In the character interpretation tables, each bit represents a specific function to be performed within the CMM. The control word associated with each port contains bits designating which character detect table and which control interpretation table is to be utilized with the port. This enables the CMM to recognize and respond to control functions in a uniform manner, even though the functions themselves may be represented by characters in different codes. Programmable procedure counters are provided for detecting various conditions such as a failure to detect an end character. Full error checking procedures are included in the CMM.