Multiplex Wiring with Microcomputer Control

A wired multiplex system has been designed specifically for automotive applications. This low-power system exploits the unique nature of the automobile environment in a cost effective way with identical, simple, relatively “dumb” transceiver units which communicate at a low-data rate over a bidirectional bus with a microcomputer master. The transceiver design, proposed for CMOS integration and packaging as a 28 pin part with sixteen input/output channels, emphasizes simplicity yet provides system flexibility. Concentrating system intelligence and authority in a commercially available microcomputer results in an effective control system which provides the opportunity to implement many new features, as well as features now requiring costly hardware, in software at minimal cost. A prototype system, constructed from standard CMOS logic plus a variety of power conditioning hardware and which controls the lighting and auxiliary functions in a station wagon demonstration vehicle, is described.