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One of the authors previously presented a new concept for the application of multiplexing technology to the automobile (SAE 880589). That concept proposes dividing the wiring harnesses into separate systems, each of which is multiplexed on an individual basis. To implement multiplexed communications in vehicle systems based on this concept, new ICs have been developed that meet the various requirements for production model use. These ICs are designed for time-division multiplexing using a pulse count scheme and are provided with the following features to assure reliable communications against wiring harness trouble. The data bus uses active high logic and a self-clocking technique is employed for the data bits which are encoded using pulse-width modulation. Marks indicating the master synchronization interval are defined as a “low” level of long duration.

This paper describes a new approach to solving various problems inherent in conventional multiplexed wiring systems. These problems include the fact that the quantity of cut leads, which determines the cost, is not reduced even though the bulk of the wire harness is decreased. Another problem is that the communications system has a very complex configuration. With the approach proposed here it has been found that the number of cut leads can be reduced by housing the communications circuits individually in each piece of electrical equipment. This can be accomplished by grouping together the wiring in which the signals activating electrical load units all flow in the same direction. Custom LSI circuits have been developed to simplify the communications circuits. All of these developments have been combined into practical multiplexed wiring systems for controlling the power Windows, automatic door locks and power seats.