As more automobile designs utilizing serial multiplex network protocols such as SAE J1850 and CAN go into production, automotive system designers must now seek ways to lower the cost of the multiplex communication devices used in order to allow the number of components communicating across the multiplex bus to expand.
The first generation of J1850 multiplex devices were designed as the different versions of the protocol were being developed and as a result seem better suited for use as development tools rather than for use in cost-sensitive production applications. As the next generation of multiplex devices is being defined, a hard look needs to be taken at the actual system requirements for communication on a multiplex bus. The amount of silicon needed to perform multiplex communication can be reduced, along with the cost, by implementing in hardware only the features absolutely necessary for communication by a majority of applications, leaving any additional features to be performed in software on an as-needed basis.
This paper will review the partitioning options and major functions of automotive multiplex devices and outline some of the cost/performance trade-offs that must be considered in order to optimize a device for high-volume production systems. While this paper focuses primarily on J1850 devices and features, the basic ideas can be applied to the development of devices used for other automotive multiplex protocols such as CAN, VAN or A-Bus.