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In applying a LAN to automotive electronics systems, an optimal protocol has been adopted for each system so far, such as body electronics system, entertainment system, service system and power train system. As low cost communication protocol “BEAN” (Body Electronics Area Network; SAE paper 970297) adopted to wider range of functions on vehicle, ECU's numbers are increased which have BEAN communication and that is branched to plural communication networks. We have succeeded in rationalization of those network systems with the gateway function on a delegated ECU for each LAN system on vehicle. And this system also realized the connection to after market products by data exchange through the gateway function, while securing vehicle fail-safe.

This paper describes the multiplex communication protocol, BEAN (Body Electronics Area Network), developed for body control system on passenger cars which in recent years has increased the scope of multiplex communication. BEAN is based on a protocol developed in 1992 (SAE920231) but expands upon the performance in areas, such as the suitability of the ID system for increase of ECUs, the variable data length enabling the transmission of diagnostic data, and the transmission rate, while keeping the cost and radiation noise level low. The software size of BEAN is compact enough to be implemented by general purpose 8bit MCUs which have recently seen improvements in performance. The BEAN communication devices are available corresponding to the scale of the application and configuration of the ECU taking into account the software capability. This protocol was evaluated using simulation with the body control system on luxury passenger cars.