1993-03-01

A Gateway for CAN Specification 2.0 Non-Passive Devices 930005

The Controller Area Network (CAN) protocol, developed by ROBERT BOSCH GmbH, offers a comprehensive solution to managing communication between multiple CPUs. In September 1991, the CAN protocol was revised (CAN Specification 2.0) to add an extended message format that increases the number of permitted message identifiers. The CAN protocol now supports 11- and 29-bit message identifiers allowing standard and extended formats, respectively.CAN Specification 2.0 implements a new message bit, the identifier extension bit (IDE bit) which allows CAN devices to differentiate standard and extended formats. However, most existing CAN implementations are based on the previous CAN protocol specification and will not recognize extended format messages and will respond with an error message. These chips are CAN Specification 2.0 non-passive.Until semiconductor makers develop a variety of chips to implement 29-bit message identifiers, CAN users may require a gateway to interconnect networks using 29-bit message identifiers to existing networks that only use CAN 1.2 11-bit message identifiers. In this context, a gateway is a system that translates messages in one protocol to another and vice versa.A gateway between two networks is typically designed to minimize transmission latency, to minimize lost messages (overruns) and to manage bus error issues. Following a brief description of the CAN message format, general gateway design considerations and performance estimates will be addressed. In addition, a method to send remote frames across the gateway is discussed.

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