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A recent extension of the Controller Area Network (CAN) protocol allows an efficient mapping of the SAE J1850 data link messages defined by SAE J2178 into the CAN message format. Compatibility between J1850 and CAN at the message header level allows designers to use the same messages and overall communications strategy for both today's medium speed SAE Class B links and tomorrow's high speed Class C bus applications. This paper presents a proposed mapping of SAE J2178 messages into extended format CAN messages and explains the benefits of this approach for vehicle systems developers.

A significant portion of communication in Automotive Networks consists of signals, which are vital to the safety of the vehicle. In addition to requirements resulting from the actual transfer of information an Automotive Communication Protocol has to incorporate properties which ensure operational safety even in presence of errors. Based upon a discrimination into reversible errors and irreversible failures, defect nodes have to be determined and subsequently disconnected from the network. In this paper proper schemes for error detection, report, recovery and confinement are presented.

All networking systems proposed for the automobile are serial in nature. Most of these systems are also multimaster. A requirement common to all of these systems is the ability to separate framing information from data. This is achieved by some form of code violation for the framing bits which violates the code form for standard data bits. In the Manchester and PWM bit representations this code violation can be signalled within a single bit, NRZ requires more bits. The concept of code violation is also used for signalling errors within a message frame. Clock tolerance is dependent on the length of time over which synchronisation between the serial bit stream and receiving circuitry must be maintained. With a given physical bus line bandwidth, the transport capacity of a protocol is a function of the number of time slots needed to transfer a given number of data bytes.

A high speed serial communication link has been developed for interconnecting electronic control units within automobiles. The incorporation of object oriented communication in conjunction with acceptance filtering introduces a new level of message handling efficiency and flexibility. Powerful error handling techniques guarantee safe operation in noisy automotive environments.

The new aerial communication protocol “Controller Area Network” (CAN) efficiently supports distributed realtime control in automotive applications. In order to unload CPUs from high-speed message transfer, dedicated CAN hardware handles messages up to the communication object level. In multiplex wiring message rates are one to two orders of magnitude lower, allowing to implement the upper communication level more cost-effectively in software. This reduces CAN interface hardware to bitwise protocol handling only. It may be incorporated even into low-end microcontrollers without significantly increasing chip size. Thus the same CAN protocol supports the entire range of serial automotive communication, matching implementation costs to requirements at each performance level.