April 2021

BY Damien Coleman, Product Manager/ EBI Specialist at Snap-on L ocal Interconnection (LIN) Bus is a low-speed, cost-effective alternative to CAN bus. LIN gets its name from being a ‘local’ sub-system. Data transfer speeds can be up to 20,000 bits per second. It is designed for sensor/actuator level. 24 AFTERMARKET APRIL 2021 TECHNICAL/SNAP-ON www.aftermarketonline.net One of Snap-on’s technical experts explains how LIN Bus works Data transfer speed The waveform seen in Fig.1 shows a typical LIN trace, the time for the transmission of 1 bit is 0.11ms, this equates to a data transfer speed of 9,480 bits per second. Network topology The bus can contain up to 16 modules or subscribers, one master (module) and fifteen slaves (intelligent components). LIN is a linear bus topology, with communication over a single wire. Fig.2 shows a basic network topology. The central electronics module (CEM) is the master module and communicates with the gateway module using controller area network (CAN) bus. Each of the LIN components is a sensor or actuator, with the ability to transmit and receive a LIN message. The master module is responsible for controlling the timing of the message data packet. Fig.3 shows a CEM and front wiper motor. The purple wire is the LIN bus wire and is used to control the speed and intermittent delay for the wipers. AUTOMOTIVE COMMUNICATION NETWORKS: PART 1: LIN BUS Fig 1 Message structure The waveform seen in Fig.4 shows a LIN message with the defined message structure. The ‘sync break’ is used to signal the beginning of the message. The delimiter indicates the completion of the sync break and serves to show the LIN wire is not shorted to ground. The sync field is to ensure the timing of the message is set prior to the data field being transmitted. This is not required for CAN bus, as each module on the network has its own time clock for message timing. The message is transmitted by manipulating the voltage on the LIN data circuit. See Fig.5. 1 equals recessive bit. 2 equals dominant bit. Fig 2 Fig 3 Fig 4 Fig 5