Can and LIN bus interfaces in automotive electronics

Modern cars have more electronics than you can think of. Almost every important part has tons of sensors on it that has a dedicated computer called ECU (Electrical Control Unit). Usually there are from several up to hundreds of ECU’s on a single car. Especially luxury ones. All modules has to work as on organized unit. So this is where reliable connection interface needed.

Probably you’ve already heard of CAN bus (Controller Area Network). It is common bus interface used in most vehicles where board computer communicates with separate control ECUs taking care of engine, gearbox, climate, security alarm, safety bags. Talking of physical interfacing CAN devices are connected by using twisted pair signal wires that are resistant to noises. Signals usually operate at 5V level. Transmit/receive can be 1Mb/s for 40m cable lengths. Engineers have put lots of thought in to CAN protocol. It was designed to be flexible reliable and robust. There can be more than one master CAN device on same buss. So there can be situation when several masters would start communication. In this case there is a message priority used to determine which one will have right to transmit data. CAN nodes act as independent units and can receive any message and take act if needed. This feature is called ‘multicast’. This allows adding new CAN devices to existing bus without need to reconfigure existing setup.

CAN interface is quite complex interface allowing to have multiple masters what makes it robust and versatile. But due to growing cost of amount of electronics used in cars, manufacturers started looking for cheaper solutions that would complement the CAN bus and be cheaper. So they came up with LIN (Local Interconnect Network) bus. LIN bus interface is simpler standard comparing to CAN. LIN can have up to 16 slave nodes controlled by one master. It is slower and cheaper as nodes are clocked by master (no crystals for each node). LIN can be simply implemented as sub-function in CAN LIN interface USART RISC microcontroller. While CAN transceiver is complex device so it usually comes as separate peripheral or as separate chip. LIN uses single wire for communications with about 40V signal voltage level. It can reach up to19.2kbps communication speed with maximum 40m length of line.

After this short overview it is obvious that LIN interface is low band, less effective bus interface comparing to CAN. In other hand where efficiency isn’t as ‘must’ factor it serves as cheap complement to CAN network.

4 Comments:

  1. I’m no tech savvy but I am aware that my driving skills won’t be as good as when I don’t have electronic gadgets showing on my dashboard. With all cars fitted with automotive electronics, auto maintenance and operation have been enhanced. Of course, with the current hard times in our economy, finding cheaper solution, like substituting CAN bus with LIN bus interface might be practical in terms of cost. However, efficiency is still a contending factor.

    • Yeah, you are no tech savvy, since we would use LIN everywhere, if it would be enough. Yet we can’t allow LIN to forward the messages of the airbag functions. You want the airbag to explode in your face a milisecond later? Look up what happens.
      And your driving skills would be a lot worse. You have servo steering, you have ABS and so on. Wanna live without those? Buy a car before 1970, or earlier, then cry about the price of technology.

  2. I totally agree with you Edmonton.

  3. Great article! Adding to the conversation, providing more information, or expressing a new point of view I suppose is the meaning of commenting. Taking for granted that blog commenting still is a great tactic, it should at least be done the right way.

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