LIN protocol: cheap CAN alternative for in-vehicle communication

Here we briefly describe LIN protocol, its applications, benefits and drawbacks.

LIN architecture and applications

Local interconnect network (LIN) bus is essentially a sub-bus system rooted in a serial communications protocol. LIN includes one master node and up to 16 slave nodes. It has lower reliability, speed and performance compared to CAN, but due to significantly lower cost could be a favorable option. Mainly, in applications where speed and fault tolerance are not crucial parameters.

LIN could be used within vehicles for interior lights, air conditioning, windows control, seat heaters, door locks, etc.

LIN is often acting as a sort of supplement to the CAN bus, and commonly utilized in simple switching applications. Nowadays LIN became a standard for in-vehicle communication but also currently employed in automation and some “in-house” devices. Having 6-bit identifiers and data forwarding speed peaking at 20 kbit/s, it could be treated as the lowest-level within the in-vehicle networking hierarchy.

Various relatively simple sensors could be connected via LIN in order to form simple networks. Afterwards they could be connected with some other networks in the vehicle by means of CAN.

LIN: introduction to the structure and workflow

LIN employs a single master / multiple slave model, where only the master is able to initiate communication. LIN frame includes the header part and response part. The header part is sent by the master to start communication with a slave, and if the master requests data from the slave, the slave sends back the response part.

A simplified LIN driver schematic is shown in the figure above. The transceiver facilitates communication between the bus and the rest of the network. The LIN transceiver converts the bit logic from the microcontroller into higher voltage levels as transmission along the bus, and vice versa. The TXD is connected to the microcontroller, where the message is sent and then broadcast on the LIN bus.

The RXD monitors the bus and converts the messages on the LIN bus to voltage levels the microcontroller can interpret. An example of a LIN bus message with 220 pf at 20 kbps is shown in the figure above. It also demonstrates the effect of having the nominal amount of capacitance, and how the effect of having too much capacitance looks like.

LIN is a simple and low-cost bus, proven to be effective in various applications where speed and great robustness are not among crucial parameters. LIN bus now employed for in-vehicle communication applications, as well as in automation and home appliances.

Original publication: https://talks.navixy.com/reviews/lin-protocol-for-in-vehicle-communication