Modern vehicles contain many electronic modules that must exchange information: engine, transmission, brakes, body, climate and diagnostics. A shared serial bus replaces large harnesses with a small number of twisted wires and a defined protocol. CAN is the dominant multi-master network; LIN is a slower, lower-cost single-master network used for simple body functions.
CAN basics
CAN uses a differential pair, so the receiver measures the voltage difference between the two wires rather than a voltage relative to ground. Differential signalling resists common-mode noise, which is essential in a vehicle. Nodes arbitrate by message priority, and the bus needs termination at its ends to control reflections.
CAN frame time
Problem. A frame of 100 bits is sent on a 500 kbit/s CAN bus. What is the approximate transmission time?
Solution. t = 100 ÷ 500 000 = 0.0002 s = 0.2 ms. Real frames include additional overhead and possible bus delays.
LIN basics
LIN uses a single wire and a master node that schedules communication with slave nodes. It is used for components where high speed is unnecessary, such as simple switches, motors and sensors. Its simplicity lowers cost but limits bandwidth and fault tolerance compared with CAN.
- A shared bus reduces harness size and weight.
- CAN is differential, multi-master and priority-arbitrated.
- CAN needs termination to control signal reflections.
- LIN is a slower single-master network for simple functions.
- A shorted, open or mis-terminated bus can stop all communication.
- A shared bus replaces a large point-to-point harness.
- CAN uses a differential pair with priority arbitration.
- LIN is a single-master network for simple body functions.
- Physical bus faults can disable several modules at once.
Worked example
A 64-bit message on a 250 kbit/s LIN bus takes about 64 ÷ 250 000 = 0.256 ms to transmit, before scheduling and response delays.