CAN and LIN bus communication

Need for in-vehicle networks

A modern car has 50 to 100 ECUs (engine, ABS, airbag, body, infotainment). Connecting each pair with separate wires would be heavy, costly and unreliable. A serial data bus lets all ECUs share data over only two or a few wires, reduces weight and makes diagnosis easy.

CAN (Controller Area Network)

Developed by Bosch (ISO 11898).

 ECU1    ECU2    ECU3    ECU4
  |       |       |       |
 ==== CAN_H =====================
 ==== CAN_L =====================
 120 ohm terminator at each end

• Two twisted wires, CAN-H and CAN-L, carry a differential signal (dominant bit: H = 3.5 V, L = 1.5 V; recessive bit: both 2.5 V), so noise is rejected.
• Speed is 125 kbit/s to 1 Mbit/s (high-speed CAN for engine and ABS).
• Message frame: start bit, identifier (11 bits, showing content and priority), control field, data (0 to 8 bytes), CRC, acknowledge and end of frame.
• It is multi-master: any node can send. Arbitration by the identifier is bitwise: the lower number wins, so there is no collision. Error checking is strong.

LIN (Local Interconnect Network)

A cheap, single-wire, master-slave bus for simple, slow devices such as mirrors, window lifts, seat motors and rain sensors.

LIN nodes connect to the CAN network through a gateway.