CAN Bus

CAN bus: High level introduction

Short for Controller Area Network, a standard designed to allow electronic control units (ECUs) to communicate without a centralised computer. It is a message based protocol.

• Mandatory in EU since 2001, us 2008
• Runs on 2 wires. CANH (high) CANL (low)
• Uses differential signaling (some exceptions)
  • When a signal comes in, CAN raises the voltage on one line and drops the other line an equal amount
  • Differential sinaling is used in environments that must be fault tolerant to noise
  • When a bit is transmitted then signal is simultaneously broadcast to both high and low, the sensors check that they match and if they don’t the packet is discarded as noise
• The two twisted pair wires require the bus to be terminated on each end. There is a 120-ohm resistor across both wires on the termination ends
• Most vehicles come with the ODB-II connector, aka Diagnostic Link Connector (dlc). It communitcates with the vehicle internal netowrk

(source: https://components101.com/connectors/obd2)