System Description: Description

• CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN-H line, CAN-L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only.
• The following control units include a gateway function and communicate signals between the different CAN communication circuits.

  CAN communication circuit	Gateway control unit	Reference
  Diagnostic CAN communication (Data link connector) Body CAN communication 1 Chassis CAN communication 1 Chassis CAN communication 2 Multifunction media CAN communication	CAN gateway	System Description
  Diagnostic CAN communication (Data link connector) Body CAN communication 1 Chassis CAN communication 1 Chassis CAN communication 2	Electronic ignition switch control unit	System Description
  Body CAN communication 1 Body CAN communication 2	BCM	--
  Chassis CAN communication 1 Powertrain CAN communication	ECM	ECM
  Body CAN communication 1 Chassis CAN communication 2	Combination meter	System Description

CAN Communication Signal Generation 

• Termination circuits (resistors) are connected across the CAN communication system. When transmitting a CAN communication signal, each control unit passes a current to the CAN-H line and the current returns to the CAN-L line.
• The current flows separately into the termination circuits connected across the CAN communication system and the termination circuits drop voltage to generate a potential difference between the CAN-H line and the CAN-L line.

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  NOTE: A signal with no current passage is called "Recessive" and one with current passage is called "Dominant".
• The system produces digital signals for signal communications, by using the potential difference.

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The Construction of CAN Communication Signal (Message) 

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