CAN COMMUNICATION SYSTEM : 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.
• 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. The system produces digital signals for signal communications, by using the potential difference.

Fig 1: CAN Communication Line Diagram

Courtesy of NISSAN MOTOR CO., U.S.A.

CAN Communication Line

The CAN communication line is a twisted pair wire consisting of strands of CAN-L (1) and CAN-L (2) and has noise immunity.

Fig 2: Identifying CAN Communication Lines

Courtesy of NISSAN MOTOR CO., U.S.A.

Since the CAN-H line and the CAN-L line are always adjacent to each other, the same degree of noise occurs, respectively, when a noise (1) occurs. Although the noise changes the voltage, the potential difference (2) between the CAN-H line and the CAN-L line is insensitive to noise. Therefore, noise-resistant signals can be obtained.

Fig 3: CAN Lines Voltage And Noise Graph

Courtesy of NISSAN MOTOR CO., U.S.A.

CAN Signal Communications

Each control unit of the CAN communication system transmits signals through the CAN communication control circuit included in the control unit and receives only necessary signals from each control unit to perform various kinds of control.

• Example: Transmitted signals

Fig 4: CAN Communication Signal Chart (Transmitted Signal)

Courtesy of NISSAN MOTOR CO., U.S.A.

• Example: Received signals

Fig 5: CAN Communication Signal Chart (Received Signal)

Courtesy of NISSAN MOTOR CO., U.S.A.