Nissan X-Trail 32. Manual - part 1497

LAN-28

< SYSTEM DESCRIPTION >

[CAN]

SYSTEM

SYSTEM

CAN COMMUNICATION SYSTEM

CAN COMMUNICATION SYSTEM : System Description

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SYSTEM DIAGRAM

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< SYSTEM DESCRIPTION >

[CAN]

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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 Signal Generation

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CAN communication circuit 

Gateway control unit

Reference

CAN communication circuit 1 

⇔

 CAN communication circuit 2

BCM

LAN-110, "System Description"

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< SYSTEM DESCRIPTION >

[CAN]

SYSTEM

• 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 cir-
cuits drop voltage to generate a potential difference between the
CAN-H line and the CAN-L line.
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.

The Construction of CAN Communication Signal (Message)

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CAN Communication Line

The CAN communication line is a twisted pair wire consisting of
strands of CAN-H 

 and CAN-L 

 and has noise immunity.

NOTE:
The CAN communication system has the characteristics of noise-resistant because this system produces dig-
ital signals by using the potential difference between the CAN-H line and the CAN-L line and has the twisted
pair wire structure.
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 

 occurs. Although the noise changes the voltage, the poten-

tial difference 

 between the CAN-H line and the CAN-L line is

insensitive to noise. Therefore, noise-resistant signals can be
obtained.

CAN Signal Communications

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

No.

Message name

Description

1

Start of frame (1 bit)

Start of message.

2

Arbitration of field (11 bit)

Priorities of message-sending are shown when there is a pos-
sibility that multiple messages are sent at the same time.

3

Control field (6 bit)

Signal quantity in data field is shown.

4

Data field (0-64 bit)

Actual signal is shown.

5

CRC field (16 bit)

• The transmitting control unit calculates sending data in ad-

vance and writes the calculated value in a message.

• The receiving control unit calculates received data and judg-

es that the data reception is normal when the calculated val-
ue is the same as the value written in the sent data. 

6

ACK field (2 bit)

The completion of normal reception is sent to the transmitting 
unit.

7

End of frame (7 bit)

End of message.

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