Controller Area Network (CAN) - Design and Function: Overview Volvo V50 I рестайлинг

GENERAL INFORMATION

CAN (Controller Area Network) is a standardized system for multiplex communication. Multiplex communication means that you can transmit messages between one or more control modules on the same wires without communication between the various control modules disrupting one another. Volvo has produced a new standard for multiplex communication, known as VOLCANO. VOLCANO is a further development of CAN and works with real-time processing, as well as prioritization. The description of prioritization is based on VOLCANO but named CAN.

The standard for Control area network (CAN) specifies

1. That two cables should be used (CAN H and CAN L)
2. Which voltage levels should be used
3. What a message should look like
4. How transfer errors should be handled.

Scheme 1495

The wires CAN H and CAN L must not be confused with HS CAN and LS CAN, which indicate the speed of the CAN network. CAN H and CAN L are the names for the wires used to distribute the signals in the multiplex communications network.

Communication takes place using two wires. These two wires are twisted together and are made of a copper material.

The voltage levels for communication take place using differential voltage levels. Two twisted-pair wires and differential voltage levels are used because this makes the network less susceptible to interference.

The same message is transferred simultaneously by both cables, but different voltage levels are used.

1. Binary 1 = 2.5 V on both CAN H and CAN L.
2. Binary 0 = 4 V on CAN H and 1 V on CAN L.

When measured between CAN L and earth, the average voltage level is approx. 2.3 V.

When measuring between CAN H and ground, the average voltage level is approx. 2.8 V. When measuring between the two CAN wires, with normal traffic on the network, the average voltage level is approx. 0.55-0.90 V (up to max. 0.6-1.4 V).

Volvo's CAN-net meets ISO 11898-2. Other standard is 11898-3 where the voltage on CAN H changes from approx. 5 V to approx. 1 V, and CAN L from approx. 0 V to approx. 4 V when changing from logic "0" to logic "1". Other standard is SAE J2411 where only one cable is used for CAN-communication.

Scheme 1496

The message consists of the following components

1. Identifier ("flag"), which indicates the message's identity and priority.
2. Data information (value, information, etc.).
3. Check sum, used to check that the message has arrived correctly
4. Stop signal, which indicates that the message has finished.

A complete CAN-message is called a frame.

The network is made up of a number of control modules (sometimes called nodes) which are connected to each other serially via two communication cables. Each control module is supplied with power and grounded individually and receives messages /commands via the two communication cables. In both networks (high and low speed sides) the control modules are serially connected. In the event of an open-circuit those control modules beyond the open-circuit will not be able to communicate with other parts of the network.

Scheme 1497

The network consists of two parts: a high speed side (HS CAN) which transmits signals/messages between the central electronic module (CEM) and control modules mainly in the engine compartment, and a low speed side (LS CAN) which transmits signals/messages between the central electronic module (CEM) and control modules in the passenger compartment and the luggage compartment.

The interface between the high and low speed sides is supplied by the central electronic module (CEM) which converts the transmission speed up or down for communication between the two network sides.

Scheme 1498

The data link connector is located in the passenger compartment near the driver's station, cables for high-speed side (HS CAN) and low-speed side (LS CAN) are connected to the data link connector.

Scheme 1499

1. Pin 3 LS CAN (low-speed side) (H-cable)
2. Pin 4 Chassis ground
3. Pin 5 Signal ground
4. Pin 6 HS CAN (high-speed side) (H-cable)
5. Pin 11 LS CAN (low-speed side) (L-cable)
6. Pin 14 HS CAN (high-speed side) (L-cable)
7. Pin 16 Voltage feed

Note. The data link connector's other connections may be used by other functions. This service information only describes connections related to CAN.

The CAN network is monitored by the central electronic module (CEM). When the central electronic module (CEM) detects a fault in the CAN network, a diagnostic trouble code (DTC) is stored in the central electronic module (CEM). There are various types of diagnostic trouble code (DTC), depending on the type of fault.

Types of error which are handled are

1. Electrical faults
2. No communication from the control module
3. Faulty communication.

Note. To troubleshoot respective CAN-net, see appropriate diagnostic service information for CAN-related diagnostic trouble codes for Central electronic module (CEM). For example, choose any of CEM-DF01 - DF17 depending on CAN-net.