CAN NETWORK DESCRIPTION
CAN (control area network) is a standardized system for multiplex-communication. Multiplex communication means that several control modules can use the same cables for communication without traffic from one control module interfering with traffic from another.
Volvo has developed a new standard for multiplex communication - VOLCANO. VOLCANO is a development of CAN and uses real time operation and prioritization. The description of prioritization is based on VOLCANO but is designated CAN.
The control area network (CAN) standard specifies
- That two cables are to be used (CAN H and CAN L)
- What voltage levels must be used
- What a message should look like
- How transmission errors should be handled.
Scheme 33
The CAN H and CAN L cables must not be confused with HS CAN and LS CAN which are speeds on the control area network. CAN H and CAN L are a way of distributing signals within the multiplex communication network.
Communication occurs through two cables. These two cables are paired together.
The voltage levels for communication occur using differential voltage levels.
The reason for communicating using paired cables and differential voltage levels is that the network becomes less sensitive to interference.
The same message is transferred simultaneously by both cables, but different voltage levels are used.
- Binary 1 = 2.5 V on both CAN H and CAN L.
- Binary 0 = 4 V on CAN H and 1 V on CAN L.
When measuring between CAN L and ground, the average voltage level during normal use is about 1.8 - 2.2 V.
When measuring between CAN H and ground, the average voltage level during normal use is about 2.8 - 3.2 V.
The difference in voltages is due to vehicle configuration and equipment level. Thus, voltages may differ between vehicles of the same model.
When measuring between the two CAN-cables, at 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 34
The message consists of the following components
- Identifier ("flag"), indicating the message identity and prioritization
- Data information (value, information, etc.).
- Check sum, used to check that the message has arrived correctly
- Stop signal, indicating that the message has finished.
A complete CAN-message is called a frame.
VIDA identifies control modules by reading off a number of codes from the control module memory.
The codes contain information about the control module
- hardware P/N (control module without software)
- hardware serial number (control module without software)
- software P/N
- diagnostic software P/N.
VIDA identifies control modules by reading off a number of codes from the control module memory. The codes contain information about the control module
- hardware P/N (control module without software)
- hardware serial number (control module without software)
- software P/N
- software number, diagnostics.