Communications Network
Communications Network
INTRODUCTION
A number of different types of communication network are incorporated into the vehicle wiring harnesses for the transmission of commands and information between control modules. The configuration installed on a particular vehicle depends on the model and equipment level.
The communication networks available on the vehicle are:
- Medium speed Controller Area Network (CAN) bus
- High speed CAN bus
- Media Orientated System Transport (MOST) ring
- Local Interconnect Network (LIN) bus
- Private CAN bus
Bus Baud Rate
Medium speed CAN bus 125 kbits/s
High speed CAN bus 500 kbits/s
MOST ring 24 mbits/s
LIN bus 9.6 kbits/s
CONTROLLER AREA NETWORK (CAN) BUS
The CAN bus is a high speed broadcast network where control modules automatically transmit information every few microseconds. Information is broadcast down a pair of twisted wires, known as 'CAN high' and 'CAN low'. Information is transmitted on the CAN bus as a voltage difference between the two wires.
Two CAN bus networks are used on the vehicle; medium speed and high speed, with the instrument cluster acting as a gateway between the two networks. The table below shows the wire colours used on both networks.
Private CAN bus
The private CAN bus networks used on the vehicle can be either medium or high speed depending on which vehicle system they are being used. All private CAN bus networks are proprietary systems and cannot be interrogated using the Integrated Diagnostic System (IDS).
Diagnostic Socket
The diagnostic socket allows the transfer of information between the vehicle electronic control modules and the IDS. The diagnostic socket is connected directly to both the medium speed CAN bus and the high speed CAN bus and is located below the drivers side of the instrument panel.
MEDIA ORIENTATED SYSTEM TRANSPORT (MOST) RING
The MOST ring uses a fibre optic cable to transport data and audio around the information and entertainment system. The fibre optic cable is arranged in a ring, with each unit on the ring having a 'MOST in' and 'MOST out' connection.
MOST is a synchronous network. A timing master supplies the clock and all other components on the ring synchronize their operation to this clock. The timing master for the MOST ring is the Information and Entertainment control module.
When handling MOST fibre optic cables the following precautions should be observed.
- Avoid looking directly into the connector of a live cable.
- After disconnection of any cables, carefully install appropriate dust caps to protect the mating faces of the connectors from damage or contamination.
- Avoid introducing bends of less than 30 mm radius or kinks into the fibre optic cable during service or repair. Tight bends or kinks could impair operation, cause immediate system failure, or future system failure.
- Avoid excessive force, strain or stress on the fibres and connectors, especially permanent stress after reinstallation.
Software Download Socket
The MOST software download socket is located below the drivers side of the instrument panel. A service loop is fitted to the end of the socket to complete the MOST ring. If the service loop is removed the MOST ring will be broken and all components on the ring will stop operating.
NOTE: The software download socket is used for engineering purposes only and must not be used in service.
LOCAL INTERCONNECT NETWORK (LIN) BUS
The LIN bus is a low speed broadcast network that employs master and slave components. The master component transmits a message to the slave components identifying which slave is to respond. This message has a header (slave identifier) and an empty data field. The identified slave component fills the data field with the relevant information and returns the message to the master component.
Unlike the CAN bus networks, the LIN bus utilizes a single wire network.
CONTROL DIAGRAM - MEDIUM SPEED CAN BUS
NOTE: Only the buttons of the Integrated control panel are connected to the medium speed CAN bus. The touch screen display is connected to the MOST ring.
CONTROL DIAGRAM - HIGH SPEED CAN BUS
CONTROL DIAGRAM - MOST RING
CONTROL DIAGRAM - LIN BUS AND PRIVATE CAN BUS