Information Bus: Description and Operation
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 CAN (controller area network) bus
- High speed CAN (controller area network) bus
- MOST (media orientated system transport) ring
- LIN (local interconnect network) bus
- Private CAN (controller area network) bus
CONTROLLER AREA NETWORK BUS
The CAN (controller area network) 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 (controller area network) high' and 'CAN (controller area network) low'. Information is transmitted on the CAN (controller area network) bus as a voltage difference between the two wires.
Two CAN (controller area network) 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 colors used on both networks.
Private CAN Bus
The private CAN (controller area network) 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 (controller area network) bus networks are proprietary systems and cannot be interrogated using a Jaguar approved diagnostic system.
Diagnostic Socket
The diagnostic socket allows the transfer of information between the vehicle electronic control modules and a Jaguar approved diagnostic system. The diagnostic socket is connected directly to both the medium speed CAN (controller area network) bus and the high speed CAN (controller area network) bus and is located below the driver side of the instrument panel.
MEDIA ORIENTATED SYSTEM TRANSPORT 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.
- 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 25 mm (0.98 inches) 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 fibers and connectors, especially permanent stress after reinstallation.
Software Download Socket
CAUTION: The software download socket is used for engineering purposes only and must not be used in service.
The MOST software download socket is located below the driver 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.
Ring Break Diagnostics
Incorporated into the AJB (auxiliary junction box) is a RBD (ring break diagnostics) link. The RBD link houses a copper link which when removed initiates the ring break diagnostics mode. The ring break diagnostics mode allows the technician to locate an optical fiber break in the MOST ring. To initiate the ring break diagnostics mode, carry out the following process:
- Connect the Jaguar approved diagnostic system.
- Ensure the vehicle is in power mode 4 or greater.
- Remove the RBD link for the length of time specified by the Jaguar approved diagnostic system.
- Replace the RBD link.
After approximately 30 seconds a DTC (diagnostic trouble code) will be logged in the Information and Entertainment Control Module, identifying the location of the fault. The DTC (diagnostic trouble code) can be read and interrogated using a Jaguar approved diagnostic system.
LOCAL INTERCONNECT NETWORK BUS
The LIN (local interconnect network) 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 (controller area network) bus networks, the LIN (local interconnect network) bus utilizes a single wire network.
CONTROL DIAGRAM - MEDIUM SPEED CAN BUS
NOTE:
N = Medium speed CAN (controller area network) bus.
NOTE:
Only the buttons of the integrated control panel are connected to the medium speed CAN (controller area network) bus. The TSD (touch screen display) is connected to the MOST ring.
CONTROL DIAGRAM - HIGH SPEED CAN BUS
NOTE:
D = High speed CAN (controller area network) bus.
CONTROL DIAGRAM - MOST RING
NOTE:
P = MOST ring.
CONTROL DIAGRAM - PRIVATE CAN BUS
NOTE:
U = Private CAN (controller area network) bus.
CONTROL DIAGRAM - LIN BUS
NOTE:
O = LIN (local interconnect network) bus.
