Body Control Systems: Description and Operation
Communications Network
General
Communication Network (Media Oriented System Transport MOST )Sheet 1 of 3
Communication Network (CAN bus) Sheet 2 of 3
Communication Network (CAN bus) Sheet 3 of 3
A number of different types of data bus are incorporated into the vehicle wiring harnesses for the transmission of commands and information between control modules. The bus configuration installed on a particular vehicle depends on the model and equipment level.
The available types of bus systems on the vehicle are:
^ High speed CAN (controller area network) bus
^ Medium speed CAN (controller area network) bus
^ Media Orientated System Transport (MOST) bus
^ Gigabit Video Interface (GVIF)
^ Local Interconnect Network (LIN) bus
^ Security Local Interconnect (SLIN) bus
^ Ai Net
CAN (controller area network)
The CAN (controller area network) bus is a high speed broadcast network where the control modules automatically transmit information on the bus every few microseconds. The other buses are low speed networks which are mainly event driven, i.e. an electronic control module outputs a message only in response to a request message from another control module or a hard wired input from a switch or sensor.
A twisted pair of wires are used for the CAN (controller area network) bus and single wires are used for all of the other buses. Bus wires can be repaired using crimped connections. The unwound length of CAN (controller area network) bus wires must not exceed 40 mm (1.6 in).
Two CAN (controller area network) busses are employed on the vehicle:
^ Medium speed (MS)
^ High speed (HS)
The medium speed bus connects the following control modules:
^ Integrated Head Unit (IHU) or low line head unit
^ Heating and ventilation control module
^ Fuel fired booster heater
^ Parking aid control module
^ TPMS control module
^ CJB (central junction box)
The high speed bus connects the following control modules:
^ Steering angle sensor
^ Air suspension
^ Electric Park Brake (EPB) control module
^ Electronic rear differential control module
^ Terrain Response"
^ RCM (restraints control module)
^ ECM (engine control module)
^ TCM (transmission control module)
^ Adaptive Front lighting System (AFS) module
^ ABS (anti-lock brake system) module.
Both the medium and high speed CAN (controller area network) bus are connected to the instrument cluster and the diagnostic socket at one end. The medium speed bus terminates at the CJB (central junction box), while the high speed bus terminates at the ABS (anti-lock brake system) control module.
Control modules are connected in either a loop, CAN (controller area network) in/ CAN (controller area network) out, or a spur configuration. Should a control module that is looped fail, the bus system will fail at that point. Should a spurred control module fail the rest of the bus system will be unaffected by the faulty control module.
Media Orientated System Transport (MOST)
The MOST bus uses a fibre optic cable to transport data and audio around the entertainment and information system. The fibre optic cable is arranged in a ring, with each unit on the bus having a MOST in and MOST out connection.
MOST is a synchronous network. A timing master supplies the clock and all other devices synchronize their operation to this clock. The timing master for the MOST network is the Integrated Head Unit (IHU).
Key features of the MOST network are:
^ High data transfer rate
^ Support for up to 64 devices
^ Support of asynchronous and synchronous data transfer Reduced cabling
^ Simple connectors
When handling the MOST fibre optic cables the following safety precautions should be observed:
^ The cable has a minimum bend radius of 25mm.
^ It is advisable not to look directly into the connector of a live cable.
^ The MOST cable cannot be repaired, replacement overlay harnesses are available to replace damaged cables.
Gigabit Video Interface (GVIF)
The GVIF bus is a Sony proprietary bus for the transmission of video between a transmitter device and a display device. In this instance it is used to transmit video from the navigation computer to the Touch Screen Display (TAD) only.
Local Interconnect Network (LIN) bus
There are two LIN buses on the vehicle. One connects the rain sensor, roof opening panel and memory seats to the central junction box and the other connects the BBUS to the CJB (central junction box).
The LIN bus has a master/ slave configuration. Within the master is stored a 'schedule table'. This is a list of all the LIN frames or packets in order of which one gets sent when and how many times within a particular cycle. The master sends out a header on the bus which will identify to the slaves whose turn it is to transmit a frame. The slave then fills the space after the header with the contents of the frame. The frame identifiers are all sourced from the LIN specification, and the frame identifiers are grouped by the size of the frame in bytes. All the LIN nodes are optional fit, consequently there is a different schedule table for each permutation. The bus master switches between these based on the information held within the car configuration file. The CJB also acts as a bi-directional gateway between the medium speed CAN (controller area network) bus and the LIN bus by passing signals between the two buses.
The LIN bus is a single wire and operates at 9.6Kbs. The protocol used on the LIN bus is defined by the LIN consortium.
Sony Philips Digital Interface Format (SPDIF)
The SPDIF is an digital optical system connected between the DVD (digital versatile disc) autochanger and the audio amplifier and is used to output the audio from the DVD (digital versatile disc) autochanger to the audio amplifier.
Diagnostic Socket
The diagnostic socket allows the transfer of information between the vehicle electronic control modules and T4 on the high or medium speed CAN (controller area network) bus, or indirectly via the instrument cluster. The diagnostic socket is located in the lower instrument panel closing panel, on the drivers side below the steering column.
IS Bus
The IS bus is a dedicated bus system used to transfer information between the RSE module and the two RSE screens.
Ai Net
The Ai Net is an Alpine proprietary bus used to communicate between the RSE module and the DVD (digital versatile disc) autochanger.