Communication Data Buses: Description: General: Notes

A number of different types of data bus are incorporated into the vehicle wiring harnesses for the transmission of commands and information between ECU's. The bus configuration installed on a particular vehicle depends on the model and equipment level:

• Controller Area Network (CAN) bus. A network connected between the brake, powertrain, steering and suspension related ECU's
• Diagnostic buses. Two networks that, directly and indirectly, connect the diagnostic socket to all of the of the ECU's installed on the vehicle
• I bus. A network connected between ECU's of the 'Information' systems
• K bus. A network connected between ECU's of the 'body' systems
• M bus. A network connected between the ATC ECU and motors on the heater assembly
• P bus. A network connected between the BCU and 'Peripheral' ECU's.

On vehicles from 2005MY, four new additional bus systems are introduced to connect components in the infotainment system. The additional buses are as follows:

• Media Orientated System Transport (MOST). A fibre optic network which connects the major components of the infotainment system in an unbroken loop. The integrated head unit is the first and last component in the system and controls the operation of the MOST ring.
• Gigabit Video Interface (GVIF). The Touch Screen Display (TSD) communicates with the navigation computer on a dedicated serial link known as GVIF. The TSD receives the navigation graphics from the navigation computer on the GVIF serial link.
• Sony Phillips Digital Interface Format (SPDIF). The SPDIF is an optical system connected between the DVD autochanger and the audio amplifier and is used to output the audio from the DVD autochanger to the audio amplifier.
• 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 autochanger.

Serial interface circuits in the ECU's transmit and receive commands and information on the buses as digital messages. ECU's connected to the same bus use a common protocol (format) and baud rate (transmission speed) for the messages they transmit. The protocol and baud rate varies between bus networks. To enable messages to be exchanged between ECU's from different bus networks, the instrument pack provides a communication gateway. A microprocessor in the instrument pack converts and/or re-transmits messages between bus networks.

The CAN bus is a high speed broadcast network where the ECU's automatically transmit information on the bus every few microseconds. The other buses are low speed networks which are mainly event driven, i.e. an ECU outputs a message only in response to a request message from another ECU or a hard wired input from a switch or sensor.

A twisted pair of wires are used for the CAN 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 bus wires must not exceed 40 mm (1.6 in).