Audio System: Description: Most

The components of the complete audio/infotainment system are all connected on the Media Orientated Systems Transport (MOST) ring. The MOST ring is a fibre optic communications bus for multi media applications. Sound and control information is passed around the MOST ring and can be picked up by any of the systems units. For example, sound information is sent from the CD autochanger along the MOST ring and is collected by the audio amplifier which then out puts the sound to the speakers.

MOST technology uses a plastic optical fibre which forms a network connecting the audio and multimedia system components. Each component in the ring is connected to the plastic optical fibre through a device known as a Fibre Optical Transceiver (FOT). Each FOT has two optical connections; one connection is sensitive to light and is the input and the second connection forms the light source and is the output. The system operates by connecting the output from one FOT to the input of another FOT.

The light signals are sent in one direction only and are formed in the following way:

• Electrical signals are converted into an electrical current
• The current then drives a Light Emitting Diode (LED) in the FOT to produce a high intensity red light
• The LED transmits the light through a fibre optic cable
• A photo diode in the FOT at the opposite end of the fibre optic cable detects the light.

The following components are connected to the MOST ring:

• Integrated Head Unit (IHU)
• Touch Screen Display (TSD)
• SDARS receiver
• TV tuner
• Traffic Message Channel (TMC) module
• Amplifier
• Rear seat entertainment module
• Personal telephone integration module
• CD autochanger.

The IHU is the timing master for the MOST system. The IHU controls and manages the MOST ring and the system components. It is also responsible for the MOST security system. Each component in the MOST ring has a unique serial number. The component serial number is stored in a registry file in the gateway module. If any component serial number is not recognised, the entire audio system will not function

A replaced component requires its serial number to programmed in the gateway module registry using T4. If the gateway module is replaced, the complete system will not function until the gateway module is programmed with the component serial numbers using T4.