MOST ring, function - GF82.00-P-0004AB

MODELS 215, 220 as of 1.9.03

MOST ring components, shown for USA version

Fig 1: MOST Ring Function Chart

Digital MOST bus (Media Oriented System Transport)

The digital MOST bus is a data transfer system that utilizes the possibilities of optical information transfer.

With this system, the data are transferred by light pulses. These are transmitted over a fiber optical cable to the components connected to the bus system (e.g. COMAND operating, display and control unit (A40/3), sound amplifier (A2/13)).

Commands for the components, e.g. pressing "Play" button on COMAND operating, display and control unit (A40/3) for the CD player with changer (in trunk) (A2/6) have to be converted to light pulses (optical data) before being forwarded via the MOST.

Light pulses are then converted back to electronic signals in the receiver components so that they can execute the commands. Because of its extremely high transfer rate the MOST ring source data and control data can be transmitted simultaneously. This reduces the quantity of wiring considerably. For this reason the connected components only require 2 lines for voltage supply, 2 lines (input/output) for the fiber optical cable of the digital MOST bus and one line for the wake-up signal.

Additionally, several audio frequency (AF) signals can be sent via the fiber optical cable, without compromising data content.

Data transfer using a fiber optical cable has many advantages:

Extremely high data transmission rate
Prevents tapping and crosstalk
Data transmission is not sensitive to electromagnetic radiation
Short-circuit resistance
Potential-free connection of bus components
No oxidation
Low weight of fiber optical cable
Minimum diameter of wiring harness

The MOST has an enclosed ring structure. The components are arranged in a ring line (series circuit). This arrangement is adapted according to the series.

Data transfer ensues in one direction only, i.e. light pulses for the E-call control unit (A35/8) pass through all the components before it in the ring.

Within the ring structure of the digital MOST bus the COMAND operating, display and control unit (A40/3) contains a primary function. This enables all other ring subscribers to be served.

When the system is first put into operation, a system test is performed. In doing so the individual components and their sequence in the ring structure of the digital MOST bus are recorded by the audio gateway control unit (N93/1) and compared against the source and control data of the equipment-specific sequence of the data stored at the plant.

With the assistance of STAR DIAGNOSIS the components in the audio gateway control unit (N93/1) can be re-coded (e.g. variant coding).

The digital MOST Bus is rendered diagnosis capable via the audio gateway control unit (N93/1).

Data transfer, function

GF82.00-P-2000AB