Data Bus System, Function

D2B ring, sequence of components in model 210 shown

Digital data bus (D2B)
The digital data bus (D2B) is a data bus system (data transfer system) which uses the possibilities of optical data transmission. Data is transmitted by light pulses. These are conveyed to the components (for example: CD changer, voice control system (VCS), cellular telephone, TELE AID emergency call system) connected in the bus system via an optical fiber.

The commands for the components e.g. pressing the "play" button on the radio (command for the CD player) have to be converted into light pulses (optical information) via the D2B for further processing. The light pulses are in turn converted into electrical signals for further processing in the receiver component and the command is carried out.

Due to its high transmission rate the D2B can transmit source data (for example: music from the CD player) and control data (for example: "play" command for a CD player) at the same time. This reduces the cost of wiring considerably.

The connected components therefore only need two cables for voltage supply (electric), two cables (input/output) for D28 optical fiber and one line for the wake-up signal (electric), for which 7-8 lines were previously required.

In addition, several low frequency (LF) signals can be transmitted at the same time without impairing the information content, for example music from the CD player and speech from the cellular telephone.

Data transmission via optical fiber has many advantages:
- Very high data transmission rate
- Eavesdropping and crosstalk security
- Insensitivity to electromagnetic radiation
- Short-circuit strength
- Potential-free connection of bus participants
- No oxidation
- Low weight of the optical fiber
- Small fiber diameter

The D2B has a connected ring structure. The components are located within a ring circuit (series circuit). This arrangement is model-specific:

Example model 210: Example model 202:
1. Radio 1. Radio
2. CD changer 2. CD changer
3. Voice control system 3. Cellular telephone
4. Cellular telephone 4. Voice control system
5. Tele Aid System

The information is only transmitted in one direction, i.e. the light pulses for the cellular telephone (model 210) pass through all the components located in the ring before they arrive at the cellular telephone.

In the examples listed it can be seen that the radio is in first position. It always has a higher-order function (master function) within the D2B ring while the other components have a subordinate function (slave function).

A system test is carried out when the system is operated for the first time. In this the individual components and their sequence in the D2B ring are detected by the radio.

At the plant a model-specific sequence was stored in the radio.

Storage of the specified sequence in the radio at the plant means in turn:
If a radio from model 210 was installed in model 202, the different sequence of the components is recognized by the radio during a system test and a fault report is filed in the fault memory. A fault report is also filed if a radio within a series is fitted with different equipment components (for example, model 210 with CD changer and model 210 without CD changer). Irrespective of the fault report the system goes into the ready-to-operate condition. The sequence of components in the radio can be changed retroactively using the Hand-Held Tester.

The D2B is capable of diagnosis via the radio system (audio).