MODEL   129 as of 1.6.98,     163,     168 as of 1.9.98,     170, 202 as of 1.6.98,     203,     208, 210 as of 1.6.98,     215, 220

D2B ring, sequence of components illustrated on model 220 A Radio Audio 30 B CD changer C Voice control system control module D Telephone transmitter-receiver E Tele Aid control module X11/4 Diagnostic data link connector
		P82.00-2009-11

Digital data bus (D2B ) The digital data bus (D2B) is a data bus system (data transmission system) which utilizes the possibilities of optical information transfer. With this system, the data is transferred by light pulses. These are transferred through a fiber optic cable to the components connected to the bus system (for example: CD changer, voice control system (VCS), telephone, Tele Aid emergency call system). Commands for the components such as pressing the "Play" button on the radio (command for CD player) or Comand unit (control module) require conversion into light pulses (optical information) before they can be transferred via the digital data bus (D2B). The light pulses are then converted back into electrical signals for further processing in

the receiving component and the command is executed. Due to the high transfer rate, the digital data bus (D2B) can simultaneously transfer source data (for example: music from CD player) and control data (for example: "Play" command for CD player). This reduces the quantity of wiring considerably. The components connected therefore require only two lines for the power supply (electrical), two lines (input/output) for the digital data bus (D2B) fiber optic cable and one line for the wake-up signal (electrical), instead of 7-8 lines required previously. Moreover, a number of audio (AF) signals, can be transferred simultaneously via the fiber optic cable without any negative effect on the information contained, for example: Music from CD player and voice from telephone.

Data transmission using fiber optic cable has many advantages: Extremely high data transmission rate Prevents tapping and cross-talk Data transmission is not sensitive to electromagnetic radiation Short circuiting cannot occur Potential-free connection of bus components No oxidation Low weight of fiber optic cable Minimum diameter of wiring harness The digital data bus (D2B) has a closed ring structure. The components are arranged in a ring line (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. Telephone 4. Telephone 4. Voice control system 5. TeleAid system

With this system, information is transferred only in one direction.This means that the light pulses for the telephone (model 210) run through all of the components in the ring before arriving at the telephone. From the examples listed, it can be recognized that the radio or Comand unit is always the first component in the ring.These components always have a (master function) within the ring structure of the digital data bus (D2B) while the remaining components have a subordinate function (slave function). When the system is first put into operation, a system test is performed.During this test, individual components and their sequence in the ring structure of the digital data bus (D2B) is detected by the radio. A model-specific sequence (see examples 202, 210) is stored at the factory in the radio or Comand unit itself. Storage of this set sequence in the radio at the factory has the following effect:

If a radio from model 210 is installed in model 202, the different sequence of the components is detected by the radio during a system test and an error message stored in the DTC memory. An error message is stored even when a radio within a series is replaced with different accessory components (for example, model 210 with CD changer and model 210 without CD changer).

The system goes to the operational state regardless of the error message. The sequence of the components can be changed later in the radio or Comand unit with the aid of the hand-held tester. The digital data bus (D2B) is capable of diagnosis via the radio system (Audio) or Comand unit (control module).