Data Transmission, Function

In the digital data bus (D2B) there is the master unit (radio) which can actuate all the D2B system components. It also serves as an interface (gateway) to the CAN data bus. For this the signals arriving at the radio are converted so that they can be transmitted from the D2B to the CAN and vice versa. In addition the master unit serves as a clock generator which specifies the cycle with which the information sections (frames) are transmitted on the bus system. A frame consists of two subframes. The sequence of many frames then contains all the information for trouble-free operation of the components (cellular telephone, CD changer etc.) in the D2B ring.

Conversion of the light pulses into electrical signals and vice versa takes place by means of the optical transmitting and receiving diodes which are integrated in each component. In the component the electrical signals are then received or transmitted by the D2B chip as a D2B protocol. Source data (music from CD player) and control data (play command on CD player) are transmitted.
Source data are transmitted synchronously, such as they are present for example on a music CD, to the subframes as blocks of 32 bits.

In contrast control data are transmitted asynchronously. They are packaged (2 bits per subframe) and distributed over several subframes).

The control data are provided in each case with an address for which component of the D2B ring the information is intended. Arriving at the component the individual data packages in the component are put back together and can be processed. A frame can therefore contain a wide range of information (source and control data of all the components in the D2B).
The transmitting and receiving diodes and D2B chip are switched off when not required in order to reduce the quiescent current (sleep mode). Switching off takes place immediately after the master unit or ignition is switched off. For a renewed start of optical information transmission, the bus system (transmitting and receiving diodes, D2B chip) can be activated by an electrical signal from the wake-up line either via the component or master unit. Irrespective of whether information is intended for the component, it feeds a processed light signal at full intensity back into the bus (repeater function).