Function

Processing buttons pressed
The control buttons and switches on the function keypad on the COMAND operating, display and control module (A40/3) are read in over the microcontroller I/O ports and transferred to the central processor. Depending on the system function, the button actuations are processed in the central processor or transferred to other system components via the bus system ((digital data bus (D2B), CAN (A1-A40/3) or CAN COMAND bus) in the form of a data telegram.

Video processing and display output
The video subsystem takes over editing and output of the control displays. The control displays are output by the video subsystem internally to the monitor via the RGB output (R= Red, G=Green, B=Blue).
The information and amplitudes for the three basic colors, red, green and blue as well as a synchronization signal are contained in the RGB signal. The electronic circuitry in the display unit evaluates the RGB signal and controls the individual display dots line by line in terms of color and intensity. A horizontal synchronization pulse is given at the end of each line. The electronic circuitry of the display unit then starts the next line. After reaching the last line of the display, the vertical synchronization pulse is given and the electronic circuitry starts the first line again.

Audio signal output
The audio signals from the various sources (CD, voice output for guidance, ...) are edited by the COMAND operating, display and control module (A40/3) and amplified for output on the vehicle loudspeakers. On vehicles with sound system (code 810), final amplification of the audio signals is accomplished by the sound system amplifier (N40/3). For this purpose, the audio source data is transferred analog to the sound system amplifier (N40/3) via separate leads.

Diagnostic interface (K bus) and error management for D2B components
During COMAND operation, the system stores all errors occurring in a non-volatile memory. These can then be read out on the diagnostic interface (K bus) with Star diagnosis. Output of the errors on the display unit is not possible.

The COMAND error management also includes the components connected to the D2B bus.
Each D2B component has its own DTC memory. The DTCs are transferred via the D2B bus to the COMAND operating, display and control module (A40/3) upon request by Star diagnosis where they can be read out on the diagnostic interface.

Navigation processor and GPS control module
The navigation processor is the central component of the COMAND navigation system. It is integrated into the COMAND operating, display and control module (A40/3) and calculates the vehicle location from the signals received and the vehicle route after the destination is entered.
The GPS control module is a part of the navigation processor. It evaluates the satellite signals coming from the GPS antenna (A2/49a2) and calculates the vehicle position from this information.

CD-ROM and CD-ROM drive
Data can be read from the special navigation CD or audio CDs can be played with the aid of the integrated CD drive.

The following are contained on the navigation CD-ROM:
- Program data for execution in navigation processor
- Voice data for voice output
- Map data.

The digitized map area on the CD-ROM contains towns, cities, streets, intersections and their attributes (e.g.: one-way streets, turn prohibitions, ...). It does not include items such as company and private grounds, farms, small settlements and rural roads.

Gyrosensor
The gyrosensor determines the direction changes of the vehicle. It is built into the navigation processor. Calibration is not required.

Traffic data memory
The integrated traffic data memory receives the traffic messages either over the CAN COMAND bus (in TCS mode) or internally from the radio tuner (in TMC mode). The data is stored for a maximum of 30 min in the traffic data memory including the shutoff delay time for the COMAND module (up to 100 messages). The traffic data memory decodes the messages and transfers them to the navigation processor as required.

The traffic data memory requires a current "location list" from the navigation processor for synchronization. In the location list, each section and every significant point (e.g. freeway exit) of the network of roads monitored for traffic problems is clearly identified by a number. This list is originally stored on the CD-ROM.

It is loaded into the non-volatile traffic data memory automatically as required (e.g. when CD-ROM is changed) from the navigation processor.