Audio gateway control unit, function - GF82.62-P-3102-04TU

The audio gateway control unit (N93/1) is the central audio communications interface within the Media Oriented System Transport (MOST).

The control commands are initialized by the COMAND operating, display and control unit (A40/3) and transmitted via the MOST (Media Oriented System Transport) to the audio gateway control unit (N93/1).

Scope of function:

• AM/FM reception
• Sound processing and sound amplification
• Realization of data exchange between MOST (Media Oriented System Transport) and interior CAN (CAN-B)
• Diagnostic interface

Function conditions:

• Circuit 15R ON
• Authentication positive
• control unit within the specified voltage values

AM/FM reception 

If the user selects a particular radio program on the COMAND operating, display and control unit (A40/3), a request is sent to the audio gateway control unit (N93/1), whereupon the radio tuner generates an oscillating circuit to receive the respective transmission frequency.

Via the radio receiver in the audio gateway control unit (N93/1) the corresponding high-frequency signals of the FM, MW, LW, SW frequency ranges and passed on to the integrated audio processing stage and audio amplifier stage.

Sound processing and amplification 

The control commands for audio sound and volume control coming in from the COMAND operating, display and control unit (A40/3), as well as all audio signals of system components transmitted are transmitted via MOST to the audio gateway control unit (N93/1).

The integral audio processing stage, Signal Processing (DSP1), digitizes and processes the incoming signals and amplifies them before output to the speakers.

Variants of audio gateway control unit (N93/1) 

The audio gateway control unit (N93/1) is supplied in the variants "Basis" (standard) and for code (810) sound system.

The expansion of the device only relates to final signal processing. The "Basis" variant is the standard version of the audio gateway control unit (N93/1) with a rated output of 4 x 25 W and a loudspeaker impedance of 4 Ω for the rear speakers and 3 Ω for the front speakers due to the special Center bass wiring.

In order to obtain an option of enhanced variation for sound quality, the audio gateway control unit (N93/1) with code (810) sound system is equipped with the enhanced audio processing stage and audio amplifier stage, Digital Signal Processing as a special option.

For a rated output of:

• 5 x 40 W for 2 Ω
• 1 x 70 W for 4 Ω

several speakers are actuated:

• Left front door loudspeaker group (H4/1)
• Right front door loudspeaker group (H4/2)
• Left rear door speaker group (H4/3)
• Right rear door speaker group (H4/4)
• Center cockpit speaker (centerfill) (H4/27)
• Bass module speaker (H4/17)

DRO microphone input 

Connection for sound amplifier microphone (B25/6) for automatic vehicle interior noise adaptation "Dynamic Range Optimization" (DRO).

The noise level inside the vehicle is measured using the sound amplifier microphone (B25/6) which is connected directly to the audio gateway control unit (N93/1). The volume of the music output signal is constantly adapted to this noise level. For this purpose, the audio gateway control unit (N93/1) must detect which signals of the measured level are driving noise and which are audio signals. This happens by comparing the output signal of the sound amplifier with the measured signal. A simple way of looking at it is to regard the difference in both signals as being the driving noise level.

Fault management of the MOST components 

The audio gateway control unit (N93/1) is the central diagnostic interface for the complete MOST (Media Oriented System Transport). During operation the system stores all the faults which occurred in the nonvolatile memory.

These can be read out via the diagnosis interface using STAR DIAGNOSIS. The faults cannot be output via the COMAND operating, display and control unit (A40/3). The inquiry is initiated via the 16-pin STAR DIAGNOSIS diagnostic connector under the instrument panel. Via the central gateway control unit (N93) the diagnostic data in the Keyword-Protocol-2000 format are transmitted directly to the interior CAN (CAN-B). The audio gateway control unit (N93/1) detects the diagnostic command and converts the incoming data into a message compatible with the MOST (Media Oriented System Transport). The diagnosis of all MOST components is controlled by the audio gateway control unit (N93/1).

Each MOST component has its own diagnostic trouble code memory.