Mercedes-Benz ML320. Manual — part 219

DATA TRANSFER, FUNCTION - GF82.00-P-2000A

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

The Digital Data Bus (D2B) contains the master unit, e.g. the radio (A2) except for model 129, and model 202,
which triggers all the components in the Digital Data Bus system (D2B). The master unit also serves as an
interface (Gateway) to the CAN interior (CAN-B). For this purpose, signals arriving at the master unit are
converted so that they can be transmitted from the Digital Data Bus (D2B) to the CAN interior (CAN B) and
vice versa. Moreover, the master unit serves as a timing circuit which provides the clock pulse with which the
information frames are transferred on the Digital Data Bus (D2B). A frame consists of 2 subframes. A series of
many data frames contains the complete information for proper operation of the components located at the
Digital Data Bus (D2B). The conversion of optical pulses into electrical signals and vice versa is done by
transmitter and receiver diodes, that are integrated into each component. Each of the components receives or
transmits the electrical signals from the chip of the Digital Data Bus system (D2B) as a "D2B log". Source data
and control data are transmitted.

The source data are transferred synchronously, for example as present on a music CD, as 32 bit blocks into the
subframes. By contrast, control data are transferred asynchronously. They are divided up (2 bits per subframe)
and distributed over several subframes. The control data are provided with an address, which indicates for
which components the data are intended in the Digital Data Bus (D2B). The individual data packages are joined
together again in the components and they can then be processed. A data frame can therefore contain highly
differing types of information (source and control data from all components mounted in the digital data bus
(D2B)). The transmission and reception diodes as well as the digital data bus (D2B) chip are switched off when
not required in order to reduce the quiescent current (sleep mode). Switch-off is accomplished immediately
when the master unit or circuit 15 is switched off. After restart, the digital data bus system (D2B) can be
activated either by the components or by the master unit by means of an electrical signal in the wake-up line for
optical data transmission.

Regardless whether the information is intended for a component, it feeds an edited light signal back into the
digital data bus (D2B) at full intensity (repeater function).

WAKE-UP, FUNCTION - GF82.00-P-2001A

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

Normal wake-up

Digital data bus (D2B), function

GF82.00-P-0001A

Data transfer, function

GF82.00-P-2000A

Wake-up, function

GF82.00-P-2001A

Survey of system components, digital
data bus (D2B),
location/task/design/function

GF82.00-P-9999A

Wake-up, function

GF82.00-P-2001A

2001 Mercedes-Benz ML320

1998-2005 ACCESSORIES & BODY, CAB Electrical System - Body - 163 Chassis

me

Since the transmitting and receiving diodes along with the digital data bus system's (D2B) chip are
automatically shut off if they are not needed (sleep mode), a wake-up pulse, which activates the system, is
required to start a new data transfer. This is accomplished via the separate wake-up line. For this purpose, the
master unit actuates the wake-up signal (electrical signal), which allows the voltage in the wake-up line to
decrease to a defined value. The chip of the digital data bus system (D2B) in the components recognizes on
account of the duration of the signal that this is a wake-up signal, and the digital data bus (D2B) is then
activated. Therefore the digital data bus (D2B) is then in an activated state. A "wake-up" can take place in a
quiescent system (sleep mode) even without the wake-up pulse of the master unit by activation of a component
located at the digital data bus (D2B).

Wake-up diagnosis

For diagnosis of the wake-up circuit in the components, the master unit can trigger a wake-up diagnosis signal
using STAR DIAGNOSIS and the data link connector (X11/4). This signal differs from the wake-up signal by
the fact that it has a significantly longer duration. The components react to this long wake-up pulse with a signal
on the wake-up line (message to master unit). This allows the master unit to recognize which components have
received the long wake-up pulse. The wake-up diagnosis signal can only be actuated when the digital data bus
(D2B) cannot be activated due to an error. If all components reply to the master unit, then their voltage supply is
correct.

FIBER OPTIC CABLE, LOCATION - GF82.00-P-4000-01GH

Model 163

Components for ECE version

Fiber optical cable,
location/task/function

Except model 208.4

GF82.00-P-4000A

2001 Mercedes-Benz ML320

1998-2005 ACCESSORIES & BODY, CAB Electrical System - Body - 163 Chassis

me

Fig. 6: Identifying Fiber Optic Cable Components Location

FIBER OPTIC CABLE, FUNCTION - GF82.00-P-4000-04A

The fiber optical cable consists of plastic with a fiber diameter of 1 mm. Each fiber optical cable is protected
against mechanical damage and against admission of outside light with the help of an orange-colored insulation.
The light for the data transfer in the digital data bus (D2B) has a wavelength of 650 nm; by comparison, visible
light lies in the range of blue with 400 nm to red with 800 nm. Optical attenuation of the light signal can occur
in the fiber optic cable. Attenuation of the optical signal in the fiber optical cable is dependent on:



the length of the line between the individual components



the bending radii when routing the fiber optical cable, which must have min. bending radius = 25 mm



the condition of the insulation of the fiber optical cable



A passive connector; this is used when a component is removed from the digital data bus (D2B) due to a
fault.

To ensure the functional availability of the remaining components, the digital data bus (D2B) is closed again
using a passive connector. The fiber optical cable has two different connection ends:



The fiber optical cable input, which is the output to each control unit. This is marked in "white".



The fiber optical cable output, which is the input to each control unit. This is marked in "red".

FIBER OPTIC CABLE, LOCATION/TASK/FUNCTION - GF82.00-P-4000A

MODEL 129 as of 1.6.98, 163, 168 as of 1.9.98, 170, 202 as of 1.6.98, 203, 208.3, 210 as of 1.6.98, 215, 220

2001 Mercedes-Benz ML320

1998-2005 ACCESSORIES & BODY, CAB Electrical System - Body - 163 Chassis

me

Exemplified on model 215 with code (819) 6-disc CD changer, with code (810) Sound System and with
code (382) MB phone "CTEL" in console on right side of dome

Fig. 7: Identifying Fiber Optic Cable, Location/Task/Function

SURVEY OF SYSTEM COMPONENTS, DIGITAL DATA BUS (D2B), LOCATION/ TASK/DESIGN/FUNCTION - GF82.00-P-
9999A

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

Fiber optic cable, location Model 129

GF82.00-P-4000-01D

Model 163 as of 01.09.01 GF82.00-P-4000-01GH

Model 168

GF82.00-P-4000-01E

Model 170

GF82.00-P-4000-01C

Model 202, 208

GF82.00-P-4000-01B

Model 203

GF82.00-P-4000-01G

Model 210

GF82.00-P-4000-01A

Models 215, 220

GF82.00-P-4000-01F

Fiber optic cable, purpose The fiber optical cable is

responsible for the optical
data transfer of the
components located at the
digital data bus (D2B).

Fiber optic cable,
function

GF82.00-P-4000-04A

Fiber optic cable,

Except model 208.4

GF82.00-P-4000A

2001 Mercedes-Benz ML320

1998-2005 ACCESSORIES & BODY, CAB Electrical System - Body - 163 Chassis

me