2007 BMW 7 SERIES MOST Bus Diagnosis Workshop Manual

Initial Print Date:03/02Revision Date:08/02
Subject Page
MOST Technology .................................................................................. 3
MOST Multimedia Network .................................................................... 3
Data Transport....................................................................................... 5
Optical Bus............................................................................................. 6
Optical Transmitter ............................................................................... 6
Optical Receiver ................................................................................... 6
Control Unit Connections...................................................................... 7
Interfaces................................................................................................. 8
Control Display .................................................................................... 9
ASK ..................................................................................................... 9
CDC ....................................................................................................10
Navigation ...........................................................................................10
Slave Control Units ..............................................................................10
Component Locations...........................................................................10
Communication Direction.....................................................................11
Diagnosis................................................................................................12
Testing.....................................................................................................15
Status Wakeup.......................................................................................18
Review Questions..................................................................................19
Table of Contents
MOST Bus Diagnosis

2
MOST Bus Diagnosis
MOST Bus Diagnosis
Model: E65 - E66
Production Date: Start of Production
Objectives:
After completing this module you should be able to:
• Understand the reason for optical busses.
 Know how optical busses transfer information.
 Relate the direction and flow of information on the MOST Bus.
 Perform diagnosis and troubleshooting of MOST Bus.

3
MOST Bus Diagnosis
System Overview
MOST Technology
Until very recently, only very few entertainment-related control units were networked. In the
course of the development, the number of components increased continuously.
In addition, the scope of functions of individual components has been extended consider-
ably. In particular, however, completely new logical networking means that all the compo-
nents are growing to become a system: individual functions work together and produce a
high-quality overall system. This results in significant growth in system complexity.
This new dimension of system complexity can no longer be managed using the existing bus
systems.
MOST Multimedia Network
MOST technology meets 2 essential requirements:
1. The MOST bus transports control data as well as data from audio, video, navigation and
other services (SMS=Short Message Service, TMC =Traffic Message Channel, in other mar-
kets).
2. MOST technology provides a logical framework model for control of the variety and com-
plexity of data: the MOST Application Framework. The MOST Application Framework
organizes the functions of the overall system.
MOST is able to control and dynamically manage functions that are distributed in the vehi-
cle.
KT-9386

4
MOST Bus Diagnosis
Principle of a Multimedia Network
An important feature of a multimedia network is that it transports not only control data and
sensor data, e.g. like the CAN bus and I bus (instrumentation bus). A multimedia network
can also carry digital audio and video signals and graphics as well as other data services.
Advantages of the Multimedia Network
All data can be transported across a shared network. This offers the following benefits:
 Additional signal wiring harnesses are eliminated.
 The only addition many control units need is the power supply.
 As each participant (= each control unit) has access to all the
data, cost-intensive assemblies for signal distribution can be
eliminated.
Different data formats also have different requirements for transmission regarding both
mechanism (synchronous or asynchronous data) and the required band-width
(baud or bits/second). The MOST format is able to meet these requirements to a satisfac-
tory extent.
Audio
Video
RGB
Data Services
Control
KT-9387
Information transmitted on MOST network

5
MOST Bus Diagnosis
Functional Description
Data Transport
MOST currently offers a band-width of 22.5 Mbits/s . In the next generation, the band-width
will be increased to 50 and then later to 150 Mbits/s (as of approx. 2002).
In order to meet the different requirements of the applications regarding data transport,
each MOST message is divided into three parts:
 Control data
 Asynchronous data: e.g. navigation system, arrow
representation
 Synchronous data: e.g. audio, video signals
The control data controls the functions and devices in the network. The information can be
compared to CAN bus data.
The control data has a band-width of 700 Kbit/s. That corresponds to around 2 27
70
00
0

mes-
sages per second.
For the data transmission of synchronous and/or asynchronous data, there is a total of 60
bytes. The limit is variable: e.g. 20 bytes of synchronous data and 40 bytes of asynchro-
nous data.
A message over the MOST
Control Data
700 kB/s
2700 Messages
Asynchronous
Data
e.g Navigation (arrow
display)
Synchronous data
Audio
Video
Data Transport on the MOST
Different data is “packaged”
and then sent as one mes-
sage to be “unwrapped” by
next device on the MOST
ring.
KT-9388
44.1 MHz

6
MOST Bus Diagnosis
Optical Bus
The MOST bus is a plastic optical waveguide. The MOST bus is coded in green in the E65
(Repair cables are black in color). The light wavelength is 650 nm (red light). The MOST
bus requires the following converter components:
 Optical transmitter
 Optical receiver
Each control unit of the MOST framework contains a transmitter and a receiver. The trans-
mitter and receiver have been developed by BMW. The low closed circuit (rest) current
properties of the transmitter and receiver enable optical wake-up by the MOST bus.
Optical Transmitter
A driver is fitted in the transmitter. The
driver energizes an LED (light-emitting
diode).
The LED transmits light signals on the
MOST bus (650 nm light, i.e. red visible
light). The repeat frequency is 44.1
MHz.
The sensing frequency on a CD player and for audio is 44.1 MHz; this means than no addi-
tional buffer is required, yet another reason why this bus system is so efficient for multi-
media.
Optical Receiver
The receiver receives the data from the
MOST bus. The receiver consists of:
 An LED
 A pre-amplifier
 A wake-up circuit
 An interface that converts the optical signal into an electrical signal
The receiver contains a diode that converts the optical signal into an electrical signal. This
signal is amplified and further processed at the MOST network interface.
Transmitter
Light LED Driver
Receiver
Light
LED
Pre-
Amp. Wake
-up
43-07-31
43-07-30

7
MOST Bus Diagnosis
Control Unit/Control Unit Connection
The MOST ring is composed of optical point-to-point connections between 2 control units.
Each control unit has a network interface. The network interface consists of:
 An opto-electrical converter (optical waveguide receiver, already mentioned).
 An opto-electrical converter (optical waveguide transmitter, already mentioned).
 A MOST transceiver (interface between the optical waveguide receiver/transmitter and
the electronic network driver).
 A network driver, the so-called NetServices.
The NetServices run on a microcontroller (main computer in the control unit)
On the application level, a control unit in the MOST framework contains stand-alone func-
tion units, so-called function blocks. Examples of function blocks include:
 Tuners
 Amplifiers
 CD players
A control unit can contain several function blocks at one time, e.g. the AVT contains the
functions:
 Antenna
 Amplifier
 Tuner
MOST Fiber Optic cable
Example
SVSNavigation
Network interface
Network interface
NetServices SWNetServices SW
Most
transceiverMost
transceiver
Optical
receiverOptical
receiver Optical
transmitterOptical
transmitter
KT-9397
1
1 22

8
MOST Bus Diagnosis
Interfaces
The following contains a brief summary of the tasks of the connected control units in the
MOST framework:
Control Display
The Control Display is the system master of all MOST bus functions and serves as the
power master. It wakes up the bus and is responsible for switching it off (power down).
The DIS Plus and GT1 will show a Control Display and a Control Display (Gateway).
Audio System Controller (ASK)
The audio system controller has the following controller functions:
Network Master
The ASK performs the role of network master for the MOST bus. The functions of the net-
work master are the following:
 Wake-up, initialization, power-down
The network master wakes up the bus and has the task of achieving an orderly
initialization of the network. The ASK can operate with KLR off. To turn it on, push in
the volume/ON/OFF knob. Adjustments and control is carried out by using the
Controller and Control Display.
Another task of the network master is to control the power-down process. Each power-
down is initiated and started by the ASK.
 Configuration control
The network master detects the exact system configuration each time that the network
is started and compares it to the stored coded configuration.
 Control of the network operation
The network master controls the MOST transceiver of the slave equipment for correct
operation. The equipment which is not operating properly will be released by a reset or
switched to low power mode so that they do not affect bus communication.
 Fault code memory
The network master includes the fault code memory of the MOST network. It stores all
the faults occurring during the network operation as well as deviations from the
nominal configuration.