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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
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MOST Bus Diagnosis
OPPS Diagnostics
Customer Complaint:Navigation and Radio not functioning, CD appears to be locked
up.
Diagnosis:Perform Short Test Using Standard Diagnostic Head
Which MOST bus components are found?
How are these components found by the DisPlus?
What procedure will be used to diagnose the MOST Bus?
What happens when this diagnostic procedure is used?
If a Ring Break Test is performed, what node number is given?
At this point what diagnostic path would be followed?
Diagnosis with OPPS
Connect the OPPS to the vehicle using the proper Diagnostic cable
PN . (Don’t forget, some diagnostic operations will occur in the
luggage compartment)
Attach the OPPS to the OPPS connector in the vehicle using fiber optic
cable PN .
Perform Short Test
Which MOST Bus components are found?
Is this different than in the previous test? Why?
Follow the DisPlus Test Plan Procedures for testing the light output of
suspect components.
What diagnostic path is followed now? Why?
