XC90 2.5T AWD L5-2.5L Turbo VIN 59 B5254T2 (2003)
The MOST network is a fiber optic network in which all the control modules are connected in a ring. All messages within the MOST network go in the
same direction from the infotainment control module (ICM) to the antenna module (ATM).
In a fiber optic network, light pulses are transmitted instead of electrical signals. The light pulses are interpreted in the same way as the electrical signals
on the CAN network. The MOST network uses the master-slave concept. This means that the infotainment control module (ICM) has overall control of
communication on the MOST network.
The fiber optic cable is made of plastic. Communication is using red light on a wavelength of 650 nm.
The optical connector
Each control module in the MOST network has an optical connector which consists of two diodes, a sender diode and a receiver diode. These transmit
and receive light pulses. The actual communication between two control modules is as follows. A sender diode transmits the message as a light pulse.
This is transmitted from the control module via the MOST network to a photo-optical receiver diode in the receiving control module.
The two optical terminals in the connector are numbered in the same way on all control modules in the MOST network. The size of the plastic housing
for the two optical terminals varies. A connector with integrated power supply is integrated with the optical terminals and one connector with only the
All messages are transmitted as light pulses in the same direction on the MOST network. This means that if other control modules are connected between
the two control modules which are communicating, the light pulses pass through these with no effect on the information. The control modules which are
passed through amplify the light pulse so that it does not become too weak.
A control module with an internal fault can be set to bypass mode. In this mode, the light pulses are sent straight through the control module without the
control module amplifying the light pulse. This means that the distance before the light pulse is amplified is longer and therefore the luminance is
weaker. If the luminance is too weak, it cannot be received by the receiving control module.
The infotainment control module (ICM) is the gateway between the MOST and CAN networks for communication to and from control modules
connected on the CAN network.
The infotainment control module (ICM) monitors the communication on the MOST network. This involves distributing sound channels on the MOST
network, so that sound data can be distributed from, for example, the CD module (MP2) to the audio module (AUD). The majority of activations on the
MOST network are initiated by the infotainment control module (ICM). The infotainment control module (ICM) also manages diagnostic trouble codes