XC90 FWD L6-3.2L VIN 98 B6324S (2007)
MOST network
General
MOST (Media Oriented Systems Transport) is a standardized network communication system for multimedia applications. The MOST protocol is
optimized for fiber optic communication. This means that signals are sent as light pulses.
MOST data
The MOST protocol determines how light pulses or their absence should be interpreted. Each pulse or absent pulse is called a "bit". The number of
"bits" transmitted on the MOST network is 24.8 million per second (24.8 Mbit/s).
A bit can be:
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binary 0, i.e. no light pulse
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binary 1, i.e. light pulse.
The light pulses are transmitted in data frames. A data frame consists of different types of data. The size of a data frame is 64 bytes, which is 64 x 8 =
512 bits.
The data frame has a frequency of 48 kHz. This means that 48000 data frames are sent per second on the MOST network.
The data types which are included in a data frame sent on the MOST network are:
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control data
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synchronous data
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asynchronous data
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administrative data.
Control data
Control data is used to check and to allocate the functions to the control modules and the functions in the MOST network.
The control data message is transmitted from, for example, the infotainment control module (ICM) to another specific control module.
The control data message automatically checks if the receiver has received the signal and that the entire message has been correctly transmitted between
the transmitting and receiving control modules.
The size of the control data is 2 bytes per data frame. A block, which consists of 16 data frames, is required for a control message to be sent. This means
that the total size of the control message is 32 bytes. A control message is the minimum size of a message to activate or deactivate functions on the
MOST network.
Examples of MOST messages are track changes or stop commands on the CD player.
Up to 1000 control data messages can be sent per second.
Synchronous data
Synchronous data is used to transmit data which requires considerable quantities of data in real time, for example to play back sound to the Audio
Module (AUD).
The length of the synchronous data message which can be sent may be up to 60 bytes per data frame, although never less than 24 bytes. This gives a
transfer rate of up to 23 Mbits per second for data transmitted as synchronous data.
Synchronous data shares the data frame with asynchronous data. The infotainment control module (ICM) controls which control modules transmit
synchronous data and which are receivers.
Asynchronous data
Asynchronous data is used to send large quantities of data, such as TCP/IP and digital images, but not in real time.
The length of the message can be up to 36 bytes (synchronous data minimum 24 bytes + asynchronous data 36 bytes = 60 bytes). This gives a maximum
transfer rate of 14 Mbits per second. When the message has been sent, a check is run to ensure that is has been correctly received.
Asynchronous data shares the data frame with synchronous data. The infotainment control module (ICM) controls which control modules transmit
asynchronous data and which are receivers.
Administrative data
Administrative data consists of two parts.
The first part is at the start of the data frame. This describes how much of the transmitted data is synchronous and how much is asynchronous.
The second part is at the end of the data frame. This part checks that the control modules on the MOST network are working correctly.
The size of administrative data is 2 bytes.
MOST data frame
