CITROEN XSARA Technical Training Manual page 17

IV - THE VAN PROTOCOL
The network consists of 2 wires, called:
• Data,
• Data B (Data bar).
The Data B wire is so called because the voltage at its terminals is always
opposite to the voltage on Data.
Two current levels are used to encode two distinct logical states.
This process is used to:
• limit the radiation given off,
• provide good resistance to interference.
There is an advantage in using these two wires and electronic circuits for emitting
and receiving signals. It allows operation in downgraded mode if one of the wires
is broken or short circuited to +12V or to earth.
If a wire breaks, the electronics compares the current level of the signal compared
to a reference. The electronics signals the data line faults.
MULTIPLEXED BSI - XSARA PICASSO AND XSARA – PART 1
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5V
Data
0V
5V
Data B
0V
3
t
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Chapter 1