Intro:
The CAN data bus
(Controller Area Network) is a data bus
system
specifically designed for
used in vehicles.
The CAN data bus is a
bi-directional bus, that is, each connected
control module is able to
send and receive information.
The CAN data bus consists
of a special twisted two-core cable. The
users (control modules)
are connected to this cable. Transmission of
data takes place
redundantly via both cables, whereby the data
bus
levels are mirrored (that
is, if the level on one cable is 0, the other
cable transmits level 1
and vice versa). The twin-line concept is used
for two reasons: for
fault identification and as a safety concept.
If a voltage peak occurs
on just one line (e.g. due to EMC problems),
the receivers can
identify this as a fault and ignore the voltage
peak. |
If a short circuit or
interruption occurs on one of the two CAN lines,
a
software-hardware linked
safety concept allows switching to singleline
operation. The defective
data line is shut down.
A specific data protocol
controls how and when the participants can
send and
receive.
The CAN data bus is
significantly different to other data bus
systems
that are based on the
participant addressing principle, in that it
uses
a message-related
addressing system.
That means, every CAN
message is assigned a fixed address
(identifier), which
identifies the CAN message content (e.g.
coolant
temperature). The CAN
protocol allows up to 2048 different CAN
messages, whereby the
addresses from 2033 to 2048 are
permanently assigned.
Data capacity per CAN message is 8 bytes. |
