17-01-2013, 04:03 PM
Controller Area Network
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CAN History
Bosch originally developed the Controller Area
Network (CAN) in 1985 for in-vehicle networks. In the
past, automotive manufacturers connected electronic
devices in vehicles using point-to-point wiring
systems. Manufacturers began using more and more
electronics in vehicles, which resulted in bulky wire
harnesses that were very heavy and expensive. They
then replaced dedicated wiring with in-vehicle
networks, which reduce wiring cost, complexity, and
weight. CAN, a high-integrity serial bus system for
networking intelligent devices, emerged as the
standard in-vehicle network. The automotive industry
quickly adopted CAN and, in 1993, it became the
international standard known as ISO 11898. Since
1994, several higher-level protocols have been
standardized on CAN, such as CAN open and Device
Net. Other markets have widely adopted these
additional protocols, which are now standards for
industrial communications. This white paper focuses
on CAN as an in-vehicle network.
INTRODUCTION
The Controller Area Network (the CAN bus) is a serial
communications bus for real-time control
applications; operates at data rates of up to 1
Megabits per second, and has excellent error
detection and confinement capabilities.
CAN was originally developed by the German
company, Robert Bosch, for use in cars, to provide a
cost-effective communications bus for in-car
electronics and as alternative to expensive,
cumbersome and unreliable wiring looms and
connectors. The car industry continues to use CAN
for an increasing number of applications, but
because of its proven reliability and robustness, CAN
is now also being used in many other control
applications.
CAN is an international standard and is documented
in ISO 11898 (for high-speed applications) and ISO
11519 (for lower-speed applications).
Low-cost CAN controllers and interface devices are
available as off-the-shelf components from several of
the leading semiconductor manufacturers. Custom
built devices and popular microcontrollers with
embedded CAN controllers are also available.
CAN technology used in Cars
To satisfy customer requirements for greater safety,
comfort, and convenience, and to comply with
increasingly stringent government legislation for
improved pollution control and reduced fuel
consumption, the car industry has developed many
electronic systems. Anti-lock Braking, Engine
Management, Traction Control, Air Conditioning
Control, central door locking, and powered seat and
mirror controls are just some examples.
The complexity of these controls systems, and the
need to exchange data between them meant that
more and more hard-wired, dedicated signal lines
had to be provided. Sensors had to be duplicated if
measured parameters were needed by different
controllers. Apart from the cost of the wiring looms
needed to connect all these components together,
the physical size of the wiring looms sometimes
made it impossible to thread them around the
vehicle (to control panels in the doors, for example).
In addition to the cost, the increased number of
connections posed serious reliability, fault diagnosis,
and repair problems during both manufacture and in
service.
Industrial Applications of CAN
CAN controllers and interface chips are physically
small. They are available as low-cost, off-the-shelf
components. They will operate at high, real-time
speeds, and in harsh environments. All these
properties have led to CAN also being used in a wide
range of applications other than the car industry.
The benefits of reduced cost and improved reliability
that the car industry gains by using CAN are now
available to manufacturers of a wide range of
products.
How does CAN works ?
Principle :
Data messages transmitted from any node on a CAN
bus do not contain addresses of either the
transmitting node, or of any intended receiving node.
Instead, the content of the message (e.g. Revolutions
Per Minute, Hopper Full, X-ray Dosage, etc.) is
labelled by an identifier that is unique throughout the
network. All other nodes on the network receive the
message and each performs an acceptance test on
the identifier to determine if the message, and thus
its content, is relevant to that particular node.
If the message is relevant, it will be processed;
otherwise it is ignored. The unique identifier also
determines the priority of the message. The lower
the numerical value of the identifier, the higher the
priority.
In situations where two or more nodes attempt to
transmit at the same time, a non-destructive
arbitration technique guarantees that messages are
sent in order of priority and that no messages are
lost.