Overview Of Can Bus - Omron CJ1W-CORT21 Operation Manual

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Overview of CAN Bus

The Controller Area Network (CAN) is a serial communications protocol which efficiently supports dis-
tributed real-time control with a very high level of security. Its domain of application ranges from high
speed networks to low cost multiplex wiring. It is especially suited for networking 'intelligent' devices as
well as sensors and actuators within a system or sub-system.
In automotive electronics, engine control units, sensors, anti-skid-systems, etc. are connected using
CAN with bitrates up to 1 Mbps. At the same time it is cost effective to build into vehicle body electron-
ics, e.g. lamp clusters, electric windows etc. to replace the wiring harness otherwise required. CAN has
the following properties:
• prioritization of messages
• guarantee of latency times
• configuration flexibility
• multicast reception with time synchronization
• system wide data consistency
• multi master
• error detection and signalling
• automatic retransmission of corrupted messages as soon as the bus is idle again
• distinction between temporary errors and permanent failures of nodes
• autonomous switching off of defect nodes
 Application Areas
CAN networks can be used as an embedded communication system for micro controllers as well as
an open communication system for intelligent devices. The CAN serial bus system was originally
developed for use in automobiles and is increasingly implemented in industrial field bus systems
because the similarities are remarkable. In both cases some of the major requirements are: low
cost, the ability to function in a difficult electrical environment, a high degree of real-time capability
and ease of use. Some users, for example in the field of medical engineering, opted for CAN
because they have to meet particularly stringent safety requirements. Similar problems are faced by
manufacturers of other equipment with very high safety or reliability requirements (e.g. robots, lifts
and transportation systems).
 Serial bus
CAN is a serial bus system with multi-master capabilities. All CAN nodes are able to transmit data
and several CAN nodes can request the bus simultaneously. The serial bus system with real-time
capabilities is the subject of the ISO 11898 international standard and covers the lowest two layers
of the ISO/OSI reference model. In CAN networks there is no addressing of subscribers or stations
in the conventional sense, but instead, prioritized messages are transmitted.
A transmitter sends a message to all CAN nodes (broadcasting). Each node decides on the basis of
the identifier received whether it should process the message or not. The identifier also determines
the priority that the message enjoys in competition for bus access. The relative simplicity of the CAN
protocol means that very little cost and effort need to be expended on personal training; the CAN
chip's interfaces make application programming relatively simple. Introductory courses, function
libraries, starter kits, host interfaces, I/O modules and tools are available from a variety of vendors
permitting low-cost implementation of CAN networks. Low-cost controller chips implementing the
CAN data link layer protocol in silicon and permitting simple connection to micro controllers have
been available since 1989. Today there are more than 50 CAN protocol controller chips from more
than 15 manufacturers announced and available.
 License of CAN
The CAN protocol is developed by Robert Bosch GmbH and protected by patents.
CJ-series User Defined CAN Unit Operation Manual for NJ-series CPU Unit (W517)
1 Features and System Configuration
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