CAN bus system

CAN is an abbreviation of Controller Area Network and is a message-based protocol originally developed for automobile in-vehicle networks. The CAN bus is a multi-drop and multi-master serial bus, which provides communications between sensors, actuators and controllers. Nowadays application areas of CAN bus systems are:

- automotive

- industrial systems

- medical systems

- marine control and navigation

- military vehicles

- agricultural machinery

- elevator control systems

CAN is defined by:

- CAN 2.0 A standard format

- CAN 2.0 B extended format

- ISO 11898-2 high speed applications up to 1 Mbit/s

- ISO 11898-3 low speed applications up to 125 Kbit/s

Network layered model:

CAN defines the data link and physical layer of the OSI-model. The higher layer protocols (application, presentation, session, transport, and network layer protocols) are defined by standards like CANOpen, CANaerospace, SAE J1939, ISO 1192, Devicenet, MilCAN, Kvaser's CAN, etc..

Communication:

- broadcasting of messages

- any node is allowed to broadcast

- every node has his own priority

- each receiver decides to process or ignore each message

- source / content of a message identifies by ID

Arbitration

The CAN communication protocol is a carrier-sense, multiple-access protocol with collision detection and

arbitration on message priority (CSMA/CD+AMP).

Message types:

- data frame

- remote frame

- error frame

- overload frame

Error detection:

- bit error

- stuff-bit error

- CRC errors

- acknowledge error

- format error

Physical medium:

Bus length / bit rate tradeoff:

1 Mbit/s 131 feet (40 M)

500 Kbit/s 328 feet (100 M)

250 Kbit/s 656 feet (200 M)

125 Kbit/s 1640 feet (500 M)

Network size:

Networks are limited by electrical loading. The maximum number of nodes is not specified.

Network devices:

- sensors

- actuators

- controllers

- bridges

- gateways (e.g. for communication with protocols like Profibus / Profinet)

- PC-interfaces