CAN bus

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CAN bus

(Controller Area Network bus) A rugged, digital serial bus designed for industrial environments. Introduced by Bosch in the mid-1980s for in-vehicle communications, it is used in myriad applications including factory automation, building automation, aircraft and aerospace as well as in cars, trucks and buses. CAN bus replaced bulky wiring harnesses with a two-wire differential cable (the two wires carry inverted voltages to decrease interference).

CAN provides services at layers 1 and 2 of the OSI model and uses a broadcast method for placing frames on the wire somewhat similar to Ethernet. Bus distance is based on speed, ranging from a maximum of 40 meters at 1 Mbps to a maximum of six kilometers at 10 Kbps. At speeds up to 125 Kbps, CAN provides fault tolerance. If one of the two wires is cut or shorted, the other keeps transmitting.

In a vehicle, both low- and high-speed CAN buses are used. For example, window, lighting and seat control only need low speeds, while engine, cruise control and antilock brakes require high speeds. Two or three CAN buses may be used in a vehicle; for example, a high-speed bus may be dedicated only for safety (air bags, seat belt tensioners, etc.).

The Bus Hampers After-Market Installations
The CAN bus has made it challenging to add certain after-market products to a vehicle. In older cars, there were discrete wires for everything, but CAN bus signals are digital frames that have to be analyzed to determine their purpose. For example, taxi meters and many GPS navigation systems need to monitor vehicle speed. If speed pulse is no longer available as a discrete wire, a CAN bus interface, such as the CANM8-NAV unit from Bridgewater Electronics (, can convert speed pulse frames to a speed pulse signal.

CANopen and CiA
Introduced in 1995, CANopen is a high-level application layer protocol that provides services for processes, data and network management. The international organization that governs the CANopen protocol is CAN in Automation (CiA). For more information, visit See automotive systems and automotive Ethernet.
References in periodicals archive ?
Ultimately, LaCourse hopes to demonstrate that this "plug-and-play" technology can be adopted by all electronic instruments in operating rooms: Beds and blood pressure monitors as well as ventilation systems, ultrasound monitors, and electrocardiogram monitors will have CANopen software installed by the manufacturers.
In addition to numerous new products from hydraulics, pneumatics, electrical drive and control technology, as well as linear motion and assembly technologies, the company is presenting in particular solutions stretching beyond just technological competence: SERCOS interfacecompatible hydraulic valves and control systems, pneumatic valves that support not only AS-i but also Device NET, CANopen and Profibus DP Bus protocols, as well as proven Soft-SPS control systems and integrated linear axes.
The device provides support for CAN transport layer protocols such as DeviceNet, CANopen and OSEK in hardware rather than leaving the responsibility to the designer to implement in software, resulting in reduced Central Processing Unit (CPU) overhead and increased power to run the application.
When used in conjunction with the ATEX certified VB-2510 Shunt Diode Barrier and the VisConnect[R] converter modules, the sensor system provides continuous viscosity and temperature measurements in a variety of output interfaces including CANopen, RS-232, 4-20mA, and 0-4V.
Additional features of the RoHS-compliant PSI 9000 Series include a galvanically isolated analog interface for voltage, current and power programming and monitoring; digital plug-and-play modules supporting RS232, Ethernet, CANopen, Modbus TCP, Profibus, Devicenet; and IEEE/GPIB and SCPI command language support.
Available protocols: EtherNet[TM], EtherNet I/P[TM], DeviceNet[TM], Profibus[R]-DP, ControlNet[TM], CC-Link, CANopen and AS-Interface (AS-i).
They can be used for communication interfaces such as Profibus, Profinet, Ethernet I/P or CANopen, as well as a module for additional inputs and outputs.
The defacto communication protocol, CANopen, makes it easy to design around because of the predefined medical device profiles available through CAN-CiA.
Selected drives provide multiple modes of operation, variety of common industrial interfaces for acquisition of reference signals, CAN-bus interface with CANOpen protocol for fieldbus connections, as well as multiple general purpose analog and digital I/O ports.
The unit accepts a broad input voltage range from +12 to +48 VDC, and is available in a choice of versions including: microstepping; motion control with intelligent programmable motion controller; speed control with built-in programmable velocity control; and CANopen communication protocol.