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 (www.bridgewater-electronics.co.uk), 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 www.can-cia.de. See automotive systems and automotive Ethernet.
References in periodicals archive ?
If a SynqNet and CANopen network each provide an Ethernet port, you could tunnel between them through an Ethernet connection.
One of the device profiles defined by CANopen is the Profile For Drives And Motion Control (DSP-402).
This development system contains everything needed to develop and test small CANopen networks.
If you already use the Controller Area Network (CAN) in a product and plan to adopt the CANopen protocol, you may find value in this book as a reference.
Example applications for the PIC18F4580 microcontroller series include: automotive (body controllers, steering position sensors, cabin environmental control, dashboard/instrument clusters); industrial (copy machines, hydraulic pressure regulators, motor control); consumer (tanning beds); medical (pharmaceutical distribution systems and wheel chairs); J1939 networks (trucks, buses, off-road vehicles, passenger/cargo trains, vending machines); CANopen networks (elevators, escalators, industrial control); DeviceNet networks (factory automation and industrial control).
The main CANopen DLL not only provides functions to read or write Object Dictionary entries of specific nodes, it also includes such powerful commands as a network scan function that within seconds detects the nodes currently connected to the network.
The drives operate as nodes on a CANopen bus under the DSP402 CANopen motion control protocol.
CAN support with a CAN device driver and CANopen protocol support.
Availability with SAE J1939 and CANopen interfaces for vehicle or mobile application.
These drives control DC brush as well as DC and AC brushless motors, and they feature a range of operating functionalities including CANopen networking for distributed intelligence applications.
Other protocols including Ethernet, Foundation Fieldbus, CanOpen, and Profibus have also gained in popularity.
maxon's (Fall River, MA) new EPOS2 24/2 was developed specifically for commanding and controlling in the CANopen network.