118 • CANopen

Description

5 CANopen

5.1 Description

CAN (Controller Area Network) was developed in the mid-eighties for data transmission in automobiles. The CAN specification defines the Data Link Layer which is the physical and data backup layer. The message structure is exactly described, however, nothing is said regarding the Application Layer. CAL, in the contrary, describes the Application Layer or the Meaning of the transmitted data. CAL is a general descriptive language for CAN networks and provides a large number of communication services.

CANopen is a networking concept based on the serial bus system CAN. CANopen is defined as a uniform application layer by the DS 301 specifications of the CIA (CAN in automation).

The network management provides a simplified start-up of the network. This network can be extended by the user as desired.

CAN is a Multimaster bus system. In contrast to other fieldbus systems, the modules connected to the bus are not addressed but the messages identified. Whenever the bus is free, the subscribers are allowed to send messages. Bus conflicts are solved in that the messages are assigned a certain priority. This priority is defined by the COB ID (Communication Object Identifier) and is clearly assigned to a communication object. The smaller the assigned identifier, the higher the priority. This also allows communication without the bus master group.

Each bus subscriber is solely decisive as to the point in time of data transmission. However, there is also a possibility to request other bus subscribers to send data. This request is performed via the so-called remote frame.

The CANopen specification (DS 301) defines the technical and functional features used to network distributed field automation devices.

Further information

CAN in Automation (CiA) provides further documents for their members in the Internet under:

can-cia.de

WAGO-I/O-SYSTEM 750

CANopen