76 • CANopen
Description
WAGO-I/O-SYSTEM
750
CANopen
4 CANopen
4.1 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 specifica-
tions 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 identi-
fier, 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 transmis-
sion. 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 fea-
tures used to network distributed field automation devices.
Further information
CAN in Automation (CiA) provides further documents for their members in the
Internet under:
