Chapter 10 CANopen Function and Operation
10.3 The CANopen Protocol
10.3.1 Introduction to the CANopen Protocol
The CAN (controller area network) fieldbus only defines the physical layer and the data link layer of a network.
See the ISO11898 standard for information. The CAN fieldbus does not define the application layer. In
practice, the hardware contains the physical layer and the data link layer. The CAN fieldbus itself is not
complete, and needs a superior protocol to define the use of 11/29-bit identifier and 8-byte data.
The CANopen protocol is the superior protocol based on the CAN fieldbus. It is one of the protocols defined
and maintained by CiA (CAN-in-Automation) and was developed on the basis of the CAL (CAN application
layer) protocol, using a subset of the CAL communication and service protocols.
The CANopen protocol contains the application layer and the communication profile (CiA DS301). It also
contains a framework for programmable devices (CiA 302), recommendations for cables and connectors (CiA
303-1), and SI units and prefix representations (CiA 303-2).
In the OSI model, the relation between the CAN standard and the CANopen protocol is described in the
following diagram.
The object dictionary
CANopen uses an object-based method to define a standard device. Every device is represented by a set of
objects and can be visited by the network. The diagram below illustrates the CANopen device model. The
object dictionary is the interface between the communication program and the superior application program.
The core concept of CANopen is the device object dictionary (OD). It is an orderly set of objects. Every object
has a 16-bit index for addressing and also defines an 8-bit subindex. Every node in the CANopen network has
an object dictionary that includes the parameters that describe the device and the network behavior. The
object dictionary of a node is also described in the electronic data sheet (EDS) for the device.
Application layer
Communication profile CiA DS-301
OSI second layer
Data link layer
Physical layer
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