DVP15MC11T Operation Manual
About CANopen protocol
The CAN (controller area network) fieldbus only defines the physical layer and data link layer. (See
ISO11898 standard.) It does not define the application layer. In the practical design, the physical
layer and the data link layer are realized by the hardware. The CAN fieldbus itself is not complete. It
needs the superior protocol to define the use of 11/29-bit identifier and 8-byte data.
The CANopen protocol is the CAN-based superior protocol. It is one of the protocols defined and
maintained by CiA (CAN-in-Automation). It is developed on the basis of the CAL (CAN application
layer) protocol, using a subset of the CAL communication and service protocols.
The CANopen protocol covers the application layer and the communication profile (CiA DS301). It
also covers a framework for programmable registers (CiA 302), the 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 as follows.
The object dictionary
CANopen uses an object-based way to define a standard device. Every device is represented by a
set of objects, and can be visited by the network. The model of the CANopen device is illustrated
below. As the figure below shows, 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 object set. Every
object adopts a 16-bit index for addressing. In order to allow the visit to the single element in the data
structure, it also defines an 8-bit subindex. Every node in the CANopen network has an object
dictionary. The object dictionary includes the parameters which describe the device and the network
behavior. The object dictionary of a node is described in the electronic data sheet.
Device profile CiA
DSP-401
Device profile CiA
DSP-404
Device profile CiA
DSP-xxx
OSI seventh layer
Application layer
Communication profile CiA DS-301
CAN controller
CAN 2.0A
ISO 11898
CAN network
OSI second layer
Data link layer
Physical layer
C-2
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