Delta DVP-ES2/EX2/SS2/SA2/SX2/SE manual ¾ The object dictionary, CANopen Communication Object

7 CANopen Function and Operation

Device profile CiA	Device profile CiA	Device profile CiA
DSP-401	DSP-404	DSP-xxx

OSI seventh layer

Application layer

Communication profile CiA DS-301

OSI second layer	CAN controller			CAN 2.0A
Data link layer
OSI first layer	+	+	-	ISO 11898
		-
Physical layer
				CAN network

¾The 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 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 (EDS).

7.3.2 The CANopen Communication Object

The CANopen communication protocol contains the following communication objects.

¾PDO (process data object)

—The PDO provides the direct visit channel for the device application object, is used to transmit the real-time data, and has high priority. Every byte in the PDO CAN message data list is used to transmit the data. The rate of making use of the message is high.

—There are two kinds of uses for PDOs. The first is data transmission and the second data reception. They are distinguished by Transmit-PDOs (TxPDOs) and Receive-PDOs (RxPDOs). Devices supporting TxPDOs are PDO producers, and devices which are able to

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