Schneider Electric DS301 manual Service data communication, Overview, SDO data exchange

3 Basics IL•1F CANopen DS301

3.3Service data communication

3.3.1Overview

Service Data Object(SDO: Service Data Object) can be used to access the entries of an object dictionary via index and subindex. The values of the objects can be read and, if permissible, also be changed.

Every network device has at least one server SDO to be able to respond to read and write requests from a different device. A client SDO is only required to request SDO messages from the object dictionary of a dif- ferent device or to change them there.

The T_SDO of an SDO client is used to send the request for data ex- change; the R_SDO is used to receive. The data frame of an SDO con- sist of 8 bytes.

SDOs have a higher COB ID than PDOs and therefore are sent over the

CAN bus at a lower priority.

3.3.2SDO data exchange

A service data object (SDO) sends parameter data between two de- vices. The data exchange conforms to the client-server relationship. The server is the device to whose object dictionary an SDO message refers.

Client
R_SDO T_SDO
	(request)
	COB-ID	data
CAN	data
COB-ID
(response)		T_SDO R_SDO
		Server

Figure 3.10 SDO message exchange with request and response

Message types Client-server communication is triggered by the client to send parameter values to the server or to get them from the server. In both cases, the cli- ent starts the communication with a request and receives a response from the server.

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