
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 |
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R_SDO T_SDO |
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| data | |
CAN | data |
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(response) | T_SDO R_SDO | |
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| Server |
Figure 3.10 SDO message exchange with request and response
Message types
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