Description of CANopen-Interface
HYDAC ELECTRONIC GMBH
07.10.2010
Mat. No. 669824
Page 14 of 63
4.2 Process- and Service-Data-Objects
Process-Data-Object (PDO)
Process-Data-Objects manage the process data exchange, such as the cyclical
transmission of the position value.
The process data exchange with the CANopen PDOs is "CAN pure", therefore without
protocol overhead. All broadcast characteristics of CAN remain unchanged. A
message can be received and evaluated by all devices at the same time.
From the measuring system the two transmitting process data objects 1800h for
asynchronous (event-driven) position transmission and 1801h for the synchronous
(upon request) position transmission are used.
Service-Data-Object (SDO)
Service-Data-Objects manage the parameter data exchange, such as the non-cyclical
execution of the Preset function.
For parameter data of arbitrary size with the SDO an efficient communication
mechanism is available. For this between the configuration master and the connected
devices a service data channel for the parameter communication is available. The
device parameters can be written with only one telegram handshake into the object
dictionary of the devices or can be read out from this.
Important characteristics of the SDO and PDO
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System parameter
Identifier with low priority
Data fragmented in
several telegrams
Data addressed via Index
acknowledged services
PDO
SDO
CiA DS-301 CANopen
Data Types Communication Profile
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Real-time data
Identifier with high priority
max. 8 bytes
Format defined before
CAN pure
no Acknowledgement
Figure 3: Comparison of PDO/SDO characteristics
