CANopen communication
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05/16/2007
4.2.2 Roles and communication relationships
8 bytes of user data
can be transported in a CAN frame. CANopen defines various
linguistic devices for the transmission of process data and demand data. So-called
PDO
s (
Process Data Objects
) are used for process data, and
SDO
s (
Service Data
Objects
) are used for demand data.
Although the CAN bus in itself represents a system with equality of rights (
Multi-
Master System
), in CANopen there are different roles, of which some are typically
performed by a control, and others typically by a node such as a drive.
Important features of SDO and PDO
"
"
"
"
"
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
"
"
"
"
"
"
Real-time data
Identifier with high priority
max. 8 bytes
Format defined before
CAN pure
no Acknowledgement
Figure 5: Comparison of PDO/SDO characteristics