Communication protocol 93
CANopen over EtherCAT
The application layer communication protocol in EtherCAT is
based on the CiA 301 communication profile and is called
CANopen over EtherCAT, or CoE. The protocol specifies the
Object Dictionary in the adapter module, as well as communication
objects for exchanging process data and acyclic messages.
The adapter module uses the following message types:
• Process Data Object (PDO)
The PDO is used for cyclic I/O communication, in other words,
process data.
• Service Data Object (SDO)
The SDO is used for acyclic data transmission.
• Emergency Object (EMCY)
The EMCY is used for error reporting when a fault has
occurred in the drive or adapter module.
The Object Dictionary is described in Appendix A – CoE Object
Dictionary.
Process Data Objects
Process Data Objects (PDOs) are used for exchanging time-critical
process data between the master and the slave. Tx PDOs are
used to transfer data from the slave to the master and Rx PDOs to
transfer data from the master to the slave.
The PDO mapping defines which application objects are
transmitted inside a PDO. These typically include the control and
status words, references and actual values.
The adapter module has six Rx PDOs and six Tx PDOs. Each
PDO can have up to 8 application objects mapped as its contents,
except Rx/Tx PDO 21 which can have up to 15 objects mapped.
The mapping of the PDOs can be changed only in the PREOP
state.
The PDO maps have been pre-defined with the following objects
as default. All PDOs can be reconfigured by the user and also
saved to the adapter module.
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