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4 EtherCAT Communications
CJ-series EtherCAT Slave Units Operation Manual (W541)
4-4 Process Data Objects (PDOs)
4
4-4-1 Introduction
4-4 Process Data Objects (PDOs)
This section describes the process data objects that are used by the EtherCAT Slave Unit.
Process data objects (PDOs) are used to transfer data during cyclic communications in real time.
There are two types of process data objects (PDOs): the RxPDOs, which are used by the EtherCAT
Slave Unit to receive data from the EtherCAT master; and the TxPDOs, which are used by the Ether-
CAT Slave Unit to send data to the EtherCAT master.
The EtherCAT application layer can hold more than one object to enable the transfer of various process
data of the EtherCAT Slave Unit.
The contents of the process data are defined in the PDO mapping objects.
EtherCAT Slave Units support PDO mapping for I/O control.
PDO mapping objects contain the I/O data for the EtherCAT Slave Units. PDO mapping objects for the
RxPDOs are managed in the object dictionary from indexes 1600 to 17FF hex. The TxPDOs are man-
aged in the object dictionary from indexes 1A00 to 1BFF hex.
The PDO mapping scheme in EtherCAT is described below.
Three application objects (A, B, and D) are allocated to the PDO (name: PDO_1) at index 1ZZZ hex.
As described here, PDO mapping shows how application objects are assigned to PDOs.
Indexes and subindexes are also assigned to application objects.
4-4-1 Introduction
4-4-2 PDO Mappings
PDO Mapping Scheme in EtherCAT
TxPDO
EtherCAT master
EtherCAT
Slave Unit
RxPDO
Output data to
EtherCAT Slave Unit
Input data to
EtherCAT master
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