Communication Types Of Ethercat - Omron GRT1-ECT Operation Manual

1 EtherCAT Network
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Communication types of EtherCAT

EtherCAT provides the following two types of communication types.
PDO communications are always updating data per communication cycle on EtherCAT, while SDO
communications are processed in between those updates.
Process Data Communication functions (PDO communication)
The PDO communication function is used to transfer process data in real time in a fixed-cycle.
By mapping logical process data space to each node by the EtherCAT Master Unit, it achieves
fixed-cycle communication among the EtherCAT Master Unit and Slaves.
EtherCAT Master Unit
Ethernet frame
Logic process data
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Data a
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Data b
Data c
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Mailbox communication functions (SDO communication)
Communication with Service Data Objects (SDO) refers to message communication.
At any timing, the EtherCAT Master Unit transmits commands to Slaves and the Slaves return
responses to the EtherCAT Master Unit.
It performs the following data communication:
• Read and write process data
• Make Slave setting
• Monitor Slave state
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Slave Unit
Ethernet EtherCAT 1st EtherCAT
header header telegram
Slave Unit Slave Unit
2nd EtherCAT 3rd EtherCAT
telegram telegram
GRT1-series EtherCAT Communication Unit - Operation Manual
Slave Unit
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