Communications Types Of Ethercat - Omron E3NX-FA Operation Manual

1 EtherCAT Network
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Communications types of EtherCAT

EtherCAT provides the following two types of communication functions.
PDO communications are always updating data per communication cycle on EtherCAT, while SDO
communications are processed in between those updates.
Process data communications functions (PDO communications)
This 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 communications among the EtherCAT Master Unit and Slave Units.
EtherCAT Master Unit
Ethernet frame
Logic process data
.
.
.
Data a
.
.
.
Data b
Data c
.
.
.
Mailbox communications functions (SDO communications)
It refers to message communications.
At any timing, the EtherCAT Master Unit transmits commands to Slave Units and the Slave Units return
responses to the EtherCAT Master Unit.
It performs the following data communications:
• Read and write process data
• Make Slave Unit setting
• Monitor Slave Unit state
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Slave Unit
Ethernet EtherCAT 1st EtherCAT
header header telegram
E3NW-ECT EtherCAT Digital Sensor Communication Unit Operation Manual (E429)
Slave Unit Slave Unit
2nd EtherCAT 3rd EtherCAT
telegram telegram
Slave Unit
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CRC