Omron GX-AD0471, User Manual, Page: 30 / 394

1 EtherCAT Network
1 - 4 GX-series EtherCAT Slave Unit User’s Manual
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.
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.
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
1-1-3 Communications types of EtherCAT
Process data communications functions (PDO communications)
Mailbox communications functions (SDO communications)
EtherCAT Master Unit
Slave Unit
Ethernet frame
Slave Unit Slave Unit
Slave Unit
Logic process data
.
.
.
.
.
.
.
.
.
Data a
Data b
Data c
Ethernet
header
EtherCAT
header
1st EtherCAT
datagram
2nd EtherCAT
datagram
3rd EtherCAT
datagram
CRC
. . .