Ethercat System - Omron 3G3AX-MX2-ECT User Manual

1 EtherCAT Network
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EtherCAT System

In EtherCAT, data is not sent to each node in the network, but the Ethernet frame is made to pass
through each node.
As the frame passes through, data is read and written at each node in the node's own area inside the
frame in several nanoseconds.
The Ethernet frame that was sent by the EtherCAT master passes through all the EtherCAT slaves
without stopping midway. Then, the frame is sent back by the final slave, and passes through all the
slaves again before returning to the EtherCAT master.
This system ensures high-speed data transmission and realtime performance.
EtherCAT master
The periodic data exchange between the EtherCAT master and EtherCAT slaves is performed with the
"EtherCAT telegrams" that are stored directly inside the Ethernet frame.
Each "EtherCAT telegram" consists of an address, data and working counter (check bit) for one or more
slaves.
If we compare an Ethernet frame to a train, EtherCAT telegrams can be considered as the carriages.
Ethernet
header
EtherCAT
header
1st EtherCAT 2nd EtherCAT
telegram
Datagram
header
1 - 4
Slave
Data
OUT IN
Ethernet frame
Ethernet frame
Ethernet data (Max. of 1,498 bytes)
1...n EtherCAT telegram
telegram
Data
Slave
Slave
• Reading of output data addressed to self
• Writing of input data
. . . . .
n th EtherCAT
telegram
WKC
WKC: Working counter
EtherCAT Communication Unit USER'S MANUAL (3G3AX-MX2-ECT)
CRC
Ethernet frame