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1 EtherCAT Network
1 - 4 EtherCAT Communication Unit USER’S MANUAL (I574-E1)
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.
The periodic data exchange between the EtherCAT master and EtherCAT slaves is performed with the
"EtherCAT datagrams" that are stored directly inside the Ethernet frame.
Each "EtherCAT datagram" 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 datagrams can be considered as the carriages.
1-2-2 EtherCAT System
EtherCAT master Slave Slave Slave
Ethernet frame
IN
OUT
Data
• Reading of output data addressed to self
• Writing of input data
Ethernet
header CRC
Ethernet data (Max. of 1,498 bytes)
DataHeader WKC
1…n EtherCAT datagram
EtherCAT
header
1st EtherCAT
datagram
2nd EtherCAT
datagram
n th EtherCAT
datagram
. . . . .
Ethernet frame
Ethernet frame
WKC: Working counter
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