1 EtherCAT – General information
1.1 How EtherCAT works
XN-312-GW-EC gateway 07/20 MN050010-EN
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1 EtherCAT – General information
This section goes over the various special characteristics behind the Ether-
CAT protocol. For more detailed information, please visit the EtherCAT Tech-
nology Group website at:
http://www.ethercat.org/
1.1 How EtherCAT works
Ethernet for Control Automation Technology, or EtherCAT for short, is an
Ethernet-based field bus system with special properties that make it ideal for
the needs of automation applications.
In an EtherCAT system, data packets are sent by a controller and go through
every EtherCAT node one after the other. Once a data packet reaches the
last node, this node will detect that its EtherCAT OUT port is not connected
to anything and will then send the data back through the line. Before this,
however, every node will process the data intended for it on the fly as the
packet keeps being sent forward, with the result being that the delay in
transmitting the data packet to the next downstream node is negligible and
has a magnitude of only a few nanoseconds. From an Ethernet perspective,
this means that an EtherCAT bus segment is a large Ethernet node and that
data is transferred between this node and the EtherCAT master. Within a
segment itself, the EtherCAT nodes are connected to each other via an
EtherCAT IN line and an EtherCAT Out line, which makes it possible for an
Ethernet data packet to reach every single node in both the transmission and
reception directions so that these nodes can process the corresponding data.
This makes it possible to make full use of the full-duplex properties of
100BASE-TX, achieving a payload data rate of over 90%.
