Ethercat Basics - Wieland samos PRO COMPACT Manual

EtherCAT Gateway
11.2

EtherCAT basics

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General information
Field buses have been established in automation engineering for many years. Since on the one
hand there is demand for ever higher speeds, but on the other hand the technical limits have
already been reached with this technology, new solutions must be sought.
The Ethernet known from the office world, with its available-everywhere 100Mbit/s, is very
fast. The type of cabling used there and the rules governing access rights mean that this
Ethernet is not real-time capable. This effect has been rectified with EtherCAT.
EtherCAT
For EtherCAT: EtherCAT is a registered trademark and patented technology, licensed by Beck-
hoff Automation GmbH, Germany.
EtherCAT stands for Ethernet for Controller and Automation Technology. It was originally deve-
loped by Beckhoff Automation GmbH and is now supported and further developed by the
EtherCAT Technology Group (ETG). The ETG is the world's largest international users and ma-
nufacturers association for industrial Ethernet with around 1450 member firms (as at October
2010).
EtherCAT is an open Ethernet-based fieldbus system that is standardized in the IEC. As an o-
pen fieldbus system, EtherCAT satisfies the user profile for the area of industrial real-time sys-
tems.
Unlike traditional Ethernet communications, in EtherCAT the I/O data are exchanged at
100MBit/s in full duplex mode, while the telegram passes through the coupler. Since in this
way a telegram reaches lots of devices in the transmit and receive direction, EtherCAT has a
useful data rate of over 90%.
The EtherCAT protocol, optimized for process data, is transported directly in the Ethernet tele-
gram. In turn, this can consists of several sub-telegrams, each serving one memory area of the
process image.
Transmission medium
EtherCAT uses Ethernet as the transmission medium. Standard CAT5 cable is used. Cable
lengths of up to 100m between 2 devices are possible.
Only EtherCAT components may be used in an EtherCAT network. To implement topologies
deviating from the linear structure corresponding EtherCAT components are required that sup-
port this. It is not possible to use hubs.
Communication principle
In EtherCAT the master sends a telegram to the first device. This extracts the data intended for
it from the data flow, inserts its response data into the telegram and sends the telegram on to
the next device. The next device processes the telegram in the same way.
If the telegram has reached the last device, this recognizes that no more devices are connected
and sends the telegram back to the master. In this way the telegram is sent via the other pair
of wires through all devices to the master (full duplex). The connection sequence and the use
of full-duplex technology means EtherCAT is a logical ring.
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Wieland Electric GmbH | BA000970 | 11/2016 (Rev. F)