The EtherCAT Couplers are the link between the EtherCAT protocol at fieldbus level and the EtherCAT plug-in modules. Since communication in the EtherCAT system is continuous right down to the last plug-in module, the coupler only changes the physical layer, without changing the process data stream.

A distinction is made between a coupler, a junction and an EJ Coupler for terminal connection. As a head station, the EtherCAT Coupler starts a new module segment. The junction can be set at any position in the module segment and facilitates the creation of a star topology. The EJ Coupler enables connection of compact Embedded PCs from the CX series and EtherCAT Terminals with the EtherCAT plug-in modules.