Here's an example: EK1100

The EK1100 coupler is used to connect EtherCAT to EtherCAT terminal modules (Elxxxx). A single station consists of one EK1100 coupler, any number of EtherCAT terminal modules, and one bus-end terminal module. This coupler converts the pass-through messages from Ethernet 100BASE-TX into E-bus signals.

The coupler connects to the network via the Ethernet interface located at the top. The RJ45 interface at the bottom can be used to connect other EtherCAT devices on the same network segment. In an EtherCAT network, the EK1100 coupler can be installed at any point along the Ethernet signal transmission segment (100BASE-TX), but it cannot be directly connected to a switch. The BK9000 coupler (for K-bus components) can be connected directly to a switch.

Here’s an example to illustrate: BK1120

BK1120 | EtherCAT Coupler for Standard Bus Terminal Modules

The BK1120 bus coupler is used to connect EtherCAT to K-bus components (KLxxxx) from Beckhoff’s established series of bus terminal modules. A single station consists of one BK1120 bus coupler, any number of terminal modules (up to 64; up to 255 when expanded via the K-bus), and a bus termination module. The bus coupler automatically recognizes the connected terminal modules and assigns them to the EtherCAT process image. The bus coupler connects to the network via the Ethernet interface located on its upper side. The RJ45 interface on its lower side can be used to connect other EtherCAT devices within the same network segment. In an EtherCAT network, the BK1120 bus coupler can be installed at any point along the Ethernet signal transmission segment (100BASE-TX); however, it cannot be directly connected to a switch. The BK9000 coupler (for K-bus components) can be directly connected to a switch.