BECKHOFF BK1120 EtherCAT Coupler is the link between the EtherCAT protocol at fieldbus level and the Bus Terminals. The coupler converts the passing telegrams from Ethernet 100BASE-TX to the internal, fieldbus-independent terminal bus. A station consists of a coupler and up to 64 Bus Terminals plus a bus end terminal. The process image of the EtherCAT system is assigned automatically. Up to 255 Bus Terminals can be connected via the K-Bus extension.