BECKHOFF EP9128 - Manual (Page 11)

Basic functioin principles
3 Basic functioin principles
3.1 Basic function principles of EtherCAT junctions
Some Beckhoff EtherCAT devices can be used for junctions in the EtherCAT segment. These include
EK1122, EK1521, EP1122, CU1128 and EP9128. In the following examples only the EK1122 is used. The
technical and system characteristics of the other devices are similar.
EtherCAT handling in the slaves
With EtherCAT as fieldbus protocol a wide range of bus topologies can be used: line, star and tree topology,
with redundancy support even ring topology. The simplest topology is the line topology, in which each
EtherCAT slave hands data over to the only available next slave.
Fig. 5: EtherCAT line topology
If EK1100 EtherCAT couplers are used, for example, junctions and therefore a kind of tree topology is
possible.
Fig. 6: Line topology with extensions
The basic principle is that internally the Ethernet frame(s) with the EtherCAT protocol data continue to be
transported in a logical ring:
• the EtherCAT master sends the frame on the two outgoing lines of the Ethernet cable
• this frame passes each slave once,
• is reversed by the last slave in the logical sequence and
EP9128 11 Version 2.1.0