The EtherCAT interface

From an Ethernet standpoint, the EtherCAT bus is simply a single large Ethernet station. This “station” re

ceives and transmits Ethernet telegrams. The station does not include an Ethernet controller with down

stream microprocessor, however, but rather a large number of EtherCAT slaves. These slaves process the

incoming telegrams during the cycle and extract the relevant payload data or add it and then forward the

telegram to the next EtherCAT slave. The last EtherCAT slave then returns the now fully processed telegram

so that it will be sent back to the master by the first slave as a kind of response telegram. This procedure

utilizes the fact that Ethernet deals separately with transfers in separate directions (Tx and Rx lines) and

operates in full-duplex mode.

The telegrams are processed in a continuous process. While the telegrams are already being sent on, de

layed by just a few bits, the slave recognizes certain commands for itself and executes them accordingly.

Processing takes place in the hardware and is therefore independent of the response times of the slave.

Each station has an addressable memory area of 64 kB, within which it is possible to read, write or write

and read simultaneously. Several EtherCAT commands can be embedded within an Ethernet telegram, each

of which addresses individual stations and/or memory areas.