BECKHOFF EP9128 - Manual (Page 13)

Basic functioin principles
Ideally link detection and therefore port handling in the ESC should be fast enough that lost frame events are
avoided even at 100 µs cycle time. Nevertheless, at least one lost frame can never be ruled out if a
connection is disconnected while an Ethernet frame is in transit on this line and in the bus segment
downstream of the separation point.
Implementation: EL terminal
A standard EtherCAT slave such as a Beckhoff EL terminal has 2 ports:
• one for incoming frames (port 0 [A])
• one for outgoing frames (e.g. port [D]).
The other two ports are internally closed in the ESC. An EtherCAT telegram enters the processing unit via
port 0 (A)/top and is forwarded to the next slave via port 3 (D)/left, if a link to this port exists ­ see green
arrows. This is the case if a further EL terminal is connected to the right.
If no link exists, the frame is forwarded to port 1(B) via the purple route. This and port 2 (C) have no link and
therefore return the frame to port 0 (A), where the frame leaves via the same Ethernet port through which it
arrived at the slave. This is the case if the terminal acts as end terminal.
An EtherCAT device with a single port is therefore only of limited use, since it can only be used as end
device.
Implementation: EK1100 EtherCAT coupler
In the EK1100 EtherCAT coupler 3 of the 4 available ports are used, so that a connection to the right to
terminals and via an RJ45 socket to further couplers is possible, see Fig. 2. In the EK1100 the processing
unit is not used for process data exchange.
Implementation: EK1122 EtherCAT junction
In the EK1122 all 4 ESC ports can be connected ­ two via the internal E­bus and two via the RJ45 sockets
with Ethernet configuration. In the TwinCAT System Manager the link statuses of ports 0, 1, 2 and 3 are
indicated via the online display as port A, B, C and D, see Fig. Topology display for interrupted line.
Implementation: EK1521 / EK1521­0010 / EK1561 EtherCAT junction
As in the EK1100, three ESC ports can be connected in these junctions: Two via E­bus within the terminal
and one via the SC socket/versatile link and optical fibre cable/POF line.
Implementation: CU1128 and EP9128 EtherCAT junctions
The CU1128 integrates three ESCs, which means eight ports in total are available to users. The three ESCs
are interconnected via E­bus.
Example configuration with EK1122
The following section describes the link characteristics under TwinCAT and its representation in the System
Manager.
EP9128 13 Version 2.1.0