Beckhoff EtherCAT EK112 Series Manual page 85

Fig. 62: Direction of data flow in the ESC
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 two ports:
• one for incoming frames (port 0 [A])
• and 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
Three of the four available ports in the EK1100 EtherCAT Coupler are used, thus enabling a connection to
the right to terminals and via an RJ45 socket to further couplers; cf. Fig. "Line topology with extensions
[} 83]". In the EK1100 the processing unit is not used for process data exchange.
EK112x, EK15xx Version: 3.6
Basics
85