BECKHOFF ET1100 - Manual (Page 9)

General Issues
Slave Controller – Application Note FAQ 5
3.9 Should I enable Enhanced Link Detection?
For MII ports, a precondition for Enhanced Link Detection is that the MII management interface is
operating with all PHYs (PHY address configuration ok), which is strongly recommended anyway. If
the ESC has only MII ports, Enhanced Link Detection is recommended regardless of the PHY link loss
reaction time. If the Enhanced Link Detection can be enabled port-wise, it is recommended to enable it
for each MII port.
If the ESC has one or more EBUS ports, Enhanced Link Detection must remain disabled for ET1200
and ET1100. This is also true if the PHY offset for ET1200 or ET1100 is not zero.
Refer to the ESC datasheet section I for more information about Enhanced Link Detection.
3.10 Why must I configure the PHYs for auto-negotiation instead of forcing 100 Mbit+FD?
EtherCAT requires that the Ethernet PHYs are configured to use auto-negotiation, and not 100 Mbit +
full duplex in force mode. The reason is interoperability.
While two devices which are forced to 100 Mbit + full duplex (FD) are perfectly operating together with
EtherCAT, a problem arises if one device uses auto-negotiation, and the other one forced mode. In
this case, the auto-negotiation device will fall back to 100 Mbit + half duplex (HD), because it has no
knowledge of the capabilities of the link partner. The half-duplex operation can lead to communication
issues especially at the master, but probably also at the slaves. That is why auto-negotiation is
mandatory for EtherCAT PHYs.
Another issue is the Auto-MDIX feature of the PHYs, which often depends on auto-negotiation being
enabled. So, without auto-negotiation, some EtherCAT links would require a cross-over cable, others
a straight cable, which complicates the situation even more.
Refer to the AN PHY selection guide for more information.
3.11 What is TX Shift and Auto TX Shift?
Beckhoff ESCs are not incorporating transmit (TX) FIFOs for the MII interfaces to reduce the latency.
Nevertheless, the PHYs have certain timing requirements for the TX signals (setup/hold), which have
to be fulfilled. The TX Shift configuration is used to move the TX signal timing to a valid window
manually. With Auto TX Shift, the ESC automatically figures out the correct shift value and shifts the
TX signals accordingly. Nevertheless, Auto TX Shift is not the same as a TX FIFO, it still requires
synchronous clocking of the ESC and the PHY.
Refer to the ESC datasheet for more information about TX Shift and Auto TX Shift.