BECKHOFF EtherCAT Technology Section I - Manual (Page 41)

Ethernet Physical Layer
Slave Controller – Technology I-21
5.3 MII Interface
Refer to Section III for ESC specific MII information.
If an ESC MII interface is not used, LINK_MII has to be tied to a logic value which indicates no link,
and RX_CLK, RXD, RX_ER, and especially RX_DV have to be tied to GND. The TX outputs can be
left unconnected, unless they are used for ESC configuration.
Table 13: Special/Unused MII Interface signals
Signal
Direction
at PHY
Description
TX_CLK OUT ESC20:
TX_CLK of one PHY is used as clock source, TX_CLK of other
PHY is unused, leave open.
ESC dependent (e.g., IP Core):
TX_CLK is optionally used for automatic TX Shift compensation.
Other Beckhoff ESCs:
Unused, leave unconnected.
COL OUT Collision detected.
ESC20:
Connected, but not used.
Other Beckhoff ESCs:
Unused. Leave unconnected.
CRS OUT Carrier sense.
ESC20:
Connected, but not used.
Other Beckhoff ESCs:
Unused. Leave unconnected
TX_ER IN Transmit error.
ESC20:
Connected, always driven low.
Other Beckhoff ESCs:
Connect to GND.
For more details about the MII interface, refer to IEEE Standard 802.3 (Clause 22), available from the
IEEE.