BECKHOFF EtherCAT Technology Section I - Manual (Page 53)

Ethernet Physical Layer
Slave Controller – Technology I-33
5.14 Back-to-Back MII Connection
5.14.1 ESC to ESC Connection
Two EtherCAT slave controllers can be connected back-to-back using MII as shown in the figure
below. The timing of RX_DV and RXD with respect to RX_CLK has to be checked at both ESCs to be
compliant with the IEEE 802.3 requirements of min. 10 ns setup time and min. 10 ns hold time. The
timing can be adjusted by configuring the TX Shift settings of each ESC.
Enhanced Link Detection cannot be enabled for the back-to-back ports on both ESCs.
Other clocking options besides using quartz oscillators are also possible. If CLK25_OUT is not
available, REF_CLK can be used instead.
ESC
REF_CLK
LINK_MII*
RX_CLK
RX_DV
RXD[3:0]
TX_CLK
TX_EN
TXD[3:0]
RX_ER
MDC
MDIO
ESC
REF_CLK
RESET*
RX_CLK
RX_DV
RXD[3:0]
TX_CLK
TX_EN
TXD[3:0]
RX_ER
MDC
MDIO
25 MHz
4
K
7
* check polarity: active Reset = no link
V
CC I/O
4
K
7
V
CC I/O
Configure TX Shift and
check RX timing
(setup/hold>10 ns)
Configure TX Shift and
check RX timing
(setup/hold>10 ns)
CLK25_OUT
25 MHz
CLK25_OUT
LINK_MII* RESET*
Single clock source is
possible, too.
Figure 14: Back-to-Back MII Connection (two ESCs)