Xilinx LogiCORE IP MAC v8.5 User Manual page 116

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Figure 11-2
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116
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illustrates the following:
Direct internal connections are made between the GMII interfaces between the two
cores.
If the GEMAC has been generated with the optional Management Interface, the
MDIO port can be connected up to that of the Ethernet 1000BASE-X PCS/PMA or
SGMII core to access its embedded configuration and status registers. See
Optional Management Interface."
Due to the embedded Receiver Elastic Buffer in the Ethernet 1000BASE-X PCS/PMA
or SGMII core, the entire GMII is synchronous to a single clock domain. For this
reason, userclk2 is used as the 125 MHz reference clock for both cores and the
transmitter and receiver logic of the GEMAC core now operate in the same clock
domain. This allows clock crossing constraints between the gtx_clk and
gmii_rx_clk clock domains to be removed from the GEMAC UCF. See
for Critical Logic within the Core."
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Chapter 11: Interfacing to Other Cores
1-Gigabit Ethernet MAC v8.5 User Guide
UG144 April 24, 2009
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