Altera Triple Speed Ethernet MegaCore Function - Manual (Page 174)

Recommended Frequency
(MHz)
Clock MegaCore Function Variant
50–100
CLK
1000BASE-X/SGMII PCS only
125 REF_CLK
125
TBI_TX_CLK
125
TBI_RX_CLK
Timing Constraints Altera Corporation
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UG-01008
Recommended Clock Frequency 9-4
2014.06.30