
8
Design Considerations
2014.06.30
UG-01008
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Optimizing Clock Resources in Multiport MAC with PCS and Embedded PMA
The following factors determine the total number of global and regional clock resources required by your
system:
• Configuration of the Triple-Speed Ethernet MegaCore function and the blocks it contains
• PCS operating mode (SGMII or 1000BASE-X)
• PMA technology implemented in the target device
• Number of clocks that can share a single source
• Number of PMAs required in the design
• ALTGX megafunction operating mode
You can use the same clock source to drive clocks that are visible at the top-level design, thus reducing the
total number of clock sources required by the entire design.
Table 8-1: Clock Signals Visible at Top-Level Design
Clock and reset signals that are visible at the top-level design for each possible configuration.
Configurations(1)
Clocks
MAC and PCS with PMAMAC and PCSMAC Only
Yes——rx_recovclkout
Yes——ref_clk
YesYesYesclk
YesYesYesff_tx_clk
YesYesYesff_rx_clk
NoNoYestx_clk
NoNoYesrx_clk
NoYes—tbi_rx_clk
NoYes—tbi_tx_clk
Yes——gxb_cal_blk_clk(2)
Yes——reconfig_clk
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