Implementing External GMII

R

Virtex-5 Devices

Figure 5-17illustrates how to create an external GMII transmitter in a Virtex-5 family device. The signal names and logic shown on the figure exactly match those delivered with the example design.

The IODELAY elements can be adjusted to fine-tune the setup and hold times at the GMII IOB input flip-flops. The delay is applied to the IODELAY element using constraints in the UCF; these can be edited if desired. See “Constraints When Implementing an External GMII” in Chapter 12 for more information.

gmii_tx_clk

IPAD

gmii_txd[0]

IPAD

gmii_tx_en

IPAD

gmii_tx_er

IPAD

 

 

IOB LOGIC

 

IBUFG

 

 

 

BUFG

 

 

 

 

gmii_tx_clk_bufg

 

 

IODELAY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

userclk2 (if RocketIO is used) gtx_clk (if TBI is used)

Transmitter

Elastic

Buffer

IBUF

 

 

 

 

gmii_txd_int[0]

 

IODELAY

 

D Q

 

 

 

 

 

 

 

 

 

 

IBUF

 

 

 

D Q

gmii_tx_en_int

 

IODELAY

 

 

 

 

 

 

 

 

 

IBUF

 

 

 

gmii_tx_er_int

 

IODELAY

 

D Q

 

 

 

 

 

 

Ethernet 1000BASE-X PCS/PMA

or SGMII LogiCORE

gmii_txd[0]

gmii_tx_en

gmii_tx_er

Figure 5-17:External GMII Transmitter Logic for Virtex-5 Devices

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1

www.xilinx.com

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UG155 March 24, 2008

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Xilinx 1000BASE-X manual 17External Gmii Transmitter Logic for Virtex-5 Devices