Xilinx LogiCORE 1000BASE-X User Manual page 63

Implementing External GMII
Spartan-3, Spartan-3E and Spartan-3A Devices
The logic described previously for Virtex-II and Virtex-II Pro devices does not meet the
input setup and hold requirements for GMII with Spartan-3, Spartan-3E, and Spartan-3A
devices. A DCM must be used on the gmii_tx_clk clock path, as illustrated in
Figure
signal names and logic match
other families.
Phase-shifting may then be applied to the DCM to fine-tune the setup and hold times at the
GMII IOB input flip-flops. The fixed phase shift is applied to the DCM with the example
UCF for the example design. See
Chapter
IOB LOGIC
IBUFG
gmii_tx_clk
IPAD
IBUF
gmii_txd[0]
IPAD
IBUF
gmii_tx_en
IPAD
IBUF
gmii_tx_er
IPAD
Figure 5-15: External GMII Transmitter Logic for Spartan-3, Spartan-3E and Spartan-3A Devices
Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
5-15. This is performed by the top-level example design delivered with the core (all
12.
DCM
gmii_tx_clk_ibufg
CLKIN
CLK0
FB
gmii_tx_clk_bufg
gmii_txd_ibuf[0] gmii_txd_int[0]
D Q
gmii_tx_en_ibuf
gmii_tx_en_int
D Q
gmii_tx_er_int
gmii_tx_er_ibuf
D Q
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Figure 5-15). This DCM circuitry may optionally be used in
"Constraints When Implementing an External GMII" in
BUFG
userclk2 (if RocketIO is used)
gtx_clk (if TBI is used)
Transmitter
Elastic
Buffer
R
Ethernet 1000BASE-X
PCS/PMA
or SGMII LogiCORE
gmii_txd[0]
gmii_tx_en
gmii_tx_er
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