Virtex-4 Fx Devices - Xilinx LogiCORE 1000BASE-X User Manual

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Chapter 7: 1000BASE-X with RocketIO Transceivers

Virtex-4 FX Devices

Figure 7-6 illustrates sharing clock resources across multiple instantiations of the core
when using MGTs. Note that the example design, when using the Virtex-4 family, can be
generated to connect either a single instance of the core, or connect a pair of core instances
to the transceiver pair present in an MGT tile. Figure 7-6 shows two instantiations of the
block level, where each block contains a pair of cores, subsequently illustrating clock
sharing between four cores in total.
More cores can be added by continuing to instantiate extra block-level modules. Share
clocks only between the MGTs in a single column. For each column, use a single
brefclk_p and brefclk_n differential clock pair and connect this to a GT11CLK_MGT
primitive. The clock output from this primitive should be shared across all used RocketIO
tiles in the column. See the Virtex-4 RocketIO Multi-Gigabit Transceiver User Guide (UG076)
for more information.
To provide the 125 MHz clock for all core instances, select a TXOUTCLK1 port from any
MGT. This can be routed onto global clock routing using a BUFG as illustrated, and shared
between all cores and MGTs in the column. Although not illustrated in Figure 7-6, dclk
(the clock used for the calibration blocks and for the Dynamic Reconfiguration Port (DRP)
of the MGTs) can also be shared.
88 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008