46 www.xilinx.com Virtex-5 FPGA User Guide
UG190 (v5.0) June 19, 2009
Chapter 1: Clock Resources
Regional Clock Nets
In addition to global clock trees and nets, Virtex-5 devices contain regional clock nets.
These clock trees are also designed for low-skew and low-power operation. Unused
branches are disconnected. The clock trees also manage the load/fanout when all the logic
resources are used.
Regional clock nets do not propagate throughout the whole Virtex-5 device. Instead, they
are limited to only one clock region. One clock region contains four independent regional
clock nets.
To access regional clock nets, BUFRs must be instantiated. A BUFR can drive regional
clocks in up to two adjacent clock regions (Figure 1-23). BUFRs in the top or bottom region
can only access one adjacent region; below or above respectively. The left side BUFRs can
feed the center column I/Os.
VHDL and Verilog Templates
The VHDL and Verilog code for all clocking resource primitives and ISE language
templates are available in the Libraries Guide.
X-Ref Target - Figure 1-23
Figure 1-23: BUFR Driving Multiple Regions
ug190_1_23_012306
BUFRs
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