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36 www.xilinx.com PCI v3.0.151 Getting Started Guide
UG157 August 31, 2005
Chapter 3: Family Specific Considerations
R
Figure 3-3 shows the small range of supply voltage values where V
IL
or V
IH
are technically
non-compliant. Note that this may occur with any PCI device if the input buffer supply
voltage is different from the supply voltage of the driving device. For best results, use a
high precision voltage regulator to generate V
CCINT
.
For 3.3 volt signaling in Virtex-II Pro, Virtex-4, Spartan-3, and Spartan-3E devices, the V
CCO
supply must be reduced to 3.0 volts and derived from a precision regulator. This reduction
of the output driver supply provides robust device protection without sacrificing PCI
electrical compliance, even in the extreme case where the 3.3 volt system supply climbs as
high as 3.6 volts as allowed by the PCI Local Bus Specification.
Figure 3-3: Relationship For 3.3V Input Buffer Compliance
VCCINT (V)
System Supply (V)
3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45 3.50 3.55 3.60
2.30
2.35
2.40
2.45
2.50
2.55
2.60
2.65
2.70
3.3V PCI COMPLIANT
REGION