Virtex-II Pro / Virtex-II Pro X 3.3V I/O Design Guidelines Application Note (XAPP659) - Describes guidelines on interfacing 3.3V I/O standards (PCI, LVTTL, and LVCMOS) in a Virtex™-II Pro / Virtex-II Pro X system design. Topics include overshoot/undershoot considerations, external regulator and bus switch solutions, device configuration, and other board level design techniques