When I configure a Virtex-II device, what voltage should I apply to Vcco_4 and Vcco_5?
Vcco_4 must meet the POR condition. Beyond this, Vcco_4 and Vcco_5 are dependent upon Configuration modes, and characteristics of the device.
Vcco_4 must be > 1.5V
If Power-up is at room temperature, Vcco_4 > or = 1.5V is acceptable.
2. Clamp diodes
Every I/O pin has intrinsic clamp diodes to Vcco and GND. Over or undervoltage will cause these diodes to turn on. While transient over or undershoot in this fashion will not cause reliability concerns, it will cause signal integrity problems. Such problems might result in functional errors, such as configuration failure.