The Virtex-II SPICE models contain a voltage node called "VGG". What does this represent? What are its minimum and maximum values?
VGG represents internal memory; thus, this voltage node should not be modified by the user. Its value has no effect on the I/O data path, so it can be safely ignored when best and worst-case simulations are performed.
For more information, please see (Xilinx Answer 6398).