In the fitter report, unused pins are labeled as TIE or PGND, depending upon the implementation settings. What do TIE and PGND mean?
TIE or PGND appear depending upon the settings selected in the Implementation Options:
If "Create Programmable Ground Pins on Unused I/O" is not selected, the report will have TIE on the unused pins. Pins marked TIE are floating. TIE signifies that the pin is floating and that Xilinx recommends the pin be tied to a known value. Tying the pin to a known value lowers power consumption and reduces noise.
If "Create Programmable Ground Pins on Unused I/O" is selected, the unused pins will have PGND on them. PGND is Programmable Ground, and it ties the unused pins to the internal device ground plane. PGND provides additional benefits when the pin is externally tied to ground.
For details on using this option in your software package, please see (Xilinx Answer 3404).