AR# 8407: 2.1i Constraints Editor - LVDS I/O standard for Virtex-E not yet supported.
2.1i Constraints Editor - LVDS I/O standard for Virtex-E not yet supported.
In the 2.1i Constraints Editor, under the "Ports" tab, there is an "I/O Configuration Options" box. If this box is checked, a column marked "IOSTANDARD" is added. Clicking inside the column brings up a listing of the various I/O standards available in Virtex-E, but LVDS is not listed among them.
The Constraints Editor will not support LVDS until the next major software release.
Until them, you must manually edit the UCF file. For more information regarding this, please see (Xilinx Solution 8187).