If two separate differential I/O standards are instantiated in the same bank, errors similar to the following appear:
"ERROR:Place:1747 - The IOB T65 is locked to site AM5 in Bank 5. This violates the SelectIO banking rules. Other incompatible IOBs may be locked to the same bank, or this IOB may be illegally locked to a VREF site. Please consult the SelectIO application node."
"ERROR:Place:993 - Due to Virtex SelectIO banking constraints, the IOBs in your design cannot be automatically placed."
You cannot define two separate differential I/O standards in the same bank if their recommended VREFs are different (as defined in the Data Book).