After I generate a memory design using MIG 3.4 in ISE software 12.1, DRC in the PlanAhead tool shows an error on an I/O standard with the pin assignment coming from MIG generated UCF:
Error Messages :
BIVB Error Unsupported IOStandard in bank 1. For example, port mcb1_dram_ck (IOStd = DIFF_SSTL18_II) (IOStd = DIFF_SSTEL18_II) at site J17, M21.mcb1_dram_dqs
BIVB Error Unsupported IOStandard in bank 3. For example, port mcb3_dram_ck (IOStd = DIFF_SSTL18_II) (IOStd = DIFF_SSTEL18_II) at site F2, L3.mcb3_dram_dqs
Customer designs might exhibit this issue as well.