Description
Due to a problem with the Quartus® II software version 12.0 and earlier, a BLVDS output made up of two single ended ALTIOBUF megafunctions and the pseudo diff out atom will have inverted OE behaviour when implemented in Arria® V devices.
This problem does not affect either RTL or post-fit simulation models.
Resolution
Instead of instantiating the pseudo diff out atom and single ended buffers, the differential output buffer should be instantiated by creating a differential output with OE variation of the ALTIOBUF megafunction.
This problem is fixed in the Quartus II software version 12.0SP1.