1.8V I/O for DDR Controller? (BeMicro SDK MDDR)

The BeMicro SDK designs come with a Microtronix MDDR controller evaluation core. They use the 1.8V I/O standard, which allows them to use the thresh pin on the bank as the CS pin of the DDR.

Whenever I try to use another DDR controller, the 1.8V I/O standard causes a fitter error.

Error (165021): The "1.8 V" I/O standard and/or the "8mA" current strength on the pin "RAM_D0" is not supported for DDR/DDR2 external memory interfaces
Info (165023): The combination of the I/O standard "SSTL-2 Class I" and the current strength "8mA" is a supported setting
Info (165023): The combination of the I/O standard "SSTL-2 Class I" and the current strength "12mA" is a supported setting
Info (165023): The combination of the I/O standard "SSTL-2 Class II" and the current strength "16mA" is a supported setting

etc, etc,

If I try to use one of the 1.8 SSTL standards for the I/O, it throws a fitter error telling me that the thresh pin is already used.

Now the 1.8V I/O standard obviously works on this board on those pins with this DDR.

Does anyone know how to force the ALTMEMPHY to use 1.8V?

Thanks!!

Bob