From LPF
If external is not available you can use DIFFRESISTOR=100 IO_TYPE=LVDS
IOBUF PORT "gp9" IO_TYPE=LVCMOS25D;
IOBUF PORT "gn9" IO_TYPE=LVCMOS25D;
IOBUF PORT "gp10" IO_TYPE=LVCMOS25D;
IOBUF PORT "gn10" IO_TYPE=LVCMOS25D;
IOBUF PORT "gp11" IO_TYPE=LVCMOS25D;
IOBUF PORT "gn11" IO_TYPE=LVCMOS25D;
FREQUENCY PORT "gp12" 25 MHZ;
IOBUF PORT "gp12" IO_TYPE=LVCMOS25D;
IOBUF PORT "gn12" IO_TYPE=LVCMOS25D;