VREF_CNTR is an attribute specific to the receiver VREF scan feature in HP I/O banks. It is used with the HPIO_VREF UNISIM primitive.
The valid values for VREF_CNTR attribute are:
- FABRIC_RANGE1 (POD standards)
- FABRIC_RANGE2 (other applicable standards)
FABRIC_RANGE1 is used with the POD standards and the FABRIC_RANGE2 is used with the other applicable standards when the receiver VREF scan feature is invoked.
The VREF_CNTR attribute should be set in the UNISIM instantiation. Refer to the UltraScale Architecture Libraries Guide (UG974) for more information.