The IOSTANDARD attribute is available to choose the values for an I/O standard for all I/O buffers. The supported I/O standards are listed in the Spartan UltraScale+ FPGA Data Sheet: DC and AC Switching Characteristics (DS930) ; however, Table 1 lists the IOSTANDARD support by I/O bank type (HP and HD). The IOSTANDARD attribute uses the following syntax in the XDC file:
set_property IOSTANDARD value [get_ports port_name
]