Spartan UltraScale+ devices have pins dedicated to the configuration functions contained in I/O bank 0. There can also be I/O pins in bank 65/66 (multi-function configuration bank) known as multi-function or multipurpose pins that can be used for configuration and converted to programmable I/O pins after configuration is complete.
During configuration, the PUDC_B (active-Low) input enables internal pull-up resistors on the SelectIO pins after power-up and during configuration, including multipurpose configuration pins when not used for the selected configuration mode. For further details, refer to Spartan UltraScale+ FPGAs Configuration User Guide (UG860).