Pullup/Pulldown Resistor Enable Registers PxREN
Each bit in each PxREN register enables or disables the pullup/pulldown
resistor of the corresponding I/O pin. The corresponding bit in the PxOUT
register selects if the pin is pulled up or pulled down.
Bit = 0: Pullup/pulldown resistor disabled
Bit = 1: Pullup/pulldown resistor enabled