GPIO_PDPU_SEL1=impedance
GPIO Input Mode Config 2. Each bit in this register enables the pull-down for the associated GPIO pin in this port.
GPIO_PDPU_SEL1 | The two bits in GPIO_PDPU_SEL0 and GPIO_PDPU_SEL1 for each GPIO pin work together to determine the pad mode when the GPIO is set to input mode. 0 (impedance): High Impedance. 1 (pd): Pull-down mode. |