General Purpose Input

• The output buffer is disabled.
• The Schmitt trigger input is active.
• The pull-up and -down resistors are active, according to PUPDR.
• Input data is sampled every AHB clock.
• Input data register holds I/O state.

The code snippet bellow shows how to configure a GPIO pin as input.

#include "reg_stm32f4xx.h"
 
GPIOA->MODER &= ~(0x3 << 20u);    /* Clear existing mode bits 20 and 21. */
 
GPIOA->PUPDR &= ~(0x3 << 20u);    /* Clear existing pull-up/-down bit 20 and 21. */
GPIOA->PUPDR |= (0x1 << 20u);     /* Set pin 10 to pull-up mode. */
 
uint32_t data = GPIOA->IDR;       /* Read the input data register. */

* Register is read only