General Purpose Output

• The output buffer is enabled (open drain or push-pull).
• 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.
• Output data register holds last written value.

The code snippet bellow shows how to configure and use a GPIO pin as output.

#include "reg_stm32f4xx.h"
 
/* Configure GPIO pin A.5 as output. */
GPIOA->MODER &= ~(0x3 << 10u);    /* Clear existing mode bits 10 and 11. */
GPIOA->MODER |= (0x1 << 10u);     /* Set pin 10 to pull-up mode. */
 
GPIOA->PUPDR &= ~(0x3 << 10u);    /* Clear existing pull-up/-down bits 10 and 11. */
GPIOA->PUPDR |= (0x2 << 10u);     /* Set pin 5 to pull-down mode. */
 
GPIOA->OTYPER &= ~(0x1 << 5u);    /* Clear existing output type bit 5. */
 
GPIOA->OSPEEDR &= ~(0x3 << 10u);  /* Clear existing output speed bits 10 and 11. */
GPIOA->OSPEEDR |= (0x1 << 10u);   /* Set pin 5 to medium speed (10 MHz) mode. */
 
/* Write to GPIO pin A.5. */
GPIOA->IDR |= (0x1 << 5u);        /* Write to data register. */
 
GPIOA->BSRR[0] = (0x1 << 5u);     /* Directly set GPIO pin A.5. */
GPIOA->BSRR[1] = (0x1 << 5u);     /* Directly clear GPIO pin A.5. */

Mode register

Push-up / pull-down register

Output type register

Output speed register

Output data register

Bit set / reset register