STM32F4 Discovery Tutorial 3 - Get Input from Button

In this tutorial, I will explain how to configure pin as an input from button. I will use user button which connected to PA0.

First, make new project called button or whatever you want. If you don’t know how to make a new project, you can learn from tutorial 2. After that don’t forget to include the library for this project.

#include "stm32f4xx.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_gpio.h"

Every time you want to use GPIO, you must configure RCC (Reset and Clock Control) for each GPIO.

// Enable peripheral clock to GPIOA module
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
// Enable peripheral clock to GPIOD module
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

GPIO_InitTypeDef is a struct which used for input initialization value for GPIO.

// This is struct for configure GPIO
GPIO_InitTypeDef GPIO_InitStruct;

User button is connected to PA0 therefore you have to configure PA0 as an input pin. This configuration is use built-in pull-down resistor.

// User button is connected to PA0
// So, configure PA0 as an input pin
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_IN;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_DOWN;

Finally you have to initialize GPIOA with GPIO_Init function which takes two parameters. First is the GPIO to be initialized and second is the initialization value that we entered before to GPIO_InitStruct.

// GPIOA initialization
GPIO_Init(GPIOA, &GPIO_InitStruct);

LED 6 is used for output. So, configure PD15 as an output pin.

// Use LED 6 (blue) for output
// So, configure PD15 as an output pin
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_15;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;

// GPIOD initialization
GPIO_Init(GPIOD, &GPIO_InitStruct);

The initialization is done, now write the code for a simple program. When the user button is pressed, then LED 6 will turn on, otherwise the LED will turn off.

while (1)
{
    // If button is pressed
    if (GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_0) == 1)
    {
        // Turn on LED 6
        GPIO_SetBits(GPIOD, GPIO_Pin_15);
    }
    else
    {
        // Turn off LED 6
        GPIO_ResetBits(GPIOD, GPIO_Pin_15);
    }
}

Build and upload your code.