Getting started with GPIO

This article explain what is and how to use GPIO through examplesl

1. GPIO definition

Stands for General Purpose Input/Output. GPIO is a type of pin found on an integrated circuit that does not have a specific function. While most pins have a dedicated purpose, such as sending a signal to a certain component, the function of a GPIO pin is customizable and can be controlled by software.

2. Configure GPIO for LED toggling

2.1. Objective

• Learn how to setup the pin and GPIO port in STM32CubeMX
• Modify the code generated by STM32CubeMX and use the HAL functions

2.2. How

• Configure the GPIO pin in STM32CubeMX and generate the code
• Add into the project the HAL_Delay function and HAL_GPIO_Toggle function
• Verify the correct functionality on toggling LED

2.3. Create the project in STM32CubeMX

• New project > Access to board selector on main panel or Menu > File > New Project
• Select NUCLEO-L476RG

File:SelectL476.png

• if you have chosen to start the project with a board, the LED pin is already setted (PA5 on NucleoL476RG, for other board check the user manual)

Note: whenever you download a firmware package with STM32CubeMX you have existing examples. You can find them for example here: c:\Users\YourUserName\STM32Cube\Repository\STM32Cube_FW_G0_V1.3.0\Projects\NUCLEO-G071RB\Examples\GPIO\GPIO_IOToggle\GPIO_IOToggle.ioc and open them with STM32CubeMX.

2.3.1. GPIO configuration

• Select the Push-pull mode
• No pull-up and pull-down
• Output speed to VERY HIGH is important for faster peripherals like SPI, USART

File:GPIO config.png

2.3.2. GPIO(Pin) output speed configuration

• Change the rising and falling edge when the pin state changes from high to low or low to high
• A higher GPIO speed increases the EMI noise from STM32 and increases the STM32 consumption
• It is good to adapt the GPIO speed with the peripheral speed. Ex.: Toggling GPIO on 1Hz is LOW optimal settings, but with SPI on 45MHz the VERY HIGH must be set

File:GPIO Speed.png

2.3.3. Set the project details for generation

File:Manage GPIO Project.png

2.3.4. Open the main.c in our IDE

• We do the LED toggling in a function inside main.c

File:Info.png

Between /* USER CODE BEGIN 3 */ and /* USER CODE END 3 */ tags

 /* USER CODE BEGIN 3 */
  /* Infinite loop */
  while (1)
  {
    HAL_GPIO_WritePin(GPIOG, GPIO_PIN_14, GPIO_PIN_SET);
    HAL_Delay(500);
    
    HAL_GPIO_WritePin(GPIOG, GPIO_PIN_14, GPIO_PIN_RESET);
    HAL_Delay(500);
  }
  /* USER CODE END 3 */

2.4. Compile and flash

• Every 500ms the green LED state changes.

All GPIOs are able to drive 5V and 3V in input mode, but they are only able to generate 3V in output Push-pull mode