This article explains what GPIO is and how to use it through examples
1. GPIO definition
GPIO stands for General Purpose Input/Output. It 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 the software.
- Pin Mode :
Each port bit of the general-purpose I/O (GPIO) ports can be individually configured by software in several modes:
- input or output
- analog.
- alternate function (AF).
- Pin characteristics :
- Input : no pull-up and no pull-down or pull-up or pull-down
- Output : push-pull or open-drain with pull-up or pull-down capability
- Alternate function : push-pull or open-drain with pull-up or pull-down capability
2. Configure GPIO for LED toggling
2.1. Objective
- In this project, you will learn how to Toggle a pin on STM32L476 Nucleo board using Hardware Abstraction Layer (HAL) library
- Learn how to setup the pin and GPIO port in STM32CubeIDE
2.2. How
- Configure the GPIO pin in STM32CubeIDE 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 STM32CubeIDE
File > New > STM32 Project in main panel.
File:GPIO2.png
- Save the project
- In case you haven't downloaded the STM32L476 Cube library, it will be downloaded automatically, it may take some time.
- Once the download is done, you can select NUCLEO-L476RG in board Selector.
- You will then get a popup asking if you want to initialize peripherals to their default configuration
- No need to configure any peripheral as only the core/Flash/SRAMs are used (default peripherals)
- If you want to start the project with a board, the LED pin is already selected (PA5 on NucleoL476RG. For other boards refer to the user manual)
- Yellow pin are related to the power supply
- Unused pins are marked as Grey
Note: During the download of a firmware package with STM32CubeMX, existing examples for some products like STM32G0 can be found at the following path:
c:\Users\YourUserName\STM32Cube\Repository\STM32Cube_FW_G0_V1.3.0\Projects\NUCLEO-G071RB\Examples\GPIO\GPIO_IOToggle\GPIO_IOToggle.ioc
You can open the GPIO_IOToggle.ioc file with STM32CubeIDE
Note: With the STM32L476, there are no ready to use examples.
2.4. GPIO Configuration
- Select the push-pull mode
- No pull-up and pull-down
- Output speed set to very high is important for faster peripherals such as SPI or USART.
2.5. 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. For example toggling GPIO on 1 Hz is low optimal settings, but with SPI on 45 MHz the very high must be set..
2.6. Set the project details for generation
The easiest way the generate the code is save your current project : Ctrl + S
The code is generated so you can see it in the left side of the screen in the project explorer
File:GPIO10.png
2.7. Open the main.c in our IDE
Now, open the main.c file which is the main source file for this application
- We do the LED toggling in a function inside main.c
/* USER CODE BEGIN 3 */
/* Infinite loop */
while (1)
{
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET);
HAL_Delay(500);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_RESET);
HAL_Delay(500);
}
/* USER CODE END 3 */
2.8. Compile and flash
- Click on Build button
to compile the project. - Click on Debug button
to run the software. - Finally, run it File:GPIO16.png
Every 500 ms the green LED state changes.
