STM32 (II) GPIO Operation (2) - Controlling the LED light on and off by pressing a button

      STM32 is a low-power chip, so its peripherals all have a corresponding clock, and these clocks are turned off when the chip is just powered on, so if you want the peripherals to work, you must turn on the corresponding clock.

      This article introduces how to control the switch of the LEN lamp by pressing buttons based on GPIO.

     (1) Button control

      The figure above shows the circuit of the key. When the key is not pressed, the output signal of KEY2 is low level (the circuit where the key is located is blocked and connected to the ground); when the key is pressed, the output state of KEY2 is high level (the circuit where the key is located is connected and connected to the 3.3V power supply). Therefore, by detecting the level of the pin, it is possible to determine whether the key is pressed.

       When the mechanical contact of the key is disconnected or closed, due to the elastic effect of the contact, the key switch will not be immediately connected or disconnected, and it will produce a ripple signal as shown in the figure below. Software debouncing processing and filtering are required, which is not convenient for input detection. In addition, the hardware can also realize the debouncing function. As shown in the figure above, the hardware debouncing function is to achieve delay through the charge and discharge of C61 to eliminate ripples, thereby simplifying the software processing, so that the software only needs to detect the level of the pin.

      As mentioned above, the first step is to turn on the GPIO clock so that the peripheral can work. This article uses the STM32 library function to write the code:

//Start the clock of the button port (port A)

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);

//Define a structure to configure the settings of the PA0 pin

GPIO_InitTypeDef GPIO_InitStructure;

//Set the pin of the structure to 0

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;

//Set the structure mode to floating input

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;

//Set the structure to port A, that is, set the PA0 pin to floating input

GPIO_Init(GPIOA, &GPIO_InitStructure);

      The above code first fills in the GPIO structure, and then writes parameters to the corresponding GPIO register through the function GPIO_Init() to complete the initialization of GPIO.

      Then we need to detect the status of the button. The code is as follows:

// Check if the button is pressed

if(GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_0) == KEY_ON) {

// Check if the button has been released

      while (GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_0) == KEY_ON);

//Subsequent code processing after pressing the key         

............................................

}

(II) GPIO output

       Similar to GPIO input, the code for GPIO output is as follows:

//Define a GPIO_InitTypeDef type structure

GPIO_InitTyopeDef GPIO_InitStructure;

// Enable GPIO related peripheral clocks

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);

//Select the GPIO pin to be controlled

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;

//Set the output mode of the GPIO pin to push-pull output

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;

//Set the pin rate to 50MHZ

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHZ;

//Call library function to initialize GPIO

GPIO_Init(GPIOB, &GPIO_InitStructure);

      After using the above code settings, you can control the LED light in the main function.

      Set GPIOB->BSRR to 1 to output a high level to light up the LED, and set GPIOB->BRR to 1 to output a low level to turn off the LED.