Home | Projects | Notes > MCU Peripheral Drivers > GPIO Application 1: Toggling On-board LED (gpio_01_led_toggle_pushpull.c, gpio_01_led_toggle_opendrain.c)

GPIO Application 1: Toggling On-board LED (gpio_01_led_toggle_pushpull.c, gpio_01_led_toggle_opendrain.c)

Requirements

• Write a program to toggle the on-board LED with some delay.

  • Case 1: Use push pull configuration for the output pin

  • Case 2: Use open drain configuration of the output pin

Code

Case 1: gpio_01_led_toggle_pushpull.c

Path: Project/Src/

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/*******************************************************************************
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 * File     : gpio_01_led_toggle_pushpull.c
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 * Brief    : Program to toggle the on-board LED
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              (Push-pull config for output pin)
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 * Author   : Kyungjae Lee
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 * Date     : May 23, 2023
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 ******************************************************************************/
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#include "stm32f407xx.h"
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/**
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 * delay()
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 * Brief    : Spinlock delays the program execution
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 * Param    : None
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 * Retval   : None
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 * Note     : N/A
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 */
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void delay(void)
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{
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    /* Appoximately ~200ms delay when the system clock freq is 16 MHz */
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    for (uint32_t i = 0; i < 500000 / 2; i++);
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} /* End of delay */
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int main(int argc, char *argv[])
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{
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    GPIO_Handle_TypeDef GPIOLed;
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    GPIOLed.pGPIOx = GPIOD;
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    GPIOLed.GPIO_PinConfig.GPIO_PinNumber = GPIO_PIN_12;
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    GPIOLed.GPIO_PinConfig.GPIO_PinMode = GPIO_PIN_MODE_OUT;
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    GPIOLed.GPIO_PinConfig.GPIO_PinSpeed = GPIO_PIN_OUT_SPEED_HIGH;
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    GPIOLed.GPIO_PinConfig.GPIO_PinOutType = GPIO_PIN_OUT_TYPE_PP;
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    GPIOLed.GPIO_PinConfig.GPIO_PinPuPdControl = GPIO_PIN_NO_PUPD;  /* Push-pull, no pupd necessary */
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    GPIO_Init(&GPIOLed);
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    while (1)
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    {
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        GPIO_ToggleOutputPin(GPIOLed.pGPIOx, GPIOLed.GPIO_PinConfig.GPIO_PinNumber);
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        delay();
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    }
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    return 0;
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} /* End of main */

Case 2: gpio_01_led_toggle_opendrain.c

Path: Project/Src/

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/*******************************************************************************
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 * File     : gpio_01_led_toggle_opendrain.c
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 * Brief    : Program to toggle the on-board LED
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 *            (Open-drain config for output pin)
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 * Author   : Kyungjae Lee
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 * Date     : May 23, 2023
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 ******************************************************************************/
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#include "stm32f407xx.h"
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/**
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 * delay()
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 * Brief    : Spinlock delays the program execution
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 * Param    : None
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 * Retval   : None
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 * Note     : N/A
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 */
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void delay(void)
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{
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    /* Appoximately ~200ms delay when the system clock freq is 16 MHz */
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    for (uint32_t i = 0; i < 500000 / 2; i++);
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} /* End of delay */
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int main(int argc, char *argv[])
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{
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    GPIO_Handle_TypeDef GPIOLed;
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    GPIOLed.pGPIOx = GPIOD;
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    GPIOLed.GPIO_PinConfig.GPIO_PinNumber = GPIO_PIN_12;
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    GPIOLed.GPIO_PinConfig.GPIO_PinMode = GPIO_PIN_MODE_OUT;
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    GPIOLed.GPIO_PinConfig.GPIO_PinSpeed = GPIO_PIN_OUT_SPEED_HIGH;
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    GPIOLed.GPIO_PinConfig.GPIO_PinOutType = GPIO_PIN_OUT_TYPE_OD;  /* Open-drain config */
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    GPIOLed.GPIO_PinConfig.GPIO_PinPuPdControl = GPIO_PIN_NO_PUPD;
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        /* Even if you use internal pull-up resistor (GPIO_PIN_PU), the LED will toggle very dim.
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         * It is because of the high resistance of the internal pull-up resistor. Instead of
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         * using the internal pull-up resistor, add an external 470 ohm resistor with a
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         * jumper wire between PD12 and +5V. Then, the LED will toggle with normal brightness.
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         *
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         * For these reasons, it is not a good idea to use open-drain configuration for
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         * a GPIO output pin in general unless it is required by the requirements.
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         */
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    GPIO_Init(&GPIOLed);
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    while (1)
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    {
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        GPIO_ToggleOutputPin(GPIOLed.pGPIOx, GPIOLed.GPIO_PinConfig.GPIO_PinNumber);
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        delay();
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    }
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    return 0;
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} /* End of main */