PWM，英文名Pulse Width Modulation，是脉冲宽度调制缩写，它是通过对一系列脉冲的宽度进行调制，等效出所需要的波形（包含形状以及幅值），对模拟信号电平进行数字编码，也就是说通过调节占空比的变化来调节信号、能量等的变化，占空比就是指在一个周期内，信号处于有效电平的时间占据整个信号周期的百分比。
PWM的输出模式
可以修改TIMx_CCRx寄存器的值来修改占空比。
PWM模式1
在向上计数时，一旦CNT<CCRx 时输出为有效电平，否则为无效电平。
在向下计数时，一旦CNT>CCRx 时输出为无效电平，否则为有效电平。
PWM模式2
在向上计数时，一旦CNT<CCRx 时输出为无效电平，否则为有效电平。
在向下计数时，一旦CNT>CCRx 时输出为有效电平，否则为无效电平。
STM32F103C8T6的PWM资源
PWM的周期和频率
周期是频率的倒数，如驱动sg90舵机时PWM信号的频率大概为50HZ，即周期为20ms（Tout，也就是定时时间）
PWM实现呼吸灯
利用调节PWM的占空比大小来实现呼吸灯，PWM周期为0.5ms即频率为2000HZ
使用STM32CubeMX创建工程
配置SYS
配置RCC
配置PWM
翻看使用手册，查看LED1使用哪个PWM
选择定时器4，打开时钟来源选择中间时钟，选择通道三输出PWM
配置定时方式，定时时间为0.5ms（即PSC为71，ARR为499），PWM的相关信息（选择PWM模式1）
配置工程名称、工程路径
选择固件库
生成工程
main函数编写
-
在main函数中打开某个PWM（HAL_TIM_PWM_Start(&htim4,TIM_CHANNEL_3);）
-
修改某个PWM的占空比，即修改TIMx_CCRx寄存器的值（HAL_TIM_SetCompare(&htim4,TIM_CHANNEL_3,pwmVal);）
/* USER CODE BEGIN Header */
/**
******************************************************************************
* @file : main.c
* @brief : Main program body
******************************************************************************
* @attention
*
* Copyright (c) 2023 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
*/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "tim.h"
#include "gpio.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
/* USER CODE BEGIN PV */
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* @brief The application entry point.
* @retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
uint16_t pwmVal = 0; //占空比大小(CCRx的大小)
uint8_t direction = 1; //呼吸灯方向： 1. 越来越亮 2. 越来越暗
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_TIM4_Init();
/* USER CODE BEGIN 2 */
//初始化之后，打开引脚PB8的PWM,即定时器4通道三的PWM
HAL_TIM_PWM_Start(&htim4,TIM_CHANNEL_3);
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
HAL_Delay(3); //控制呼吸灯呼吸速率
//控制占空比大小，即修改CCRx的大小
if(direction){
pwmVal++;
}else{
pwmVal--;
}
//设置了ARR为499，因此每计数500为一个周期
if(pwmVal > 500){
direction = 0; //改变呼吸灯方向
}else if(pwmVal == 0){
direction = 1; //改变呼吸灯方向
}
//修改定时器4通道三的PWM的占空比
__HAL_TIM_SetCompare(&htim4,TIM_CHANNEL_3,pwmVal);
}
/* USER CODE END 3 */
}
/**
* @brief System Clock Configuration
* @retval None
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}
/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
{
Error_Handler();
}
}
/* USER CODE BEGIN 4 */
/* USER CODE END 4 */
/**
* @brief This function is executed in case of error occurrence.
* @retval None
*/
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
__disable_irq();
while (1)
{
}
/* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t *file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */
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