PWM

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是脉冲宽度调制。

• 有效电平持续的时间占整个周期的百分比称为占空比。

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

• 高级定时器（TIM1）:7路的PWM

• 通用定时器（TIM2~TIM4）:每个定时器各4路的PWM

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）

• 由于需要手动改变PWM的占空比，所以设置为0

• 由于点亮LED1的有效电平为低电平，所以PWM的极性选择LOW

配置工程名称、工程路径

选择固件库

生成工程

main函数编写

1. 在main函数中打开某个PWM（HAL_TIM_PWM_Start(&htim4,TIM_CHANNEL_3);）

2. 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PWMHAL_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 */