stm32f407pwm输出

在STM32F407芯片中，可以使用定时器模块来实现PWM输出。下面是一个示例代码：

#include "stm32f4xx.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_tim.h"

int main(void)
{
    // 初始化时钟
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

    // 初始化GPIO口
    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_12;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOD, &GPIO_InitStruct);

    // 将GPIO口与定时器模块关联
    GPIO_PinAFConfig(GPIOD, GPIO_PinSource12, GPIO_AF_TIM4);

    // 初始化定时器模块
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
    TIM_TimeBaseInitStruct.TIM_Prescaler = 84 - 1;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInitStruct.TIM_Period = 1000 - 1;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStruct.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(TIM4, &TIM_TimeBaseInitStruct);

    // 配置PWM输出
    TIM_OCInitTypeDef TIM_OCInitStruct;
    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStruct.TIM_Pulse = 500;
    TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM4, &TIM_OCInitStruct);
    TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);

    // 启动定时器
    TIM_Cmd(TIM4, ENABLE);

    while (1) {
        // 在此处可以修改占空比，以改变PWM输出的占空比
        TIM_SetCompare1(TIM4, 800);
        delay_ms(1000);
        TIM_SetCompare1(TIM4, 200);
        delay_ms(1000);
    }
}

以上代码实现了在PD12口输出PWM信号，占空比为50%（即高电平和低电平的时间相等）。你可以通过修改`TIM_OCInitStruct.TIM_Pulse`的值来改变占空比，取值范围为0到1000。