想问下我这个PWM输出波形貌似有哪里不对

不过六级不改名 · 发表于 2018-9-6 16:14:28

基本上是按着视频改的，最后LED常亮且亮度不变是怎么回事
//初始化pwm
void tim3_pwm_init(u16 arr,u16 psc)
{
  GPIO_InitTypeDef TY;
  TIM_TimeBaseInitTypeDef ZY;
  TIM_OCInitTypeDef QY;
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);

  TY.GPIO_Mode=GPIO_Mode_AF_PP;
TY.GPIO_Pin=GPIO_Pin_8;
  TY.GPIO_Speed=GPIO_Speed_50MHz;
  GPIO_Init(GPIOA,&TY);
  GPIO_PinRemapConfig(GPIO_PartialRemap_TIM3,ENABLE);

  ZY.TIM_ClockDivision=TIM_CKD_DIV1;
  ZY.TIM_CounterMode=TIM_CounterMode_Up;
  ZY.TIM_Period=arr;
  ZY.TIM_Prescaler=psc;
  TIM_TimeBaseInit(TIM3,&ZY);

  QY.TIM_OCMode=TIM_OCMode_PWM2;
  QY.TIM_OCPolarity=TIM_OCPolarity_High;
  QY.TIM_OutputState=TIM_OutputState_Enable;
  TIM_OC2Init(TIM3,&QY);

  TIM_OC2PreloadConfig(TIM3,TIM_OCPreload_Enable);
  TIM_ARRPreloadConfig(TIM3,ENABLE);
  TIM_Cmd(TIM3,ENABLE);
}

//主函数
int mian(void) {
u16 led0pwmval=0;
u8 dir=1;
delay_init();
LED_Init();
tim3_pwm_init(899,0);
while(1)  {
  delay_ms(10);
  if(dir)led0pwmval++;
  else led0pwmval--;
  if(led0pwmval>400)dir=0;
  if(led0pwmval==0)dir=1;
  TIM_SetCompare2(TIM3,led0pwmval);
}
}