关于stm32L476的TIM2 输出PWM波形

alisa123 提问时间：2016-7-21 17:05 /

我配置TIM2的通道输出PWM波形，用寄存器操作的，但是怎么输出一直是个高电平，求高手指点，谢谢！配置程序如下：
void PWM_Timer2_Init(void)
{
GPIO_Pin_Init(PORTA，GPIO_Pin_3，GPIO_MODE_AF_PP，GPIO_PULLUP, GPIO_SPEED_HIGH,AF1);

TIM_TypeDef *Timer = TIM2;
/* Enable the Low Speed APB (APB1) peripheral clock  */
RCC->APB1ENR1 |= RCC_APB1ENR1_TIM2EN;          //__TIM2_CLK_ENABLE()
/* Timer2 control register 1 (TIMx_CR1) */
Timer->CR1 &= ~(TIM_CR1_DIR | TIM_CR1_CMS); // Clear direcion and center aligned mode bits
Timer->CR1 |= TIM_COUNTERMODE_CENTERALIGNED1;
Timer->CR1 &= ~TIM_CR1_CKD;                            // clesr clock division bits
   Timer->CR1 |= TIM_CLOCKDIVISION_DIV1;       // division = 1
// Timer2 prescaler (TIMx_PSC)
Timer->PSC = TIM2_PRESCALER_VALUE;                // initialize Timer2 prescale value = 1

// TIM2 capture/compare mode register 4  (TIMx_CCMR2)
Timer->CCMR2 &= ~TIM_CCMR2_CC4S;             // Capture/Compare Channel4 is configured as output
// Timer->CCMR2 &= ~TIM_CCMR2_OC4PE;          // Output Compare Channel4 Preload disabled, TIMx_CCR1 can be written at anytime
Timer->CCMR2 |=  TIM_CCMR2_OC4PE;             // Output Compare 4 preload enable
Timer->CCMR2 &= ~TIM_CCMR2_OC4M;             // clear Output compare 4 mode
Timer->CCMR2 |=  TIM_CCMR2_OC4M_1;             // OC1M: Output compare 4 mode = 6, PWM mode 1
Timer->CCMR2 |=  TIM_CCMR2_OC4M_2;

Timer->CCER  |=  TIM_CCER_CC4P;
Timer->CCMR2 &=  ~TIM_CCMR2_OC4FE;
Timer->CR2  &=  ~TIM_CR2_OIS1;

Timer->CCMR2 |=  TIM_CCMR2_OC4CE;             // Output Compare Ch4 Clear Enable

   // TIM2 auto-reload register (TIM2_ARR)          // initialize PWM frequency
   Timer->ARR = 699;                                     // initialize Timer2 Auto Reload Register
// TIM2 capture/compare register 4 (TIM2_CCR4)       // initialize duty cycle
   Timer->CCR4 = 200;                                     // initialize Timer2 Capture/Compare Register 4

// TIM2 control register 1 (TIMx_CR1)
   Timer->CR1 |= TIM_CR1_CEN;       // Timer2 enable
   // TIM2 capture/compare enable register (TIMx_CCER)
Timer->CCER = Timer->CCER |=  TIM_CCER_CC4E;
}