使用STM32的TIMER捕获功能，求取输入PWM信号的周期，误差很大

只看该作者 · 2015-4-18 20:51

使用的是TIMER2的CH1通道，PWM信号接在PA0脚。输入PWM的周期信号为100Hz，根据捕获值计算出来却是105Hz，这误差也太大了吧！！哪位高手知道是什么原因呀，指点一下呀，万分感谢呀！！
下面是我的相关部分程序：
1、时钟部分，TIMER2的时钟频率，我是初始化为36M.
   RCC_PCLK1Config(RCC_HCLK_Div2);          //设置低速AHB时钟=系统时钟/2
   RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9); // 倍频系数为9  PLLCLK=8*9=72
2、TIMER初始化
TIM_DeInit(TIM2);
TIM_TimeBaseStructure.TIM_Period = 65535;
TIM_TimeBaseStructure.TIM_Prescaler = 18;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;
TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV4;
TIM_ICInitStructure.TIM_ICFilter = 0x0;
TIM_PWMIConfig(TIM2, &TIM_ICInitStructure);

TIM_SelectInputTrigger(TIM2, TIM_TS_TI1FP1);
TIM_SelectSlaveMode(TIM2, TIM_SlaveMode_Reset);                      //复位模式为从模式
TIM_SelectMasterSlaveMode(TIM2, TIM_MasterSlaveMode_Enable);       //使能主从模式

TIM_Cmd(TIM2, ENABLE);                         //使能TIM2计数器
TIM_ITConfig(TIM2, TIM_IT_CC2, ENABLE);       //使能CC2中断请求
3、TIMER中断处理
void TIM2_IRQHandler(void)
{
  /* Clear TIM2 Capture compare interrupt pending bit */
  TIM_ClearITPendingBit(TIM2, TIM_IT_CC2);

  /* Get the Input Capture value */
  IC2_Value = TIM_GetCapture2(TIM2);

}