采用STM32的PWM输入功能计算输入PWM的周期

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);

}

注意事项：

不知道为什么，STM32的TIMER时钟经过分频率后，时钟的精度误差会随分频值变大而变大。在不分频的情况下，我检测1KHz的PWM输入信号，误差为0.5us。在18分频的情况下，误差已经不能看了。测量100Hz，根据捕获值计算出来却是105Hz。

确实如STM32朋友所讲，在分频处我理解错了，分频值=TIM_TimeBaseStructure.TIM_Prescaler +1，所以如果要分18分频，只要将TIM_Prescaler=17即可。经这样修改后测量误差在万分之5以内。