采用STM32的PWM輸入功能計(jì)算輸入PWM的周期

1、時(shí)鐘部分，TIMER2的時(shí)鐘頻率，我是初始化為36M.

RCC_PCLK1Config(RCC_HCLK_Div2); //設(shè)置低速AHB時(shí)鐘=系統(tǒng)時(shí)鐘/2

RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9); //倍頻系數(shù)為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); //復(fù)位模式為從模式

TIM_SelectMasterSlaveMode(TIM2, TIM_MasterSlaveMode_Enable); //使能主從模式

TIM_Cmd(TIM2, ENABLE); //使能TIM2計(jì)數(shù)器

TIM_ITConfig(TIM2, TIM_IT_CC2, ENABLE); //使能CC2中斷請(qǐng)求

3、TIMER中斷處理

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);

}

注意事項(xiàng)：

不知道為什么，STM32的TIMER時(shí)鐘經(jīng)過分頻率后，時(shí)鐘的精度誤差會(huì)隨分頻值變大而變大。在不分頻的情況下，我檢測(cè)1KHz的PWM輸入信號(hào)，誤差為0.5us。在18分頻的情況下，誤差已經(jīng)不能看了。測(cè)量100Hz，根據(jù)捕獲值計(jì)算出來卻是105Hz。

確實(shí)如STM32朋友所講，在分頻處我理解錯(cuò)了，分頻值=TIM_TimeBaseStructure.TIM_Prescaler +1，所以如果要分18分頻，只要將TIM_Prescaler=17即可。經(jīng)這樣修改后測(cè)量誤差在萬分之5以內(nèi)。