STM32 外部計數(shù)ETR計算頻率，測量100K頻率，用定時器2定時250ms，定時器3PD2（TIM3_ETR）計數(shù)，計算公式f=n*t;

void Tim3_Configuration(void)

{

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

TIM_TimeBaseStructure.TIM_Prescaler = 0x00;

TIM_TimeBaseStructure.TIM_Period = 0xFFFF;

TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;

TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); // Time base configuration

TIM_ETRClockMode2Config(TIM3, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);

TIM_ITConfig(TIM3, TIM_IT_Update, ENABLE);

TIM_SetCounter(TIM3, 0);

TIM_Cmd(TIM3, ENABLE);

}

void Tim2_Config(void)

{

TIM_TimeBaseInitTypeDef TIM2_TimeBaseStructure;

NVIC_InitTypeDef NVIC_InitStructure;

TIM_DeInit(TIM2);

TIM2_TimeBaseStructure.TIM_Period =（2500-1）;

TIM2_TimeBaseStructure.TIM_Prescaler = (7200-1);

TIM2_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;

TIM2_TimeBaseStructure.TIM_CounterMode =TIM_CounterMode_Up;

TIM_TimeBaseInit(TIM2, &TIM2_TimeBaseStructure); // Time base configuration

TIM_ClearFlag(TIM2,TIM_FLAG_Update);

TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE );

TIM_Cmd(TIM2, ENABLE);

NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;

NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

NVIC_Init(&NVIC_InitStructure);

}

void TIM2_IRQHandler(void)

{

if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)

{

TIM_ClearITPendingBit(TIM2, TIM_IT_Update);

CAPTURE=(u32)TIM_GetCounter(TIM3);

}

sum+=CAPTURE;

count++;

if(count==4)

{

Frequency=sum*4;//求頻率公式F=n*t;這里求了4次的計數(shù)值，合起來是1S的頻率

sum=0;

count=0;

}

TIM_SetCounter(TIM3,0);

}