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我用外部计数STM32 ETR计算频率，测量100K频率，用定时器2定时1S，定时器三PD2（TIM3_ETR）计数，计算公式f=n/t;测量出来的结果是9999 HZ，整整少了一位数字，这是什么原因呢，大家分析一下，谢谢，附我的程序 void Time3_Configuration() { TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure; TIM_TimeBaseStructure.TIM_Prescaler = 0x00; TIM_TimeBaseStructure.TIM_Period = 0xFFFF; TIM_TimeBaseStructure.TIM_ClockDivision = 0x0; 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); } /*1S定时*/ void Tim2_Config(void) { TIM_TimeBaseInitTypeDef TIM2_TimeBaseStructure; NVIC_InitTypeDef NVIC_InitStructure; TIM_DeInit(TIM2); TIM2_TimeBaseStructure.TIM_Period =999; TIM2_TimeBaseStructure.TIM_Prescaler = (7200-1); TIM2_TimeBaseStructure.TIM_ClockDivision = 0x0;//ÉèÖÃʱÖÓϵÊý ²»·ÖƵ TIM2_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;//ÏòÉϼÆÊýģʽ TIM_TimeBaseInit(TIM2, &TIM2_TimeBaseStructure); // Time base configuration TIM_ClearFlag(TIM2,TIM_FLAG_Update);//Çå³þ¸üбê־λ 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); } 最后的计算部分： void TIM2_IRQHandler(void) { if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) { TIM_ClearITPendingBit(TIM2, TIM_IT_Update); CAPTURE1=(u32)TIM_GetCounter(TIM3); } sum+=CAPTURE1; count++; if(count==4) { Frequency1=sum/4;//求频率公式F=n/t;这里求了4次的计数平均值，结果是1S的频率 sum=0; count=0; } TIM_SetCounter(TIM3,0); }