STM32采用定时器捕获的方法测低频信号很准确，我测高频100K-120K就误差太大了，大概200Hz,这儿的误差是个范围，不是某个值。有的人说两个定时器一个定时，一个计数，这样太浪费资源了吧。STM32定时器分为高级定时器（TIM1、TIM8）、通用定时器（TIM2、 TIM3、 TIM4和TIM5）及基本定时器（TIM6和TIM7）。本文用定时器捕获的方法，用的是通用定时器3通道2来实现测量频率。如下是通用定时器框图：
下面示例是用捕获的方法计算频率,列举几个主要函数配置讲一下：
void Time3_Configuration()
{
TIM_ICInitTypeDef TIM_ICInitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
//RCC_ClocksTypeDef freq;
//RCC_GetClocksFreq(&freq);
/*TIM3时基*/
TIM_DeInit(TIM3);
TIM_TimeBaseStructure.TIM_Period = 0xffff;
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); // Time base configuration
/*TIM3输入捕获*/
TIM_ICInitStructure.TIM_Channel = TIM_Channel_2;
TIM_ICInitStructure.TIM_ICPolarity = TIM_CounterMode_Up;
TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1; /*输入预分频*/
TIM_ICInitStructure.TIM_ICFilter = 0;
TIM_ICInit(TIM3, &TIM_ICInitStructure);
TIM_PWMIConfig(TIM3, &TIM_ICInitStructure);
/* Select the TIM3 Input Trigger: TI2FP2 */
TIM_SelectInputTrigger(TIM3, TIM_TS_TI2FP2);
/* Select the slave Mode: Reset Mode */
TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_Reset);
/* Enable the Master/Slave Mode */
TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable);
/* TIM enable counter */
TIM_Cmd(TIM3, ENABLE);
/* Enable the CC2 Interrupt Request */
TIM_ITConfig(TIM3, TIM_IT_CC2, ENABLE);
}
中断部分计算频率：
void TIM3_IRQHandler(void)
{
if(TIM_GetITStatus(TIM3, TIM_IT_CC2) == SET)
{
/* Clear TIM5 Capture compare interrupt pending bit */
TIM_ClearITPendingBit(TIM3, TIM_IT_CC2);
if(capture_number == 0)
{
/* Get the Input Capture value */
ic3_readvalue3 = TIM_GetCapture(TIM3);
capture_number = 1;
}
else if(capture_number == 1)
{
/* Get the Input Capture value */
ic3_readvalue4 = TIM_GetCapture(TIM3);
/* Capture computation */
if (ic3_readvalue4 > ic3_readvalue3)
{
CAPTURE = ic3_readvalue4 ;
}
/* Frequency computation */
Frequency = (u32)72000000 / CAPTURE;
capture_number = 0;
}
else
{
Frequency=0;
}
}
}
还有一种方法就是用外部中断计算频率。更精确的计算方法得慢慢研究。
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關鍵字: 捕获 定时器 TimeBaseStructure
