问题描述
我正在使用NUCLEO-F411RE板(STM32F411RET)研究STM32 MCU编程。我最近观看了有关输入捕获计时器的教程,并对代码有疑问。下面是源代码:
/*
Write a program to generate 1Hz frequency in PA5 as an output using TIMER 2
and read the frequency using input capture in PA6 using TIMER 3
*/
#include "stm32f4xx.h" // Device header
int timeStamp = 0;
int main()
{
//GPIO A configuration
RCC->AHB1ENR |= 1; //enable GPIO A
GPIOA->MODER |= (0b10<<10)|(0b10<<12); //set GPIO A pin 5 and 6 to alternate function mode
GPIOA->AFR[0] |= (0b0001<<20)|(0b0010<<24); //SET pin 5 as AF1 and pin 6 as AF2
//TIMER 2 configuration
//output compare mode
RCC->APB1ENR |= 1; //enable TIMER 2
TIM2->PSC = 1600-1;
TIM2->ARR = 10000-1; //set a 1Hz clock
TIM2->CCMR1 |= (0b011<<4)|(0b11<<8); //set output to toggle on match
TIM2->CCR1 = 0; //set the CCR value to 0 (toggle when CNT = CCR1)
TIM2->CCER |= 1; //enable CH1 compare mode
TIM2->CNT = 0; //reset the count value to 0;
TIM2->CR1 = 1; //enable TIM2
//input capture mode
RCC->APB1ENR |= 2; //ENABLE TIMER 3
TIM3->PSC = 1600; //divide by 16000
TIM3->CCMR1 |= (0b01<<0)|(0b0100<<4); //set CH1 to capture every edge
TIM3->CCER = 1; //enable CH1 input capture
TIM3->CR1 = 1; //enable TIM3
while (1)
{
while (!(TIM3->SR & 2));
timeStamp = TIM3->CCR1;
}
}
问题1:为什么我们需要将CC2S位设置为0b11?
TIM2->CCMR1 |= (0b011<<4)|(0b11<<8); //set output to toggle on match
问题2:为什么我们需要将预分频器设置为输入捕捉模式?
TIM3->PSC = 1600; //divide by 16000
问题3:如何在输入捕获模式下选择合适的采样频率?上面的源代码的采样频率是多少?
期待您的反馈,非常感谢您的支持!
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