初学stm32之USART进行无奇偶校验位的异步串口通信

  今天学习了如何使用stm32通过USART进行简单的无奇偶校验位的异步串口通信，USART：通用同步异步收发器。在学习之前应先了解硬件设备的连接情况，stm32f407的PA9，PA10分别是USART1的TX和RX，通过对这两个GPIO口的配置，完成对一部串口通信的初始化函数，以及收发函数。

  串口通信的初始化包括以下五个步骤：

    第一步：打开USART1和GPIOA的时钟；

    第二步：对GPIOA的第九第十管脚进行配置；

    第三步：打开USART1发送和接受使能；

    第四步：对小数波特率进行配置；

    第五步：打开串口通信使能

  下面是通过串口通信对单片机开发板上的led和蜂鸣器进行控制。led与蜂鸣器电路图参考上一篇文章。点击打开链接

usart.c

#include "usart.h"

void Usart_Init(void)
{
	RCC->AHB1ENR |= (1<<0);//开启GPIOA时钟
	RCC->APB2ENR |= (1<<4);//开启USART1时钟
	//对PA9，PA10进行端口配置
	GPIOA->MODER &=~ (0xF<<18);
	GPIOA->MODER |= (0xA<<18);//复用功能
	GPIOA->OTYPER &=~ (3<<9);//推挽输出
	GPIOA->OSPEEDR |= (0xf<<18);//输出速率最高
	GPIOA->PUPDR &=~ (0xf<<18);
	GPIOA->PUPDR |= (5<<18);    //上拉模式
	GPIOA->AFR[1] &=~ (0xFF<<4);
	GPIOA->AFR[1] |= (0x77<<4);//复用功能高位寄存器 配置为USART1功能
	
	USART1->CR1 |= (1<<2)|(1<<3);//打开USART1的接收器和发送器使能
	

	float USARTDIV = 84000000.0f/16/115200;//定义一个浮点型USARTDIV用来表示将要配置的波特率
	uint32_t Mantissa,Fraction;//定义两个int型数据用来存放整数部分和小数部分
	Mantissa = USARTDIV;
	Fraction = (USARTDIV - Mantissa)*16;
	//将设置好的数据存放到波特率寄存器中 USART1->BRR波特率寄存器  低四位是小数部分
	USART1->BRR = (Mantissa<<4) + Fraction;
	
	USART1->CR1 |= (1<<13);//开启串口使能
}
void Usart_Tx(uint8_t data)    //发送一位数据
{
	while((USART1->SR & (1<<6)) == 0);
	USART1->DR = data;
}

uint8_t Usart_Rx(void)        //接收一位数据
{
	while((USART1->SR & (1<<5)) == 0);
	return USART1->DR;
}

usart.h

#ifndef USART_H
#define USART_H

#include "stm32f4xx.h"

void Usart_Init(void);
void Usart_Tx(uint8_t data);
uint8_t Usart_Rx(void);
#endif

gpio.c

#include "gpio.h"

void Gpio_Init(GPIO_TypeDef * GPIOx, uint8_t Pin)
{
	GPIOx->MODER &=~ (3<<(Pin+Pin));
	GPIOx->MODER |= (1<<(Pin+Pin));
	GPIOx->OTYPER &=~ (1<OSPEEDR |= (3<<(Pin+Pin));
	GPIOx->PUPDR &=~ (3<<(Pin+Pin));
	GPIOx->PUPDR |= (1<<(Pin+Pin));
}

void Led_Init(void)
{
	RCC->AHB1ENR |= (1<<5);
	RCC->AHB1ENR |= (1<<2);
	Gpio_Init(GPIOF,6);
	Gpio_Init(GPIOF,9);
	Gpio_Init(GPIOF,10);
	Gpio_Init(GPIOC,0);
}

void Beep_Init(void)
{
		RCC->AHB1ENR |= (1<<5);
		Gpio_Init(GPIOF,8);
}

gpio.h

#ifndef GPIO_H
#define GPIO_H

#include "stm32f4xx.h"

#define LED1_TOGGLE() GPIOF->ODR ^= (1<<6)
#define LED2_TOGGLE() GPIOF->ODR ^= (1<<9)
#define LED3_TOGGLE() GPIOF->ODR ^= (1<<10)
#define LED4_TOGGLE() GPIOC->ODR ^= (1<<0)
#define BEEP_TOGGLE() GPIOF->ODR ^= (1<<8)

void Gpio_Init(GPIO_TypeDef * GPIOx, uint8_t Pin);
void Led_Init(void);
void Beep_Init(void);
#endif

main.c

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "usart.h"
#include "gpio.h"

/**
  * @brief  Main program
  * @param  None
  * @retval None
  */
	
int main(void)
{
	uint8_t temp;
	Usart_Init();
	Led_Init();
	Beep_Init();
	while (1)
	{
		temp = Usart_Rx();
		Usart_Tx(temp);
		switch(temp)
		{
			case '1': LED1_TOGGLE();break;
			case '2': LED2_TOGGLE();break;
			case '3': LED3_TOGGLE();break;
			case '4': LED4_TOGGLE();break;
			case '5': BEEP_TOGGLE();break;
			default: break;
		}
	}
}

#ifdef  USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t* file, uint32_t line)
{
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */

  /* Infinite loop */
  while (1)
  {
  }
}
#endif

/**
  * @}
  */

/**
  * @}
  */

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