Serial communication based on STM32F4 (usart)

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foreword

Serial communication is a commonly used serial communication method between devices, because it is simple and convenient, and most devices support this communication method. Today, a ttl-to-usb module is used to connect usart1 to communicate with the debugging assistant.

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1. Basic introduction of serial port

1 Introduction

Serial communication involves USART. TX, RX, GND three lines can complete the communication between the serial port assistant and STM32. Among them, this experiment needs to connect the tx and rx pins of the ttl to usb module with the crossover on the board. As shown in the picture:

2. Serial protocol

A data packet includes 1 start bit, 5-8 data bits, 1 parity bit, 0.5-2 stop bits, the start bit is generally 0, and the level of the stop bit is 1.

two,

1. Configuration steps

We need to configure three structures, which are GPIO, USART, and NVIC; this is a bit similar to the previous external interrupt configuration, and an interrupt function (receive interrupt) also needs to be configured.

2. Complete code

code show as below:

#include "stm32f4xx.h"                  // Device header
#include "sys.h"
#include "stdio.h"
#include "stm32f4xx_usart.h"

static GPIO_InitTypeDef  GPIO_InitStructure;
static USART_InitTypeDef USART_InitStructure;
static NVIC_InitTypeDef NVIC_InitStructure;


struct __FILE {
    
     int handle; /* Add whatever you need here */ };
FILE __stdout;
FILE __stdin;
int fputc(int ch, FILE *f) 
{
    
    
	
	USART_SendData(USART1,ch);
	while(USART_GetFlagStatus(USART1,USART_FLAG_TC)==RESET);
	USART_ClearFlag(USART1,USART_FLAG_TC);
	return ch;
}


void delay_ms(uint32_t n)
{
    
    
	while(n--)
	{
    
    
		SysTick->CTRL = 0; // Disable SysTick
		SysTick->LOAD = (168000)-1; // Count from 255 to 0 (256 cycles)
		SysTick->VAL = 0; // Clear current value as well as count flag
		SysTick->CTRL = 5; // Enable SysTick timer with processor clock
		while ((SysTick->CTRL & 0x00010000)==0);// Wait until count flag is set
	}
	
	SysTick->CTRL = 0; // Disable SysTick
}


void usart1_init(uint32_t bound)
{
    
    
	
	//打开硬件时钟
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
	
	//打开串口1硬件时钟
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
	
	//配置PA9和PA10为服用功能
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9|GPIO_Pin_10;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;//复用功能模式
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;//推挽输出
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;//100MHz
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;//上拉
	GPIO_Init(GPIOA, &GPIO_InitStructure);//初始化
	
	
	//将PA9和PA10引脚连接到串口1的硬件
	GPIO_PinAFConfig(GPIOA,GPIO_PinSource9,GPIO_AF_USART1);
	GPIO_PinAFConfig(GPIOA,GPIO_PinSource10,GPIO_AF_USART1);
	
	//配置串口1相关参数：波特率、无校验位、8位数位、1位停止位
	USART_InitStructure.USART_BaudRate = bound;//波特率设置
	USART_InitStructure.USART_WordLength = USART_WordLength_8b;//字长为8位数据格式
	USART_InitStructure.USART_StopBits = USART_StopBits_1;//一个停止位
	USART_InitStructure.USART_Parity = USART_Parity_No;//无奇偶校验位
	USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;//无硬件数据流控制
	USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; //收发模式
	USART_Init(USART1, &USART_InitStructure); //初始化串口1

 
	//配置串口1的中断触发方法 接收一个字节触发中断
	USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
	
	//配置串口1的中断优先级
	NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;//串口1中断通道
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=3;//抢占优先级3
	NVIC_InitStructure.NVIC_IRQChannelSubPriority =3; //子优先级3
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ通道使能
	NVIC_Init(&NVIC_InitStructure); //根据指定的参数初始化VIC寄存器

	
	//使能串口1工作
	USART_Cmd(USART1,ENABLE);
}






int main(void)
{
    
    
	
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOF, ENABLE);//使能GPIOF时钟

	//GPIOF9,F10初始化设置
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;//复用功能模式
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;//推挽输出
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;//100MHz
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;//上拉
	GPIO_Init(GPIOF, &GPIO_InitStructure);//初始化
	
	
	GPIO_SetBits(GPIOF,GPIO_Pin_9);
	
	usart1_init(115200);
	
	printf("123\r\n");
	
	while(1)
	{
    
    
		
	}
}


void USART1_IRQHandler(void)
{
    
    
	char d;
	//检查标志位
	if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET) //接收中断
	{
    
    
		d=USART_ReceiveData(USART1);
		
		
		USART_SendData(USART1,d);
		//清空标志位
		USART_ClearITPendingBit(USART1,USART_IT_RXNE);
	}
	
	
}