Part 7: STM32 serial communication programming

1. Basic concepts of communication

 

（1） Serial communication and parallel communication

（2） Simplex , Half duplex and full duplex

 （3） Communication rate

     The number of bits transmitted per unit time indicates the transmission speed , It's called baud rate (bps)

（4） Communication protocol ( A serial port )

     Communication protocol is the data format agreed by both parties

2. Hardware connection of serial port

    UART -----------------  Universal asynchronous transceiver

    USART ---------------  Universal synchronization / Asynchronous transceiver

3.stm32 Serial port development

（1） Schematic diagram

USB The debugging port is connected to CPU Of PA9 PA10, They have the function of serial port multiplexing

（2）CPU Chip manual

 

 

（3） Programming of serial interface

Add serial port library function source code in the project

1） Turn on GPIOA and USART1 The clock of

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);

2） take PA9 PA10 Configured as multiplexing function , And mapped to serial port 1

GPIO_Init(...); GPIO_PinAFConfig(GPIOA,GPIO_PinSource9,GPIO_AF_USART1); GPIO_PinAFConfig(GPIOA,GPIO_PinSource10,GPIO_AF_USART1);

3） Initialize serial port

void USART_Init(USART_TypeDef* USARTx, USART_InitTypeDef* USART_InitStruct); Parameters ： USARTx - Which serial port

USART_InitStruct - Serial port initialization structure

typedef struct

{

uint32_t USART_BaudRate; /*!< Baud rate */

uint16_t USART_WordLength; /*!< Data bit length @ref USART_Word_Length */

uint16_t USART_StopBits; /*!< Stop bit length @ref USART_Stop_Bits */

uint16_t USART_Parity; /*!< Verification method @ref USART_Parity */

uint16_t USART_Mode; /*!< send out / Reception mode @ref USART_Mode */

uint16_t USART_HardwareFlowControl; /*!< Hardware flow control @ref USART_Hardware_Flow_Control */ } USART_InitTypeDef;

4） Enable serial port

USART_Cmd(USART1,ENABLE);

5） Sending and receiving data

send out ：

// polling

void USART_SendData(USART_TypeDef* USARTx, uint16_t Data);

// What data is sent to which serial port

// Before each transmission, check whether the previous data has been sent

FlagStatus USART_GetFlagStatus(USART_TypeDef* USARTx, uint16_t USART_FLAG);

// What symbol of the serial port to be transmitted , return SET Indicates that there is this flag , return RESET Indicates that there is no such flag

//USART_FLAG_TC ----- Send completion flag

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practice ：

Realize serial port 1 Sending strings

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// Function code

#include <stm32f4xx.h>
#include <usart.h>
#include <stdio.h>
#include <string.h>
#include <includes.h>

//stm32 Run the program on the development board , If the host runs the debugger , The program will use the input and output devices of the host 
// This is called semi host mode ,printf If you want to print through serial port , Half host mode must be turned off 
#pragma import(__use_no_semihosting)

struct __FILE{
    int handle;
};

FILE __stdout;

// Definition _sys_exit Function avoid using semi host mode 
void _sys_exit(int x)
{
    x = x;
}

// redefinition fputc
int fputc(int ch,FILE *F)
{
	// Wait for the last data to be sent 
	while(USART_GetFlagStatus(USART1,USART_FLAG_TC)!=SET);
    // send out 
    USART_SendData(USART1,ch);
    
	return ch;
}

void usart1_init(void)
{
	GPIO_InitTypeDef GPIO_InitStruct;
	USART_InitTypeDef USART_InitStruct;
	NVIC_InitTypeDef NVIC_InitStruct;
	
	//1. Turn on GPIOA and USART1 The clock 
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);

	//2. To configure PA9 PA10 Serial port function 
	GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;// Reuse mode 
	GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;// Push pull output 
	GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;// High speed 
	GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;// No up and down 
	GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9|GPIO_Pin_10;
	GPIO_Init(GPIOA,&GPIO_InitStruct);
	
	GPIO_PinAFConfig(GPIOA,GPIO_PinSource9,GPIO_AF_USART1);
	GPIO_PinAFConfig(GPIOA,GPIO_PinSource10,GPIO_AF_USART1);
	
	//3. Initialize serial port   8N1
	USART_InitStruct.USART_BaudRate = 115200;// Baud rate 
	USART_InitStruct.USART_WordLength = USART_WordLength_8b;//8 Digit bit 
	USART_InitStruct.USART_StopBits = USART_StopBits_1;//1 Bit stop bit 
	USART_InitStruct.USART_Parity = USART_Parity_No;// No verification 
	USART_InitStruct.USART_Mode = USART_Mode_Rx|USART_Mode_Tx;// Send receive mode 
	USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;// No hardware flow control 
	USART_Init(USART1,&USART_InitStruct);
	
	//4. Open serial port receive interrupt ( Clear interrupt flag )
	USART_ClearITPendingBit(USART1, USART_IT_RXNE);
	USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
	
	//5. initialization NVIC
	NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;// A serial port 1 Interrupt channel 
	NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0x2;// preemption 
	NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0x2;// Response priority 
	NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;// Can make 
	NVIC_Init(&NVIC_InitStruct);
	
	//. Enable serial port 
	USART_Cmd(USART1,ENABLE);
}

// Send a character ( polling )
void uart1_putc(char ch)
{
	// Wait for the last data to be sent 
	while(USART_GetFlagStatus(USART1,USART_FLAG_TC)!=SET);
	
	USART_SendData(USART1,ch);
}