Learning records: serial communication and solutions to errors encountered

List of articles

Learning notes ： The concept of serial communication and programming to realize serial communication .
Encountered …\OBJ\Project.axf: Error: L6200E: Symbol USART1_IRQHandler multiply defined (by usart.o and main.o). Error resolution ！

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Preface

I've been reading 《 The embedded C Self cultivation of language 》 Learned a lot of knowledge , Especially compilation and C Function call for , This is also used in learning serial communication C Language calls assembly functions and NVIC Writing of interrupt program .
The following is my summary of knowledge, as well as how to write serial communication programs and NVIC Interrupt the procedure （ It mainly refers to the reference manual of punctual atoms ）.

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One 、 Basic knowledge of serial communication

1. There are two ways for the processor to communicate with external devices ：

Parallel communication
- Transmission principle ： All bits of data are transmitted at the same time .
- advantage ： Fast
- shortcoming ： It takes up a lot of pin resources
serial communication
- Transmission principle ： Data transmission in bit order .
- advantage ： Less pin resources
- shortcoming ： Relatively slow

1.1 serial communication

According to the data transmission direction , It is divided into ：
Simplex ：
Data transmission only supports data transmission in one direction .
Half duplex ：
Allows data to be transmitted in both directions , however , At some point , Only number allowed
It is transmitted in one direction , It's actually a kind of direction switching simplex communication ;
full duplex ：
Allows data to be transmitted in both directions at the same time , therefore , Full duplex communication is two
Combination of simplex communication , It requires that both the sending device and the receiving device have independent
Ability to receive and send .
There are three transmission modes of serial communication ：

1.2 Communication mode of serial communication

Synchronous communication ： With clock Synchronous signal transmission .
-SPI,IIC communication interface ;
asynchronous communication ： Without clock Synchronous signal .
-UART( Universal asynchronous transceiver ), Single bus ;

2. Common serial communication interface

Communication standards	Pin description	communication mode	Direction of communication
UART( Universal asynchronous transceiver )	TXD: The sender ;RXD: The receiving end ;GND: In public	asynchronous communication	full duplex
Single bus （1-wire)	DQ: send out / The receiving end	asynchronous communication	Half duplex
SPI	SCK: Synchronous clock ;MISO: Host input , Slave output ;MOSI: Host output , Slave input	Synchronous communication	full duplex
IIC	SCL: Synchronous clock ;SDA: data input / Output terminal	Synchronous communication	Half duplex

2.1、STM32 Serial communication interface

UART: Universal asynchronous transceiver ;
USART: Universal synchronous asynchronous transceiver ;

2.2、UART Asynchronous communication mode pin connection method ：

-RXD: Data input pin . Data reception .
-TXD: Data transmission pin . Data sending .

2.3、UART Characteristics of asynchronous communication mode ：

• Full duplex asynchronous communication .
• Fractional baud rate generator system , Provide accurate baud rate .
  - Send and receive common programmable baud rate , Up to 4.5Mbits/s
• Programmable data word length （8 Bits or 9 position ）;
• Configurable stop bits （ Support 1 perhaps 2 Bit stop bit ）;
• Configurable use DMA Multi buffer communication .
• Separate transmitter and receiver enable bits .
• Detection marks ：① Accept buffer ② Send buffer empty ③ End of transmission flag
• Multiple interrupt sources with flags . Trigger interrupt .
• other ： Calibration control , Four error detection flags .

3.STM32 Parameters to be defined for serial asynchronous communication

• Start bit
• Data bits （8 Bits or 9 position ）
• Parity bit （ The first 9 position ）
• Stop bit （1,15,2 position ）
• Baud rate setting
  USART block diagram
  

Two 、 Programming

1. Writing steps

1. Serial clock enable ,GPIO Clock enable :RCC_APB2PeriphClockCmd();
2. Serial reset :USART_DeInit(); This step is not necessary
3.GPIO Port mode settings :GPIO_Init(); The mode is set to GPIO_Mode_AF_PP
4. Initialization of serial port parameters ：USART_Init();
5. Turn on interrupt and initialize NVIC（ If you need to turn on interrupt, you need this step ）
NVIC_Init();
== USART_ITConfig();==
6. Enable serial port :USART_Cmd();
7. Write interrupt handling functions ：USARTx_IRQHandler();
8. Serial data transmission ：
void USART_SendData();// Send data to serial port ,DR
uint16_t USART_ReceiveData();// Receive data , from DR Read the received data
9. Serial port transmission state acquisition ：
FlagStatus USART_GetFlagStatus
(USART_TypeDef* USARTx, uint16_t USART_FLAG);
void USART_ClearITPendingBit
(USART_TypeDef* USARTx, uint16_t USART_IT);

2. Program instance

The code is as follows （ Shown ）：

#include "stm32f10x.h"

void Bitter_USART_Init(void)
{
    
		GPIO_InitTypeDef GPIO_InitStruct;
		USART_InitTypeDef USART_InitStruct;
		NVIC_InitTypeDef NVIC_InitStruct;
	
		RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);// Can make GPIOA
		RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);// Enable serial port one 
	
		GPIO_InitStruct.GPIO_Mode=GPIO_Mode_AF_PP;
		GPIO_InitStruct.GPIO_Pin=GPIO_Pin_9;
		GPIO_InitStruct.GPIO_Speed=GPIO_Speed_10MHz;
		GPIO_Init(GPIOA,&GPIO_InitStruct);
	
		GPIO_InitStruct.GPIO_Mode=GPIO_Mode_IN_FLOATING;
		GPIO_InitStruct.GPIO_Pin=GPIO_Pin_10;
		GPIO_InitStruct.GPIO_Speed=GPIO_Speed_10MHz;
		GPIO_Init(GPIOA,&GPIO_InitStruct);
		
		USART_InitStruct.USART_BaudRate=115200;// Baud rate 
		USART_InitStruct.USART_HardwareFlowControl=USART_HardwareFlowControl_None;// Hardware flow control 
		USART_InitStruct.USART_Mode=USART_Mode_Rx|USART_Mode_Tx;// Send and receive 
		USART_InitStruct.USART_Parity=USART_Parity_No;// Parity check 
		USART_InitStruct.USART_StopBits=USART_StopBits_1;// Stop bit 
		USART_InitStruct.USART_WordLength=USART_WordLength_8b;// The word is long 
	
		USART_Init(USART1,&USART_InitStruct);// Serial initialization 
		USART_Cmd(USART1,ENABLE);// Serial port enable function 
		
		USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);// Turn on the interrupt service function ; Receive interrupt 
		
		NVIC_InitStruct.NVIC_IRQChannel=USART1_IRQn;// Interrupt channel 
		NVIC_InitStruct.NVIC_IRQChannelCmd=ENABLE;// Open interrupt channel 
		NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority=1;// Set preemption priority 
		NVIC_InitStruct.NVIC_IRQChannelSubPriority=1;// Sub priority 
		
		NVIC_Init(&NVIC_InitStruct);
}

void USART1_IRQHandler(void)
{
    
		u8 tea;
		if(USART_GetITStatus(USART1,USART_IT_RXNE))// Determine the interrupt type 
		{
    
				tea=USART_ReceiveData(USART1);// Read the data received by the serial port ;
				USART_SendData(USART1,tea);// send data 
		}
}

int main(void)
{
    
		NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);// Interrupt priority , Two people preempt priority , Two response priorities 
		Bitter_USART_Init();
		while(1);
}

3、 ... and 、…\OBJ\Project.axf: Error: L6200E: Symbol USART1_IRQHandler multiply defined (by usart.o and main.o). Error resolution

stay usart.c Found in and USART1_IRQHandler Same function , Just comment it out .

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summary

Writing serial port can also use HAL Library to achieve serial port configuration and use methods .. stay HAL In the library , The functions and definitions related to serial port are mainly in the file stm32f1xx_hal_uart.c and stm32f1xx_hal_uart.h in .