STM32 how to use serial port

One 、 Relevant knowledge reserve

1、 Serial communication and parallel peer

• serial communication ： Serial communication is to use only one data line to transmit data in data communication , Transmit data bit by bit ;
• Parallel communication ： Parallel communication means using multiple data lines to transmit data , Multiple data can also be transmitted at one time , Generally, it is transmitted in the form of words or bytes ;
  difference ： Data communication is like a car driving on the road , Serial communication is that there is only one single lane on this road , At the same time, vehicles traveling in the same direction can only pass one by one ; And parallel communication , Parallel communication means that there are multiple lanes on this road , Multiple cars can be driven in the same direction at the same time .

2、 Synchronous communication and asynchronous communication

• Asynchronous communication data transmission is transmitted by frame , A frame of data contains the start bit 、 Data bits 、 Check bit and stop bit .
• Synchronous communication is made by 1~2 Synchronous characters and multi byte data bits , The synchronization character is used as the starting bit to trigger the synchronization clock to start sending or receiving data ; No gap is allowed between multi byte data , Each person takes up the same amount of time ; The idle bit needs to send synchronization characters .

3、 The mechanism of serial communication

• Simplex （Simplex） It means that both parties can only transmit data in one direction when communicating . After the system is composed , The sender and receiver are fixed .
• Half duplex （Half Duplex） It means that both sides of communication have transmitters and receivers , You can send or receive , But it cannot receive and send at the same time , Cannot receive when sending , Cannot send when receiving .
• Full duplex system （Full Duplex） It means that both sides of the communication are equipped with transmitters and receivers , And the channel is divided into sending channel and receiving channel , Therefore, the full duplex system can realize two-way simultaneous sending and receiving data , Can receive when sending , It can also be sent when receiving

4、 data verification

• Parity check
       Parity when sending data , Data bits follow 1 The bits of are parity bits （1 or 0）, When set to odd check , In the data 1 Number of and check bits 1 The sum of the number of should be odd ; When set to even check , In the data 1 The number of and in the check digit 1 The sum of the number of should be an even number .
• Add up and check
       Cumulative sum check refers to the sender summing the sent data blocks , And will “ The checksum ” Append to end of data block . When receiving data, the receiver also sums the data blocks , Compare the result with the sender's “ The checksum ” Compare , If it is consistent, there is no error , Otherwise, there will be a mistake .
• Cyclic redundancy check
       The basic principle of cyclic redundancy code check is to treat a data block as a binary number with a long number of digits , Then divide it by a specific number , The remainder is attached to the data block as a check code and sent together .

5、 Baud rate

     Baud rate is the rate of analog line signal , Also known as modulation rate , Measured by the number of oscillations per second of the waveform . Wave refers to the modulation rate of the data signal to the carrier , It is expressed by the number of carrier modulation state changes per unit time , Its unit is baud (Baud). The relationship between baud rate and bit rate is bit rate = Baud rate X The number of bits corresponding to a single modulation state . In the information transmission channel , The signal unit carrying data information is called symbol , The number of symbols transmitted through the channel per second is called the symbol transmission rate , Baud rate for short . Baud rate is the index of transmission channel bandwidth . The amount of information transmitted through the channel per second is called bit transmission rate , Bit rate for short . The bit rate represents the transmission rate of effective data .

• 1 potter =1 position / second （1bit/s）

6、 The mechanism of serial communication

• Simplex communication ： Simplex communication means that after the communication mechanism is established , Fix the receiver and sender , Both cannot be changed , The receiver can only receive , The sender can only send ;
• Half duplex communication ： Half duplex communication means that after the communication mechanism is established , The receiver and the sender can be interchanged , But the same port cannot be the sender , As the receiver ;
• Full duplex communication ： Full duplex communication means that after the communication mechanism is established , The receiver can also act as the sender , Again , The sender can also act as the receiver ;

Two 、 A serial port （USART）

1、 Introduction of serial port

     A serial port （USART）, Also known as universal synchronous asynchronous transceiver (Universal Synchronous/Asynchronous Receiver/Transmitter USART), It provides a flexible approach with the use of industry standards NRZ Full duplex data exchange between external devices in asynchronous serial data format . USART Using fractional baud rate generator to provide a wide range of baud rate selection . It supports synchronous one-way communication and half duplex single line communication , Also support LIN( Local Internet ), Smart card protocol and IrDA( Infrared data organization )SIR ENDEC standard , And modem (CTS/RTS) operation . It also allows multiprocessor communication . Using a multi buffer configuration DMA The way , It can realize high-speed data communication .

2、 Function introduction

（1）、USART_InitTypeDefstructure Structure introduction

• USART_InitTypeDefstructure Defined in "stm32f10x_usart.h" In file , The member variables of the structure are as follows ：
  

• USART_InitTypeDefstructure member USART Pattern contrast
  

• USART_InitTypeDefstructure Member variables USART_BaudRate The definition of
  This member is set USART Baud rate of transmission , Baud rate can be calculated by the following formula :
  IntegerDivider =((APBClock)/ (16*(USART_InitStruct->USART_BaudRate)))FractionalDivider = ((IntegerDivider - ((u32)IntegerDivider))*16)+0.5

• USART_InitTypeDefstructure Member variables USART_WordLenth The definition of
  USART_WordLenth Defines the number of bits of data transmission in a frame , It has two values USART_WordLeth_8b（ Eight digit data ） And USART_WordLeth_9b（ Nine digit data ）.

• USART_InitTypeDefstructure Member variables USART_StopBits The definition of
  USART_StopBits Is a variable used to set the stop bit of transmission at the end of the frame , The following table is a detailed description of the variable value ：
  

• USART_InitTypeDefstructure Member variables USART_Parity The definition of
  
  ( Be careful ： Once parity is enabled , Sending data MSB Bit inserts the computed parity bit （ The word is 9 The first of bit 9 position , The word is 8 The first of bit 8 position ）.)

• USART_InitTypeDefstructure Member variables USART_HardwareFlowControl The definition of
  USART_HardwareFlowControl Specifies whether the hardware flow control mode is enabled or disabled . Please see the table below for the specific mode ：
  

• USART_InitTypeDefstructure Member variables USART_Mode Definition
  USART_Mode Set the enable or disable sending and receiving mode of the serial port , The following table shows the detailed mode selection ：
  

• USART_InitTypeDefstructure Member variables USART_CLOCK Definition
  USART_CLOCK Set up USART Is the clock enabled or disabled , The following is a detailed description of the options of this variable ：
  

• USART_InitTypeDefstructure Member variables USART_CPOL The definition of
  USART_CPOL Specify the following SLCK Polarity of clock output on pin . The following table is a detailed description of the variable value ：
  

• USART_InitTypeDefstructure Member variables USART_APHA The definition of
  USART_CPHA Specify the following SLCK The phase of the clock output on the pin , and CPOL Bits work together to produce the user's desired clock / Sampling relationship of data . The detailed description of its value is shown in the figure below ：

• USART_InitTypeDefstructure Member variables USART_LastBit The definition of
  USART_LastBit To control whether it is in synchronous mode , stay SCLK The last data word sent is output on the pin (MSB) Corresponding clock pulse . The following figure shows the optional values and descriptions of parameters ：
  

（2）、 Interrupt register USART_Init function

（3）、 Interrupt data transmission USART_SendData function

（4）、 Interrupt data reception USART_ReceiveData function

（5）、 Check the specified interrupt flag bit function USART_GetFlagStatus function

2、 Example

     utilize STM32 The development board receives PC Data sent by the end , Displayed on the nixie tube , And send the cumulative total number of received data to PC End .

(1)、 Global variables

// Save serial port 1 Data received 
unsigned char uart1_date[6];
// Define the amount of data received 
u8 uart1_date_number = 0;
// Save serial port 1 Data received 
unsigned char d1,d2,d3;

(2)、 The main function

extern unsigned char d1,d2,d3;
 
int main(void)
{
     
	u8 old_number = uart1_date_number;
	time6_init();
	seg_GPIO_Init();
	uart1_init();
	while(1){
    
		
		segbuff[0] = d1/16;
		segbuff[1] = d1%16;
		segbuff[2] = d2/16;
		segbuff[3] = d2%16;		
		segbuff[4] = d3/16;
		segbuff[5] = d3%16;
		
		// Determine whether data is received , Send the data after receiving the data 
		if(old_number != uart1_date_number){
    
			sendData(uart1_date_number);
			old_number = uart1_date_number;
		}
		
	}
}

(3)、 Interrupt initialization function

/* * @ The functionality ： A serial port 1 The initialization  * @ Parameters   nothing  * @ Return value   nothing  */
void uart1_init(void)
{
    
	/*  Define initialization variables  */
	GPIO_InitTypeDef GPIO_InitStructrue;//GPIO initialization 
	USART_InitTypeDef USART_InitStructrue;// A serial port uart1 initialization 
	NVIC_InitTypeDef NVIC_InitStructrue;//NVIC initialization 
	
	/*  Turn on timer  */
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA|RCC_APB2Periph_USART1|RCC_APB2Periph_AFIO,ENABLE);
	
	/*  To configure GPIO Patterns and IO mouth   be used for GPIO initialization  */
	GPIO_InitStructrue.GPIO_Pin = GPIO_Pin_9;// choice GPIO The pin of  UART1 The output related pin is Pin9
	GPIO_InitStructrue.GPIO_Speed = GPIO_Speed_50MHz;// Set up GPIO The frequency of 
	GPIO_InitStructrue.GPIO_Mode = GPIO_Mode_AF_PP;// Set up GPIO The mode is multiplex push-pull output mode 
	GPIO_Init(GPIOA,&GPIO_InitStructrue);
	GPIO_InitStructrue.GPIO_Pin = GPIO_Pin_10;// choice GPIO The pin of  UART1 The output related pin is Pin9
	GPIO_InitStructrue.GPIO_Speed = GPIO_Speed_50MHz;// Set up GPIO The frequency of 
	GPIO_InitStructrue.GPIO_Mode = GPIO_Mode_IN_FLOATING;// Set up GPIO The mode is analog input mode 
	GPIO_Init(GPIOA,&GPIO_InitStructrue);
	
	/*  Serial initialization  */
	USART_InitStructrue.USART_BaudRate = 9600;// Set the baud rate of the serial port 
	USART_InitStructrue.USART_WordLength = USART_WordLength_8b;// Set the data length to 8 position 
	USART_InitStructrue.USART_StopBits = USART_StopBits_1;// The setting data has 1 Stop bit of bit 
	USART_InitStructrue.USART_Parity = USART_Parity_No;// Serial port data has no check bit 
	USART_InitStructrue.USART_HardwareFlowControl = USART_HardwareFlowControl_None;// Set the serial port to disable hardware flow 
	USART_InitStructrue.USART_Mode = USART_Mode_Tx|USART_Mode_Rx;// Turn on the sending and receiving mode of the serial port 
	USART_Init(USART1,&USART_InitStructrue);// initialization USART1
	USART_Cmd(USART1,ENABLE);// Enable serial port 1
	USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);// Can make USART1 interrupt 
	USART_ClearFlag(USART1,USART_FLAG_TC);// eliminate USARTx Pending flag bit 
	
	/*  Set up NVIC Parameters of  */
	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);// Set up NVIC The grouping 
	NVIC_InitStructrue.NVIC_IRQChannel = USART1_IRQn;// Appoint NVIC Passageway is USART1 passageway 
	NVIC_InitStructrue.NVIC_IRQChannelPreemptionPriority = 0;// Set interrupt preemption priority 
	NVIC_InitStructrue.NVIC_IRQChannelSubPriority = 0;// Set interrupt response priority 
	NVIC_InitStructrue.NVIC_IRQChannelCmd = ENABLE;// Set interrupt nesting to enable 
	NVIC_Init(&NVIC_InitStructrue);//NVIC initialization  
}

(4)、 Interrupt service function

/* * @ The functionality ： A serial port 1 The interrupt service function of  * @ Parameters   nothing  * @ Return value   nothing  */
void USART1_IRQHandler(void)	
{
    
	USART_ClearFlag(USART1,USART_FLAG_TC); // Clear the flag bit of interrupt transmission completion   Indicates that sending data has been completed 
	if(uart1_date_number == 0){
    
		d1 = USART_ReceiveData(USART1);
	}else if(uart1_date_number == 1){
    
		d2 = USART_ReceiveData(USART1);
	}else{
    
		d3 = USART_ReceiveData(USART1);
	}
	uart1_date_number++;
	uart1_date_number = uart1_date_number%3;
}

(5)、 Data sending function

/* *  The functionality   Send serial data  * Parameters  u8 data： Data sent  * Return value   nothing  */
void sendData(u8 data)
{
    
	USART_SendData(USART1,uart1_date_number);// Peripherals through USARTx Send single data 
	// Check whether the null flag bit of the transmit data register is reset   If it is empty, it means that data can be stored inside 
	while(USART_GetFlagStatus(USART1,USART_FLAG_TXE)==Bit_RESET)
		;
}

3、 ... and 、 Problems encountered

     In the above code, we need to pay attention to ： Receiving PC It's better not to use an array to receive data when sending data from the client .（ Xiaobian has tried , However, the data sent does not correspond to the data of the array ） The methods of receiving data and displaying data are attached below ：

• Method of receiving data ：

uart1_date[uart1_date_number]=USART_ReceiveData(USART1);// Accept serial port 1 The data of 

• Method of displaying data ：

		// Try 1
		segbuff[0] = uart1_date[1];
		segbuff[1] = uart1_date[0];
		segbuff[2] = uart1_date[3];
		segbuff[3] = uart1_date[2];		
		segbuff[4] = uart1_date[5];
		segbuff[5] = uart1_date[4];

		// Try 2
		segbuff[0] = uart1_date[0]/16;
		segbuff[1] = uart1_date[0]%16;
		segbuff[2] = uart1_date[1]/16;
		segbuff[3] = uart1_date[1]%16;	
		segbuff[4] = uart1_date[2]/16;
		segbuff[5] = uart1_date[2]%16;

Four 、 attach

• When sending data , You can not put the function that sends data in the main function , It can also be placed when the serial port receives data , To do so , We don't have to judge whether the data is received , It can be sent every time the serial port interrupt function is triggered .
• You can go to other related functions STM32- Refresh the nixie tube