STM32 USART serial communication

1. Simple demo 
communicates with the host computer through the 232 serial port. First, ensure that the MCU 232 serial port is connected to the computer's serial port. Of course, the computer is a USB interface, and the essence of the USB interface is also a serial port. We implement the host computer to send a hexadecimal data, and the MCU displays the data after receiving it, and sends it twice to the host computer. 
1. usart_init(); Serial port initialization

void usart_init()
{
   GPIO_InitTypeDef GPIO_InitStructure;
   USART_InitTypeDef USART_InitStructrue;
   NVIC_InitTypeDef NVIC_InitStructure;
   RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_USART1,ENABLE); //Turn on GPIOA and USART clocks
   RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE); //Function multiplexing IO clock
   //GPIO initialization configuration
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;//TX PA9
   GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; //Multiplexed push-pull output
   GPIO_Init(GPIOA,&GPIO_InitStructrue);
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;//RX PA10
   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; //Floating input
   GPIO_Init(GPIOA,&GPIO_InitStructure); //USART initialization configuration
   USART_InitStructure.USART_BaudRate = 9600; //Set the baud rate to 9600
   USART_InitStructure.USART_WordLength = USART_WordLength_8b;
   USART_InitStructure.USART_StopBits = USART_StopBits_1;
   USART_InitStructure.Parity = USART_Parity_No;
   USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
   USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; //Serial port mode is send and receive mode
   USART_Init(USART1,&USART_InitStructure);
   USART_Cmd(USART1,ENABLE);
   USART_ITConfig(USART1,USART_IT_RXNE,ENABLE); //Turn on the transmit interrupt, and a data interrupt is generated in the buffer
   USART_ClearFlag(USART1,USART_FLAG_TC); //Clear the send completion flag   
   //NVIC interrupt configuration
   NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1); //Priority group 1, with 1 preemptive priority and 3 slave priorities
   NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn; //Open the global interrupt of USART1
   NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; //Preemption priority is 0
   NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; //Response priority is 0
   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //Enable
   NVIC_Init(&NVIC_InitStructure);
}12345678910111213141516171819202122232425262728293031323334

2. USART1_IRQHandler() serial port interrupt function

void USART1_IRQHandler(void)
{   static u8 d;
   USART_ClearFlag(USART1,USART_FLAG_TC); //When the receive buffer is not empty, receive data if(USART_GetITStatus(USART1,USART_IT_RXNE)!=RESET){
   d = ReceiveData(USART1);
   d = 2*d;
   USART_Send(USART1,d); //Check if the send completion flag is set to 1 while(USART_GetFlagStatus(USART1,USART_FLAG_TXE) != SET);}
}12345678910111213

3. main() main function

int main()
{
   usart_init(); //Serial port 1 initialization
   while(1);   return 0;
}123456

The effect of this main function is to set the serial port baud rate to 9600, set HEX sending and 
display  ,
and  add 1 to the hexadecimal number for display.