PIC microcontroller RS232 serial communication program (USART)

//Single-signal machine model: PIC16F877A
//Function description: Application of PIC microcontroller USART, serial port debugging assistant sends data to 877, and 877 forwards it back to the serial port assistant after receiving it
//Assist work through "serial port debugging assistant"

#include //Includes the predefined
 __CONFIG(0xf73a) of the internal resources of the MCU;        
//Chip configuration word, watchdog off, power-on delay on, power-off detection off, low voltage programming off, encryption, 4M crystal HS oscillation

//=======================================================================
//Function description: main program  
//Function name: void main()
 
void main()
 {
  TRISC=0XFF; //Set the direction of port C to all output
  SPBRG=0XC; //Set the baud rate to 19200BPS
  TXSTA=0X24; //Enable serial port sending, select high-speed baud rate
  RCSTA=0X90; //Enable serial port work, continuous reception
  RCIE=0X1; //Enable receive interrupt
  GIE=0X1; //Open global interrupt
  PEIE=0X1; //Enable external interrupt
  while(1) //Wait for interrupt
   {;}
  }

//========================================================================
//Function description: interrupt function
//Function name: void interrupt usart(void)
void interrupt usart(void)
  {
   if(RCIE&&RCIF) //Judge whether it is a serial port receive interrupt
     {
      TXREG=RCREG; //Send the received data back
     }
   }