51 MCU serial port sending and interrupt receiving program

void leddisplay(); // digital tube display
void delayms(unsigned int k); // delay n ms
void USART_SEND(unsigned char dat); // serial port sending subroutine
unsigned char data ledxs[8]={16,16,16,16,16,0,0,18}; // digital tube display buffer
unsigned char code tab[]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0,0xff,0x76};
                          // common cathode code 0-F, all off, all on, H
void main()
{
   unsigned char dat=0,i;
   delayms(200);
   TMOD=0x20; // Timer 1 mode 2, 8-bit auto-reload
   TL1=0xe6;
   TH1=0xe6; // Baud rate 1200
   TR1=1;
   SCON=0x50; // Serial port mode 1, receive enabled, 8-bit data, no parity, 1 start bit, 1 end bit
   EA=1; // Enable serial port interrupt
   ES=1; // Enable total interrupt
   while(1)
   {
     for(i=0;i<60;i++)
       leddisplay(); // Loop display 60 times, delay 480ms
     USART_SEND(dat); // Serial port sends data (0-255)
     dat++;
     if(dat==256) dat=0;
     
   }
}
void USART_SEND(unsigned char dat) // Serial port sending subroutine
{

   SBUF=dat; // Send data
   while(TI==0); // Wait for sending to complete
   TI=0;
}
void USART_RCV_INT(void) interrupt 4 using 1 // Serial port receive interrupt service routine
{
  unsigned char dat;
  if(RI==1) // Determine whether it is a receive interrupt
  {
    RI=0;
    dat=SBUF; // Receive data
    ledxs[5]=dat/16;
    ledxs[6]=dat%16; // Convert received data to hexadecimal display
    ledxs[7]=18;       
  }
}
void leddisplay() // LED display subroutine
{
  P2=0xdf;
  P0=tab[ledxs[0]];
  delayms(1);
  P0=0x00;

  P2=0x5f;
  P0=tab[ledxs[1]];
  delayms(1);
  P0=0x00;

  P2=0x9f;
  P0=tab[ledxs[2]];
  delayms(1);
  P0=0x00;

  P2=0x1f;
  P0=tab[ledxs[3]];
  delayms(1);
  P0=0x00;

  P2=0xff;
  P0=tab[ledxs[4]];
  delayms(1);
  P0=0x00;

  P2=0x7f;
  P0=tab[ledxs[5]];
  delayms(1);
  P0=0x00;

  P2=0xbf;
  P0=tab[ledxs[6]];
  delayms(1);
  P0=0x00;

  P2=0x3f;
  P0=tab[ledxs[7]];
  delayms(1);
  P0=0x00;
}
void delayms(unsigned int k) //Delay n ms
{
  while(k)
  {
    int i;
    i=110;
    while(i--);
    k=k-1;
  }
}