MCU + 8255 keyboard scanning c51 program

The following is the circuit diagram: The keyboard scanning function of the 51 single-chip microcomputer + 8255 chip only does simple input and output, and uses the P1 port to control the light-emitting diode. If the key value is 7, the key code is 0x07;

Source program:

#include
#include
#define uchar unsigned char
#define uint unsigned int
#define LScan XBYTE[0x7f00] //column scan address
#define HScan XBYTE[0x7f02] //row scan address

//Delay function
void delay(uint i)
{uint j;
  for(j=i;j>0;j--)
   { ; }
}

//Function to detect whether a key is pressed
uchar CheckKey() //Returns 0xff if a key is pressed, otherwise returns 0
{ uchar i;
 LScan = 0x00;
  i=(HScan & 0x0f);
  if(i==0x0f) return(0);
  else return(0xff);
 }
//********Keyboard scanning subfunction***********
uchar KeyScan()          
{ //If no key is pressed, return oxff; if yes, return the key code        
    uchar ScanCode;
 uchar CodeValue;
 uchar k;
 uchar i,j;
 if(CheckKey()==0) return(0xff); //No key pressed, return 0xff
 else
  {
   delay(200); //delay
   if(CheckKey()==0)
     return(0xff); //No key pressed, return 0xff
   else
    {
     ScanCode=0x01; //Set the column scan code, the initial value of the lowest bit is 0
     for(i=0;i<8;i++) // Scan column by column 8 times
      {
       k=0x01; //Assign initial value to row scan code
       LScan=~ScanCode; //Send column scan code
       CodeValue=i; //The key code is the value of i. The key code of each column in the zeroth row is 0, 1, 2, ... 7, which is consistent with the value of i
       for(j=0;j<4;j++)
        {
         if((HScan & k) ==0) //Is it in the current column?
          {
           while(CheckKey()!=0); //If yes, wait for the key to be released
           return(CodeValue); //Return key code
          }
         else //Otherwise, the key code is increased by 8, and the key codes on each row of the same column differ by exactly 8
          { // Shift column scan code k right one position and scan the next row
           CodeValue+=8;
           k<<=1;
          }
                   
         }
         ScanCode<<=1; //After scanning each row, the column scan code is shifted right by one position and the next column is scanned
      }   
         }
  }
}


 main()
 { uchar Key;
       P1=0x00;
                //Initialize, turn off the digital tube first
  XBYTE[0x7f03]=0x81; //8255 initialization, set port A output, port C low 4 bits input
  while(1)
   {Key=KeyScan();
      if(Key!=0xff)
     P1=Key;
   }
}