#include <reg51.h>
#define COL  P2			
#define ROW  P1			
void MSDelay(unsigned int value);
void SerTX(unsigned char);
unsigned char keypad[4][4] =	{'0','1','2','3',
						'4','5','6','7',
						'8','9','A','B',
						'C','D','E','F'};
void main()
  {
    unsigned char colloc, rowloc;
    TMOD = 0x20;			
    TH1 = -3;				
    SCON = 0x50;			
    TR1 = 1;				
  
  
  COL = 0xFF; 				
  while(1) 				
    {	
    do
      {
      ROW = 0x00;     		
      colloc = COL;     		
      colloc &= 0x0F;   		
      } while(colloc != 0x0F);	
    do
      {
      do
        {
        MSDelay(20);			
        colloc = COL;		
        colloc &= 0x0F;		
        } while(colloc == 0x0F);
      MSDelay(20);			
      colloc = COL;			
      colloc &= 0x0F;			
      } while(colloc == 0x0F);	
      while(1)
        {
          ROW = 0xFE;		
          colloc = COL;		
          colloc &= 0x0F;		
          if(colloc != 0x0F) 	
            {
              rowloc = 0;		
              break;			
            }
          ROW = 0xFD;		
          colloc = COL;		
          colloc &= 0x0F;		
          if(colloc != 0x0F) 	
            {
              rowloc = 1;		
              break;			
            }
          ROW = 0xFB;		
          colloc = COL;		
          colloc &= 0x0F;		
          if(colloc != 0x0F) 	
            {
              rowloc = 2;		
              break;			
            }
          ROW = 0xF7;		
          colloc = COL;		
          colloc &= 0x0F;		
          rowloc = 3;		
          break;			
        }
      
      if(colloc == 0x0E)
        SerTX(keypad[rowloc][0]);
      else if(colloc == 0x0D) 
        SerTX(keypad[rowloc][1]);
      else if(colloc == 0x0B)
        SerTX(keypad[rowloc][2]);
      else
        SerTX(keypad[rowloc][3]);
      }
    
  }
void SerTX(unsigned char x)
  {
    SBUF = x;			
    while(TI==0);		
    TI = 0;			
  }
void MSDelay(unsigned int value)
  {
    unsigned int x, y;
    for(x=0;x<1275;x++) 
      for(y=0;y<value;y++);
  }