#include"reg52.h"
#define uchar unsigned char


sbit a1=P2^4;
sbit a2=P2^5;
sbit a3=P2^6;
sbit a4=P2^7;

sbit R1=P3^5;
sbit R2=P3^6;
sbit R3=P3^7;
uchar RR;
void delay()
     {uchar i,j;
      for (i=0;i<200;i++)
	     {for(j=0x00;j<20;j++) {}  }
	  }
uchar keynum(uchar i)
      {uchar j;
	   j=((0xf0&i)>>4); 
	   i=i&0x0f;
	   if (i==0xf) return 0xff;
	   switch(i)
	   {case 0x0e: while(a1==0){ P2=0xf0;}; return(j+0x00);//break;
	    case 0x0d: while(a2==0){ P2=0xf0;}; return(j+0x01);//break;
	    case 0x0b: while(a3==0){ P2=0xf0;}; return(j+0x02);//break;
	    case 0x07: while(a4==0){ P2=0xf0;}; return(j+0x03);//break;
	   }
	  }
uchar keyscan()
      {uchar LL;
	   
	   R1=0;
	   R2=0;
	   R3=0;
	   P2=0xf0;
	   //P0=0x30;
	  if((P2&0xf0)!=0xf0)
	     {delay();
		  if((P2&0xf0)!=0xf0)
		   {
			 R1=0;
	         R2=1;
	         R3=1;
			 if((P2&0xf0)!=0xf0)
			   {LL=((P2&0xf0)>>4);
			    if (RR!=(0x10|LL))  {RR=0x10|LL; return (keynum(0x10|LL));}		
			    else return (0xff);}    
			 R1=1;
	         R2=0;
	         R3=1;
			 if((P2&0xf0)!=0xf0)
			   {LL=((P2&0xf0)>>4);
			    if (RR!=(0x50|LL))   {RR=0x50|LL;return (keynum(0x50|LL));}
			    else return (0xff);}			    
             R1=1;
	         R2=1;
	         R3=0;
			 if((P2&0xf0)!=0xf0)
			   {LL=((P2&0xf0)>>4);
			    if (RR!=(0x90|LL))  {RR=0x90|LL ;return (keynum(0x90|LL));}
			    else return (0xff);}
		}	   
	 }      
	 else  
	      {    RR=0xff;
	      return (0xff);
          }
}