I use software for debounce switch. Get this
//--------------------------------------------------------------------------
#include <reg51.h>
#define inkey P0
#define scan P2

void init_key(void)
{inkey=0xFF; /* set all row to high */}

unsigned char scankey(void) /* 0-255 value available return. */
{ /* Use it for index lookup table ascii
char in,out,row,col,pressed;
while(1)
{pressed=0; /* flag for chek key has pressed */
out = 0x01;
for(col=0;col<=5;col++)
{ scan = ~out;
in = ~inkey;
if(in!=0) /* key pressed */
{
pressed = 1; /*set flag for find key that prssed*/
break;
}
out<<=1; /* shift bit for scan next column */
}
if(pressed) /* find what key has pressed */
{
row=0;
while(in>>(row+1)!=0){row++;}
return ((row*6)+col);
}
}
}
//---------------------------------------------------------------------------
void main(void)
{
unsigned char ch;
init_key();
char co_key[]={
'0','1','2','3','4','5','6','7',
'8','9','a','b','c','d','e','f',
'g','h','i','j','k','l','m','n',
'o','p','q','r','s','t','u','v',
'w','x','y',0x21,0x22,0x23,0x24,0x25,
0x26,0x27,0x28,0x29,0x2A,0x2B,0x2C,0x2D };
ch = co_key(scankey());
// get character on variable 'ch'

....
....
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}
/* CE KMITL 2006 ake*/