I didnot understand what u say about bouncing,my eng.is also poor and knowledge too.
i have written this code. we i a decimal no. and when i press * key it outputs at P3.
can anyone tell how i can input values from 0--255. my program just reads 1 key.. after pressing another it
overwrites the 1st . should i use arrays??? actually i want to input values from 0-255 and after pressing * key on keypad.
LEDs turn ON at port 3, according to input . e.g input 255... 7 LEDs On.
tell me what is pullup resistance.
and now how can i made keypad.is keypad is simple arrangement of rows or columns or i need some resistances to make a keypad/


#include <ATMEL/AT89X51.H>
sbit column1=P2^0;
sbit column2=P2^1;
sbit column3=P2^2;
sbit row1=P1^0;
sbit row2=P1^1;
sbit row3=P1^2;
sbit row4=P1^3;
void keyscan(void);

void main(void)
{
while(1)
{
P2=0x00;
P1=0x0F; //1 to each row
if (P1!=0x0F)
{
keyscan();
}
}
}


void keyscan(void)
{
int key;
P2=0x03; //00000011 1st column 0
if (row1==0)
{
key=1;
while(row1==0)
{}
}
if (row2==0)
{
key=4;
while(row2==0)
{}
}
if (row3==0)
{
key=7;
while(row3==0)
{}
}
if (row4==0)
{
key=0;
while(row4==0)
{}
}
P2=0x05; //0000101 2nd column 0
if (row1==0)
{
key=2;
while(row1==0)
{}
}
if (row2==0)
{
key=5;
while(row2==0)
{}
}
if (row3==0)
{
key=8;
while(row3==0)
{}
}
if (row4==0)
{
key=0;
while(row4==0)
{}
}
P2=0x06; //00000110 3rd column 0.
if (row1==0)
{
key=3;
while(row1==0)
{}
}
if (row2==0)
{
key=6;
while(row2==0)
{}
}
if (row3==0)
{
key=9;
while(row3==0)
{}
}
if (row4==0)
{
P3=key;
while(row4==0)
{}
}
}