/************************************************************************
*Program to scan a keypad on P1 and output the pressed kay value to P0	*
*P1.0 - P1.3 rows		P1.4 - P1.7 columns			*
*Process key flag = 4OH	
************************************************************************/

#include <stdio.h>
#include <reg51.h>

int index;
int id;
int num;
sbit P1four = P1^4;
sbit P1five = P1^5;
sbit P1six = P1^6;
sbit P1seven = P1^7;
int cscan (void);

void main (void){

	if (IE0 == 1){
		index = 0;
		while (index == 0){
			P1 = ~1;
			id = cscan;
           		P1 = ~2;
  			id = cscan;
			P1 = ~3;
			id = cscan;
		}
		IE0 = 0;
	}
}
int cscan (void){
	if (P1four == 0){
		index = 1;
		return (num);
	}
	num ++;
	if (P1five == 0){
		index = 1;
		return (num);
	}
	num ++;
	if (P1six == 0){
		index = 1;
		return (num);
	};
	num ++;
	if (P1seven == 0){
		index = 1;
		return (num);
	}
	num ++;
	return (num);
}