Interfacing of Keypad with PIC

Matrix Keypad: Matrix Keypads are commonly used in calculators, telephones etc where a number of input switches are required. We know that matrix keypad is made by arranging push button switches in row and columns. In the straight forward way to connect a 4×4 keypad (16 switches) to a microcontroller we need 16 inputs pins. But by connecting switches in the following way we can read the status of each switch using 8 pins of the microcontroller.

Program:

#include<pic.h>

#include<htc.h>

#define __PIC16f877A_H

__CONFIG(WDTE_OFF&FOSC_HS&PWRTE_ON&LVP_OFF);

#include"lcd_header.h"

void main()

{

TRISB=0x00;

TRISC=0x00;

TRISD=0x00;

unsigned int i,a,b;

init();

while(1)

{

PORTC=0x0F;

a=PORTC;

PORTC=0xF0;

b=PORTC;

i=a|b;

switch(i)

{

case 0xE7:

  datta('0');

  delay(5000);

  break;

case 0xEB:

  datta('1');

  delay(5000);

  break;

case 0xED:

  datta('2');

  delay(5000);

  break;

case 0xEE:

  datta('3');

  delay(5000);

  break;

case 0xD7:

  datta('4');

  delay(5000);

  break;

case 0xDB:

  datta('5');

  delay(5000);

  break;

case 0xDD:

  datta('6');

  delay(5000);

  break;

case 0xDE:

  datta('7');

  delay(5000);

  break;

case 0xB7:

  datta('8');

  delay(5000);

  break;

case 0xBB:

  datta('9');

  delay(5000);

  break;

case 0xBD:

  datta('A');

  delay(5000);

  break;

case 0xBE:

  datta('B');

  delay(5000);

  break;

case 0x77:

  datta('C');

  delay(5000);

  break;

case 0x7B:

  datta('D');

  delay(5000);

  break;

case 0x7D:

  datta('E');

  delay(5000);

  break;

case 0x7E:

  datta('F');

  delay(5000);

  break;

default:

            PORTC=0x00;

break;

}

}

}