COMSATS
UNIVERSITY ISLAMABAD
MICROPROCESSOR
SYSTEMS AND INTERFACING
LAB REPORT 6
SUBMITTED TO:
SIR
KHIYAM IFTIKHAR
SUBMITTED BY:
JUNAID
AHMAD
IBRAR
AHMAD
JARRAR
MALIK
REGISTRATION NO:
CIIT/FA19-BEE-089/ISB
CIIT/FA19-BEE-083/ISB
CIIT/FA19-BEE-087/ISB
DATE:
01-10-2021
Keypad Interfacing Using Digital I/O
Ports
Objectives:
•
Using
digital I/O ports of AVR microcontroller for digital Inputs.
•
Use
I/O ports To Interface matrix keypad with microcontroller.
Tools:
Software Tools:
•
AVR
Studio/ Microchip Studio
•
Proteus
ISIS
•
AVRDUDESS
Hardware
Tools:
|
Name |
Value |
Quantity |
|
Arduino
Nano |
- |
1
|
|
4X4
Keypad |
- |
-
|
|
Resistors |
100Ω
|
8
|
PRE-LAB:
6.1 4x4
Membrane Keypad:
The
Keypad 4x4 features 16 push buttons arranged in 4x4 matrix to form standard
alphanumeric keypad. It provides a useful human interface component for
microcontroller projects.Matrix keypads uses a combination of four rows and
four columns to provide button states to the microcontroller. Underneath each
key is a pushbutton, with one end connected to one row, and the other end
connected to one column. These connections are shown in figure 6.1.
Key Specifications
•
Maximum
Rating: 24 VDC, 30 mA
•
Interface:
8-pin access to 4x4 matrix
•
Operating
temperature: 32 to 122 °F (0 to 50°C)
•
Dimensions:
Keypad, 2.7 x 3.0 in (6.9 x 7.6 cm) Cable: 0.78 x 3.5 in (2.0 x 8.8 cm)
This keypad can be used in Security systems, Menu selection, Data entry for embedded systems and various other applications.
6.2 Working
of keypad:
As can
be seen in figure 6.1, the buttons consist of 16 switches that are normally
open. When one button is pressed, a pair of pins are connected, as seen in
figure 6.2. As shown in the figure, the R2 and C2 pins will help determine the
button that is pressed.
 |
|
Figure 6.2 – Standard 4x4 Keypad |
To use a keypad with a microcontroller, it should be
connected to in a way where either the rows are the input to the controller and
the columns are the output to the microcontroller, or vice-versa. Suggested
connections are shown in figure 6.3.
 |
|
Figure 6.3 – Button Matrix
Connection |
You
should remember the role of IO-registers in the ATmega328p as illustrated in
figure 6.4. Assume all the 4 rows are initially set as input (by virtue of DDRx
register). The programmer will have to scan the rows to determine if a button
is pressed. Normally, the values on the row would be all 0 i.e. R4-R1 == 0000.
When the button is pressed as shown in figure 5.2, the value would change to
R4-R1 == 0010.
The
fundamental idea is that the program keeps scanning the rows as long as no
button is pressed. However, as soon as a button is pressed, inverse the rows to
outputs and the columns to input. This would happen so fast that the button
will still be pressed. So, on scanning the columns, C4-C1 == 0010. In this one
can identify the button that is pressed, which in this case is ‘5’. [hint: the
sequence 0010-0010 could signify ‘5’, or R1-C4 can be represented by 1000-0001
signifying ‘A’]
 |
|
Figure 6.4 – ATmega328p port
registers roles |
|
|
In order
for the microcontroller to determine which button is pressed, following steps
are followed:
1) Create a look-up table filled with 16
entries for all keys of the keypad.
2) Four microcontroller pins should be
defined as outputs, and other four pins should be defined as inputs.
3) Connect columns of the keypad to
input port and rows to the output port. Pull up the input port and then read
the value of columns.
4) Now connect rows of the keypad to
input port and columns to the output port. Pull up the input port and then read
the value of rows.
5) If no key is pressed, the value of
rows and columns will be 0000. If any key is pressed, the value of rows and
columns can be 0000,0001,0010,0100,1000 (1,2,4,8).
6) If no key is pressed, return 0. If a
key is pressed, find its location in the keypad look-up table and return the
key pressed.
IN-LAB TASK:
TASK 1:
Interfacing Atmega 328P with Keypad:
Connect a keypad to the microcontroller. Scan the keypad for key press
and display the pressed key on the serial monitor using serial communication.
MAIN.C
#include "maininc.h"
#include "keypadtable.h"
#include <avr/io.h>
int main(void)
{
/* Replace with your application code */
unsigned char ch;
UCSR0B&=~(1<<TXEN0);
UCSR0B&=~(1<<RXEN0);
while (1)
{
ch=readkeypad();
//if (ch==0b01111110)
//{DDRB=0xff; PORTB=1;}
switch(ch){
case one: writetoport(1); break;
case 0b10111110: writetoport(2); break;
case 0b11011110: writetoport(3); break;
case 0b01111101: writetoport(4); break;
case 0b10111101: writetoport(5); break;
case 0b11011101: writetoport(6); break;
case 0b01111011: writetoport(7); break;
case 0b10111011: writetoport(8); break;
case 0b11011011: writetoport(9); break;
case 0b10110111: writetoport(0); break;
default: writetoport(ch);
}
//writetoport(1);
}
}
READKEYPADALGO.C
#include "readkeypadinc.h"
#define F_CPU 16000000UL
#include <util/delay.h>
#include <avr/io.h>
#define rlength 4 //Number of row pins
#define clength 3
char readkeypad(){
char row,col,in;
//TWCR=0x00;
DDRC=0xff;
setrowoutcolin();
waitforpress();
_delay_ms(80);//For debouncing
col=readport();
_delay_ms(10);
setcoloutrowin();
_delay_us(5);//If this delay is less than 4us, correct value is not updated in PIND
row=readport();
waitforrelease();
_delay_ms(80);// For debouncing
in=(col+row);
return (in);
}
WRITETOPORT.C
#include <avr/io.h>
void writetoport(char ch){
PORTC=ch;
}
ACCESSPINS.C
#include <avr/io.h>
#include <util/delay.h>
#define col0 PORTD4
#define col1 PORTD5
#define col2 PORTD6
#define col3 PORTD7
#define row0 PORTD0
#define row1 PORTD1
#define row2 PORTD2
#define row3 PORTD3
#define colpins(a,b,c,d) (((1<<a)|(1<<b)|(1<<c)|(1<<d)))
#define rowpins(e,f,g,h) (((1<<e)|(1<<f)|(1<<g)|(1<<h)))
void setcoloutrowin(){
DDRD&=~ rowpins(row0,row1,row2,row3); //ROWS in (first change status to input )
PORTD=rowpins(row0,row1,row2,row3); //Pullup (modify complete
port, not selected bits otherwise previously
DDRD|=colpins(col0,col1,col2,col3); //col out(if this is used 1st
then both connected
// will be output i.e output connected to
other output)
}
void setrowoutcolin(){
DDRD&=~ colpins(col0,col1,col2,col3);//cols in
PORTD=colpins(col0,col1,col2,col3); //Pullup (modify complete
port, not selected bits otherwise previously
//pulled up remain at 1. So
set them to zero. This way input pulled to output also goes through
intermediate stage
//_delay_ms(2);
DDRD|=rowpins(row0,row1,row2,row3); //row out
//PORTC=(PIND&0xF0)>>4;
}
void waitforpress(){
_delay_us(5); //If this delay is removed PIND remains
zero and thus doesn't wait for press. If set >1us and < 5us than PIND
gets set correctly for while check but not for the next debug instruction i.e
PORTC=PIND&0xF0. Half the bits still remain zero
//PORTC=(PIND&0xF0)>>4;
while ((PIND&0xF0)==0xF0)
{
}
}
void waitforrelease(){
//PORTC=(PIND&0x0f);
//_delay_us(1);
while ((PIND&0x0F)!=0x0F)
{
}
PORTC=(PIND&0x0f);
}
char readport(){
return PIND;
}
BUILD ON AVR:
TASK 2:
SIMULATION:
TASK 3:
HARDWARE:
CRITICAL
ANAYSIS:
In
this lab experiment we got to know how to interface keypad by using digital I/O
ports. An Avr code was created and burned in Arduino and was connected to
keypad. After compiling the code on AVR, we simulated it on proteus and checked
the functioning of 4*4. For the functioning of keypad we used look-up table
filled with 16 entries for all keys of the keypad and used four microcontroller
pins as outputs, and other four pins should be defined as inputs. For reading
the values of columns we set the columns to input and pulled up the columns
whereas we set the rows to output and pulled them down. Secondly, for reading
the values of rows we set the rows to input and pulled up the rows whereas we
set the columns to output and pulled them down. The Keypad 4x4 features 16 push
buttons arranged in 4x4 matrix form so that when we implemented this task on hardware
and one of the 16 buttons were pressed, a pair of pins were connected together,
and the numeric value was displayed on Arduino IDE.
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