Keypad/keyboard
interface to LPCXpresso
This module explains how to use 4x3 membrane keypad with
NXP's LPCXpresso microcontroller board
Requirements:
1. 4x3 Membrane Keypad
2. Seven segment display & 3K3 ohms resistors
3. Connecting wires.
4. General purpose printed circuit board.
Keypad is an array of switches. Matrix keypads are very
common input devices in embedded systems. They have simple
architecture and are easy to interface. One good thing about
them is that they allow you to interface a large number
of input keys to a microcontroller with minimum usage of
I/O resources. This tutorial type module explains how to
read input data from a 3×4 (12 keys) matrix keypad
interfaced to a ARM Cotex M0 based LPCXpresso microcontroller
embedded board from NXP Semiconductor and display the data
on a seven segment display. In short this project is to
display the pressed key symbol on the seven segment display.
Working: There will be 2 wires connected to each
switch of the keypad, they get short circuited whenever
a button is pressed. For example; when button '1' is pressed,
pin P0.7 and pin P3.2 are connected (as shown in the picture
below). Normally when no switch is pressed there is no connection
between rows and columns. Whenever a button is pressed contact
is made between particular row and column. 4x3 Keypad pins
can be directly connected to microcontroller i/o port of
this board.
Figures above : Keypad logic table and keypad's row
and column pins
Keypad Interfacing circuit: The below circuit connects
4x3 Membrane Keypad with port 3 and port 2 and port 0 of
microcontroller. The 7-seg display is connected to port
2 and port 3 of microcontroller.
Programming :The sample C-program/code below displays
coresponding numbers pressed on the keypad . The text below
in red color-font is the sample code which you can directly
use in your compiler:
#include "driver_config.h"
//for including the header file
#include "target_config.h"
#include "gpio.h"
void delay()//delay function
{
int a;
for(a=0;a<30000;a++);
}
void display(int a)
{
LPC_GPIO2->DIR=0x7C8;
LPC_GPIO3->DIR=0x030;
switch(a)
{
case 0:
// for 0
LPC_GPIO2->DATA=0x388;// (set the P2 bits as 0011 1000
1000)
LPC_GPIO3->DATA=0x030;// (set the P3 bits as 0000 0011
0000)
delay();// delay function calling
break;
case 1:
// for 1
LPC_GPIO2->DATA=0x080;// (set the P2 bits as 0000 1000
0000)
LPC_GPIO3->DATA=0x020;// (set the P3 bits as 0000 0010
0000)
delay();// delay function
break;
case 2:
// for 2
LPC_GPIO2->DATA=0x588; //(set the P2 bits as 0101 1000
1000)
LPC_GPIO3->DATA=0x010; //(set the P3 bits as 0000 0001
0000)
delay();// delay function
break;
case 3:
// for 3
LPC_GPIO2->DATA=0x580; //(set the P2 bits as 0101 1000
0000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 4:
//for 4
LPC_GPIO2->DATA=0x680; //(set the P2 bits as 0110 1000
0000)
LPC_GPIO3->DATA=0x020; //(set the P3 bits as 0000 0010
0000)
delay();// delay function
break;
case 5:
//for 5
LPC_GPIO2->DATA=0x700; //(set the P2 bits as 0111 0000
0000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 6:
//for 6
LPC_GPIO2->DATA=0x708; //(set the P2 bits as 0111 0000
1000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 7:
//for 7
LPC_GPIO2->DATA=0x180; //(set the P2 bits as 0001 1000
0000)
LPC_GPIO3->DATA=0x020; //(set the P3 bits as 0000 0010
0000)
delay();// delay function
break;
case 8:
//for 8
LPC_GPIO2->DATA=0x788; //(set the P2 bits as 0111 1000
1000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 9:
//for 9
LPC_GPIO2->DATA=0x780; //(set the P2 bits as 0111 1000
0000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 10:
//for *
LPC_GPIO2->DATA=0x780; //(set the P2 bits as 0111 1000
1000)
LPC_GPIO3->DATA=0x000; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
break;
case 11:
//for #
LPC_GPIO2->DATA=0x408; //(set the P2 bits as 0111 1000
0000)
LPC_GPIO3->DATA=0x030; //(set the P3 bits as 0000 0011
0000)
delay();// delay function
}
return ;
}
int main ()
{
while(1)//Infinite loop
{
uint32_t regVal;
/* Use port0_7 as input event, interrupt
test . */
GPIOSetDir (PORT0, 7, 0);
/* Port2_1, single trigger, active low. */
GPIOSetInterrupt (PORT0, 7, 1, 0, 0);
GPIOIntEnable (PORT0, 7);
GPIOIntStatus(0,7);
/* Use port2_0 as input event, interrupt test . */
GPIOSetDir (PORT2, 0, 0);
GPIOSetInterrupt (PORT2, 0, 1, 0, 0);
GPIOIntEnable (PORT2, 0);
GPIOIntStatus(2,0);
/* Use port2_1 as input event, interrupt test . */
GPIOSetDir (PORT2, 1, 0);
GPIOSetInterrupt (PORT2, 1, 1, 0, 0);
GPIOIntEnable (PORT2, 1);
GPIOIntStatus(2,1);
/* Use port2_2 as input event, interrupt
test . */
GPIOSetDir (PORT2, 2, 0);
GPIOSetInterrupt (PORT2, 2, 1, 0, 0);
GPIOIntEnable (PORT2, 2);
GPIOIntStatus(2,2);
GPIOSetDir (PORT3, 0, 1);
GPIOSetValue(PORT3,0,0);
GPIOSetDir (PORT3, 1, 1);
GPIOSetValue(PORT3,1,1);
GPIOSetDir (PORT3, 2, 1);
GPIOSetValue(PORT3,2,1);
{
regVal = GPIOIntStatus( PORT0, 7 );
if ( regVal )
display(1);
regVal = GPIOIntStatus( PORT2, 0
);
if ( regVal )
display(4);
regVal = GPIOIntStatus( PORT2, 1
);
if ( regVal )
display(7);
regVal = GPIOIntStatus( PORT2, 2);
if ( regVal )
display(10);
}
GPIOSetDir (PORT3, 0, 1);
GPIOSetValue(PORT3,0,1);
GPIOSetDir (PORT3, 1, 1);
GPIOSetValue(PORT3,1,0);
GPIOSetDir (PORT3, 2, 1);
GPIOSetValue(PORT3,2,1);
{
regVal = GPIOIntStatus( PORT0, 7 );
if ( regVal )
display(2);
regVal = GPIOIntStatus( PORT2, 0
);
if ( regVal )
display(5);
regVal = GPIOIntStatus( PORT2, 1
);
if ( regVal )
display(8);
regVal = GPIOIntStatus( PORT2, 2);
if ( regVal )
display(0);
}
GPIOSetDir (PORT3, 0, 1);
GPIOSetValue(PORT3,0,1);
GPIOSetDir (PORT3, 1, 1);
GPIOSetValue(PORT3,1,1);
GPIOSetDir (PORT3, 2, 1);
GPIOSetValue(PORT3,2,0);
{
regVal = GPIOIntStatus( PORT0, 7 );
if ( regVal )
display(3);
regVal = GPIOIntStatus( PORT2, 0
);
if ( regVal )
display(6);
regVal = GPIOIntStatus( PORT2, 1);
if ( regVal )
display(9);
regVal = GPIOIntStatus( PORT2, 2);
if ( regVal )
display(11);
}
}//paramesh
return 0;
}
Click below to visit next and other embedded system
course modules
Module 7: Serial communication
concepts -1
Module 8: RS-232 Basics
Module 9: Controller Area Networking
(CAN)
Module 10: LIN
Module 11: I2C Bus Interface
Module 12: SPI Bus Interface
Module14: USB Interface
Module15: SRAM memory interface
Module16: Flash memory interface
Module17: LCD display panel interface
Module18: Touch pane interface
Module19: Audio/video interface
Previous Modules
Module 1: Introduction
to Embedded Systems: Definition, application and future.
Module 2: Microprocessor, Microcontroller,
MCU Manufacturers, introduction to programming.
Module 3a: Installation of ARM Cortex M0 based LPCXpresso
kit from NXP and sample code
Module 4a: Sample program
for LPCXpresso
Module 3b: Installation of ARM Cortex M0 based STM32F0
Discovery kit from ST Microelectronics and sample code
Module 4b: Sample program for STM32F0 Discovery
Module 5a: ARM Cotex M0
Architecture
