EC501-EMBEDDED SYSTEM APPLICATION

LCD & KEYPAD

Izwanizam bin Yahaya / JKE/ PTSB

1. Describe LCDs mode of operation and to interface with PIC Microcontroller

2. Construct a program code to send commands and data to LCD

3. Describe 4 x 4 Matrix keypad basic of operation

4. Illustrate key press detection and key identification mechanism

5. Apply program code to Write keypad and display to LCD in C programming

OBJECTIVES

• LCD stands for Liquid Crystal Display

• Most LCDs with one controller have 14 pins or 16 pins • Two extra pins are for back-light LED connections while LCDs with two controllers have two more pins to enable the additional controller• Most commonly used character based LCDs are based on Hitachi’s HD44780 controller or other which are compatible with HD44580.

LCD Interfacing

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The three control lines are referred to as EN, RS, and RW.

The EN line is called “Enable.” -to tell the LCD that you are sending in data.

-To send data to the LCD, your program should make sure this line is low (0) and then set the other two control lines and/or put data on the data bus.

-When the other lines are completely ready, bring EN high (1) and wait for the minimum amount of time required by the LCD datasheet and end by bringing it low (0) again.

LCD Control lines

The RS line is the “Register Select” line. When RS is low (0), the data is to be treated as a command or special instruction (such as clear screen, position cursor, etc.). When RS is high (1), the data being sent is text data which sould be displayed on the screen. For example, to display the letter “T” on the screen you would set RS high.

The RW line is the “Read/Write” control line. When RW is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively querying (or reading) the LCD. Only one instruction (“Get LCD status”) is a read command. All others are write commands–so RW will almost always be low.

The data bus consists of 4 or 8 lines (depending on the mode of operation selected by the user). In the case of an 8-bit data bus, the lines are referred to as DB0, DB1, DB2, DB3, DB4, DB5, DB6, and DB7.

RS & RW & DATA BUS ???

For 4 bits data

For 8 bits data

LCD Modes Operation

RB5, RB6 and RB7 of PIC are used for the control signals while PORTD of the microcontroller is the data bus.

LCD hardware connection to PIC microcontroller

#include <p18f45k22.h>

#define FREQ 4 //MHz#define MSLOOP ((FREQ*16)+(FREQ/4))

// PORTB & PORTD#define LCD_DATA LATD //-> RD0..RD7#define LCD_EN LATBbits.LATB7 //-> LCD EN#define LCD_RS LATBbits.LATB5 //-> LCD RS#define LCD_RW LATBbits.LATB6 //-> LCD R/W

<=PIC16

<= PIC18

Programming Code

Find the control lines LCD to PIC pin & 4 bit data bus pin???Find the control lines LCD to PIC pin & 4 bit data bus pin???

RS = _____________ D4 = ___________RW = ________________ D5 = ____________E = ________________ D6 = ____________

D7 = ____________

TASK 1

Mode operation ?

TASK 2

# Define?

Write the define programming code ???Write the define programming code ???

#define LCD_DATA LATB //-> RB4..RB7#define LCD_EN LATBbits.LATB3 //-> LCD EN#define LCD_RS LATBbits.LATB2 //-> LCD RS#define LCD_RW LATBbits.LATB1 //-> LCD R/W

• Matrix keypads are very useful when designing certain system which needs user input.

• By arranging push button switches in rows and columns.

• To scan which button is pressed, we need to scan it column by column and row by row.

• Make rows as input and columns as output.• For keypad wiring , need to pull up or pull down to avoid floating.

Keypad Interfacing

Pull-up RActive HIGH

Pull-down RActive LOW

ROWS & COLUMNS ??

Pull-up Resistor

COL(OUTPUT) = HIGH

Key Press Detection ??

case 1 kp = 49 ' 1 ‘ Uncomment this block for keypad4x4 case 2 kp = 50 ' 2 case 3 kp = 51 ' 3 case 4 kp = 65 ' A case 5 kp = 52 ' 4 case 6 kp = 53 ' 5 case 7 kp = 54 ' 6 case 8 kp = 66 ' B case 9 kp = 55 ' 7 case 10 kp = 56 ' 8 case 11 kp = 57 ' 9 case 12 kp = 67 ' C case 13 kp = 42 ' * case 14 kp = 48 ' 0 case 15 kp = 35 ' # case 16 kp = 68 ' D

ASCII code

#include <p18f45k22.h>

//IO define#define ROW1 PORTAbits.RA5 //Keypad Row (input)#define ROW2 PORTEbits.RE0#define ROW3 PORTEbits.RE1#define ROW4 PORTEbits.RE2#define COL1 LATAbits.LATA1 //Keypad Col (output)#define COL2 LATAbits.LATA2#define COL3 LATAbits.LATA3#define COL4 LATAbits.LATA4

#define LED0 LATBbits.LATB0#define LED1 LATBbits.LATB1#define LED2 LATBbits.LATB2#define LED3 LATBbits.LATB3

Keypad Define code

//MAIN PROGRAMvoid main(void){

unsigned char Key,Run; //local variablesOSCCON=0x52; //PIC18F45K22 : INTOSC 4MHzInitialize();Key=0; // activate key by col

//Main Loopwhile(1){

COL2=0;if (!Key)Key=1;

{if (!COL2){

if(!ROW1) LED0=1; else LED=0;if(!ROW2) LED1=1; else LED1=0;if(!ROW3) LED2=1; else LED2=0;if(!ROW4) LED3=1; else LED3=0;COL2=1;Nop();Nop();COL3=0;//Key=1;

}

if (!COL3){if(!ROW1) LED3=1; else LED3=0;if(!ROW2) LED2=1; else LED2=0;if(!ROW3) LED1=1; else LED1=0;if(!ROW4) LED0=1; else LED=0;

}}}

}

Pull-up RCOLLUMN2 is ACTIVE !Can press any ROW…

COLLUMN3 is ACTIVE !

//Init Micro-controllervoid Initialize(void){

//Init IOANSELA=0; //ANSEL=0; ANSELH=0 => PIC887ANSELB=0;ANSELC=0;ANSELD=0;ANSELE=0;PORTB=0;TRISA=0b11100001; //RA1-RA4 o/p RA5 i/pTRISB=0b11110000; //PORTB I/O Direction (0:Output 1:Input)LATA=0b00011110; //RA1-RA4 set Hi

}

LED output pin

COLUMNS output pin

LCD & Keypad Microcontroller Circuit

Question ??1.Give the combination ROW & COL for:

i. Keypad number 5 ROW2 & COL2

ii. Keypad # ROW4 & COL3 iii. Keypad B ROW2 & COL4

2. State the ASCII key for this arrangement keypad press:

i. Row2 & Col3 case ASCII code= 54 // => 6

ii. Row3 & Col4 case ASCII code= 67 // => C