Interface LCD to 8051

Now a days Electronics Projects without LCD look incomplete.Interfacing LCD with Atmel microcontroller is very easy task.You just have to know the proper lcd programming algorithm.Lcd used here has HD44780u dot matrix lcd controller.
LCD module have 8-bit data interface and control pins.

One can send data as 8-bit or in pair of two 4-bit nibbles.To display any character on LCD micro controller has to send its ASCII value to the data bus of LCD.For e.g. to display 'AB' microcontroller has to send two hex bytes 41h and 42h respectively.LCD display used here is having 16x2 size. It means 2 lines each with 16 character.

Circuit Diagram

Pin Information of LCD:

Algorithm to send data to LCD:

1.Make R/W low

2.Make RS=0 ;if data byte is command

RS=1 ;if data byte is data (ASCII value)

3.Place data byte on data register

4.Pulse E (HIGH to LOW)

5.Repeat the steps to send another data byte

LCD Initialization:

This is the pit fall for beginners.Proper working of LCD depend on the how the LCD is initialized. We have to send few command bytes to initialize the lcd. Simple steps to initialize the LCD

1.Specify function set:

Send 38H for 8-bit,double line and 5x7 dot character format.

2.Display On-Off control:

Send 0FH for display and blink cursor on.

3.Entry mode set:

Send 06H for cursor in increment position and shift is invisible.

4. Clear display:

Send 01H to clear display and return cursor to home position.

Assembly Language Code

; Interfacing LCD 16x2 in 4-bit mode.
; Port0 to higher nibble data pins of LCD
; Crystal 3.579545 MHz

; AT89C51

;P2.0 to RS pin

;P2.1 to Enable Pin

ORG 0000H
AJMP MAIN
ORG 0030H
MAIN:
MOV SP,#60H ;STACK POINTER
ACALL LCD_INIT ;Initialize lcd
MOV DPTR,#MESSAGE1
CALL LCD_STRING ;Display message on LCD
CALL NEXT_LINE ;Place cursor to;second Line
MOV DPTR,#MESSAGE2
CALL LCD_STRING ;Display message on LCD
HERE: AJMP HERE

LCD_INIT: ;initialize LCD in 4-bit mode
ANL P0,#0F0H
CALL LOOP
MOV DPTR,#LCDCODE
MOV A,#0H
MOV R6,#0H
MOV R7,#0H
CLR P2.0 ;RS COMMAND
NEXT: ;8-bit code is split into two 4-bit nibbles.
INC R6
MOVC A,@A+DPTR
MOV R7,A
ANL A,#0F0H
SWAP A
ANL P0,#0F0H
ORL P0,A
ACALL ENABLE ;PULSE E sending first nibble
MOV A,R7
ANL A,#0FH
ANL P0,#0F0H
ORL P0,A
ACALL ENABLE ;PULSE E sending second nibble
MOV A,R6
CJNE R6,#09H,NEXT
RET

LCD_STRING:
MOV P0,#00H
SETB P2.0 ;RS DATA
MOV A,#00H
MOV R6,#00H
NC: ;checks the end of message string
MOVC A,@A+DPTR
CJNE A,#2FH,NC1
RET
NC1:
LCALL LCD_WRITE
INC R6
MOV A,R6
AJMP NC

LCD_WRITE:
SETB P2.0 ;RS DATA
CALL LO
RET

NEXT_LINE:
MOV P0,#00H
CLR P2.0 ;RS COMMAND
MOV A,#0C0H
CALL LO
RET

LCD_CLEAR: ;This Subroutine is used to clear LCD
CALL DELAYL
ANL P0,#00H
MOV A,#01H
CLR P2.0 ; RS command
LO: ;8-bit code is split into two 4-bit nibbles.
MOV R7,A
ANL A,#0F0H
SWAP A
ANL P0,#0F0H
ORL P0,A
CALL ENABLE
MOV A,R7
ANL A,#0FH
ANL P0,#0F0H
ORL P0,A
CALL ENABLE
RET


ENABLE: ;Give High-to-low pulse at enable pin
SETB P2.1
CALL DELAYL
CLR P2.1
CALL DELAYL
RET


;With respect to crystal frequency 3.579 MHz
DELAYL: ; 5ms DELAY
SETB PSW.4 ; SELECT BANK 2
MOV R7,#25
HDH:
MOV R6,#60
DJNZ R6,$
DJNZ R7,HDH
CLR PSW.4 ;DEFAULT BANK
RET

LOOP: ;1 SEC DELAY
MOV R7,#100
LOOP1:
CALL DELAYL
CALL DELAYL
DJNZ R7,LOOP1
RET

;LCD INITIALIZING CODE (DO NOT DISTURB THIS)

LCDCODE:
DB 02H
DB 02H
DB 02H
DB 28H
DB 28H
DB 28H
DB 0CH
DB 06H
DB 01H


;DATA TO BE DISPLAYED

;Maximum message length = 16 characters.

;To notify end of message place '/' at the end.

MESSAGE1: DB "LCD INTERFACING /" ;Change Message1

MESSAGE2: DB " IT IS EASY /" ;Change Message2

END


Source: http://www.lcdinterfacing.info/Interface-LCD-to-8051.php