8/6/2019 Interface 8051 With Lcd

http://slidepdf.com/reader/full/interface-8051-with-lcd 1/4

~: How to interface LCD with 89C51? :~  

This is special section of web-site. In this section we will learn how we can display

a character or a message on LCD display. You can choose any standard LCDavailable in market. I have experimented with 20×2 LCD. It means LCD has 2 lines

of 20 characters each. Many other LCDs like 16×2, 24×2, 32×2, 20×4 etc. areavailable. Functionally all these LCDs are same. To develop a protocol to interface

this LCD with 89C51 first we have to understand how they functions.

These displays contains two internal byte-wide registers, one for command and

second for characters to be displayed. There are three control signals called R/W,

DI/RS and En. The table given below will tell you what is the use of these three

signals. 

Control Signals  It's function 

R/W 

= 0 Writes character in display  

= 1 Reads from display 

RS/DI = 0 Selects command register  

= 1 Selects Data register to display character  

En = 0 Disables the display  

= 1 Enables the display 

By making RS/DI signal 0 you can send different commands to display. These

commands are used to initialized LCD, to select display pattern, to shift cursor or

screen etc. The different commands and their functions are as given below  

Bits Function 

RS/DI R/W  D7  D6  D5  D4  D3  D2  D1  D0 

0  0  0  0  0  0  0  0  0  1  Clear LCD memory, Home cursor 

0  0  0  0  0  0  0  0  1  0  Clear and Home cursor only 

0  0  0  0  0  0  0  1  I/O  s s = 1/0 : Shift screen/cursor, I/O = 1/0 :

shift R/L 

0  0  0  0  0  0  1  D  C  B 

D = 1/0 : Screen On/Off. C = 1/0 :

cursor On/Off. B = 1/0 : Cursor blink/no

blink 

0  0  0  0  0  1  S/C  R/L  0  0  S/C = 1/0 : Screen / Cursor. R/L = 1/0 :

Shift one space right / left 

0  0  0  0  1  DL  N  F  0  0 

D/L = 1/0 : 8/4 bits per character. N =

1/0 : 2/1 rows of char. F = 1/0 : 5×10/5×7 

dots/char. 

0  0  0  1  Char address  Write to char. RAM address after this 

0  0  1  Display data address  Writes to display RAM address after this

8/6/2019 Interface 8051 With Lcd

http://slidepdf.com/reader/full/interface-8051-with-lcd 2/4

1  BF  Current address  BF = 1/0 : display is busy/not busy 

1  0  Character type  Write byte to last RAM chosen 

1  1  Character type  Read byte from last RAM chosen 

The figure shows connections of LCD with 89C51 

All the data lines of LCD are connected with port P1. En pin is connected with

P0.0, DI (RS) is connected with P0.1 and R/W pin is connected with P0.2.  

Next the program is given in 8051 assembly language with necessary comments

that can display a message or single character on screen.

com equ 0fch ; command follows this header 

dat equ 0fdh ; Data follows this header 

eof equ 0feh ; End of message 

org 00h 

mov dptr,#2000h ; Initilize LCD and display message 

acall msg ; "Wel - Come To

mov a,#c0h ; Go to the next line  acall cmmd 

mov a,#'L' ; and display character 'L'

acall dis 

mov a,#'C' ; and display character 'C'

acall dis 

mov a,#'D' ; and display character 'D'

acall dis 

mov dptr,#3000h ; display word 'program' in next line 

8/6/2019 Interface 8051 With Lcd

http://slidepdf.com/reader/full/interface-8051-with-lcd 3/4

acall msg ; after character 'D'.here: sjmp here ; continue loop 

msg:

acall ready ; wait until display is busy

clr a

movc a,@a+dptr ; get the character inc dptr ; point to next character 

cjne a,#eof,cmd ; if end of message then

ret ; return from sub routine

cmd:cjne a,#com,data ; if command then DI (RS) = 0

clr p0.1

sjmp msg ; go until done

data:cjne a,#dat,send ; if data then DI (RS) = 1

setb p0.1

sjmp msg ; go until done

send: mov p1,a ; send data/command to displayclr p0.2 ; write enable

setb p0.0 ; strobe character to displayclr p0.0

sjmp msg ; go until done

cmmd:

acall ready ; wait until display is busymov p1,a ; command chara. in p1

clr p0.1 ; select com. register 

clr p0.2 ; write enable

setb p0.0 ; strobe the chara.

clr p0.0

ret

dis:

acall ready ; wait until display is busy

mov p1,a ; data chara. in p1

setb p0.1 ; select data register 

clr p0.2 ; write enable

setb p3.7 ; strobe the chara.

clr p3.7 

ret

ready:

mov r 7,p0 ; save content of P0

clr p0.0 ; disable displayclr p0.1 ; select command register 

setb p0.2 ; read enable

wait:clr p0.0 ; strobe display

setb p0.0 ; read busy status of display

 jb p1.7,wait ; wait for busy

clr p3.7 mov p0,r 7 ; restore content of P0

ret

8/6/2019 Interface 8051 With Lcd

http://slidepdf.com/reader/full/interface-8051-with-lcd 4/4

 org 2000h ; messages are stored at

db com ; locations 2000h and 3000hdb 3ch

db 0fh

db 01h

db datdb 'Wel-Come To'

db eof 

org 3000h

db com

db 0c5h

db dat

db 'Program'

db eof 

end