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  IQUID CRYSTA DISP AY

LCD stands for Liquid Crystal Display. LCD is finding wide spread use replacing LEDs

(seven segment LEDs or other multi segment LEDs) because of the following reasons:

. !he declining prices of LCDs.

". !he ability to display numbers# characters and graphics. !his is in contrast to LEDs# which are

limited to numbers and a few characters.

$. %ncorporation of a refreshing controller into the LCD# thereby relieving the C&' of the tas of 

refreshing the LCD. %n contrast# the LED must be refreshed by the C&' to eep displaying the

data.

. Ease of programming for characters and graphics.

!hese components are *speciali+ed, for being used with the microcontrollers# which means that

they cannot be activated by standard %C circuits. !hey are  used for writing different messages on

a miniature LCD.

  Fig 4.4.1: LCD Display

- model described here is for its low price and great possibilities most frequently used in

 practice. %t is based on the D/01 microcontroller ( Hitachi) and can display messages in two

lines with 2 characters each.

%t displays all the alphabets# 3ree letters# punctuation mars# mathematical symbols etc.

%n addition# it is possible to display symbols that user maes up on its own. -utomatic shifting

message on display (shift left and right)# appearance of the pointer# baclight etc. are considered

as useful characteristics.

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Table: Pin Description of LCD

  FunctionPin

NumberName

Logic

StateDescription

3round 4ss 5 14

&ower supply " 4dd 5 674

Contrast $ 4ee 5 1 5 4dd

Control of 

operating

891

D1 D/ are interpreted as

commands

D1 D/ are interpreted as data

7 8;< 1

ormal operating

Data;commands are transferred to

LCD

Data ; commands

/ D1 1; ?it 1 L9?

0 D 1; ?it

@ D" 1; ?it "

1 D$ 1; ?it $

D 1; ?it

" D7 1; ?it 7

$ D2 1; ?it 2

D/ 1; ?it / A9?

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PIN FNCTI!NS

!here are pins along one side of the small printed board used for connection to the

microcontroller. !here are total of pins mared with numbers (2 in case thebacground light

is built in). !heir function is described in the above table.

LCD screen:

  F

i g

:

LCD Interfacing 

LCD screen consists of two lines with 2 characters each. Each character consists of 7B/

dot matriB. Contrast on display depends on the power supply voltage and whether messages are

displayed in one or two lines. =or that reason# variable voltage 154dd is applied on pin mared as

4ee. !rimmer potentiometer is usually used for that purpose. 9ome versions of displays have

 built in baclight (blue or green diodes).

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8ead from C38-A or

DD8-A D/ D2 D7 D D$ D" D D1 1u9

% D: %ncrement (by ) 8;L: 9hift right

  1 Decrement (by ) 1 9hift left

9: Display shift on DL: 05bit interface

  1 Display shift off 1 5bit interface

 D: Display on

 >: Display in two lines

  1 Display off 1 Display in one line

 ': Cursor on =: Character format 7B1 dots

  1 Cursor off 1 Character format 7B/ dots

 ?: Cursor blin on D;C: Display shift

  1 Cursor blin off 1 Cursor shift

LCD Initialiation:

Fnce the power supply is turned on# LCD is automatically cleared. !his process lasts for 

approBimately 7m9. -fter that# display is ready to operate. !he mode of operating is set by

default. !his means that:

. Display is cleared

". Aode

DL Communication through 05bit interface

 > 1 Aessages are displayed in one line

= 1 Character font 7 B 0 dots

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$. Display;Cursor on;off

D 1 Display off

' 1 Cursor off

? 1 Cursor blin off

. Character entry

%D -ddresses on display are automatically incremented by

9 1 Display shift off

-utomatic reset is mainly performed without any problems. Aainly but not alwaysG %f for any

reason power supply voltage does not reach full value in the  course of 1m9# display will start perform completely unpredictably. %f voltage supply unit can not meet this condition or if it is

needed to provide completely safe operating# the process of initiali+ation by which a new reset

enabling display to operate normally must be applied.