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LCD

An LCD display uses liquid crystal molecules between two polarized filters to display pixels in the form of text or images. It requires a microcontroller to output data through a small number of control lines that specify read/write operations, register selections, and enable access to the display. Data can be written to specific address locations on the display to output text or instructions through setting the states of the control lines in the proper sequence.

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117 views4 pages

LCD

An LCD display uses liquid crystal molecules between two polarized filters to display pixels in the form of text or images. It requires a microcontroller to output data through a small number of control lines that specify read/write operations, register selections, and enable access to the display. Data can be written to specific address locations on the display to output text or instructions through setting the states of the control lines in the proper sequence.

Uploaded by

pandi
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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3.

5 LIQUID CRYSTAL DISPLAY

3.5.1 INTRODUCTION:
A liquid crystal display is thin flat display device made up of any number of color or
monochrome pixels arrayed in front of a light source or reflector. Each pixel consists of a
column of liquid crystal molecules suspended between two transparent electrode and two
polarizing filter the axes of polarity of which are perpendicular to each other. Without the
liquid crystal between them, light passing through one would be blocked by the other. The
liquid crystal twists the polarization of light entering one filter to allow it to pas through the
other.

Many microcontroller devices use smart LCD display to output visual information.LCD
display designed around Hitachis LCD HD44780 module, are inexpensive, easy to use and
it is even possible to produce a readout using the 8*80 pixels of the display. They have a
standard ASCII set of characters and mathematical symbols.

For an 8 bit data bus the display requires a 5v supply plus 11 I/O lines for a 4 bit data
bus it only requires the supply lines plus seven extra lines. When the LCD display is not
enabled data lines are tri-state and they do not interface with the operation of the
microcontroller.
Data can be placed at any location on the LCD.F or 16*2 LCD, the address locations
are
First line 80 81 82 83 84 85 86 Through
8f
Second C0 C1 C2 C3 C4 C5 C6 Through
line CF

1
3.5.2 SIGNALS TO THE LCD
The LCD requires 3 control lines from the microcontroller Enable.
This line allows access to the display through R/W and RS lines. When this line is
low, the LCD is disabled and ignores signals from R/W and RS. When line is high the LCD
checks the state of the two control lines and responds accordingly.

3.5.2.1Read/Write:
This line-determines the direction of data between the LCD and micro controller. When it is
low, data is written to the LCD .When it is high data is read from the LCD.

3.5.2.2 Register selects:


With the help of this line the LCD interprets the type of data on data lines. When it is
low an instruction is being written to the LCD.When it is high character is being written to
the LCD.

3.5.3 Logic status on control lines


E-0 Access to LCD disabled
-1 Access to LCD enabled

R/W-0 Writing data to LCD


-1 Reading data from LCD

RS - 0 Instructions

2
-1 Character

Writing and reading the data from the LCD


Writing data to the LCD is done in several steps
1) Set R/W bit to low
2) Set RS bit to logic 0 or 1
3) Set data to data lines
4) Set line to high
5) Set E line to low

Read data from data lines


1) Set R/W bit to high
2) Set RS bit to logic 0 or1
3) Set data to data lines
4) Set E line to high
5) Set E LINE TO LOW

3.5.4 PIN DESCRIPTION:

3
FIG: LCD DISPLAY

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