Interface LCD and Keypad

8/19/2019 Interface LCD and Keypad

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INTERFACING

LCD

DIVISION OF MECHATRONICS

DEPARTMENT OF PRODUCTION TECHNOLOGY

MIT CAMPUS

ANNA UNIVERSITY - CHENNAI


2/23

Overview LCD display working.

LCD specs.

Concepts.

Algorithm.

rogramming

Initiali!ation in atmega"#.

Display strings.


3/23

Inp$t and o$tp$t de%ices

Outputs:

Mtrs ! DC" Stepper" Serv#$

LEDS$

LCD$ % se&'e(t$

I(puts:

Se(srs$

Swit)*$

+e,p.$


4/23

LCD

LCD &Li'$id Crystal Display( screen is anelectronic display mod$le.

A /012 LCD means it can display "# charactersper line and there are * s$ch lines.

LCD each character is displayed in +,- pi,el

matri,.

LCD has two registers namely Command andData.


5/23

LCD in con/g$rations


6/23

LCD pin description

RS !Re&ister Se3e)t#: 0hen R123 this allowthe $ser to send command s$ch as &clearscreen go home 4link c$rsor(. 0hen R12"

this allow the $ser to send data. E(43e: It $sed to latch the in5ormation to the

data pins this done 4y send a high to low p$lse&o5 width o5 6+3 ns( so the LCD latches the datapresented on the data pins.


7/23

LCD Initiali!ation &he, %al$e(


8/23

1ending commands and

data to LCD The 5ollowing steps sho$ld 4e done to send the

command and data to the LCD7

"( Initiali!ed the LCD.

*( 1ending Commands to the LCD.

8( 1ending data to the LCD


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Initiali!ing the LCDFor e,ample to initiali!e LCD 9* lines +:- matri,

;4it mode< the 5ollowing commands sho$ld 4e$sed7

". 3,8; to select the type and mode o5 operation

*. 3,3E to display the c$rsor 4linking.

8. 3,3" to clear the LCD display.1ending commands to LCD

To send commands to the LCD the 5ollowing steps sho$ld 4e done7

". R123 R023.

*. The command n$m4er sho$ld 4e p$t on the data pins &D3 toD-(.

8. A p$lse &high to low( sho$ld 4e sent on the Ena4le pin. A5tereach command a delay o5 &"33$s( sho$ld 4e placed


10/23

1ending data to LCD

To send data to the LCD the 5ollowing steps sho$ld4e done7 R12" R023.

". The data sho$ld 4e p$t on the data pins &=3 to

=-(.*. A p$lse &high to low( sho$ld 4e sent on the

Ena4le pin.

A5ter each data a delay o5 &"33$s( sho$ld 4eplaced.


11/23

Inter5acing LCD

Can 4e inter5aced either in ;>4it mode or 6>4itmode.

In ;>4it mode all data lines are connected.

In 6>4it mode only 5o$r data lines areconnected.


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5si) ) i(stru)ti( set 6rLCDLCD_Init(); /* Initilize the lcd before displaying any thing on the lcd */

LCD_DisplayString("hello, world"); /*Display "hello, world" on first line*/

LCD_GoToLineTwo() /*Go to second line and display "good morning" */

LCD_DisplayString("good morning")

void LCD_Init()

{

delay_us(5000);

LCD_CmdWrite(0x38); // LCD 2lines, *! matri

LCD_CmdWrite(0x0E); // Display #$ c%rsor #$ &lin'ing off

LCD_CmdWrite(0x01); // Clear the LCD

LCD_CmdWrite(0x80); // C%rsor to (irst line (irst )osition

}

LCD i(iti3i7ti(


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void LCD_DataWrite( char dat)

{ databus=dat; // end the data to LCD rs=1; // elect the Data +egister by p%lling + IG

rw=0; // elect the -rite #peration by p%lling +- L#-

en=1; // end a igh.to.Low )%sle at nable )in

delay_us(10);

en=0;

delay_ms(1); }

T write .t t LCD

void LCD_CmdWrite( char cmd)

{

databus=cmd; // end the command to LCD rs=0; // elect the Command +egister by p%lling + L#-

rw=0; // elect the -rite #peration by p%lling +- L#-

en=1; // end a igh.to.Low )%sle at nable )in

delay_us(10);

en=0;

delay_ms(1); }

T write )'(. t LCD


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INTERFACING

?E@ADDIVISION OF MECHATRONICS

DEPARTMENT OF PRODUCTION TECHNOLOGY

MIT CAMPUS

ANNA UNIVERSITY - CHENNAI


15/23

Matrix Keyboard Connection to ports

?ey4oards are organi!ed in a matri, o5 rows and

col$mns.

The C accesses 4oth rows and col$mnsthro$gh ports.

There5ore with two 8>4it ports an 8,8

matri, o5 keys can 4e connected.

I5 all the rows aregro$nded and akeyis pressed one o5 the col$mns willha%e 3 since thekeypressed pro%idesthepath to gro$nd

I5 no key has4een pressedreading the

inp$t port willyield "s 5or allcol$mns sincethey are allconnected tohigh &Bcc(


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It is the 5$nction o5 the microcontroller to scanthe key4oard contin$o$sly to detect andidenti5y the key pressed.

To detect a pressed key the microcontrollergro$nds all rows 4y pro%iding 3 to the o$tp$tlatch then it reads the col$mns.

I5 the data read 5rom col$mns is D8 D3 2""""

no key has 4een pressed and the processcontin$es till key press is detected.

I5 one o5 the col$mn 4its has a !ero this meansthat a key press has occ$rred

For e,ample i5 D8 D3 2 ""3" this means thata key in the D" col$mn has 4een pressed

A5ter detecting a key press microcontroller willgo thro$gh the process o5 identi5ying the key


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Task

Identi5y the row and col$mn o5 the pressed key 5or each o5

the 5ollowing.

&a( D8 D3 2 """3 5or the row D8 D3 2 "3"" 5or thecol$mn

&4( D8 D3 2 ""3" 5or the row D8 D3 2 3""" 5or the

col$mn


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Algorithm To make s$re that the preceding key has 4een

released 3s are o$tp$t to all rows at once and thecol$mns are read and checked repeatedly $ntil allthe col$mns are high.

0hen all col$mns are 5o$nd to 4e high the programwaits 5or a short amo$nt o5 time 4e5ore it goes to the

ne,t stage o5 waiting 5or a key to 4e pressed. To see i5 any key is pressed the col$mns are

scanned o%er and o%er in an in/nite loop $ntil one o5them has a 3 on it.

Remem4er that the o$tp$t latches connected torows still ha%e their initial !eros making themgro$nded

A5ter the key press detection it waits *3 ms 5or the4o$nce and then scans the col$mns again


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&a( it ens$res that the /rst key press detection wasnot an erroneo$s one d$e a spike noise

&4( the key press. I5 a5ter the *3>ms delay the key isstill pressed it goes 4ack into the loop to detect a realkey press.

To detect which row key press 4elongs to itgro$nds one row at a time reading the col$mns

each time. I5 it /nds that all col$mns are high this means that

the key press cannot 4elong to that row

• There5ore it gro$nds the ne,t row andcontin$es $ntil it /nds the row the key press

4elongs to

• pon /nding the row that the key press 4elongs toit sets $p the starting address 5or the look>$p ta4leholding the scan codes &or A1CII( 5or that row.


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To identi5y the key press it rotates the col$mn

4its one 4it at a time into the carry ag andchecks to see i5 it is low.

• pon /nding the !ero it p$lls o$t the A1CIIcode 5or that key 5rom the look>$p ta4le

•

otherwise it increments the pointer to point tothe ne,t element o5 the look>$p ta4le


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Flow chart

1tart

Gro$ndall rows

Allkeysopen

"

Read allcol$mns

"

Read allcol$mns

Allkeysdown

0ait 5orde4o$nce

Read allcol$mns

Allkeysdown

*

No

@es

No

@es


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*

Findwhich keyis pressed

Allkeysdown

Gro$ndNe,t row

Get scan code

5rom ta4le

Ret$rn

@es

No


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T*(8 Yu Fr

YurAtte(ti(

Documents

Interface LCD and Keypad