Interfacing of lcd with 8051

 LCD (Liquid Crystal Display) : LCD screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segment and other multi segment LED's. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom character (unlike in seven segments), animation and so on. A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data.

                      The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. Click to learn more about internal structure of a LCD.

           

Block Diagram of LCD:

LCD stands for liquid crystal display. They come in many sizes 8x1 , 8x2 ,10x2, 16x1 , 16x2 , 16x4 , 20x2 , 20x4 ,24x2 , 30x2 , 32x2 , 40x2 etc . Many multinational companies like Philips Hitachi Panasonic make their own special kind of lcd's to be used in their products. All the lcd’s performs the same functions (display characters numbers special characters ASCII characters etc).Their programming is also same and they all have same 14 pins (0-13) or 16 pins (0 to 15). 

ALL LCDs have

• Eight(8) Data pins
• VCC (Apply 5v here)
• GND (Ground this pin)
• RS (Register select)
• RW (read - write)
• EN (Enable)
• V0 (Set Lcd contrast)

8-Data pins carries 8-bit data or command from an external unit such as microcontroller. 

Lcd have two registers:

1)    Command Register 

2)    Data Register

•      Command Register:   When we send commands to lcd these commands go to Command register and are processed their. Commands with their full description are given in the picture below.
  When RS=0    Command Register is Selected.

•      Data Register: When we send Data to lcd it goes to data register and is processed their.

  When RS=1    Data Register is selected.

Pin diagram of  LCD:

Pin description:

Pin No:	Name	Function
1	VSS	This pin must be connected to the ground
2	VCC	Positive supply voltage pin (5V DC)
3	VEE	Contrast adjustment
4	RS	Register selection
5	R/W	Read or write
6	E	Enable
7	DB0	Data
8	DB1	Data
9	DB2	Data
10	DB3	Data
11	DB4	Data
12	DB5	Data
13	DB6	Data
14	DB7	Data
15	LED+	Back light LED+
16	LED-	Back light LED-

16×2 LCD module commands:

16×2 LCD module has a set of preset command instructions. Each command will make the module to do a particular task. These commands are very important for displaying data in LCD. The list of commands given below:

Command	Function
0F	For switching on LCD, blinking the cursor.
1	Clearing the screen
2	Return home.
4	Decrement cursor
6	Increment cursor
E	Display on and also cursor on
80	Force cursor to beginning of the first line
C0	Force cursor to beginning of second line
38	Use two lines and 5x7 matrix
83	Cursor line 1 position 3
3C	Activate second line
0C3	Jump to second line position 3
0C1	Jump to second line position1

LCD initialization:

The steps that has to be done for initializing the LCD display is given below and these steps are common for almost all applications.

§  Send 38H to the 8 bit data line for initialization

§  Send 0FH for making LCD ON, cursor ON and cursor blinking ON.

§  Send 06H for incrementing cursor position.

§  Send 01H for clearing the display and return the cursor.

Sending data to the LCD:

The steps for sending data to the LCD module is given below. I have already said that the LCD module has pins namely RS, R/W and E. It is the logic state of these pins that make the module to determine whether a given data input  is a command or data to be displayed.

- Make R/W low.

-  Make RS=0 if data byte is a command and make RS=1 if the data byte is a data to be displayed.

-  Place data byte on the data register.

-  Pulse E from high to low.

-   Repeat above steps for sending another data.

Interfacing of LCD with 8051:

1)    Display  Welcome  to all on the 1^st line:

a)    Circuit:

b)  Code

·        ASM Code:

$mod51

org 00h

back:

  mov A,#01h

  acall command

mov a,#06h

acall command

mov a,#38h

acall command

mov a,#0eh

acall command

mov a,#80h

acall command

mov A,#'C'

acall display

mov A,#'E'

acall display

mov A,#'T'

acall display

mov A,#'P'

acall display

mov A,#'A'

acall display

mov A,#' '

acall display

mov A,#'I'

acall display

mov A,#'N'

acall display

mov A,#'F'

acall display

mov A,#'0'

acall display

mov A,#'T'

acall display

mov A,#'E'

acall display

mov A,#'C'

acall display

mov A,#'H'

acall display

SJMP back

command:

mov P1,A

Clr P3.0

Clr P3.1

setb P3.2

Acall delay

clr P3.2

ret

display:

mov P1,A

setb P3.0

Clr P3.1

setb P3.2

Acall delay

clr P3.2

ret

delay:

   mov R1,#100

    L13: mov R2,#100

       L12: mov R3,#50

         L11: DJNZ R3,L11

        DJNZ R2,L12

      DJNZ R1,L13

  ret

end

Alternate way :

$mod51

org 00h

rs equ p3.0

rw equ p3.1

en equ p3.2

lcd equ p1

mov a,#01h

acall command

mov a,#06h

acall command

mov a,#38h

acall command

mov a,#0eh

acall command

mov a,#80h

acall command

mov r0,#13

mov dptr,#L4

L1: clr a

movc a,@a+dptr

                     acall dATAA

inc dPTR

djnz r0,L1

                     command:

mov lcd,a

clr rs

clr rw

setb en

acall delay

clr en

ret

DATAA:

MOV LCD,A

SETB RS

CLR RW

SETB EN

ACALL DELAY

CLR EN

RET

delay:

   mov r2,#255

o: mov r3,#255

n: mov r4,#10

m: djnz r4,m

   djnz r3,n

   djnz r2,o

ret

org 200h

L4:DB 'Welcome To all',0

                     END

·        C Code:

  #include<reg51.h>

sbit rs=P3^0;

sbit rw=P3^1;

sbit en=P3^2;

unsigned char arr1[]={0x0e,0x01,0x06,0x80,0x38};

unsigned char arr2[]={"Welcome To All"};

void command();

void display();

int j,k,l,m,n;

void delay()

{          int x,y;

for(x=0;x<=100;x++)

{

for(y=0;y<=1275;y++);

}

}

void main()

{

while(1)

{

for(j=0;j<5;j++)

{

P1=arr1[j];

command();

}

for(k=0;k<15;k++)

{

P1=arr2[k];

display();

}

  }

  }

void command()

{

rs=0;

rw=0;

en=1;

delay();

en=0;

}

void display()

{

rs=1;

rw=0;

en=1;

delay();

en=0;

}

c)     Simulation

2)    Display  Welcome  to all on the 1^st line and God Bless You on the 2^nd line.

a)    Code

·        ASM Code

$mod51

org 00h

rs equ p3.0

rw equ p3.1

en equ p3.2

lcd equ p1

mov a,#01h

acall command

mov a,#06h

acall command

mov a,#38h

acall command

mov a,#0eh

acall command

mov a,#80h

acall command

mov r0,#13

mov dptr,#L4

L1: clr a

movc a,@a+dptr

acall dATAA

inc dPTR

djnz r0,L1

mov a,#0c0h

acall command

mov r1,#13

mov dptr,#L3

L2: clr a

movc a,@a+dptr

acall dATAA

inc dptr

djnz r1,L2

command:

mov lcd,a

clr rs

clr rw

setb en

acall delay

clr en

ret

DATAA:

MOV LCD,A

SETB RS

CLR RW

SETB EN

ACALL DELAY

CLR EN

RET

delay:

   mov r2,#255

o: mov r3,#255

n: mov r4,#10

m: djnz r4,m

   djnz r3,n

   djnz r2,o

ret

org 200h

L4:DB 'Welcome  to all ',0

L3:DB 'God Bless You ',0

END

·        C Code

#include<reg51.h>

sbit rs=P3^0;

sbit rw=P3^1;

sbit en=P3^2;

unsigned char arr1[]={0x0e,0x01,0x06,0x80,0x38};

unsigned char arr2[]={"Welcome To All"};

unsigned char arr3[]={"God Bless You "};

void command();

void display();

int j,k,l,m,n;

void delay()

{          int x,y;

for(x=0;x<=100;x++)

{

for(y=0;y<=1275;y++);

}

}

void main()

{

while(1)

{

for(j=0;j<5;j++)

{

P1=arr1[j];

command();

}

for(k=0;k<15;k++)

{

P1=arr2[k];

display();

}

P1=0xc0;

  command();

for(k=0;k<15;k++)

{

P1=arr3[k];

display();

}

  }

  }

void command()

{

rs=0;

rw=0;

en=1;

delay();

en=0;

}

void display()

{

rs=1;

rw=0;

en=1;

delay();

en=0;

}

b)    Simulation

    3)       Trafic Light

a)    ASM  Code

$mod51

lcd equ p1

rs equ p3.3

rw equ p3.2

en equ p3.1

egr equ p2.0

erd equ p2.1

eyl equ p2.2

wgr equ p2.3

wrd equ p2.4

wyl equ p2.5

ngr equ p0.0

nrd equ p0.1

nyl equ p0.2

sgr equ p0.3

srd equ p0.4

syl equ p0.5

nsen equ p3.7

ssen equ p3.6

esen equ p3.5

wsen equ p3.4

org 0h

acall lcd_ini

mov dptr,#welcome

acall hind

mov a,#0c0h

acall cmd

mov dptr,#welcome1

acall hind

acall delay1

mov a,#01h

acall cmd

mov dptr,#direction

acall hind

mov a,#0c0h

acall cmd

go:

mov dptr,#northgo

acall hind

clr ngr

clr wrd

clr srd

clr erd

acall delay1

acall delay1

acall start

mov dptr,#nerdy

acall hind

setb erd

clr eyl

setb ngr

clr nyl

acall delay2

acall start

mov dptr,#eastgo

acall hind

setb nyl

clr nrd

setb eyl

clr egr

acall delay1

acall delay1

acall start

mov dptr,#esrdy

acall hind

setb srd

clr syl

setb egr

clr eyl

acall delay2

acall start

mov dptr,#southgo

acall hind

setb syl

clr sgr

setb eyl

clr erd

acall delay1

acall delay1

acall start

mov dptr,#swrdy

acall hind

setb sgr

setb wrd

clr syl

clr wyl

acall delay2

acall start

mov dptr,#westgo

acall hind

setb wyl

clr wgr

setb syl

clr srd

acall delay1

acall delay1

acall start

mov dptr,#wnrdy

acall hind

setb wgr

clr wyl

setb nrd

clr nyl

acall delay2

acall start

setb wyl

setb nyl

ajmp go

delay1:

mov r4,#07h

gh: mov r5,#0ffh

ru: acall delay

    djnz r5,ru

    djnz r4,gh

ret

delay2:

mov r3,#04h

gj: mov r2,#0ffh

eu: acall delay

    djnz r2,eu

    djnz r3,gj

ret

start:

mov a,#01h

acall cmd

mov dptr,#direction

acall hind

mov a,#0c0h

acall cmd

ret

hind:

clr a

movc a,@a+dptr

acall dat

inc dptr

jnz hind

ret

lcd_ini:

mov a,#38h

acall cmd

mov a,#01h

acall cmd

mov a,#06h

acall cmd

mov a,#0eh

acall cmd

mov a,#80h

acall cmd

ret

delay:

mov r6,#02h

yu: mov r7,#0ffh

rt:

jnb nsen,ngr1

jnb wsen,wgr1

jnb ssen,sgr1

jnb esen,egr1

djnz r7,rt

djnz r6,yu

ret

ngr1:

acall again

mov p2,#0ffh

mov p0,#0ffh

clr ngr

clr wrd

clr erd

clr srd

ii4: sjmp ii4

wgr1:

acall again

mov p2,#0ffh

mov p0,#0ffh

clr wgr

clr nrd

clr erd

clr srd

nh: sjmp nh

sgr1:

acall again

mov p2,#0ffh

mov p0,#0ffh

clr sgr

clr wrd

clr erd

clr nrd

ii: sjmp ii

egr1:

acall again

mov p2,#0ffh

mov p0,#0ffh

clr egr

clr wrd

clr nrd

clr srd

ii1: sjmp ii1

again:

mov a,#01h

acall cmd

mov dptr,#emergency

acall hind

ret

cmd:

mov lcd,a

clr rs

clr rw

setb en

acall delay

clr en

ret

dat:

mov lcd,a

setb rs

clr rw

setb en

acall delay

clr en

ret

welcome: db 'Welcome to Smart',0

welcome1: db  'Traffic Light Controller',0

direction: db 'N   E   S   W  ',0

northgo: db   'GO  STP STP STP',0

southgo: db   'STP STP GO  STP',0

eastgo:  db   'STP GO  STP STP',0

westgo: db    'STP STP STP GO ',0

nerdy: db     'WaitRDY STP STP',0

esrdy: db     'STP WaitRDY STP',0

swrdy: db     'STP STP WaitRDY',0

wnrdy: db     'RDY STP STPWait',0

emergency: db 'EMERGENCY Plz Wait',0

end

 b) Simulation

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