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16x2 LCD Interfacing with 8051 in 8-bit Mode

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16x2 LCD Interfacing with 8051 in 8-bit Mode

     The most commonly used Character based LCDs are based on Hitachi's HD44780 controller. A 16x2 Character LCD can display 16 Characters in each of two lines. They are available in the market in the name of JHD162A. They operate on a 5V Dc Power supply.

 

Pin NO

Name

Function of the Pin

1

VSS

Power supply (GND)

2

VCC

Power supply (+5V)

3

VEE

Contrast adjust

4

RS

0 = Instruction Register Select
1 = Data Register Select

5

R/W

0 = Write to LCD module
1 = Read from LCD module

6

EN

Enable signal (Clock input)

7

D0

Data bus line 0 (LSB)

8

D1

Data bus line 1

9

D2

Data bus line 2

10

D3

Data bus line 3

11

D4

Data bus line 4

12

D5

Data bus line 5

13

D6

Data bus line 6

14

D7

Data bus line 7 (MSB) / Busy Flag Check

15

LED+

+5V supply for the LED Backlight

16

LED-

Ground for the LED Backlight

 

The contrast can be adjusted by using a Potentiometer to provide a voltage between 0V to 5 V to the VEE, with 0, means Highest Contrast.

The Initialization routine (The algorithm to interface the LCD With 8051 in 8 bit Mode with checking busy flag:)

:

 

The Schematic of Interfacing LCD with 8051 in 8 bit mode

 

 Assembly code for Busy Flag Checking and LCD Interfacing in 8-bit mode:

 

;lcd interfacing to at89c51 in 8-bit mode
;with busy flag checking

RS  BIT P2.0        ;define the pins we are going
RW  BIT P2.1        ;to use in our code
EN  BIT P2.2        ;for simplicity
BF  BIT P1.7

    MOV A, #38H     ;8 bit 2 line display 5x7 font
    ACALL   SEND_CMD    ;call the instruction write sub-routine
    MOV A, #0EH     ;lcd on cursor on
    ACALL   SEND_CMD
    MOV A, #01H     ;clear lcd
    ACALL   SEND_CMD
    MOV A, #06H     ;cursor position auto increment move cursor to right
    ACALL   SEND_CMD

    MOV A, #'E'
    ACALL   SEND_DATA   ;call the data write sub routine
    MOV A, #'S'
    ACALL   SEND_DATA
    MOV A, #'R'
    ACALL   SEND_DATA
    MOV A, #'T'
    ACALL   SEND_DATA
    MOV A, #'.'
    ACALL   SEND_DATA
    MOV A, #' '
    ACALL   SEND_DATA

HERE:   SJMP    HERE        ;wait here indefinitely

SEND_CMD:       ;the sub-routine to write command to the instruction register
    ACALL   READY       ;goto busy-flag check subroutine, to determine if lcd is ready
    MOV P1, A
    CLR RS      ;select the instruction register
    CLR RW      ;going to write command
    SETB    EN      ;initiate high to low pulse on enable
    CLR EN
    RET

SEND_DATA:          ;the sub-routine to write data to the instruction register
    ACALL   READY
    MOV P1, A
    SETB    RS      ;select data register
    CLR RW      ;going to write data
    SETB    EN      ;initiate high to low pulse on enable
    NOP
    CLR EN
    RET

;subroutine to check busy-flag and determine if the lcd is ready for next operation 
READY:  SETB    BF      ;make the bf pin logic 1
    CLR RS      ;select command register
    SETB    RW      ;going to read
BACK:   CLR EN      ;initiate low to high transition on enable pin
    NOP
    SETB    EN
    JB  BF, BACK    ;keep checking busy flag, till it becomes logic 0
    RET         ;return from the ready sub-routine

    END


The Assembly code and the Proteus Simulation file can be downloaded from here (zip) or here (rar)