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Introduction about LED interfacing

 

Advantages of LCD over LED

wDeclining prices of LCD.

wAbility to display numbers, characters and graphics.

wEase of programming for characters and graphics.

wRelieving CPU from refreshing task of LCD

 

Pin Description

Pin No                         Description

w1                                Vss

w2                                Vcc

w3                                Contrast Voltage

w4                                RS

w5                                R/W

w6                                EN

w7-14                          Data Input/Output Pins (D0-D7)

w15                              Anode (K)

w16                              Cathode (K)

 

w1) Vss- Vss is connected to the ground.

w2) Vcc- Vcc is connected to +5V.

w3) Contrast Voltage- Vee is used for controlling LCD Contrast. Variable pin of Variable Resistor of 10K is connected to this pin.

w4) RS- RS is used for the selection of internal resistors of LCD.

wCommand Code Register – It allows the user to send command such as clear display, cursor at home etc.

wData Register – It allows the user to send data to be displayed on LCD.

If RS=0, then Command Register is selected.

If RS=1, then Data Register is selected.

 

w5) R/W- R/W input allows user to write information to the LCD or read information from it.

                        R/W=1 when Reading

                        R/W=0 when Writing

w6) EN- This enable pin is used by the LCD to latch information presented to its data pins.

            When data is supplied to data pins, a High-to-low pulse must be applied to this pin.

w7) Pin 7-14 – The 8-bit data pins, D0-D7 are used to send information to LCD or read the contents of the LCD’s internal registers.

            To Display letters and numbers, ASCII codes for letters and numbers are sent to these pins while making RS=1.

 

Table of LCD Control Signals

 

 

Hardware Connection of 8051 With LCD

LCD Command Codes

Code                Command to LCD Instruction register

(Hex)  

w01                 Clear display screen

w02                 Return home

w04                 Decrement cursor (shift cursor to                                  left)

w06                 Increment cursor (shift cursor to                                    right)

 

LCD Command Codes

Code                Command to LCD Instruction register

(Hex)  

w08                 Display off, cursor off

w0A                 Display off, cursor on

w0C                 Display on, cursor off

w0E                 Display on, cursor on

 

LCD Commands Codes

Code                Command to LCD Instruction register

(Hex)

w0F                 Display on, cursor blinking

w80                 Force cursor to beginning of 1st line

wC0                 Force cursor to beginning of 2nd line

w38                 2 Lines and 5x8 matrix

w30                 1 Line and 5x8 matrix

Program for writing Command to LCD

                                    mov P2,a

                                    clr RS

                                    clr R/W

                                    setb EN

                                    clr EN

                                    acall busy

Program for writing Data to LCD

                                    mov P2,a

                                    setb RS

                                    clr R/W

                                    setb EN

                                    clr EN

                                    acall busy

Routine for checking LCD Busy state

busy:                setb D7

back:                setb EN

                                                clr EN

                                                jnb D7, back

                                                ret

 

 

LCD Initialising Routine

                                    mov a,#38h

                                    acall command

                                    mov a, #0eh

                                    acall command

                                    mov a,#01h

                                    acall command

                                    mov a,#06h

                                    acall command

Contd…

                                                mov a,#80h

                                                acall command

                                                mov a,#’J’

                                                acall data

                                                mov a,#’A’

                                                acall data

                                                mov a,#’J’

                                                acall data

 

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