How to interface LCD with PIC18f4550 microcontroller?

LCD connection with PIC microcontroller

Introduction to LCD

How to interface LCD with PIC18f4550 microcontroller? LCD also known as liquid displays are widely used these days for displaying characters, numbers, and graphics. They are more advanced displaying devices as compared to simple LEDs or Seven Segment displays. They are also used because of the following reasons:

  • The declining prices of LCDs.
  • Ease of Programming.
  • They have the latching ability.
  • Incorporation of refreshing controlling sets CPU free to refresh it.
16x2 LCD
16×2 LCD

There are different manufacturers of  LCDs and they do come in many styles. Some of the LCDs are are 16×2 size, some are 20×2 etc.

Manufacturers of LCDs

Optrex is one of the largest manufacturers of  LCD. You can easily find datasheet of LCDs from their website. Other famous manufacturers are:

  • digikey.om
  • jameco.com
  • elexp.com
  • bgmicro.com

For alphanumeric displays, 16×2 is recommended and it is easy to configure.

Pin description of LCD

There are 8 data lines (8 pins) for displaying the characters/numbers on LCDs. On these data lines microcontroller will be sending data for display. There are control pins: RS (Register Select), R/W (Read/write: W is an active low pin. It means write operation can be performed by sending 0 logic to it). E (enable Pin).

What is the RS pin of LCD?

Register Select (RS) is used for selecting the internal register of LCD. There are two internal registers corresponding to this pin.

Data Register

Command Register

Command Register

If RS=0 then command register is selected. The command register is used for issuing commands to LCD. These commands are used for configuring the LCD. The configuration involves the selection of the internal matrix, clearing data of LCD, cursor blinking and positioning the cursor etc. Here is the list of the commands that can be used for configuring the LCD.

Hex Code Command instructions
1 Clear display scree
2 Return home
4 Decrement cursor
6 Increment cursor
5 Shift display right
7 Shift display left
8 Display off, power off
A Display off, cursor ON
C Display ON, cursor OFF
E Display ON, cursor blinking
F Display OFF, cursor blinking
10 Shift cursor position to left
14 Shift cursor position to right
18 Shift the entire display to the left
1C Shift the entire display to the right
80 Force cursor to the beginning of the 1st line
C0 Force cursor to the beginning of the 2nd  line
38 2 lines and 5X7 matrix

Data Register

If RS=1 then data register is selected. In order to send the data for display we will set RS=1.

R/W= If R=0 it means writing operation is being performed on the LCD for displaying the data. It is an active low pin as explained above. If we want to program the LCD for displaying the data by monitoring the busy pin (D7) of LCD then we will be reading its state by setting R/W=1.

Enable pin

This pin is used for latching the data on data lines of LCD. In order to display a character on LCD it needs to be latched for a small duration. This is done by sending a high to low pulse on enable pin. The duration of this pulse should be around 150 msec.

Vcc/Vdd pin of LCD

For powering up the LCD, we need to provide +5V on Vcc or Vdd pin.

Vss pin

It is grounded.

Vee

This pin is used for controlling the contrast of LCD display. We will connect a variable resistor on this pin for controlling the contrast.

Pin Number Pin Name Description
1,2,3 Vss,Vcc,Vee Ground, Power Supply +5V, Contrast control
4 RS RS=0 (command Register)

RS=1 (Data Register)

5 R/W R/W=0 (Write Operation)

R/W=1 (Busy status test)

6 E Enable pin for latching the data on datalines
7-14 DB0-DB7 Data Lines

LCD connection with PIC microcontroller

LCD connection with PIC microcontroller
LCD connection with PIC microcontroller

Flow chart for connecting/interfacing the LCD with PIC18f4550 Microcontroller

Code for interfacing LCD with pic microcontroller in assembly language

In this code PORTD is connected with data lines of LCD and first three pins of PORTB are used for control signals RS, R/W and Enable

PORTB.0 (RS)

PORTB.1 (R/W)

PORTB.2 (E)

The following code is run on MPLAB software.

#INCLUDE<P18F4550.INC>
ORG 0X00
R1 EQU 0X04
R2 EQU 0X05
R3 EQU 0X06
R4 EQU 0X07
R5 EQU 0X08
R6 EQU 0X09

CLRF TRISD
CLRF TRISB
BCF PORTB,2
CALL DELAY
MOVLW 0X38
CALL COMMAND
CALL DELAY
MOVLW 0X0E
CALL COMMAND
CALL READY
MOVLW 0X01
CALL COMMAND
CALL READY
MOVLW 0X06
CALL COMMAND
CALL READY
MOVLW 0X85
CALL COMMAND
CALL READY
MOVLW A’H’
CALL SHOW
CALL READY
MOVLW A’I’
CALL SHOW
YOU BTG PORTB,0
BRA YOU

SHOW
MOVWF PORTD
BCF PORTB,1
BSF PORTB,2
BSF PORTB,0
CALL SDELAY
BCF PORTB,2
RETURN

COMMAND MOVWF PORTD
BCF PORTB,0
BCF PORTB,1
BSF PORTB,2
CALL DELAY
BCF PORTB,2
RETURN

READY SETF TRISD
BCF PORTB,0
BSF PORTB,1
BAC BSF PORTB,2
CALL DELAY
BCF PORTB,2
BTFSC PORTD,7
BRA BAC
CLRF TRISD
RETURN

DELAY MOVLW D’20’
MOVWF R1
L22 MOVLW D’52’
MOVWF R2
L11 MOVLW D’50’
MOVWF R3
HEREA1
NOP
NOP
DECF R3,F
BNZ HEREA1
DECF R2,F
BNZ L11
DECF R1,F
BNZ L22
RETURN

 

SDELAY MOVLW D’10’
MOVWF R4
L2 MOVLW D’10’
MOVWF R5
L1 MOVLW D’100′
MOVWF R6
HEREA
NOP
NOP
DECF R6,F
BNZ HEREA
DECF R5,F
BNZ L1
DECF R4,F
BNZ L2
RETURN

END

circuit diagram of LCD interfacing with PIC microcontroller
circuit diagram of LCD interfacing with PIC microcontroller

Lab Manual for LCD and Keypad Interfacing

LCD and Keypad Interfacing

 

Also read here

How to perform serial communication on PIC microcontroller?

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