Understanding LCD Interfacing with PIC 18F Microcontroller

Welcome back to the channel! In this post, we will explore the topic of LCD interfacing with the PIC 18F microcontroller. This is a crucial topic for students, especially from an exam perspective, where you may be asked to draw the interfacing diagram and write a specific program.

Overview of LCD Interfacing

The interfacing diagram we will discuss involves a 16x2 line LCD display, which is commonly used in various applications. The diagram includes a potentiometer, data lines, and control pins connected to the microcontroller.

Components Required

• 16x2 LCD Display: This is the main component for displaying information.
• PIC 18F Microcontroller: The microcontroller that will control the LCD.
• Potentiometer (10k ohm): Used to adjust the contrast of the LCD display.
• Crystal Oscillator: Connected between OSC1 and OSC2 pins of the microcontroller.

Interfacing Diagram

The LCD display is connected to the PIC 18F microcontroller as follows:

• Data Lines (D0 to D7): These are connected to Port B of the microcontroller (RB0 to RB7).
• Control Pins: The RS (Register Select), RW (Read/Write), and E (Enable) pins are connected to Port C (RC0, RC1, and RC2).

Explanation of Control Pins

1. RS (Register Select): This pin determines whether the command register or data register is being accessed.

   • If RS = 0, the command register is selected.
   • If RS = 1, the data register is selected.

2. RW (Read/Write): This pin indicates the operation mode.

   • If RW = 0, data is written to the LCD.
   • If RW = 1, data is read from the LCD.

3. E (Enable): This pin is used to latch the data into the command or data register. A high-to-low transition on this pin is required to latch the data.

Writing Commands and Data

Before we dive into coding, it's essential to understand how to write cursor addresses and the corresponding LCD commands. Below is a table of commands for a 16x2 LCD display:

Important Commands

• 0x01: Clear LCD display.
• 0x04: Shift cursor left.
• 0x06: Shift cursor right.
• 0x0C: Display on, cursor off.
• 0x38: Initialize 5x7 matrix for 2-line display.

Command and Data Subroutines

To effectively communicate with the LCD, we need to create subroutines for sending commands and data:

Command Subroutine

This subroutine sends commands to the LCD:

1. Set RS = 0 (command register).
2. Set RW = 0 (write mode).
3. Latch the command using the E pin.

Data Subroutine

This subroutine sends data to the LCD:

1. Set RS = 1 (data register).
2. Set RW = 0 (write mode).
3. Latch the data using the E pin.

Sample Program

Now, let's look at a sample program to display the words "My" at the fourth position of line one and "Book" at the fifth position of line two.

Program Structure

#include <xc.h>

#define LCD_DATA_PORT PORTB
#define RS PORTCbits.RC0
#define RW PORTCbits.RC1
#define E PORTCbits.RC2

void LCD_Command(unsigned char cmd) {
    LCD_DATA_PORT = cmd;
    RS = 0; // Command register
    RW = 0; // Write mode
    E = 1; // Enable high
    __delay_ms(1);
    E = 0; // Enable low
}

void LCD_Data(unsigned char data) {
    LCD_DATA_PORT = data;
    RS = 1; // Data register
    RW = 0; // Write mode
    E = 1; // Enable high
    __delay_ms(1);
    E = 0; // Enable low
}

void main() {
    TRISB = 0; // Set PORTB as output
    TRISC = 0; // Set PORTC as output
    LCD_Command(0x38); // Initialize LCD
    LCD_Command(0x0C); // Display on, cursor off
    LCD_Command(0x01); // Clear display
    LCD_Command(0x84); // Move cursor to line 1 position 4
    LCD_Data('M');
    LCD_Data('y');
    LCD_Command(0xC4); // Move cursor to line 2 position 5
    LCD_Data('B');
    LCD_Data('o');
    LCD_Data('o');
    LCD_Data('k');
}

Explanation of the Program

• The program begins by including the necessary header file and defining the ports.
• The LCD_Command and LCD_Data functions handle sending commands and data to the LCD.
• In the main function, we initialize the LCD and display the desired text.

Conclusion

In this blog post, we covered the essentials of interfacing a 16x2 LCD display with the PIC 18F microcontroller. We discussed the wiring, control pins, commands, and provided a sample program to help you get started. With this knowledge, you should be able to write your own programs for LCD interfacing. Thank you for reading!