Interfacing ATmega8 with 16x2 LCD
in 8-Bit Mode

Using an LCD with the ATmega8 microcontroller in 8-bit mode involves connecting the 8 data lines of the LCD to 8 GPIO pins of the ATmega8.

This mode allows for straightforward communication between the microcontroller and the LCD but requires more I/O pins.

atmega8 LCD 16x2 interfacing

Components Required

  • ATmega8 Microcontroller
  • Alphanumeric LCD Display (16x2 or similar)
  • Potentiometer (for contrast adjustment)
  • Breadboard and connecting wires
  • Power supply (typically 5V)

Circuit Design

ATmega8 with LCD 16x2 Schematic Design

LCD Pinout Connection

  1. Connect the data pins (D0 to D7) of the LCD to 8 GPIO pins on the ATmega8. For simplicity, you can use PORTB or PORTD.
  2. RS (Register Select) pin of the LCD is connected to another GPIO pin, which is used to switch between sending commands and data.
  3. R/W (Read/Write) pin is generally grounded in simple projects, as writing is more common.
  4. E (Enable) pin is connected to another GPIO pin, which is used to enable writing to the registers of the LCD.
  5. VSS and VDD pins of the LCD are connected to GND and +5V respectively.
  6. V0 is connected to the middle terminal of the potentiometer for contrast control.
  7. LED+ and LED- are the backlight pins, connect them to +5V and GND respectively (through a resistor if necessary).

Power Connections

Ensure that both the ATmega8 and the LCD are powered with a stable 5V supply.

Contrast Adjustment

Connect a potentiometer to V0 for contrast control.

Programming the ATmega8

Initialization

Initialize the LCD in 8-bit mode by sending specific commands to the LCD. This includes setting the display size, font, and the entry mode.

Set the DDR (Data Direction Register) of the port connected to the data pins of the LCD as output.

Writing Commands and Data

Create functions to send commands and data to the LCD.

Use the RS pin to select whether you are sending a command (RS=0) or data (RS=1).

Toggle the E pin to signal the LCD to accept the data or command.

Creating Custom Characters (Optional)

You can create custom characters by writing to the CGRAM (Character Generator RAM) of the LCD.

Displaying Text

Write text to the DDRAM (Display Data RAM) of the LCD to display it on the screen.

Basic Code Example 

#include <avr/io.h>
#include <util/delay.h>
#define LCD_DATA_PORT PORTD
#define LCD_DATA_DDR DDRD
#define LCD_CONTROL_PORT PORTB
#define LCD_CONTROL_DDR DDRB
#define RS PB0
#define EN PB1

void LCD_Command(unsigned char cmd) {
    LCD_DATA_PORT = cmd;
    LCD_CONTROL_PORT &= ~(1 << RS); // RS = 0 for command
    LCD_CONTROL_PORT |= (1 << EN);  // EN = 1 for H-to-L pulse
    _delay_ms(1);
    LCD_CONTROL_PORT &= ~(1 << EN); // EN = 0 to complete the H-to-L pulse
    _delay_ms(3);
}

void LCD_Char(unsigned char char_data) {
    LCD_DATA_PORT = char_data;
    LCD_CONTROL_PORT |= (1 << RS);  // RS = 1 for data
    LCD_CONTROL_PORT |= (1 << EN);  // EN = 1 for H-to-L pulse
    _delay_ms(1);
    LCD_CONTROL_PORT &= ~(1 << EN); // EN = 0 to complete the H-to-L pulse
    _delay_ms(1);
}

void LCD_Init() {
    LCD_DATA_DDR = 0xFF; // Make PORTD as output
    LCD_CONTROL_DDR |= (1 << RS) | (1 << EN); // Make RS and EN as output
    _delay_ms(20); // LCD Power ON delay
    
    // Initialization sequence
    LCD_Command(0x38); // Function set: 8-bit, 2 Line, 5x7 Dots
    LCD_Command(0x0E); // Display on, Cursor blinking
    LCD_Command(0x01); // Clear display
    LCD_Command(0x06); // Entry mode, auto increment with no shift
}

void LCD_String(char *str) {
    int i;
    for(i=0; str[i]!=0; i++) {
        LCD_Char(str[i]);
    }
}

void LCD_String_xy(char row, char pos, char *str) {
    if (row == 0 && pos < 16) {
        LCD_Command((pos & 0x0F) | 0x80); // Command for 1st row and required position
    } else if (row == 1 && pos < 16) {
        LCD_Command((pos & 0x0F) | 0xC0); // Command for 2nd row and required position
    }
    LCD_String(str); // Print string
}

int main(void) {
    LCD_Init(); // Initialize LCD

    LCD_String_xy(0, 0, "Hello World!"); // Print string on 1st row
    LCD_String_xy(1, 0, "ProgPtr.com");      // Print string on 2nd row

    while(1) {
        // Your application code
    }
}

This code initializes the LCD in 8-bit mode and defines functions to send commands and data to the LCD.

It then displays the string "Hello, World!" on the first line and "ATmega8" on the second line of the LCD.

The LCD_String_xy function allows you to specify the row and position where the string starts.

Remember, you may need to adjust the delay times depending on your specific LCD's speed and the clock speed of your ATmega8.

Interfacing an LCD in 8-bit mode with ATmega8 involves setting up a circuit with a parallel data connection and writing a program to control the LCD. This mode is straightforward in terms of the programming logic but uses more I/O pins of the microcontroller. This setup is ideal for applications where the display of text or custom characters is required and sufficient I/O pins are available.

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