ATmega8 with 16x2 LCD in 4-Bit Mode

Interfacing a 16x2 LCD with the ATmega8 microcontroller in 4-bit mode is a common practice in embedded systems, especially when conserving I/O pins is essential.

In 4-bit mode, only four data lines are used to send data and commands to the LCD, which makes the connection more efficient in terms of pin usage.

Components Required

  • ATmega8 Microcontroller
  • 16x2 Alphanumeric LCD Display
  • Potentiometer (10k) for contrast adjustment
  • Breadboard and jumper wires
  • Power supply (5V)

Circuit Design

ATmega8 With 16X2 LCD Schematic Diagram

LCD Pin Connections

Data Pins

Connect D4, D5, D6, and D7 of the LCD to four GPIO pins on the ATmega8 (for example, PB4 to PB7).

Control Pins

Connect the RS (Register Select) and E (Enable) pins of the LCD to two other GPIO pins (e.g., PB0 and PB1).

R/W (Read/Write) pin is typically grounded in write-only applications.

VSS pin to ground and VDD to +5V.

V0 (contrast control) to the middle pin of the potentiometer. The other two potentiometer pins connect to +5V and GND.

LED+ (backlight power) to +5V and LED- to GND through a current-limiting resistor if needed.

Microcontroller Setup

Ensure the ATmega8 is powered with a stable 5V supply.

Connect the ATmega8 GND to the breadboard's ground rail.

Programming the ATmega8

Initialization in 4-bit Mode

Initialize the LCD in 4-bit mode by first sending commands to set up the 4-bit communication. Start by sending the function set command with the high nibble (upper four bits) first.

Writing Commands and Data

Create functions to send commands and data to the LCD.

In 4-bit mode, each byte (command/data) is sent as two separate nibbles, starting with the high nibble.

Displaying Text

Once initialized, use similar functions to send data to display characters.

#include <avr/io.h>
#include <util/delay.h>
// Define LCD pin connections
#define LCD_RS  PB0
#define LCD_E   PB1
#define LCD_D4  PB4
#define LCD_D5  PB5
#define LCD_D6  PB6
#define LCD_D7  PB7

// Function Prototypes
void lcd_command(unsigned char cmd);
void lcd_data(unsigned char data);
void lcd_init();
void lcd_string(char *str);

// Main Function
int main(void)
{
    // Set data direction registers for Port B
    DDRB = 0xFF; // Set all pins of Port B as output

    lcd_init(); // Initialize the LCD

    lcd_string("Hello World!"); // Display string on LCD

    while(1)
    {
        // Your application code
    }

    return 0;
}

// Function Definitions
void lcd_init()
{
    // LCD initialization sequence
    lcd_command(0x02); // Initialize LCD in 4-bit mode
    lcd_command(0x28); // 2 line, 5x7 matrix
    lcd_command(0x0C); // Display on, cursor off
    lcd_command(0x06); // Increment cursor
    lcd_command(0x01); // Clear display
    _delay_ms(2);
}

void lcd_command(unsigned char cmd)
{
    // Send command to LCD
    PORTB = (PORTB & 0x0F) | (cmd & 0xF0); // Send higher nibble
    PORTB &= ~ (1<<LCD_RS); // RS=0 for command
    PORTB |= (1<<LCD_E); // E=1
    _delay_us(1);
    PORTB &= ~(1<<LCD_E); // E=0

    _delay_us(200);

    PORTB = (PORTB & 0x0F) | (cmd << 4); // Send lower nibble
    PORTB |= (1<<LCD_E); // E=1
    _delay_us(1);
    PORTB &= ~(1<<LCD_E); // E=0

    _delay_ms(2);
}

void lcd_data(unsigned char data)
{
    // Send data to LCD
    PORTB = (PORTB & 0x0F) | (data & 0xF0); // Send higher nibble
    PORTB |= (1<<LCD_RS); // RS=1 for data
    PORTB |= (1<<LCD_E); // E=1
    _delay_us(1);
    PORTB &= ~(1<<LCD_E); // E=0

    _delay_us(200);

    PORTB = (PORTB & 0x0F) | (data << 4); // Send lower nibble
    PORTB |= (1<<LCD_E); // E=1
    _delay_us(1);
    PORTB &= ~(1<<LCD_E); // E=0

    _delay_ms(2);
}

void lcd_string(char *str)
{
    // Display string on LCD
    while(*str != '\0')
    {
        lcd_data(*str);
        str++;
    }
}

This code initializes the ATmega8 microcontroller and a 16x2 LCD in 4-bit mode. It defines the necessary functions for sending commands and data to the LCD, initializes the LCD upon start-up, and then displays the string "Hello World!" on the LCD.

Before compiling and uploading this code to the ATmega8, ensure that your hardware connections match the pin definitions in the code. Also, this code assumes the use of the AVR GCC compiler.

Interfacing a 16x2 LCD with the ATmega8 in 4-bit mode is an efficient way to utilize fewer I/O pins while maintaining full control over the display. This setup is ideal for many embedded projects that require alphanumeric output without the need for extensive I/O resources.

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