#define LCD_ADDRESS 0x27  // I2C Adresse des PCF8574T (mit R/W-Bit)
#define LCD_RS 0          // P0 - Register Select Pin
#define LCD_RW 1          // P1 - Read/Write Pin (immer auf GND)
#define LCD_EN 2          // P2 - Enable Pin
#define LCD_P3 3          // P3 - Muss auf 1 gesetzt werden

void i2c_start() {
    TWCR = (1 << TWSTA) | (1 << TWEN) | (1 << TWINT);
    while (!(TWCR & (1 << TWINT)));
}

void i2c_stop() {
    TWCR = (1 << TWSTO) | (1 << TWINT) | (1 << TWEN);
}

void i2c_write(uint8_t data) {
    TWDR = data;
    TWCR = (1 << TWINT) | (1 << TWEN);
    while (!(TWCR & (1 << TWINT)));
}

void lcd_command(uint8_t cmd) {
    i2c_start();
    i2c_write(LCD_ADDRESS << 1);  // Schreibadresse

    i2c_write((cmd & 0xF0) | (0 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));
    i2c_write((cmd & 0xF0) | (1 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));  // high nibble
    i2c_write((cmd & 0xF0) | (0 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));

    i2c_write((cmd << 4) | (0 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));    // low nibble
    i2c_write((cmd << 4) | (1 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));
    i2c_write((cmd << 4) | (0 << LCD_EN) | (0 << LCD_RS) | (1 << LCD_P3));

    i2c_stop();
    _delay_us(1);
}

void lcd_write(uint8_t data) {
    i2c_start();
    i2c_write(LCD_ADDRESS << 1);  // Schreibadresse
  
    i2c_write((data & 0xF0) | (0 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));  // high nibble
    i2c_write((data & 0xF0) | (1 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));
    i2c_write((data & 0xF0) | (0 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));
   
    i2c_write((data << 4) | (0 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));    // low nibble
    i2c_write((data << 4) | (1 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));
    i2c_write((data << 4) | (0 << LCD_EN) | (1 << LCD_RS) | (1 << LCD_P3));

    i2c_stop();
    _delay_ms(200);
}

void lcd_init() {
    // Function Set (4-bit mode)
    lcd_command(0x02); // 4-bit mode
    lcd_command(0x28); // 2 lines, 5x8 matrix
    lcd_command(0x0C); // Display on, cursor off, blink off
    lcd_command(0x06); // Increment cursor

    // Clear Display
    lcd_command(0x01);
}

void lcd_print(char *str) {
    while (*str) {
        lcd_write(*str++);
    }
}

int main(void) {
    lcd_init();
    lcd_print("Hallo AVR!");
    while (1);
    return 0;
}