AVR LCD display in 4-bit-mode (필요한 부분만 발췌)

https://www.electronicwings.com/avr-atmega/interfacing-lcd-16x2-in-4-bit-mode-with-atmega-16-32-

LCD 16x2 can be used in 4BitMode or 8BitMode
depending on requirement of application.

★LCD command 0x28 is for 4-Bit Mode

Programming LCD 16x2 4-bit mode with AVR ATmega16/ATmega32

Initialization

1. Wait for 15ms or more, Power on initialization time for LCD 16x2.

2. Send 0x02 command which is initializes LCD 16x2 in 4-bit mode.

3. Send 0x28 command which configures LED in 2-line, 4-bit mode and 5x8 bits

4. Send any Display ON command (0x0E, 0x0C)

5. Send 0x06 command (increment cursor) (=커서가 오른쪽으로 계속 Shift)