HD44780 — Dot Matrix Liquid Crystal Display Controller/Driver

Overview

The HD44780 (and its updated revision HD44780U) is an industry-standard dot-matrix liquid crystal display (LCD) controller and driver IC developed by Hitachi. It handles character generation, display refresh, and internal RAM management for alphanumeric displays, most commonly 16x2 (16 characters, 2 lines) and 20x4 modules.

The controller includes an integrated Character Generator ROM (CGROM) containing 208 $5 \times 8$ dot font characters, a Character Generator RAM (CGRAM) for 8 custom user-defined characters, and a Display Data RAM (DDRAM) storing up to 80 characters of display text.

Quick reference


Operating voltage (`VCC`)	4.5 V – 5.5 V (typically 5.0 V)
Logic level	5V TTL compatible
Display format	16x2 or 20x4 alphanumeric characters
Interface	4-bit / 8-bit parallel, or I2C via PCF8574 backpack
Current draw	1.5 mA (IC only, excluding LED backlight ~100–120 mA)
Character fonts	208 $5\times8$ characters in CGROM + 8 custom $5\times8$ in CGRAM

Pinout

Standard 16-Pin Parallel Interface

Pin	Name	Type	Description
1	`VSS`	Power	Ground (0 V)
2	`VDD`	Power	Supply voltage (+5 V)
3	`V0`	Analog Input	Contrast adjust (0 V to 5 V via 10 kΩ potentiometer)
4	`RS`	Digital Input	Register Select (`LOW`: Instruction register, `HIGH`: Data register)
5	`RW`	Digital Input	Read/Write select (`LOW`: Write to LCD, `HIGH`: Read from LCD)
6	`E`	Digital Input	Enable signal (falling-edge latch for data/commands)
7	`DB0`	Digital I/O	Data bus bit 0 (Unused in 4-bit mode)
8	`DB1`	Digital I/O	Data bus bit 1 (Unused in 4-bit mode)
9	`DB2`	Digital I/O	Data bus bit 2 (Unused in 4-bit mode)
10	`DB3`	Digital I/O	Data bus bit 3 (Unused in 4-bit mode)
11	`DB4`	Digital I/O	Data bus bit 4
12	`DB5`	Digital I/O	Data bus bit 5
13	`DB6`	Digital I/O	Data bus bit 6
14	`DB7`	Digital I/O	Data bus bit 7
15	`LED+` / `A`	Power	Backlight Anode (+5 V via current-limiting resistor)
16	`LED-` / `K`	Power	Backlight Cathode (GND)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Operating Voltage	`VDD`	4.5	5.0	5.5	V	Standard supply
Supply Current	`IDD`	—	1.5	3.0	mA	$V_{DD} = 5.0\text{ V}$ , no backlight
High-level Input Voltage	`VIH`	2.2	—	`VDD`	V	TTL compatible
Low-level Input Voltage	`VIL`	-0.3	—	0.6	V	TTL compatible
Enable Pulse Width	`PWEH`	450	—	—	ns	High period for `E` pulse
Enable Rise/Fall Time	`tEr`, `tEf`	—	—	25	ns	Data latch timing

Instruction set

HD44780 accepts commands when RS = 0 and RW = 0. Data is latched on the falling edge of the Enable (E) pin.

Instruction	DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0	Description	Execution Time
Clear Display	0	0	0	0	0	0	0	1	Clears DDRAM and sets DDRAM address 0 in address counter	1.52 ms
Return Home	0	0	0	0	0	0	1	*	Sets DDRAM address 0 and returns display to original position	1.52 ms
Entry Mode Set	0	0	0	0	0	1	I/D	S	Sets cursor move direction (`I/D`) and spec. display shift (`S`)	37 µs
Display ON/OFF	0	0	0	0	1	D	C	B	Sets Display (`D`), Cursor (`C`), and Blink (`B`) ON/OFF	37 µs
Cursor/Shift	0	0	0	1	S/C	R/L	*	*	Shifts display or moves cursor without changing DDRAM	37 µs
Function Set	0	0	1	DL	N	F	*	*	Sets Data Length (`DL`: 8/4 bit), Lines (`N`: 2/1 line), Font (`F`)	37 µs
Set CGRAM Addr	0	1	AGC	AGC	AGC	AGC	AGC	AGC	Sets CGRAM address	37 µs
Set DDRAM Addr	1	ADD	ADD	ADD	ADD	ADD	ADD	ADD	Sets DDRAM address (Line 1: `0x00`–`0x27`, Line 2: `0x40`–`0x67`)	37 µs

Wiring

4-Bit Parallel Mode (Arduino Uno)

HD44780 Pin	Arduino Uno Pin	Notes
1 (`VSS`)	`GND`	Ground
2 (`VDD`)	`5V`	Power
3 (`V0`)	Potentiometer Wiper	10 kΩ pot between 5V and GND for contrast control
4 (`RS`)	Pin `12`	Register Select
5 (`RW`)	`GND`	Tied to GND for Write-only mode
6 (`E`)	Pin `11`	Enable
11 (`DB4`)	Pin `5`	Data Bit 4
12 (`DB5`)	Pin `4`	Data Bit 5
13 (`DB6`)	Pin `3`	Data Bit 6
14 (`DB7`)	Pin `2`	Data Bit 7
15 (`LED+`)	`5V`	Backlight Anode
16 (`LED-`)	`GND`	Backlight Cathode

Info

When using an I2C backpack (PCF8574 expansion board soldered to the LCD), the 16-pin interface is converted to a 4-pin I2C interface (VCC, GND, SDA, SCL) with default I2C address 0x27 or 0x3F.

Common mistakes

Blank screen / Solid black blocks: The contrast pin (V0) is floating or set incorrectly. Adjust the 10 kΩ potentiometer connected to pin 3 until characters become visible.
Incorrect line addresses: Line 1 DDRAM addresses start at 0x00, while Line 2 DDRAM addresses start at 0x40 (not 0x10). On 20x4 displays, Line 3 starts at 0x14 and Line 4 starts at 0x54.
Missing initialization delays: The HD44780 requires a strict startup timing sequence (>15 ms after $V_{DD}$ reaches 4.5 V) before receiving initialization instructions.

Notes

Custom Characters: Up to 8 custom characters can be stored in CGRAM (addresses 0x00–0x07). Each character is defined as an 8-byte array representing $5 \times 8$ pixel patterns.

Interface	Parallel (4-bit/8-bit), I2C (via PCF8574 backpack)
Supply	4.5–5.5 V
Package	80-pin QFP / COB module