HD44780 display

Hitachi HD44780 compatibele LCD

Pinout

A HD44780 compatible display has 14 or 16 pins, depending whether it has backlight. For a working display, you need a minimum of 6 microcontroller ports: RS, EN and D4-D7.

HD44780 pinout

Pin	Name	Description
1	VSS	Ground
2	VDD	+5 volts
3	VLC	Contrast voltage, normally < 1V
4	RS	Register Select (high=Data write, low=Command write)
5	R/W	Read/Write (high=read, low=write)
6	EN	Enable: high pulse latches command or data
7-10	DB0-DB3	8-bit mode only: data/command bits 0-3
11-14	DB4-DB7	8-bit mode: data/command bits 4-7, or both nibbles in 4-bit mode
15,16	AB,KB	(optional) Background light: anode, kathode

Operation

The display can operate in both 8 and 4-bit mode. By default, it will start at 8-bit mode, so you need extra initialization before you can start bit banging per nibble.

For most of the things you do, you need to write either a command (instruction) or just data (text). Therefore, you need a write routine. RS (Pin4) determines the type (command/data), the rest is just nibbles and bytes ;)

Note: for a better timing, refer to table 6 (page 24 and 25) of the datasheet. Also, waiting on the the busy flag is recommended.

8-bit

4-bit mode write sequence

Pin	Action	Description
EN	0	make sure chip is in normal operation
RS	0 or 1	command->0 or data->1
D0-D7	bits 0 to 7	place byte on bus
EN	1	latch the data onto the chip
	wait	> 450ns for the data to latch
EN	0	resume normal operation
	wait	> 5ms for a command to execute, or > 200us for data to set

4-bit

Note that setting the display in 4-bit mode seems to require two commands (three write instructions: the first in 8-bit mode, the other in 2x4-bit: see page 24, 42 and 46 of the datasheet).

4-bit mode write sequence

Pin	Action	Description
EN	0	make sure chip is in normal operation
RS	0 or 1	command->0 or data->1
D4-D7	bits 4 to 7	place high nibble on bus
EN	1	latch the data onto the chip
	wait	> 450ns for the data to latch
EN	0	make sure chip resumes normal operation (waiting for the next nibble in 4bit mode)
	wait	> 5ms for memory to prepare command, or > 200us for data to set
D4-D7	bits 0 to 3	place low nibble on bus
EN	1	latch the data onto the chip
	wait	> 450ns for the data to latch
EN	0	resume normal operation
	wait	> 5ms for a command to execute, or > 200us for data to set

physical device

Xopr 23:02, 22 June 2011 (CEST) as of today, there are two HD44780 displays in the space:

• 2x16 line/char
• 2x16 line/char for the visually impaired (bigger version)

You can find them in the 'take-off chinese box' in the right most cabinet. Use at will, but be kind to solder a connector to it, so others can take advantage of it too (be nice, share ;).

references

• joshuagalloway.com's lcd page
• HD44780 datasheet from sparkfun
• Alternative display: PVG120303

Location: Somewhere (probably in the left 'soldering cabinet')