HD44780 Character LCD

An HD44780 Character LCD is an industry standard liquid crystal display (LCD) display device designed for interfacing with wikipedia:embedded systems. These screens are often found in copiers, fax machines, laser printers, industrial test equipment, networking equipment such as routers and storage devices, etc. These are not the kind of screens one would find in a cell phone, portable television, etc. They are limited to text only, with eight customizable characters.

Character LCDs can come with or without backlights, which may be LED, fluorescent, or electroluminescent.

Character LCDs use a standard 14-pin or 16-pin interface if it has a backlight.

Pinout

HD44780 pinout example.

1. Ground
2. VCC (+5V)
3. Contrast adjustment
4. Register Select (R/S)
5. Read/Write (R/W)
6. Clock (Enable)
7. Bit 0
8. Bit 1
9. Bit 2
10. Bit 3
11. Bit 4
12. Bit 5
13. Bit 6
14. Bit 7
15. Optional backlight power rail
16. Optional backlight power rail

The backlight power rail differs often, the polarity can be different and some screens need an external resistor. Usually the supply voltage is 5V DC.

Character LCDs can operate in 4-bit or 8-bit mode. In 4 bit mode, pins 7 through 10 are unused and the entire byte is sent to the screen using pins 11 through 14 by sending 4-bits at a time.

Standard Sizes

These screens come in common configurations of 8x1, which is one row of eight characters, 16x2, and 20x4, among others. The largest commonly manufactured configuration is 40x4 characters, and actually requires two individually addressable HD44780 controllers with expansion chips.

Font

The character generator ROM contains 208 characters in a 5x8 dot matrix, and 32 characters in a 5x10 dot matrix.

There is a Japanese version of the ROM which includes kana characters, and a European version which includes Cyrillic and Western European characters.

The 7-bit ASCII subset for the Japanese version is non-standard: it supplies a Yen symbol where the backslash character is normally found, and left and right arrow symbols in place of tilde and the rub-out character.

See also

LCD Smartie - open source driver for Microsoft Windows

External links

• Hitachi HD44780U (LCD-II) datasheet