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Hitachi HD44780 LCD controller

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An HD44780 Character LCD is a de facto industry standard liquid crystal display (LCD) display device designed for interfacing with embedded systems. These screens come in a variety of configurations including 8x1, which is one row of eight characters, 16x2, and 20x4. The most commonly manufactured configuration is 40x4 characters, which requires two individually addressable HD44780 controllers with expansion chips as the HD44780 can only address up to 80 characters[citation needed]


These LCD screens are limited to text only and are often used in copiers, fax machines, laser printers, industrial test equipment, networking equipment such as routers and storage devices.

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

Character LCDs use a standard 14-pin interface and those with backlights have 16 pins. The pinouts are as follows:

  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. Backlight Anode (+)
  16. Backlight Cathode (-)

There may also be a single backlight pin, with the other connection via Ground or VCC pin. The two backlight pins may precede the pin 1.

The nominal backlight voltage is around 4.2V at 25˚C using a VDD 5V capable model.

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 (nibble) at a time.

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 display driver for Microsoft Windows
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