HD44780 Character LCD
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An HD44780 Character LCD is an industry standard liquid crystal display (LCD) display device designed for interfacing with embedded systems. These screens come in common configurations of 8x1 characters, 16x2, and 20x4 among others. The largest such configuration is 40x4 characters, but these are rare and are actually two separate 20x4 screens seamlessly joined together.

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 8 customizable characters.

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

Character LCDs use a standard 14-pin interface. If the screen has a backlight, it will have 16 pins. The pinouts are as follows:

Ground
VCC (+5V)
Contrast adjustment
Register Select (R/S)
Read/Write (R/W)
Clock (Enable)
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
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 a nibble at a time.