Maxim > Design Support > Technical Documents > Application Notes > Display Drivers > APP 3658
Keywords: LCD driver, op amp, I/O port expander, contrast control, backlight-intensity control, digital-to-
analog converter, DAC
APPLICATION NOTE 3658
Serializing an HD44780 LCD Display
Nov 23, 2005
Abstract: Besides reducing the number of required GPIO lines from eleven to two, this circuit also
provides programmable contrast and backlight control.
Most LCD character displays connect to the outside world through a controller IC, such as the HD44780
(Hitachi) or equivalent. That interface has serious drawbacks, however. It uses up a large number of the
microcontroller's general-purpose input/output (GPIO) pins, and it isn't capable of providing digital-
contrast or backlight-intensity control.
The circuit in Figure 1 reduces the required number of GPIOs from eleven to two, and also provides
digital control of the LCD's contrast and backlight intensity. A versatile I/O-port expander (U1) emulates
the typical 8-bit I/O port of a microcontroller. You can implement this interface with little or no extra code
if your microcontroller integrates an I²C peripheral. As an alternative, you can bit-bang the required
signals through the regular GPIO pins.
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