
DocID024597 Rev 5
757/1830
RM0351
Liquid crystal display controller (LCD)
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25
Liquid crystal display controller (LCD)
25.1 Introduction
The LCD controller is a digital controller/driver for monochrome passive liquid crystal display
(LCD) with up to 8 common terminals and up to 44 segment terminals to drive 176 (44x4) or
320 (40x8) LCD picture elements (pixels). The exact number of terminals depends on the
device pinout as described in the datasheet.
The LCD is made up of several segments (pixels or complete symbols) which can be turned
visible or invisible. Each segment consists of a layer of liquid crystal molecules aligned
between two electrodes. When a voltage greater than a threshold voltage is applied across
the liquid crystal, the segment becomes visible. The segment voltage must be alternated to
avoid an electrophoresis effect in the liquid crystal (which degrades the display). The
waveform across a segment must then be generated so as to avoid having a direct current
(DC).
Glossary
Bias
: Number of voltage levels used when driving an LCD. It is defined as 1/(number of
voltage levels used to drive an LCD display - 1).
Boost circuit:
Contrast controller circuit
Common
: Electrical connection terminal connected to several segments (44 segments).
Duty ratio
: Number defined as 1/(number of common terminals on a given LCD display).
Frame:
One period of the waveform written to a segment.
Frame rate
: Number of frames per second, that is, the number of times the LCD segments
are energized per second.
LCD
: (liquid crystal display) a passive display panel with terminals leading directly to a
segment.
Segment
: The smallest viewing element (a single bar or dot that is used to help create a
character on an LCD display).