228
2552K–AVR–04/11
ATmega329/3290/649/6490
23. LCD Controller
The LCD Controller/driver is intended for monochrome passive liquid crystal display (LCD) with
up to four common terminals and up to 25/40 segment terminals.
23.1
Features
Display Capacity of 25/40 Segments and Four Common Terminals
Support Static, 1/2, 1/3 and 1/4 Duty
Support Static, 1/2, 1/3 Bias
On-chip LCD Power Supply, only One External Capacitor needed
Display Possible in Power-save Mode for Low Power Consumption
Software Selectable Low Power Waveform Capability
Flexible Selection of Frame Frequency
Software Selection between System Clock or an External Asynchronous Clock Source
Equal Source and Sink Capability to maximize LCD Life Time
LCD Interrupt Can be Used for Display Data Update or Wake-up from Sleep Mode
Segment and Common Pins not Needed for Driving the Display Can be Used as Ordinary I/O Pins
Latching of Display Data gives Full Freedom in Register Update
23.1.1
Overview
A simplified block diagram of the LCD Controller/Driver is shown in
Figure 23-1. For the actual
An LCD consists of several segments (pixels or complete symbols) which can be visible or non
visible. A segment has two electrodes with liquid crystal between them. When a voltage above a
threshold voltage is applied across the liquid crystal, the segment becomes visible.
The voltage must alternate to avoid an electrophoresis effect in the liquid crystal, which
degrades the display. Hence the waveform across a segment must not have a DC-component.
LCD module.
23.1.2
Definitions
Several terms are used when describing LCD. The definitions in
Table 23-1 are used throughout
this document.
Table 23-1.
Definitions
LCD
A passive display panel with terminals leading directly to a segment
Segment
The least viewing element (pixel) which can be on or off
Common
Denotes how many segments are connected to a segment terminal
Duty
1/(Number of common terminals on a actual LCD display)
Bias
1/(Number of voltage levels used driving a LCD display -1)
Frame Rate
Number of times the LCD segments is energized per second.