ATmega169P
22. 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 segment terminals.
22.1 Features
• Display Capacity of 25 Segments and Four Common Terminals
• Support Static, 1/2, 1/3 and 1/4 Duty
• Support Static, 1/2, 1/3 Bias
• LCD Output Voltage (Contrast) Software Selectable from 2.6 to 3.35V for VCC in the Entire
Operating Range
• 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
22.2 Overview
A simplified block diagram of the LCD Controller/Driver is shown in Figure 22-1. For the actual
placement of I/O pins, see ”Pinout ATmega169P” on page 2.
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.
The PRLCD bit in ”PRR – Power Reduction Register” on page 44 must be written to zero to
enable the LCD module.
22.2.1
Definitions
Several terms are used when describing LCD. The definitions in Table 22-1 are used throughout
this document.
Table 22-1. Definitions
LCD
A passive display panel with terminals leading directly to a segment
The least viewing element (pixel) which can be on or off
Segment
Common
Duty
Denotes how many segments are connected to a segment terminal
1/(Number of common terminals on a actual LCD display)
1/(Number of voltage levels used driving a LCD display -1)
Number of times the LCD segments is energized per second.
Bias
Frame Rate
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8018A–AVR–03/06