ATmega169P datasheet(233/393 Pages) ATMEL

233 / 393 page

233

8018N–AVR–08/09

ATmega169P

23. LCD Controller

23.1

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

• 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

23.2

Overview

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.

A simplified block diagram of the LCD Controller/Driver is shown in Figure 23-1. For the actual

placement of I/O pins, see ”64A (TQFP)and 64M1 (QFN/MLF) 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 45 must be written to zero to

enable the LCD module.

23.2.1

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.

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