Datasheet

223
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
24. LCD Controller
24.1 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
24.2 Overview
The LCD Controller/driver is intended for monochrome passive liquid XTAL display (LCD) with up to four common
terminals and up to 25/40 segment terminals.
A simplified block diagram of the LCD Controller/Driver is shown in Figure 24-1. For the actual placement of I/O
pins, refer to ”Pin configurations” 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 XTAL between them. When a voltage above a threshold voltage is applied across
the liquid XTAL, the segment becomes visible.
The voltage must alternate to avoid an electrophoresis effect in the liquid XTAL, 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.
24.2.1 Definitions
Several terms are used when describing LCD. The definitions in Table 24-1 are used throughout this document.
Table 24-1. 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.