Lcd Interface; Overview - Intel PXA27 Series Design Manual

LCD Interface

This chapter describes examples of hardware connections between Intel
Family (PXA27x processor) and various types of Liquid Crystal Display (LCD) controllers. Active
LCD displays, such as the Thin Film Transistor (TFT) display and passive LCD displays such as
the Supertwist Nematic (STN) display, are discussed as well as single and dual-scan displays.
Smart panels are relatively new devices in the LCD panel market and are yet to have standardized
connections. An example connection for a smart panel is provided; however, the example requires
verification of the connectivity of the LCD panel with the panel vendor.
The diagrams in this chapter serve as guidelines in connecting LCD panel to the PXA27x
processor. These diagrams are intended to assist in system hardware design.
7.1

Overview

The PXA27x processor supports both active and passive LCD displays. Active displays generally
produce better looking images, but at a higher cost. Passive displays are generally less expensive,
but their displays are inferior to active displays. However, recent advances in dithering technology
are closing the quality gap between passive and active displays.
Several different types of passive monochrome displays are available. These passive displays are
either single or dual-scan displays. Additionally, some monochrome displays use double-pixel data
mode (twice the number of pixels as a normal monochrome display). With the exception of the
number of data pins required, all of these choices affect the software configuration and support, not
the system hardware design. In fact, most passive displays use a single interconnection scheme. For
information on the software changes and performance considerations of the various display
options, refer to the Intel
Passive displays drive dithered data to the LCD panel, which means that for each pixel clock cycle,
a single data line drives an ON/OFF signal for one color of a single pixel.
Active panels have fixed data pins assignments. For instance, LDD<0> is always the least
significant byte (LSB) of the blue data, except for 24 bits per pixel (bpp) panels. The color depth
determines the number of pins used. All 16 bpp active displays require 16 data lines. All 18 bpp
active displays require 18 data lines. Only with 24 bpp does the PXA27x processor use a different
number of pins than the color depth; the processor outputs the data on 8 lines.
Active displays do not dither the data to the LCD panel. The data driven is the direct intensity level
for the pixel being transferred.
Smart panels offer greater flexibility in their use and also offer much greater power savings. To
obtain the power savings requires additional communications between the LCD controller and the
panel. Communications are attained by use of either additional signals or expanded use of existing
signals on the processor. The particular implementation of smart panels is not yet standardized and
is considered as customized implementation of each panel. While an example connection for this
type of display is provided in this chapter, verify the proper connection of the LCD panel per
recommendation of the panel vendor.
®
Intel PXA27x Processor Family Design Guide
®
PXA27x Processor Family Developers Manual.
7
®
PXA27x Processor
II:7-1