Cirrus-logic AN179 User Manual download pdf

AN179REV2

P.O. Box 17847, Austin, Texas 78760

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AN179

Application Note

Interfacing a Color LCD Module to the EP72xx and EP73xx

Introduction

As the world of PDAs and other hand-held devices evolves, more and more of these products need the support of

color displays. Today, the use of color displays constitutes only a small market share. However, the desire for color

support is growing dramatically. This application note is created to support this trend.

This application note describes how the LCD Controller integrated into the Cirrus Logic EP72xx embedded

processor can be used to drive a color LCD module. This application note will first describe in detail how the

EP72xx’s LCD Controller can be used to support color displays. Next, it will provide an example of an application

using a Sharp LM057QCTT03 ¼ VGA Color LCD module. Finally, it will provide a list of other color LCD modules

that are known to be compatible with LCD Controller in the EP72xx.

EP72xx LCD Controller Description

The LCD Controller provides all the necessary control signals to interface directly to a single-panel, multiplexed

LCD module. The EP72xx uses the Universal Memory Architecture (UMA) for storing the video frame buffer. It

shares the main memory bus with the core processor (i.e., the ARM720T). The total frame buffer size can be

programmed up to 128 kbytes. The panel size is programmable and can basically support any panel size available,

including the support for full VGA sizes. Any width (line length) from 32 to 1024 in 16-pixel increments can be

programmed. The total number of lines (rows) supported is solely determined by the total frame buffer size

programmed, divided by the panel width and color depth programmed.

The controller can also be programmed to provide 1-, 2-, or 4-bits-per-pixel color depth. The use of these bits is up

to the application. They can be used to support a monochrome, gray-scale, or color display.

As an example: If a 1/2 VGA display is used, and 4 bpp is desired, the Video Buffer Size field in the LCD Control

Length field in the register will have to be programmed to equal 640, and the color depth field will have to be

programmed to equal 4. These three settings will result in the support for the 240 lines.

To support the various possible colors and gray-scale levels, the LCD Controller has two 32-bit palette registers.

These palette registers are broken down into eight addressable nibbles each. This makes a total of sixteen nibbles.

The nibbles are addressed by the data in the frame buffer. When the LCD Controller is configured to support

4 bpp, each four bits of data in the frame buffer is used to represent one pixel. Each of these nibbles addresses one

of the sixteen nibbles in the two palette registers.

For example, if a nibble in the frame buffer contained the decimal value of ten, it would point to the tenth nibble in

the two palette registers. This addressing scheme is used to map the data value in the frame buffer to the actual

gray-scale level that will be supplied to the display interface. When 4 bpp mode is configured, all sixteen nibbles in

the palettes registers are used for the mapping. This of course, is due to the fact that four bits can provide sixteen

different values. When 2 bpp mode is configured, only the lowest addressable four nibbles are used. When in

1 bpp mode, only the lowest two nibbles are used.

Each palette register nibble can be programmed with a value from 0 to 15. These sixteen different values

correspond to 16 different color depth levels. When the value programmed into each nibble matches its nibble

1 2 3 4 5 6 7 8

Summary of Contents

Page 1 - Application Note

Page 2 - Color Support

Page 3 - The LCD Module Interface Port

Page 4 - EP72xx and EP73xx

Page 5 - Known Compatible LCD Modules

Page 6

Page 7 - • Notes •

• Notes •

Page 8

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