CL-GD6420 datasheet(12/146 Pages) CIRRUS

12 / 146 page

CL-GD6420

Notebook VGA Controller

July 1993

DATA BOOK

The CL-GD6420 tracks the active and unused

areas of the screen and cursor positions and

consequently supplies screen control signals —

VSYNC, HSYNC, and BLANK*.

When the CL-GD6420 is connected to a dual-scan

LCD display, an additional 64K x 4 DRAM is

needed. This Frame-Accelerator is used for split-

panel data formatting. The reconstituted data from

the Frame-Accelerator and video memory is then

supplied in parallel to the LCD 4-bit upper and

lower panel data buses. This technique not only

maintains display contrast, but also reduces the

power consumption of the video circuitry. The

panel frame rate is twice the rate that the data is

fetched from video memory.

3.2

CRT Display Modes

The CL-GD6420 includes all registers and data

paths required for VGA compatibility. VGA en-

hancements include 16 simultaneously loadable

text fonts (twice the capability of IBM VGA), and

Readable Registers.

Extended graphics resolutions beyond the 640 x

480 IBM VGA standard are available. Using multi-

frequency monitors, 800 x 600 and 1024 x 768

Modes with a 4:3 aspect ratio can be displayed in

either 16 or 256 colors. (1024 x 768 with 256 colors

is available only in Interlaced Mode).

High-resolution text modes offer from 100 columns

by 50 rows up to 132 columns by 60 rows.

3.3

Flat Panel Display Modes

The CL-GD6420 will directly drive all of the popular

monochrome dual-panel/dual-scan LCD panels.

Proprietary techniques minimize flicker, noise and

pattern motion while enhancing contrast within the

grayscales being used.

Grayscaling is accomplished by modulating the

ON-to-OFF time of individual pixels in the panel

and allowing the eye to integrate the superposed

pixels to 16 perceptible grayscales. Flicker is elim-

inated by proprietary techniques involving distribu-

tion of time between ON and OFF pixels during

frame modulation.

The CL-GD6420 allows the full spectrum of PC

applications written for analog monitors and

various video modes to run on standard 640 x 480

flat panels. This is accomplished through color

emulation, attribute remapping, and resolution

mapping.

In addition, summing circuitry allows rapid genera-

tion of IBM-compatible grayscale equivalents of

color images. Up to 64 grayscale levels are avail-

able by using proprietary two-dimensional stippling

logic. This technique permits all applications that

generate monochrome, 4,- 16-, or 256-color imag-

es to be run on a monochrome flat-panel display.

Cirrus Logic AutoMap logic can map 256 colors

into a monochrome image; the colors then appear

either in 16 shades of gray with grayscale en-

hancement (640 x 480 256 color mode), or 64

shades of gray (320 x 200 256 color mode). The

hardware-based algorithm tracks the particular

palette map being used by the internal RAMDAC.

RAMDAC data may be stored, as desired by the

application, in orderly or random sequences. Real-

istic renditions of color images are not affected.

In color text modes, foreground and background

attributes can be automatically remapped to black

and white for maximum contrast. Positive or nega-

tive raster may be selected under program control

to match the visual qualities of the display and/or

needs of the application.

The video resolutions that an application has se-

lected are remapped to a flat panel according to

whether Compatibility Mode, Compression Mode,

or Expanded Mode was selected.

3.4

Intelligent Power Management and

Sequencing

Notebook and laptop PCs have stringent power

limitations due to battery operation and heat dissi-

pation. To meet these needs, the CL-GD6420 is

manufactured using low-power CMOS technology.

In addition, the CL-GD6420 has programmable

output pins as well as other intelligent power man-

agement features that will permit the controller to

enter the modes explained below to conserve

power.

CL-GD6420 Datasheet(PDF) 12 Page - Cirrus Logic

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