CL-GD6420
Notebook VGA Controller
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*.
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.
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.
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.
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).
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.
High-resolution text modes offer from 100 columns
by 50 rows up to 132 columns by 60 rows.
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.
3.3 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.
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.
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.
12
July 1993
DATA BOOK
CIRRUS [ CIRRUS LOGIC ]
