Computer graphics processing and selective visual display system – Plural display systems – Diverse systems
Reexamination Certificate
1993-10-01
2001-04-10
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural display systems
Diverse systems
C345S001300, C345S519000
Reexamination Certificate
active
06215459
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to video controllers and video controller integrated circuits for computer displays. The present invention has particular application to so-called multimedia methodology.
BACKGROUND ART
It is common to provide so-called transportable, lap-top, notebook or palm-top computers with built-in displays. Within the computer industry the term “transportable” is generally defined as a computer relatively easily transported for use at another site, but without internal battery power. These transportable computers are sometimes referred to as “luggables”. The term “lap-top” refers to a computer usually somewhat smaller than a transportable computer, with an internal battery power supply for portable use. The term “notebook” refers to a later generation of computers than so-called lap-tops, generally smaller than lap-tops (i.e., the size of a notebook, or approximately 9″ by 12″) and also internally powered by batteries. The term “palm-top” refers to a new generation of portable computer, even smaller than the notebook, and also powered by internal batteries. So-called “palm-top” computers are sometimes referred to by the acronym PA for “personal assistant”. For the purposes of this disclosure, all four of these types of computers will be collectively referred to herein as “portable” computers.
Due to the generally limited size or resolution of built-in displays in portable computers, it has been known in the art to provide an external output for a stand-alone display, such as a CRT display monitor or the like. For example, early Osborne (TM), Compaq (TM) and IBM (TM) transportable computers included internal CRT displays of limited size (e.g., 9″ diagonal monochrome CRT display or the like). In many instances, these early portable computers were provided with an external output port (MDA, CGA, MCGA or the like) so that a larger external monitor could be attached to the portable computer when higher resolution was desired.
Later generation lap-top computers (e.g., Toshiba (TM) 3100SX or the like) were equipped with similar output ports such that an output intended for an internal monochrome display (e.g., gas plasma flat panel display, LCD flat panel display or the like) could be more effectively displayed on an external color monitor (e.g., VGA, SGVA or the like). More recent notebook size computers (e.g., Apple (TM) Powerbook (TM), Toshiba (TM) 2200 or the like) have provided similar external display outputs.
In most of these computers, the external output ports made available are designed such that only one display at a time can be activated. In other words, either the internal display or the external display can be viewed, but not both simultaneously. Improved VGA controllers designed by Cirrus Logic (TM), the assignee of the present application, incorporate SimulScan (TM), a feature which allows a user to simultaneously view the same image on both an internal display and an external display.
FIG. 1
is a block diagram of a prior art video controller
100
which can display the same video image to both CRT display
106
(or external display) and an internal flat panel display
107
(e.g., LCD flat panel display or the like). Video memory
108
comprises a random access memory (e.g., DRAM, SRAM or the like) which may be accessed through memory controller
101
. The size of video memory
108
is determined by the amount of video data to be displayed at one time. For example, for a 640 by 480 pixel monochrome display, a minimum of 307,200 bits of data is needed. If a multi-color or gray scaled monochrome display is desired, then the necessary number of bits per pixel may be increased. For example, if eight bits are provided for each pixel, then each pixel may take one of 2
8
or 256 colors (or gray scales). For eight bits of data per pixel, a 640 by 480 pixel display requires a minimum of 2,457,600 bits of information, or 76.8 Kilobytes of DRAM, where each word comprises 32 bits (four 8-bit bytes), representing four pixels. In practice, a standard size memory of 1 Megabytes may be used and more than one frame of video stored at one time.
As shown in
FIG. 1
, memory controller
101
accesses video memory
108
and passes to attribute controller
102
one word
150
(32 bits) from video memory
108
, preferably using a page mode addressing scheme. Attribute controller
102
contains a register (not shown) for holding four pixel bytes
151
of eight bits each, from 32 bit word
150
supplied by from video memory
108
. Attribute controller
102
outputs each of the eight bit pixel bytes
151
in sequence to look-up table
103
. Look-up table
103
comprises another random access memory having, in this example, at least 256 addresses. Look-up table
103
converts each of the eight bit pixel bytes
151
into an eighteen bit binary number (hereinafter referred to as pixel word
152
) representing a pixel color (or gray scale). Look-up table
103
takes one of the four eight bit pixel bytes
151
as an address for its internal random access memory and outputs an eighteen bit binary number stored as that address as pixel word
152
representing the color (or gray scale) for that pixel. Individual computer application programs may be able to alter the contents of look-up table
103
such that any or all of the 256 available colors may be selected from a palette of 2
18
or 262,144 colors. Of course, other numbers of bits may be used to provide a broader range or palette of available colors. Further, although only 256 of these colors are shown here as being available at one time, other numbers of colors per pixel may be used by increasing the number of bits per pixel byte
151
.
From look-up table
103
, the eighteen bit pixel word
152
is transferred to DAC
104
. DAC
104
comprises a digital-to-analog converter which converts the eighteen bit pixel word
152
into analog RGB (Red, Green, Blue) signals
153
,
154
, and
155
to drive analog CRT display
106
. In the embodiment shown in
FIG. 1
, six bits each from eighteen bit pixel word
152
are used to create analog signals
153
,
154
, and
155
for Red, Green and Blue levels. DAC
104
typically comprises a number of current sources which may be added together in a binary fashion to create an appropriate analog signal level for each of the outputs
153
,
154
,
155
corresponding to a selected six bits of the eighteen bit pixel word
152
.
Flat panel display
107
(which may comprise an active or passive LCD flat panel display, plasma display, electroluminescent display or the like), however, does not rely upon an analog signal to determine pixel intensity or color. Thus, in order to provide a simultaneous display on both CRT display
106
and flat panel display
107
, two different drive signals must be generated. As shown in
FIG. 1
, eight bit pixel bytes
151
are converted via look-up table
103
into eighteen bit pixel words
152
. Flat panel controller
105
uses eighteen bit pixel words
152
to generate an appropriate video display on flat panel display
107
. For a monochrome display, the eighteen bit pixel word
152
may be converted into a grayscale value using an appropriate internal conversion algorithm. Flat panel controller
105
, using dithering techniques, generates this grayscale on flat panel display
107
. For a color display, eighteen bit pixel word
152
may be converted into separate red, green and blue sub-pixels. Flat panel controller
105
, using dithering techniques, generates appropriate color intensities for each subpixel. Such dithering techniques are described in Bassetti, Jr., U.S. Pat. No. 5,122,783, issued Jun. 16, 1992, assigned to the same assignee as the present application and incorporated herein by reference. Thus, with the apparatus of
FIG. 1
, it is possible to display the same image on both flat panel display
107
and CRT display
106
.
Recently, however, so-called “multimedia” presentations have become increasingly popular. These presentations usually, as the name implies, use a variety of media (e.g., sound, image, video
Bassetti, Jr. Chester Floyd
Reddy Dayakar C.
Chang Kent
Cirrus Logic Inc.
Rutkowski Peter
Stewart David L.
Violette J. P.
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