Computer graphics processing and selective visual display system – Plural display systems – Tiling or modular adjacent displays
Reexamination Certificate
1998-11-16
2001-07-17
Shalwala, Bipin (Department: 2778)
Computer graphics processing and selective visual display system
Plural display systems
Tiling or modular adjacent displays
C345S030000, C345S099000, C345S204000, C345S212000, C345S213000, C348S500000, C348S505000, C348S510000, C348S512000, C348S518000
Reexamination Certificate
active
06262695
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatus for displaying information, and more particularly, to methods and apparatus for causing two or more display devices to display information. The present invention also relates to video display drivers, and more particularly, to multi-level video display drivers and methods for their use with and in apparatus for displaying information.
BACKGROUND OF THE INVENTION
Video circuit designs for providing synchronized video signals are useful with personal computers (PCs). Such designs place one image over another image on a PC display system and phase-lock multiple rasters (such as might be used in multiple display systems). The images can then be moved independently with movement commands to the video circuits. Further, a foreground image, such as an animation character surrounded by other background imagery, can be generated by giving portions of image around the animation character on the foreground image a transparency attribute, allowing the background imagery to be seen through the portions of the foreground image that have the transparency attribute. In the prior art, video circuit designs for providing synchronized video signals for the use of personal computers (PCs) in such applications are too large and expensive to be widely marketable to the public.
In the past, the method of painting top images on clear mylar or cellulose has been used and is widely accepted by animation artists. This is the same method that video game electronics companies use to electronically show small images known as sprites over large images. However, this has never been done with common video graphics adapter (VGA) PC-compatible computers. This overlaying of images is also known as color-keying, as a key color indicates transparency to the circuits. Color keying has been done before, but never on two or more raster images that had achieved the required synchronization and phase lock with a low cost circuit of the inventive type. Achieving synchronization of video raster scan circuits is easy and can even be done accidentally, if the same pixel clock is used for two or more taster scan circuits. However, phase lock is a concept that typically requires considerably circuitry.
The vast majority of video raster circuits that are available now cannot be synchronized. This is because the manufacturers of these circuits do not wish to add the expense of having all the horizontal pixel counters and vertical line counters with the feature of a zero reset. A zero reset feature is necessary to synchronize video raster circuits.
It is also desirable to have software that can operate effectively with multiple-monitor display systems. As operating systems and other portions of software on a PC change, the drivers necessary to correctly drive the display systems also change. It is, therefore, advantageous to have the driver software organized so that it can easily be changed in accord with the changes to the software that is involved in producing the information and images that are to be displayed.
SUMMARY OF THE INVENTION
According to one aspect, the invention is a method for phase-locking a plurality of display devices. Each of the display devices displays an image under the control of a distinct clock having a distinct clock rate. Each of the images contains a predetermined periodic indexing event. The method includes the steps of a) designating one of the distinct clocks to be a master clock and the remaining clocks to be slave clocks and b) synchronizing the distinct clocks. Step b) includes the steps of: b1) first causing the greatest difference between the clock rates of all of the distinct clocks to be within a predetermined difference rate of one another, and b2) then causing the predetermined difference rate to be reduced to zero.
The method also includes the steps of c) comparing the times of occurrence of the indexing event for the image displayed under the control of the master clock to the times of occurrence of the indexing events for the images displayed under the control of the slave clocks, d) if any one of said times of occurrence under the control of one of the slave clocks differs from the time of occurrence under the control of the master clock by more than a predetermined amount of time, causing said time of occurrence of said slave clock to occur within the predetermined amount of time of the time of occurrence of the master clock; and e) repeating steps c) and d) until the slave clocks are phase-locked.
In accordance with another aspect, the invention is an apparatus for phase-locking a plurality of display devices. Each of the display devices displays an image under the control of a distinct clock having a distinct clock rate. Each of the images contains a predetermined periodic indexing event. The apparatus includes a designation circuit to receive each of the distinct clocks and to designate one of the distinct clocks to be a master clock and the remaining clocks to be slave clocks, and a synchronization circuit to synchronize the distinct clocks. The synchronization circuit includes a clock rate comparison circuit to compare the clock rates of all of the distinct clocks and to determine the greatest difference between the rates of all of the distinct clocks, a control circuit to receive said greatest difference and to cause said greatest difference to be within a predetermined difference rate of one another, and a rate difference circuit to cause said predetermined difference rate to be reduced to zero.
The apparatus further includes a times-of-occurrence comparison circuit to receive the times of occurrence of the indexing events for the images displayed under the control of the master clock and the slave clocks, to compare the times of occurrence of the indexing event for the image displayed under the control of the master clock to the times of occurrence of the indexing events for the images displayed under the control of the slave clocks, and to produce signals indicative of the differences between the time of occurrence of the indexing event for the image displayed under the control of the master clock and the times of occurrence of the indexing events for the images displayed under the control of the slave clocks.
In addition the apparatus includes a reset circuit to receive the signals indicative of said differences, to compare the signals indicative of said differences, and, if any one of said differences exceeds a predetermined amount of time, to cause said corresponding time of occurrence of said slave clock to occur within the predetermined amount of time of the time of occurrence of the master clock; and a repetition circuit to iteratively cause the times-of-occurrence comparison circuit and the reset circuit to operate until the slave clocks are phase-locked.
In accordance with a still further aspect, the invention is an apparatus for phase-locking a plurality of display devices. Each of the display devices displays an image under the control of a distinct clock having a distinct clock rate. Each of the images containing a predetermined periodic indexing event. The apparatus includes means for designating one of the distinct clocks to be a master clock and the remaining clocks to be slave clocks and means for synchronizing the distinct clocks. The means for synchronizing the distinct clocks includes means for first causing the greatest difference between the clock rates of all of the distinct clocks to be within a predetermined difference rate of one another, and means for then causing the predetermined difference rate to be reduced to zero.
The apparatus further includes comparison means for comparing the times of occurrence of the indexing event for the image displayed under the control of the master clock to the times of occurrence of the indexing events for the images displayed under the control of the slave clocks, time control means for causing said time of occurrence of said slave clock to occur within the predetermined amount of time of the time of occurrence of the master clock if any one o
Kovalick Vincent E.
Shalwala Bipin
Storwick Robert M.
Tridium Research, Inc.
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