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1996-04-03
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Video Display Modes
-------------------
This is file VGAINFO.TXT. You might
want to print it out for reference if
you have any video display problems.
All VGA Display Adapters are capable of operating with a
variety of different graphics modes. These modes differ by
the width and height of the display and the maximum number
of simultaneous colors.
For example, the standard display resolution is 640 x 480.
This has 640 dots or "pixels" on each line and 480 scan lines.
Early VGA Display Adapters could display only 16 colors at
this resolution or 256 colors at 320 x 200 resolution.
More modern Super VGA (SVGA) Display adapters can handle
higher resolution and more colors.
Each display mode has an associated number, usually written
as a hexadecimal (base 16) number. In the PC world,
hexadecimal numbers are often indicated with an "H" at the end.
For instance, display mode 13H means 320 x 200 pixels with
256 colors. The lower numbered modes are all standardized
because everyone copied what IBM had done.
Unfortunately, SVGA developers didn't talk to each other
when adding extensions to the IBM standard. As a result,
they didn't use the same numbers for the new graphics modes.
For example, these different display modes were used for
640 x 480 with 256 colors:
67H Video Seven FastWrite VGA
201H Orchid Fahrenheit 1280
5FH STB Evolution VGA
What a mess! This is why SVGA display adapters came with
disks full of drivers for numerous applications and MS-DOS
software applications come supplied with display drivers
for numerous brands and models of SVGA adapters. This mess
is a big headache for everyone involved, especially the poor
user who can't get incompatible products to work with each
other.
VESA to the Rescue
------------------
Eventually, the Video Electronics Standards Association (VESA)
came to the rescue. New graphics modes in the 1xxH range were
established. For example, 640 x 480 with 256 colors is now:
101H for all adapters adhering to VESA standard
Note: This software standard for applications talking to
display adapters is not related to the VESA Local Bus
which is a hardware interface.
Software applications and VGA Display Adapter hardware now
operate together with one standard. No more disks full of
drivers for all the different combinations of applications
and hardware.
Nearly all VGA display adapters made during the last few years
have this VESA-compatiblity built into their hardware ROMs
(read only memories). However, there are still some very old
VGA cards still in use. You can often get more colors and/or
resolution from them by installing a VESA driver.
VESA Drivers
------------
For older VGA cards, most manufacturers (or at least those who
show concern for supporting their customers) supply separate
VESA driver software. These are generally TSR (Terminate &
Stay Resident) programs which are run from the AUTOEXEC.BAT
file. Every time you reboot the computer, the program runs and
remains in memory.
The VESA driver intercepts some of the requests from the
application program and translates them before passing them
along to the video display hardware. For example, a request
for video mode 101h would be changed to 67h, 201h, 5Fh, or
whatever is appropriate for the hardware. The application
program doesn't have to worry about about all the different
types of video display hardware. There is one common
standard way of talking to all of them.
Video Memory
------------
The VGA display adapter has its own memory for storing the
screen contents. This is completely separate from the main
memory of the computer. For example, you might have 4 or 8
megabytes of main memory but the video display might have
only 1 megabyte, or 512k, or even less.
Higher resolution needs more video memory.
More colors needs more video memory.
There is a tradeoff. For example if your display has 1 megabyte
of video memory you might be able to choose between:
640 x 480, 16 million colors or
800 x 600, 32 thousand colors
but not
800 x 600, 16 million
because this requires 2 meg of video memory. Video memory
requirements are shown below:
Width Height Colors Video Memory
----- ------ ------ ------------
640 480 16 256k
640 480 256 512k
640 480 32k,64k 1 meg
640 480 16M 1 meg
800 600 256 512k
800 600 32k,64k 1 meg
800 600 16M 2 meg
You can find out more about your VGA display adapter by running
the Microsoft Diagnostic program (usually C:\DOS\MSD.EXE) and
picking "V" for Video.
If you have 512k or less, you should consider adding more, if
possible, or upgrading to a better model.
If you have 1 megabyte of video memory and can get 32k or 64k
colors at 800 x 600, don't feel compelled to buy a new video
card capable of 16 million at this resolution. When fewer
than 16M colors are available, Pasokon TV uses dithering to
increase the perceived number of colors. 32k colors combined
with dithering gives the appearance of 4 million colors.
Most people won't be able to tell the difference unless they
have a suitable test pattern and know what to look for.
VGAINFO.EXE
-----------
This is a handy test program to test for compatibility between
Pasokon TV and your VGA display.
VGAINFO asks the VGA card what graphics modes are available.
It then tests all modes of interest to Pasokon TV and leaves a
report in a file called VGAINFO.LOG.
Pasokon TV
----------
When Pasokon TV starts up, it also determines which graphics
modes are available and picks the best one in this order:
800 x 600, 16M colors
32k
64k
256
640 x 480, 16M colors
32k
64k
256
16
Only 16 colors would be absolutely horrible but it means that
Pasokon TV should work with any VGA card in the world.
If you must choose between 64k and 32k colors, I'd suggest
32k. The reason is that with 64k there are more shades of
green than red and blue. The result is that gray scales
come out with a little green and purple instead of pure gray.
You won't notice this in most images. Only in a gray scale.
There have been cases of a VGA display adapter lying about its
capabilities. The most sinister is the Trident TVGA 8900C.
Many Pasokon TV version 2 users reported they worked fine in
32k color mode. A few found that the 8900C claimed to have a
32k color mode when asked using the standard VESA method.
However the colors were all messed up and another diagnostic
program said only 256 colors were supported. Apparently
there were different variations of this particular model.
It might also turn out that the VGA display adapter is capable
of 800 x 600 resolution but the montor can't handle the
different scan rate. In this case you will have to override
the automatic mode selection. This is described below.
Faster 16 Million Colors
------------------------
In many cases you can get faster display of 16M color images
by placing this command in the PKTV.CFG file:
FAST_16M
This will cause the image window to be displayed with a faster
technique instead of the standard slower one. This is off by
default because it does not work in all cases. It is known
to work with these:
Hercules Dynamite
but not these:
Hercules Terminator
The VGAINFO test program does not try the special fast method.
You will have to try adding FAST_16M to the configuration file
manually and see what happens.
In Case of Difficulty
---------------------
1. Run the VGAINFO program and print out a copy of VGAINFO.LOG
which it creates.
2. If you think your VGA display is capable of higher resolution
and/or more colors, try installing UNIVBE or a vendor-supplied
VESA driver, and run VGAINFO again. If results are better,
you will need to run this driver before Pasokon TV.
For example, the INSTALL procedure creates a batch file called
TV.BAT which simply runs PKTV.EXE. It also creates a batch
file called TVV.BAT which installs UNIVBE before running
PKTV.EXE.
3. If Pasokon TV's automatic selection of the best graphics
mode doesn't produce desired results, you can force a
particular graphics mode with a command in the configuration
file. Edit the PKTV.CFG file and add a line with the
desired mode determined from VGAINFO. For example, if you
wanted to force 640 x 480 with 32k colors, add a line:
GMODE 110H
4. Do not telephone for assistance until you have tried the
steps above and assembled the following information:
- Brand and EXACT model. For example, "Diamond
SpeedStar" is completely useless because there were
many totally different and incompatible models
with this name. The SpeedStar 24 and 24X were
totally different.
- See what the Microsoft Diagnostic (MSD) program
has to say about your video display. For example,
with 1 megabyte of video memory (not the same as
main - DRAM - memory!!!) you can have 16 million
colors or 800 x 600 but not both.
- Print out results of VGAINFO with and without
UNIVBE and any vendor-specific VESA drivers you
can find.
- Review this entire file again.
What Kind of VGA Card Should I Buy?
-----------------------------------
That's a tough question because there are hundreds of different
models with new ones being introduced all the time and older
ones being discontinued just as fast. Some companies are
totally disinterested in you after you give them your money.
For example, I had a Diamond SpeedStar 24X which is capable
of 16 million colors. After searching the Diamond BBS and
talking to customer support a couple times I came to the sad
realization that they do not and will not supply a VESA
driver for this model to allow 16M colors. This is one
of the few models that UNIVBE does not handle properly.
I now happen to be using a Hercules Dynamite with 2 meg of
video memory. This allows 16 million colors at 800 x 600.
All I can suggest is to take a copy of VGAINFO to your local
computer store and use it to test for compatibility with a
particular model before buying. Do not settle for anything
that requires a VESA driver if such things still exist.