RoboCAD Technical Bulletin #1000
There is little standardization among the different vendors of SuperVGA display boards. If the specific board you are using appears in the list of supported displays, simply select it, and all will be well. If it does not, you may have to determine some details about your board, and tell RoboCAD about them by means of a "patch file." Please note that simply selecting the SuperVGA driver will not usually work.
Compatible SuperVGA boards
Some VGA boards claim compatibility with other well-known boards,
such as the Paradise board, from Western Digital. If your board uses the
same mode numbers as the compatible board, and the compatible board is
listed in the initial configuration, select the compatible, and all will
be well. If your board is hardware compatible but uses different mode numbers,
it will still work, but only after you create a patch file for it.
What happens if I get it wrong?
The most likely symptom of RoboCAD not being correctly configured
for your video card is that it will appear to "hang" at the name
and address screen, after selecting " 1 Run RoboCAD "
from the system menu. It has not actually hung: it is displaying a graphics
screen which you cannot see, because the mode switching is wrong. The difference
is academic, however, as you will have to re-boot your computer.
What is mode switching?
All SuperVGA cards that we have seen are capable of displaying
text and graphics in a number of different modes. Some of these modes are:
40 column by 24 line monochrome text, 80 column by 24 line color text,
CGA graphics, EGA graphics, and VGA graphics. The function of the mode
number is telling the card which kind of display it should work like. Changing
from one mode (for example, 80 column, 24 row, color text) to another (like
EGA Graphics) is done by sending the card a new mode number.
Why do I suddenly need to bother with mode numbers?
All the commonly used text modes, and all the graphics modes
up to 640 x 480 x 16 color VGA use standardized mode numbers. So to switch
into regular VGA, you don't need to know which particular card is installed:
they all use the same mode number for standard VGA. Unfortunately, for
800 x 600 x 16 color, and higher resolutions and numbers of colors, there
is no such standardization. You must determine the mode number that applies
to your card, and tell RoboCAD about it by means of a patch file.
What is a patch file?
A patch file contains (only) the mode number of the desired
display mode on your card. The number is expressed as a single 8 bit ASCII
character. For the SuperVGA driver, this must be the mode number corresponding
to 800 x 600 x 16 color graphics. The mode number is usually given as a
hexadecimal number in the range 00 to FF. Leading zeros are sometimes dropped.
To make the patch file, you will first need to convert the hexadecimal
number into a decimal one, which will be in the range 0 to 255. You can
use the table below to do this:
Hexadecimal to Decimal Conversion Table
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Making a patch file.
Making a patch file is quite simple, and is done in three steps.
1 Get the Hexadecimal Mode Number
First, find the table of mode numbers for your video card. It will
be in the documentation that came with it. Find the mode number corresponding
to 800 x 600, 16 color, graphics. This will be in hexadecimal notation,
a mixture of digits 0 - 9 and letters A - F. Note that it could legitimately
contain only digits (like 54), only letters (like AB), or both (like 3B).
For the purposes of this explanation, assume that the mode number for your
video card is 4E.
2 Convert to Decimal
The next step is to convert the hexadecimal number (in this example
4E) to a decimal number. Using the above table, look up 4E under a column
headed "Hex," and read the decimal number to the right of it,
under the column heading "Dec." In this case, it is 78. Make
a note of it.
3 Create the patch file
The patch file is called RZ_SCRN.MOD, and to create it you
can use the DOS COPY command. If you are operationg under DOS,
then from the Robo System Menu (1 Run RoboCAD, etc.)
press the escape (Esc) key once. Windows users should run the command prompt,
and switch to the RoboCAD directory. You will now be in DOS, and probably
will have a prompt on the screen similar to this:
C:\ROBO2O>
To check that you are in DOS you can type DIR and press the Enter key. A long list of files will scroll down the screen, and the DOS prompt will reappear at the bottom. At the prompt type:
COPY CON RZ_SCRN.MOD
and press the Enter key. Be careful to include the spaces between COPY and CON, and between CON and RZ_SCRN.MOD, and to type the underscore character (usually Shift Hyphen) correctly.
Next press these keys, exactly like this:
The message: " 1 file(s) copied " will appear. This means you have created the patch file.
The most likely cause of error is mis-typing, or using the number keys above the letter keys - you MUST use the numeric keypad. Of course, at step 2 you type the one, two, or three decimal digits you determined that represent the mode number for your specific video card.
Installing RoboCAD with the SuperVGA (800 x 600) Driver
Now that you know all about patch files, the procedure to install
the SuperVGA driver is quite straightforward. As usual, insert the RoboCAD
System diskette into drive A: and log on to that drive. Type RC
and press the Enter key. After a few moments, a list of displays will appear.
Select the SuperVGA driver, and then proceed with the installation, following
the screen prompts. If you are re-installing RoboCAD in the same directory
as previously, you will probably want to answer "N"
to the various questions about over-writing files. This will keep your
layer table and several other selections the way they were before. Before
you run RoboCAD, ensure that the RZ_SCRN.MOD patch file is in
the same directory as the video driver. In a stand-alone application this
will be the main RoboCAD directory. In a network or multi-user installation,
it will be the directory assigned to the environment variable RCAD_MACHINE.
What if it still won't work?
First, carefully check the mode number for 800 x 600 x 16 color
graphics. It must be this mode: the SuperVGA driver does not support other
resolutions or a different number of colors. Next, check the translation
of mode number to decimal. Finally, check the contents of the RZ_SCRN.MOD
file by using the DOS command:
TYPE RZ_SCRN.MOD
Check that the output is a single character, and use an ASCII table (such as can be found in Appendix D of the IBM PC BASIC Reference Manual) to verify that the ASCII value for the displayed character is the same as the mode number.
Finally, note that an 800 x 600 x 16 color display requires at least 256K of memory on the display card itself - that is, in addition to any computer memory.
All the Super VGA video cards that we have tested have worked properly as regular 640 x 480 x 16 color VGA boards. You may wish to re-install RoboCAD, in a different directory (RC_VGA for example), using the VGA display option. This will at least give you a system you can use while evaluating the SuperVGA problem. If regular VGA doesn't work, we can say with some confidence that there is a problem with your display board.
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