SIMCGA - A CGA SIMULATOR FOR MONOCHROME
GRAPHICS CARDS


SIMCGA and this document copyright 1987 by C. P. Guzis
All rights reserved.

Reproduction of SIMCGA or this document is prohibited
without the express written permission of C. P. Guzis.

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This is version 4.1 of SIMCGA, released in September, 1987. If you
have questions or inquiries concerning this product, please be
sure to mention that this is the "July 1987" version of SIMCGA.


-WHAT IS THIS PROGRAM?-

SIMCGA is a program written for those IBM PC or "compatible"
users who have a Hercules Monochrome Graphics adapter card or
Hercules-compatible display adapter and would like to be able to
run programs requiring the IBM Color Graphics display adapter
facility.


-WHAT WILL AND WON'T WORK?-

Because SIMCGA is a software product, there are certain hardware
limitations on its use. Programs which access the Color Graphics
Adapter hardware registers directly generally will not operate in
a satisfactory manner - the hardware just isn't there to interact
with! In general, try running the program - you won't clobber your
disks if it doesn't work.

SIMCGA will not work with a plain old IBM monochrome adapter or-
with an Enhanced Graphics Adapter (EGA).

Version 4.0 incorporates support for non-DOS diskettes which con-
tain their own operating system rather than using DOS.


-WILL SIMCGA RUIN MY MONITOR?-

No. SIMCGA programs your display adapter so that the frequencies
generated are very much within the specifications of your
monochrome monitor. (18.5 KHz horizontal and 53 Hz vertical).
However, you should avoid using programs which will cause
problems with a Hercules or Hercules-compatible card. Most
"screen-saver" programs are in this category and may cause damage
to your monitor whether or not you are using SIMCGA.


-HOW DO I USE SIMCGA?-

To run SIMCGA, copy the programs (all files ending with .COM) on
this disk to the directory or diskette where you normally keep
your system programs. Then decide if you want to run in "stand-
alone" or DOS mode. Standalone mode is used with programs which
"boot up" without DOS; many games fall in this category. DOS mode
is used with programs which require DOS to execute. In either case,
first load DOS.

If you want to run a "standalone" program, enter -

SIMCGA S
( means press the "Return" key on your keyboard). SIMCGA
will display the product notice and request that a program diskette
be inserted into diskette drive "A". Place the diskette containing
the program you wish to run in the "A" drive and press any key. The
program will be loaded and begin execution in CGA emulation mode.
To remove SIMCGA from your computer, turn the computer's power switch
off, then on again. A Ctl-Alt-Del keyboard reset will, on most com-
puters, also cause SIMCGA to disappear.

If you want to run a DOS-based program enter -

SIMCGA

( means press the "Return" key on your keyboard).
SIMCGA will load its resident part (or tell you why it won't) and
set your display to 80x25 color text mode.Your display adapter
will appear to be a Color Graphics Adapter board to most programs
accessing it.

To resume ordinary monochrome text operations, enter -

MONO

To go back to CGA 80x25 mode, enter -

CGA

To set 640x200 high-resolution graphics mode, enter -

HIRES

To set 320x200 medium-resolution graphics mode, enter -

MEDRES

For most applications, MONO and CGA will suffice to set either
monochrome or graphics modes.

To completely remove SIMCGA from your computer's memory, enter -

RMVCGA

Like the standalone mode, the DOS mode SIMCGA will disappear
with a Ctl-Alt-Del keyboard reset.

If you desire, you may also run DOS as a standalone program.
Just insert your DOS diskette when the program diskette is re-
quested.

-IF YOUR PROGRAM RUNS TOO SLOWLY-

Some programs, especially games, require large amounts of atten-
tion from your computer. SIMCGA also requires some of your com-
puter's attention to keep the display looking good. If you find
that there is not enough computer to go around, you may instruct
SIMCGA to use less of your machine's resources. However, nothing
is free, and the display will exhibit more "ghosting".

To change the amount of time SIMCGA "steals" from your application,
use a number from 0 to 9 on the SIMCGA command line. 0 tells
SIMCGA to use the largest portion of your computer's power to
maintain the display; hence programs will run more slowly.9 tells
SIMCGA to use the least practical amount of your computer's
power to maintain the display; you will however, see the greatest
amount of "ghosting". If you are using SIMCGA in the "standalone"
mode, the number may either precede or follow the "S" parameter.

For example -

SIMCGA 3
SIMCGA S 2
SIMCGA 5S

are all forms that SIMCGA can understand.


-"IT LOOKS LIKE I'M LOOKING THOUGH A SCREEN WINDOW"-

If you're running a program (most likely a game) and you notice
that the display has fine black lines running horizontally across
it, try using SIMCGA up with the letter "I" on the command line.
This has to do with how SIMCGA deals with the timer on your com-
puter, but should not otherwise affect program operation. The
"I" parameter may be combined with any of the others.

For example -

SIMCGA I
SIMCGA I 2
SIMCGA 3SI

are forms acceptable to SIMCGA.


-STARTING OUT IN GRAPHICS MODE-

Some programs start execution in one of the graphics modes; SIMCGA
defaults to the 80x25 text mode when it intializes. To get SIMCGA
to come up in either the 320x200 or 640x200 graphics modes, use the
letters "M" for medium resolution (320x200) or "H" for high resolu-
tion (640x200) on the SIMCGA control statement. "M" and "H" may be
combined with other SIMCGA options; for example -

SIMCGA 5ISH
SIMCGA H 3

are forms acceptable to SIMCGA.


-THINGS YOU MAY NOTICE-

"Ghosting" of moving graphics images - this is just the way the
program operates and is nothing to be worried about.

Some lines are thicker than others in graphics mode - SIMCGA
fills out the displayed image by "doubling" every other line.


-COMPATIBILITY-

When you run SIMCGA, you may get a message to the effect that
SIMCGA has detected that your monochrome graphics adapter is not
CGA-compatible. What this is trying to say is that not all
"clones" -accurately- reproduce the functionality of the Hercules
monochrome graphics adapter. SIMCGA will attempt to make the
best of the situation; however, the simulation may not be perfect
in the 80x25 and 40x25 CGA text modes. Graphics modes will work
correctly regardless of the brand of monochrome graphics adapter
used.


-DISTYPE - DETERMINE DISPLAY TYPE-

A utility program for use in batch files is provided for the purpose
of determining the type of the current active display adapter. DIS-
TYPE may be invoked by the following statement -

DISTYPE

DISTYPE returns an error code corresponding to the display adapter
configuration found -

0 A monochrome adapter with no graphics capabilities has been
detected.
1 SIMCGA is currently installed with a monochrome graphics
adapter.
2 A Color Graphics Adapter (CGA) is in use.
3 An Enhanced Color Graphics Adapter (EGA) is in use.
4 A monochrome graphics adapter (HGC) is installed, but SIMCGA
has not been run.


The code returned by DISTYPE may be queried by use of the DOS "IF
ERRORLEVEL" statement (consult the DOS reference manual for details).
Here is an example of the use of DISTYPE in a batch file -

ECHO OFF
DISTYPE
IF ERRORLEVEL 4 GOTO DOSIM
IF ERRORLEVEL 3 GOTO EGA
IF ERRORLEVEL 2 GOTO CGA
IF ERRORLEVEL 1 GOTO SETCGA
ECHO *** ERROR ***
ECHO GRAPHICS ADAPTER REQUIRED
GOTO QUIT
:DOSIM GOT HGC WITH NO SIMCGA YET
SIMCGA
GOTO QUIT
:EGA GOT EGA, OKAY
:CGA GOT CGA, OKAY
GOTO QUIT
:SETCGA SIMCGA AROUND, ENABLE EMULATION
CGA
:QUIT COMMON EXIT POINT


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"Hercules" is a trademark of Hercules Computer Technology; "IBM" is a
trademark of International Business Machines Corporation.