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push_pop.doc
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1985-08-24
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..PUSH-POP.DOC by Larry Lockwood, Orange County IBM PC Users Group
Push.com is designed to take "snapshots" of CRT displays and
store them in a file. POP.COM restores the screen image and allows
you to modify almost everything.
PUSH.COM, once loaded, remains resident in memory. When it
has been loaded, the CRT display can be copied to a screen-image file
by concurrently depressing the Shift-PrtSc keys. You can no longer
use Shift-PrtSc to copy the CRT display to the printer until you
reboot the computer.
The syntax for loading PUSH.COM is:
PUSH drive:filename (do not use a file extension)
For example, suppose PUSH.COM is on the diskette in drive A
and you wish to create a series of screen-image files named SNAPSHOT
on a diskette in drive B. The installation entry would be:
PUSH b:snapshot
When you first press the Shift-PrtSc keys, PUSH will create a
screen-image file named SNAPSHOT.001 on the diskette in drive B. The
second time the Shift-PrtSc keys are pressed, another screen-image file,
SNAPSHOT.002, will be created, and so on.
When you save a text screen, the corresponding screen-image file
size is 4100 bytes. A graphics screen will create a corresponding 16,300
byte screen-image file. You can copy approximately 88 text images or
22 graphics images to a 360KB diskette. Once you create a series of
screen-image files, use the DOS RENAME command to give your files more
meaningful names.
POP.COM restores a screen-image file to the display. The syntax,
using the example above, would be:
POP B:SNAPSHOT.001
When I first tried POP.COM, I found that it always restored
graphics images on a black background with the palette ) foreground
colors (cyan, white, and magenta). After digging through the Technical
Reference Manual, I concluded that these are the default IBM PC color
settings and there was no way that I could rewrite PUSH.COM to capture
the Color Select Register setting (it's a write-only register). My
only choice was to modify POP.COM to provide a means of restoring the
original colors via function keys. While I was at it, it occurred to
me that the function keys could also be used to change the attributes
of individual characters in text files.
One thing led to another and what finally evolved was a POP.COM
program that restores the original screen image and allows you to modify
almost everything. The function keys do the following:
F1-Changes background colors of graphics images
and border colors of text images.
F2-toggles graphics foreground colors back and
forth between palettes 0 and 1.
F3-Selects background colors for individual
characters in text mode.
F4-Selects foreground colors for individual
characters in text mode.
F5-Exercises your left forefinger.
F6-Controls individual character blinking.
Shift-F7-Reloads the original screen-image
file again. (Use this if you've made
modifications that you don't like and
decide it would be quicker to just start
all over again.)
Shift-F8-Saves modified image back to the
disk with the original filename. (Careful-
this destroys the original image.)
Esc-Exits and returns to DOS without saving
modified screen.
Other keys-The cursor keys are functional in
text and graphics modes, as are the alpha-
numeric keys. In graphics mode, however,
the cursor is implemented as a one-pixel
dot that moves around the screen. It starts
in the upper left-hand corner of the screen,
but you won't see it until one of the cursor
keys is depressed. The Home key moves the
cursor up-left and the End key moves it
down-left. The Ctrl key, when used in con-
junction with the alpha-numeric keys, produces
the IBM PC symbols associated with the various
control codes. If you have the IBM Technical
Reference Manual, the symbols are shown on page
C-1. If not, just experiment.
These programs were witten specifically for an IBM
PC with a Color/Graphic Monitor Adapter. Any compatibility
with other PC's or adapters is strictly coincidental. These
programs will not work with a Monochrome Dispay Adapter,
because both PUSH and POP read from, and write to,the
color display memory at B800H. Also, the IBM Monochrome
Dispay Adapter has no graphics capabilities.
Perhaps the simplest way to provide continuous,
sequential viewing of screen-images files is to create
BATch files with the filenames separated by PAUSE commands.
Note: This file appeared in the August 1985 issue of
EXCHANGE, published by & copy write by International
Business Machines. Exchange is distributed free of
charge to IBM computer user group members. PUSH.COM
& POP.COM were downloaded from the IBM PC User Group
Support Electronic bulletin board system in Boca Raton,
Florida. The electronic bulletin board system is
available to all user group members.