Contents of the ZAP.DOC file
EGAZAP.COM and VGAZAP.COM by Mark Adler Pasadena, CA 1988.
ZAP is a resident utility that blanks the screen after a specified
period of inactivity. The ZAP.ASM program actually generates two
different programs depending on the assembler options: EGAZAP and
VGAZAP. The first is for the IBM Enhanced Graphics Adapter or
compatibles, and the second is for IBM PS/2's, the IBM Video Graphics
Adpater, and comaptibles. From here on, ZAP will be used to mean EGAZAP
or VGAZAP, whichever is appropriate for your hardware.
To install ZAP, simply put the command ZAP in your AUTOEXEC.BAT file.
From then on, when there is five minutes of inactivity at the keyboard,
ZAP will blank the screen until any key (even just a shift key) is hit.
The time can be changed with a command line option which specifies the
time in seconds. For example:
will install ZAP (if not already installed) and change the time to 10
You can also turn the installed ZAP on and off using ZAP. For example:
will turn off the installed ZAP, so it will not blank the screen. Then
will turn ZAP back on.
ZAP can also be installed in the "off" state, awaiting a "zap on"
command, simply by using:
in AUTOEXEC.BAT. You can also specify on or off along with a new
inactivity time. For example, the command:
zap off 600
in AUTOEXEC.BAT will install ZAP in the off state with a 10 minute
inactivity time. Then a subsequent "zap on" will turn it on. The time
must be in the range of one to 3600 seconds (one hour). Specifying a
new time does not change whether ZAP is enabled or not and turning ZAP
on or off does not change the time. Also, the two options can be in
either order. For example, "zap 600 off" does the same thing as the
example above. If ZAP is already installed, subsequent invocations of
ZAP will not install it again. If the command:
is entered after ZAP is already installed, this has the same effect as
the command "zap on", that is it turns on ZAP if it was off.
ZAP turns the display back on not only when any key is hit, but also if
any video BIOS calls (int 10h) are made. Since most application
programs seem to bypass the BIOS for video, this added feature has
There are a few, rare programs that also completely take the keyboard
from the BIOS, in which case ZAP can no longer find out when keystrokes
occur. An example is STSC APL (a programming language). In this case,
ZAP will blank your display, even though you have been merrily typing
away for the last five minutes in the application. And the only way to
get the display back on is to return to DOS (assuming you can get out
while driving the application blindfolded). For such applications, you
should include the commands "zap off" and "zap on" in a batch file that
runs the application to disable ZAP before entering and enabling ZAP
after leaving the application. You will quickly discover if you have
any such applications.
Version history -
1.0 18 Nov 1988 First public version
1.1 14 Dec 1988 Fixed bug in EGAZAP
Feel free to send any problems with or comments on ZAP to:
P.O. Box 60998
Pasadena, CA 91106