Q35241: Using Dual Video Display Cards and Monitors with QuickBASIC

Article: Q35241
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 16-DEC-1989

QuickBASIC allows limited use of two video-display system cards within
the same application if the host computer has both a color video card
and monitor, plus a monochrome card and monitor. Only the default
display (the one that was active when QuickBASIC was invoked) has a
cursor and graphics capability.

The method requires OPENing "CONS:" FOR OUTPUT AS #n, POKEing the
video-mode specifier of the desired output screen into memory location
449 hex, then using a PRINT #n to display text on the desired output
monitor. It is important to use "CONS:", not "SCRN:" in the OPEN
statement. "SCRN:" is always associated with the default display.

This information applies to Microsoft QuickBASIC Versions 4.00 4.00b
and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b for
MS-DOS, and to Microsoft BASIC PDS Version 7.00 for MS-DOS.

There is no practical way to put graphics images on the secondary
display in QuickBASIC. See Pages 54 and 55 of "The Peter Norton
Programmer's Guide to the IBM PC" (published by Microsoft Press, 1985)
for a list of settings for the video mode. The following code example,
which uses 7 (for a monochrome adapter) and 3 (for 80-column text, 16
colors), works with a computer that has a Hercules-compatible
monochrome adapter and an EGA color display:

OPEN "cons:" FOR OUTPUT AS #1
DEF SEG = 0
PRINT #1, "This should be on the DEFAULT Screen."
POKE &H449, 7
PRINT #1, "This should be on the MONO Screen."
POKE &H449, 3
PRINT #1, "This should be on the COLOR Screen."

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