KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q40548: Using CALL INTERRUPT to Determine Current Video Mode

Article: Q40548
Product(s): See article
Version(s): 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom SR# S881221-34 | mspl13_basic
Last Modified: 15-JAN-1991

Microsoft QuickBASIC cannot determine which kind of video card is
installed on your machine. However, you can use the CALL INTERRUPT
statement to invoke ROM BIOS video interrupt 10 Hex, function 0F Hex
(Get Video Mode), to find out which video mode the machine is
currently using. From the information returned by this interrupt, you
can determine whether the video card installed is a monochrome card,
such as a Hercules or compatible card, or if it is a color card, such
as an IBM CGA, EGA, VGA, or compatible card.

This information applies to Microsoft QuickBASIC versions 4.00, 4.00b,
and 4.50 for MS-DOS. It also applies to Microsoft BASIC Compiler
versions 6.00 and 6.00b and Microsoft BASIC PDS versions 7.00 and 7.10
running under MS-DOS or in MS OS/2 real mode in the DOS compatibility
box.

In QuickBASIC versions 2.00, 2.01, and 3.00, you can use the CALL
INT86 routine instead of CALL INTERRUPT to invoke the video interrupt.

A BASIC application may need to determine whether or not the video
system in the machine it is running on is monochrome or color (that
is, to decide which colors to use for its output, etc.).

The ROM BIOS interrupt 10 Hex, function 0F Hex, will return the
current video mode. If this interrupt returns a 7 in the AL register,
the video card is a monochrome card and cannot support color. If it
returns something other than 7, the video card can support color;
however, this does NOT determine whether or not a color monitor is
connected to the computer.

Also, this function can determine where video memory for text mode
begins. If the function returns 7, video memory begins at the segment
paragraph address of B000 hex; otherwise, it begins at segment B800
hex.

For more information, see Page 415 of "Advanced MS-DOS" by Ray Duncan
(Microsoft Press, 1986) and Page 45 of "Microsoft QuickBASIC
Programmer's Toolbox" by John Clark Craig (Microsoft Press, 1988).

The following sample listing demonstrates the use of CALL INTERRUPT to
obtain the current video mode. This program can be compiled in
QuickBASIC 4.00, 4.00b, or 4.50 with QB /L QB.QLB or linked with
QB.LIB, which contains the INTERRUPT routine:

' Note: The QB.BI file includes the TYPE definition of RegType.
' If you are using BASIC PDS version 7.00/7.10, the include file
' name should be 'QBX.BI' and the Quick library should be QBX.QLB.

REM $INCLUDE: 'QB.BI'
FUNCTION GetVMode% STATIC
'--------------------------------------------------------------------
'Function to return the current video mode. The mode value returned is
'the same value returned from INT 10H, function 0FH -- Get Video Mode
'(7 = Monochrome card, other = color graphics card)
'--------------------------------------------------------------------
  DIM InRegs AS RegType, OutRegs AS RegType
  InRegs.ax = &HF00                    'INT 10H, fn. 0FH (get vmode)
  CALL INTERRUPT(&H10, InRegs, OutRegs)
  GetVMode% = OutRegs.ax AND 255       'AL returns the Video Mode
END FUNCTION

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.