DOCUMENT:Q154819  11-JAN-2001  [vbwin]
TITLE   :HOWTO: Access PC Bus Devices in Visual Basic for Windows
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:
OPER/SYS:
KEYWORDS:kbGrpDSVB

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
 - Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
-------------------------------------------------------------------------------

SUMMARY
=======

This article describes how to access PC bus devices in Visual Basic for Windows.
Many programs written in MS-DOS versions of BASIC used Peek, Poke, and In and
Out to access the PC bus directly. This functionality is not supported in Visual
Basic for Windows.

MORE INFORMATION
================

MS-DOS did not implement any memory protection; this meant that BASIC
applications were able to write to any memory location directly, giving fast
access to the hardware of the PC, including custom hardware that plugged into
the expansion ports. In a multitasking environment it was clearly unacceptable
for an application to write to memory owned by another application. The hardware
port addresses are deemed to belong to the system. Accordingly, applications are
unable to write directly to the PC bus addresses.

It is often desirable to port MS-DOS BASIC code to a Windows environment.
However, programs that attempt to control custom devices will fail to port
directly.

Effectively, there are two potential solutions:

1. Use a custom Virtual Device Driver (VxD). It is likely that the manufacturers
   of more popular custom devices will have a VxD. However, there may be no VxD,
   or the VxD interface may be structured differently.

   Versions of Visual Basic prior to 5.0 may require extra steps to use a VxD.
   Versions prior to 5.0 did not have the AddressOf operator needed by many VxDs
   to use Callback procedures. The workaround is have the Visual Basic program
   call a C DLL which would in turn call the VxD.

2. Use a third-party DLL or OCX that emulates the functionality. There are a
   number available commercially or as shareware.


REFERENCES
==========

For more information, please see the following articles in the Microsoft
Knowledge Base:

   Q29519 : How to Write a Driver for a Custom Hardware Device

   Q87004 : Differences Between QuickBasic and Visual Basic Statements

Additional query words: kbVBp400 kbVBp500 kbVBp600 kbVBp kbdsd kbDSupport kbintluk kbNoKeyWord

======================================================================
Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600 kbVB400Search kbVB400 kbVB16bitSearch
Issue type        : kbhowto

=============================================================================

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.

Copyright Microsoft Corporation 2001.