Why Basic Doesn't Support COM3 or COM4 Serial Port (21789)
The information in this article applies to:
- Microsoft QuickBASIC 1.0
- Microsoft QuickBASIC 1.01
- Microsoft QuickBASIC 1.02
- Microsoft QuickBASIC 2.0
- Microsoft QuickBASIC 2.01
- Microsoft QuickBASIC 3.0
- Microsoft QuickBASIC 4.0
- Microsoft QuickBASIC 4.0b
- Microsoft QuickBASIC 4.5
- Microsoft BASIC Compiler for MS-DOS and OS/2 6.0
- Microsoft BASIC Compiler for MS-DOS and OS/2 6.0b
- Microsoft Basic Professional Development System for MS-DOS 7.0
- Microsoft Basic Professional Development System for MS-DOS 7.1
This article was previously published under Q21789 SUMMARY
QuickBasic does not support more than two communications ports.
QuickBasic supports serial devices COM1 and COM2, but does not support
COM3 or COM4. Some computers supply COM3 and COM4 devices, but these
are not supported in QuickBasic.
This information applies to Microsoft QuickBasic versions 1.0, 1.01,
1.02, 2.0, 2.01, 3.0, 4.0, 4.0b, and 4.5; to Microsoft Basic Compiler
versions 6.0 and 6.0b; and to Microsoft Basic Professional
Development System (PDS) versions 7.0 and 7.1 for MS-DOS.
MORE INFORMATION
QuickBasic and Basic PDS currently support serial communications ports
COM1 and COM2 through the use of the OPEN "COM" statement. For more
information about using COM1 and COM2, see the OPEN statement in the
language reference manual for Microsoft QuickBasic versions 4.0 and
4.0b, for Basic Compiler 6.0 and 6.0b, and for Basic PDS 7.0 and 7.1.
See also the OPEN statement in the online Help in QB.EXE for
QuickBasic 4.5 and in QBX.EXE in Basic PDS 7.0 and 7.1. See also the
TERMINAL.BAS program released with these products.
Why Basic Doesn't Support COM3 or COM4
Adding support for COM3 and COM4 communications ports would require
a larger code size in the development environment, compiler, and
run-time module. Also, COM3 and COM4 support requires MS-DOS 3.3 or
later, plus implementation in the computer's BIOS. Microsoft Basic
products are targeted to run on as wide a variety of systems as
possible, but COM3 and COM4 have not been widely available on the
existing hardware base.
A combination of these and other factors have resulted in Microsoft
not currently supporting COM3 and COM4.
COM3 and COM4 Support from Third-Party Developers
To access COM3 and COM4, it may be possible for a compiled Basic
program to call third-party library routines listed in catalogs, such
as the "Provantage Buyer's Guide," which can be obtained
by calling Provantange at (800) 336-1166 in the United
States; (800) 225-1166 in Canada; or (216) 494-8899 (customer
service).
For example, you can use this catalog to find the number for Software
Interphase, (401) 397-2340, to determine if their product QuickComm
supports COM3 and COM4 called from a compiled Microsoft Basic program.
Also, Crescent Software (800-35-Basic) offers a product called
PDQComm to support COM3 and COM4 from Microsoft QuickBasic versions
4.0, 4.0b, and 4.5, and from Microsoft Basic PDS versions 7.0 and 7.1
for MS-DOS.
When purchasing add-on products, make sure the vendor has tested its
product under your version of Basic. For a list of other catalogs,
query on the following words:
programmer and tool and catalog
| Modification Type: | Minor | Last Reviewed: | 8/16/2005 |
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| Keywords: | KB21789 |
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