Article: Q95103
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.0,5.0a,6.0,6.2,6.21,6.22
Operating System(s):
Keyword(s):
Last Modified: 19-NOV-1999
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22
-------------------------------------------------------------------------------
SUMMARY
=======
QBasic supports only serial communication ports COM1 and COM2. COM3 and COM4 are
not supported. QBasic supports no more than two serial communications ports
because QBasic is a subset of Microsoft QuickBasic 4.5, which also does not
support COM3 and COM4.
MORE INFORMATION
================
Microsoft does not support more than two serial COM ports with Microsoft
QuickBasic versions 1.0 through 4.5 because of a combination of the following
factors:
1. MS-DOS 3.3 is the first operating system to support COM3 and COM4. It uses
ROM BIOS Interrupt 14h to access those COM ports.
2. The ROM BIOS of a computer system must support COM3 and COM4.
3. COM3 and COM4 have not been widely available on computer systems.
4. A larger code size would be required for support due to the possible conflict
created by IRQ sharing; COM1 and COM3 use the same IRQ as do COM2 and COM4.
Additional query words: 6.22 5.00 5.00a 6.00 6.20 6.21 5.0a 5.0
======================================================================
Keywords :
Technology : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version : MS-DOS:5.0,5.0a,6.0,6.2,6.21,6.22
=============================================================================