Dec 272017
Add COM3 and/or COM4 if your BIOS does not support it. C source included.
File ADDPORT.ZIP from The Programmer’s Corner in
Category Communications
Add COM3 and/or COM4 if your BIOS does not support it. C source included.
File Name File Size Zip Size Zip Type
ADDPORT.C 2528 727 deflated
ADDPORT.DOC 2496 1077 deflated
ADDPORT.EXE 9998 5986 deflated

Download File ADDPORT.ZIP Here

Contents of the ADDPORT.DOC file


This program was written to address a few very specific problems.

1. Certain makes of BIOS do not support beyond COM2. This means
that at the power-up equipment check they do not add COM3 and
COM4 to the low-memory equipment list and/or do not add the
appropriate base addresses to the BIOS data area even though
you may have a modem or I/O card configured as COM3 or COM4.

2. This same problem seems to occur occasionally as a result of
conflicts between various boards.

3. The equipment list may be incorrect if an internal modem is
installed as COM2 (or COM3 or COM4) with no COM1 serial port
in the computer.

The result of all these problems is that any serial I/O involving DOS
redirection will not work properly. For instance, one may use COM3
successfully with a terminal program until "shelling out of Host
Mode," which often involves DOS CTTY redirection. Another symptom
would be a "WRITE FAULT ERROR WRITING DEVICE COMx" following simple
redirection such as "DIR >COMx".

ADDPORT will write information about your serial ports into the
appropriate low-memory areas. It may be used to make your system
aware of your specific serial hardware.


example: addport com3 3e8

If the COM port is already listed in the low-memory equipment list,
ADDPORT will simply change the base address to what you specify in
the second argument to the command. Typing ADDPORT alone will show
what ports are currently in the equipment list along with their base

A typical use of ADDPORT would be to put the line ADDPORT COM3 3E8 in
the autoexec.bat file for BIOS versions that do not support COM3.


COM1 - 3F8 the addresses for COM1 and COM2
COM2 - 2F8 are pretty much a standard

COM3 - 3E8 these addresses for COM3 and COM4 are
COM4 - 2E8 are common, though it's sometimes reversed


COM1 - 3F8
COM2 - 2F8
COM3 - 3220
COM4 - 3228

Currently ADDPORT does not support beyond COM4.

 December 27, 2017  Add comments

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