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1990-09-03
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Reprinted Article From The Oct 17, 1989 PC Magazine Advisor Column
By: Lori Grunin Title: Beyond COM2
LETTER:
I've been stumped by IBM's design limit for serial ports. I'd
like to add a COM3 and COM4 beyond the two already installed in
my 386 clone. I put the new board in and properly set the jump-
ers, but when I attempted to set the communications parameters
via DOS's MODE command, I got "illegal device" error messages.
I've looked for books to tell me how to get around this problem,
but to no avail. Is there a software driver that I must install
to effect valid operation of these ports?
Thomas Emery
Goleta, California
RESPONSE:
IBM's original PC architecture supported only two COM ports, and
although compatible makers, and eventually IBM, added more serial
capability, there are still no standard addresses or IRQ (Inter-
rupt Request) lines for the additional ports.
The addresses for COM1 and COM2 are 3F8h and 2F8h, respectively,
with COM1 on IRQ4 and COM2 on IRQ3. When you install more serial
ports, COM3 usually uses 3E8h and IRQ4, while COM4 uses 2E8h and
IRQ3. Unfortunately, some I/O card makers like to blaze their
own trails; IBM even added uncommon COM port addresses and IRQs
to the long list of PS/2 eccentricities.
The DOS MODE command doesn't work with serial ports above COM2
because DOS gets its I/O information from the BIOS, which finds
out what's installed where in your system during the Power-On
Self-Test (POST). The POST checks only for the first two in-
stalled ports.
To get around this problem, communications software and some
serial peripherals (such as mice) will occasionally support
higher COM ports by addressing them directly, rather than making
DOS function calls. Of course, if your peripherals don't support
these extra ports or you need to redirect data using the MODE
command, that's where trouble arises.
There are a couple of public-domain utilities that allow you to
append your COM port information to the BIOS, making the ports
DOS-accessible. COMSET (COMSET.ARC) and Port Finder (PF2.ARC)
are available in the "general hardware" data library of the IBMHW
forum on Compuserve; Port Finder can also be obtained from its
author, mcTRONic Systems (7426 Cornwall Bridge Ln., Houston, TX
77041;(713)462-7687).
Both packages activate COM3 and COM4 (if they're installed, of
course), and require DOS 3.3 or later. They basically do two
things: activate the extra ports by giving the BIOS the address-
es, and provide utilities for swapping the addresses among the
different ports. Address-swapping allows programs that don't
support COM3 and COM4 to access them. Software that directly
addresses the ports will usually be unaffected.
Keep in mind, however, that you probably won't be able to swap
two ports that share an IRQ (such as COM1 and COM3) if you've got
a mouse attached to one of them, because the system will get
confused when the interrupt triggers.
Port Finder is the more flexible of the two. In addition to the
aforementioned features, it provides the same capabilities for
LPT3, including swapping among printer ports. Furthermore, it
lets you easily restore all your original settings.
Even if you think you've correctly configured the board, it can't
hurt to double check a couple of things. If you've got a bus
mouse, for instance, make sure that you're not stepping on its
IRQ; although interrupt sharing is one of the touted features of
the PS/2, PCs can't do it very well.
Also, don't leave any port holes-if you've got three, they should
be COM1,COM2, and COM3, not COM1,COM2, and COM4. [END]
Excerpt from July 1990 issue of "Vulcan's Computer Monthly"
10 Indispensable Online Utilities
Commentary by Ron Albright
Heaven knows that the communication voyager has enough
problems to deal with to find the jewels that await successful
connections. Incompatible baud speeds, word length, and stop
bits, noisy phone lines, busy signals, and other frustrations
stand in our way almost at every turn. We battle on, however,
knowing that once we succeed, a wealth of information and soft-
ware awaits.
Fortunately, there are several tools that every good commu-
nications should be aware of and keep in their armamentarium.
This article will examine 10 of these gems. Each handles a
specific problem the electronic journeyman faces, and alleviates
it to a large degree. Here are my picks.
PORT FINDER ...
As you are probably well aware, setting up a PC for communi-
cations is not a walk in the park. The first battle you face is
getting a modem to coexist with your current hardware. If you
are like me, and have more hardware hanging from your computer
than you can manage, you can run into problems right there. I
for example, currently (it changes from week to week) have a
Logitech ScanMan Plus and Trackman connected as Bus- devices
(their own cards rather than using my serial ports), a voice mail
board, and an internal modem configured as COM3. Since the PC
handles any hardware device through an "interrupt" ("IRQ"), you
can quickly run into conflicts that immobilize devices. You end
up doing the "jumper shuffle," changing those little jumpers,
replacing the boards, re-booting, and crossing your fingers-
hoping to find a montage that works.
Well with "Port Finder" (mcTRONic Systems, 7426 Cornwall
Bridge Ln., Houston, TX 77041; (713) 462-7687; Shareware,
$12.50), at least some of the guesswork is eliminated. PORT
FINDER is a very versatile program. It will display your
computer type, BIOS date, DOS version, display adapter type,
total base memory , extended memory, expanded memory and EMS
version. It will detect and display COM1 to COM4 and LPT1
to LPT3 ports that are responding with the actual HEX ad-
dress. Because PORT FINDER displays the HEX port addresses
you can also use PORT FINDER as a diagnostic tool. You can
swap COM or LPT ports addresses instead of swapping cables.
On AT systems Port Finder will check to see if a game port is
present and if so it will be added to the equipment list.
If you are using DOS 3.3 or higher and have COM3 and/or
COM4, PORT FINDER will activate both COM3 and/or COM4. DOS
will then recognize these ports and you will be able to use the
DOS MODE command. Most system information type programs such as
the Norton Utilities System Information (SI) program will
correctly indicate the number of serial ports that you have
including the COM3 and/or COM4 ports after you run PORT
FINDER. Any other programs that operate through DOS should
also accept COM3 and/or COM4 after you run PORT FINDER (if
the program does not allow you to enter COM3 or COM4 then you
will need to swap COM3 or COM4 with COM1 or COM2 before you run
such a program then select either COM1 or COM2 in said program).
If you have a new IBM PS/2 computer COM3 and/or COM4 will
already be activated . You can use PORT FINDER to reset both
COM and LPT port addresses in case you forget what
addresses have been swapped.
PORT FINDER can also be used in a BATCH file to detect which
COM ports are present. An Errorlevel is set for all possible
combinations. An example batch file COMMTEST.BAT is included.
Port Finder will work under Microsoft Windows and a .PIF in now
included with Port Finder. Due to the fact that Desqview moves
the COM and LPT port addresses to a nonstandard location, Port
Finder will not be able to properly work when Desqview is loaded.
For those, like me, who find themselves swapping hardware in
and out of a machine with great regularity, Port Finder is an
indispensable tool for managing your ports. I couldn't live
without it.
PKZip ... TELEDISK ...
PKware, Inc. Sydex
7545 N. Port Washington Rd. 153 North Murphy Ave.
Glendale, WI 53217 Sunnyvale, CA 94086
414-352-3670 408-739-4866
Shareware, $47 Shareware, $25
LIST ... MSGVU ...
Vernon Buerg Dave Briccetti and Associates
139 White Oak Circle P.O. Box 1713
Pateluma, CA 94952 Lafayette, CA 94549
$29.95 Shareware, $30
VDE ... Elsewhere ...
Eric Meyer INTERLINK TECHNOLOGIES
401 12th Ave SE - # 139 1222 5th Street
Norman, OK 73071 Sarasota, FL 34236
405-329-5777 Updates $20
Site Licenses $50
ZMODEM ... Checkup ...
Omen Technology Incorporated's Levine & Associates
17505-V 9405 Bustleton Ave.
Northwest Sauvie Island Road P.O. Box 14546
Portland, Oregon 97231 Phila., PA 19115
Shareware, $20 215-333-8274
$24.94
Procomm 4.2 ...
DataStorm Technologies
P.O. Box 1471
Columbia, MO 65205