[ct-user] HOW MANY COM PORTS - update
Setzler, James M
Setzler, James M" <Setzler_James_M@code80.npt.nuwc.navy.mil
Mon, 1 Dec 1997 11:52:08 -0500
A short time ago I posed a question regarding the maximum number of COM
ports usable at any one particular time. Thanks to Hank/K8DD,
Glenn/KB1GW, Mike/K1NR, Jim/AD1C, and Don/K2KQ for their inputs. Their
responses are attached below. I received a few requests to pass along
any information I might learn from this, so I've provided a few details
on what I've encountered to date.
The short answer is: you can have a bunch of COM ports connected and
open at once.
It seems that two of the more significant controlling factors are the
ability to assign the ports separate high COM addresses and high IRQs.
I had added a Siig board a few years ago that added just one additional
serial port to the two I already had open with the installed Controller
card. To expand, I recently activated the third serial port available
with the existing Controller for a total of for serial ports. That
was OK. Then, to expand further, I found a 4 serial port high speed
board from Jameco (significantly cheaper than Dalco for this board). It
has 2 DB9 and 2 DB25 ports that allow COM 1 - 8, as well as high IRQs
values, to be assigned via jumpers. I've only used one of the new COM
ports so far, but it looks like I'm headed in the right direction.
Right now I have the following connected:
COM IRQ Device
1 4 Serial Mouse
2 3 Radio (FT-1000)
3 5 Packet TNC (PK-88)
4 3 Internal Modem
5 10 RTTY TNC (PK-232)
- 7 DVP (K1EA's)
- 14 CD ROM
LPT1 ? Printer
Note that the Radio and Modem are assigned the same IRQ. I never use
the radio and modem at the same time and, so far, there's no conflict in
the system. They both remain connected all the time and work fine
within their separate applications.
So far I've successfully run CT and EQF-Log with the mouse, rig control,
and packet active at once. No problems. I've also run NA with radio
and packet. DVP seems OK with both CT and NA. RTTY by WF1B has worked
successfully with mouse, radio control, and the RTTY TNC. I need to
check out a few more things, but I don't see any reason why I can't add
additional COM ports and IRQs.
As an informational addendum, the various programs have been run within
separate WIN95 DOS windows at the same time, as well. I've had RTTY by
WF1B and Log-EQF running FB in two separate windows. They both couldn't
have rig control at the same time, but, I think, they both (all three,
actually) shared the mouse OK. I haven't yet tried all of the
possible combinations and permutations, but the applications I've run so
far seem to work equally well either in a WIN95 DOS window, booted
directly to the WIN95 DOS prompt, or booted to my previous version of
DOS (v 6.2).
For some reason, WIN95 does not recognize COM 3 or 5 in the above
configuration. When I check MY COMPUTER/CONTROL PANEL./SYSTEM/COM PORTS
it only shows ports 1, 2, and 4. When the system initially boots it
shows the four serial address for COMs 1 - 4, but not COM 5 (I guess
that's the BIOS data screen that flashes by so quickly). So, even
though all of the COM ports are not identified for some reason, they
seem to be there when they're needed, and that's what's important!
I've a few more items I want to add to the system as time and money
permit: Radio #2, Radio 1/2 switching, rotator control, SoundBlaster,
??? . . . (gawd, where will it all end !!)
Thanks again for the help
73 James / k1sd
+++++++=========++++++++++ ORIGINAL MESSAGE ++++++++++=========++++++
Here's a real basic computer question.
I've a 486 DX4/100 mother board with WIN 95 installed. The MB does not
have on-board controllers. I usually run CT or NA or Loq-EQF booted to
the WIN95 DOS prompt or boot to DOS 6.2. I don't usually use the WIN95
DOS window; although sometimes I do with no real apparent problems.
I want to expand the computers connections capabilities by having almost
everything connected to it at one time. I want to be able to connect
mouse, Radio #1, Radio #2, Packet TNC, RTTY TNC, modem, DVP, Printer,
2-radio switch, etc, etc.... you get the picture. This takes a lot of
How many ports can I have active at one time? Am I limited to
a total of 4 COM and 3 LPT ports operating at one time? Or, with the
appropriate I/O boards installed, could I have, say, 6 COM and 2 LPT
ports active at one time?
If I am limited to no more than 4 COM and 3 LPT ports active at
any one time, can I have 6 serial and 2 parallel devices physically
connected to the computer all the time and, with various programs, use
no more than the requisite 4 COM / 3 LPT ports at one time?
thanks & 73 James / k1sd
=======++++++++========== REPLIES =========++++++++++==========
You have basically two options, but depending on what else you have,
you might run out of IRQ's...
There are many 4 port COM boards that have "high" IRQ's for COM3 and 4.
These are available at Comp-USA, Computer City, etc. They don't need
special drivers, however, if you want to use all 4 ports at the same
time, you need to use seperate IRQ's. There are also 3 port printer
cards that can be configured the same way. With those 2 boards, you
spend 7 IRQ's. There are only 9 available at the most.
However, CT Version 9 does have a driver for a Digiboard (or is it
Digiport) 8 port serial card that uses a single IRQ. These require
special drivers for Windows, DOS, CT9 etc. because of the IRQ sharing.
They are also quite expensive last time I looked. They may or may not
work with some software.
I use a 4 port card from SIDE that I bought at Comp-USA (Around $100
with all 4 ports populated with UART's). I also have a PS/2 mouse which
lets me use all 4 serial ports for other things. A mouse must be on
COM1 or COM2 or be a PS/2 or BUS type mouse.
The answer to your question depends somewhat on the software you
running. If you are running straightforward DOS applications, you are
generally limited by the number of spare interrupt lines (IRQs) you
have. Simple-minded software will usually want a single interrupt to map
to a single port.
I run as many as 6 COM ports and 2 LPTs on my Dell 100 MHz
machine comes with 2 COM ports and 2 LPTs. I added a COM port board with
4 16550 UARTs on it and a completely configurable set of base memory
addresses and IRQs. It's sold at Comp USA for about 80 bucks with the
four ports. If your software will tolerate it, you can have separate
interrupts for all of the ports, but you might have to disable (or swear
to not use) something on your machine that uses one you need when you
are running something that would conflict.
There are also boards that use shared interrupts (as many as 8
ports). I don't have any experience with them, but they are mentioned on
the CT support site on the internet. CT has special drivers to handle
them (there's also a 4-port card).
An alternative you might want to think about is to add an
adapter (about the same cost as a COM port). As long as your software
will accommodate it, you can hang all sorts of stuff on an Ethernet
party line. K1TTT has written an Ethernet driver for CT...(see his stuff
on the CT support pages).
Win 95, through its Plug and Play interface can use dynamic
sharing and hide most of the above restrictions. However, I would NEVER
run CT under Win95 in an important contest (and aren't they all
We've just been faced with a similar problem networking laptops
J39A operation. Laptops don't have many COM ports and usually use up
interrupts to run things like IR adapters. The only decent way to add
COM ports to a laptop is through a PCMCIA card. Not for the
As long as the IRQs are unique, I think you can have up to 8 separate
ports. The trouble of course is finding that many spare IRQs, but it
not be that hard:
Also see the CT web page, where (if you pound around enuf) you'll find a
sub-page of multi-com port venders--with pricing...
I have had 6 COM ports active in Win 95. IRQ's 4,3,2,5,7,11. Ran out
and initiative, but not IRQ's or I/O addresses. The boards that I have
are two COM ports with DIP addressable I/O address and available IRQ
jumpers for 2,3,4,5,6,7,10,11,12,14,15. Real flexible. UART is 16450 -
much over 9600 baud, but then again, neither can I.
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