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Accessing COM Ports Past COM4

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  • Accessing COM Ports Past COM4

    Hi, Wondering the best way (or if a way) to access COM ports say 4-16 directly from DOS. No Windows. COM4-COM16 Direct read/write in a DOS 6.22 only environment with PB 3.5?

    Any suggestions or rude noises would be appreciated.

  • #2

    I use all four COMM ports all the time simultaneously in DOS apps.
    I've never tried to add more. I personally use Ray Gwinn's SIO code
    utility which I paid for in OS/2 since I work in OS/2 DOS-VDM's a

    If you read the documentation on X00 and VX00, you will discover that
    Ray describes that he can furnish management code for more than the
    customary four port serial I/O we all love! Well .. maybe we love.

    It costs a little more for that service, both as a DOS app and an OS/2
    native app as well.

    Ray speaks of a couple of multi-port boards he can service. A couple
    he reccomends highgly, for being able to do the job with an on-baord
    implementation of sharing IRQ's in DOS. That's where the rub comes
    in for normal DOS boxes, although interrupt sharing for same IRQ use
    for DOS in IBM's old PS/2 series of desktop boxes is another horse.

    By combining these more-than-four port special boards, with a properly
    enable shared IRQ operation, the special drivers for DOS that go with
    these boards, and, as well, perhaps Ray's X00.SYS, you may get where
    you are going.

    The X00 DOS, I think free-ware package is:

    X00150 .ZIP 106,146 06-01-96 05:47

    I haven't looked, as I write this. If your email address is listed,
    I'll file attach it to an email to you. If you haven't wanted it
    posted, simply email me and I'll reply to it with the attach. The
    attach is commonly found on many BBS sites as a utility.

    In general, Ray has done a wonderful job teaching folks the work
    of port I/O and so on.

    I will offer you one other curious comment. I happen to use all the
    stuff in pretty hot RF environments at transmitter sites. For that
    reason, if you happen to want to use these multi-port I/O cards, be
    sure that you choose one which as a complete shielded cable connector
    operation and fully shielded serial port cable operation. I have
    found that the customary use of the little RJ-11 type port connections
    on these multi-port four port cards is suicide at transmitter sites.

    What you will see is that the RF gets into the RS-232 (488?) lines.
    Especially where these lines are a quarter-wave multiples of the
    transmitter frequency(ies), unshielded serial lines go nuts with
    high power RF around! For safety sake, I recommend that you stay
    away from any card that does not have fully shielded line I/O. You
    may not think it critical even if you don't have a transmitter site
    in which to work. Not necessarily so. If, for example, you happen
    to be within a mile or so of a small AM radio station, or a few
    miles of a 50KW directional site, you may wind up with all kinds
    of problems even though you aren't making the RF! It's better
    to be safe than sorry, plus who knows where the 750,000 ham radio
    operators live in the USA, alone and what they use? They can
    be perfectly totally legal running 2KW PEP and these problems are
    your problem as the user of the board; they are doing nothing
    wrong. The problem, like that of all telephone interference, for
    example, is user equipment, not the transmitter service...

    Mike Luther
    [email protected]
    Mike Luther
    [email protected]


    • #3
      I would think you would run out of interupts before you used 16
      com ports at the same time.



      • #4
        Normally, you would be right.

        What these special cards and drivers do is to enable you to properly
        share the same interrupt. That's not possible in normal DOS and the
        ordinary ISA slot cards. It is the special hardward on the cards
        and the special software that make it possible.

        That's, so I am told, not true with the IBM PS2 version of the PC
        that can still be found floating around. In that box they did
        the necessary work to let you actually share the same interrupt
        on the box itself.

        Also involved here, so I think I understand, is the business of
        whether the interrupt is a level-state or an edge-triggered deal.
        DOS, as I understand it, uses leve-state interrupts. That means,
        for the brave at heart and whatever, that is *MAY BE* possible to
        share an interrupt in some ways between two applications whicn,
        for other purposes, may not get in the way of each other when ]
        they are tied to the same I/O port! As long as the operator
        can keep the cows from both trailers from trying to squeeze
        through the same loading chute at the same time, all may go well.

        However, OS/2, for example, uses edge-triggered interrupts. That
        means that if any application has touched the port, it is, unless
        some very special work is done, not possible for any other code
        to touch that same port without producing an error. This is
        more or less the general state of things.

        I don't use WIN-95/NT/2K, but am told that they too, use edge-
        triggered interrupts, which I would expect to be the deal in any
        multi-tasking box.

        SIO, as code, for example, as a method of helping overcome this
        problem, can take a port with a real interrupt of, say 15, and
        reflect it back to the DOS application you write with PB 3.5,
        as IRQ 3 or 4 or whatever. It re-directs the interrupts. Now
        I'm not saying that PB 3.5 can live with this at all, just what
        SIO purports to let one do. I personally gave up trying to use
        that stunt in SIO a long time ago when I got the ability to use
        programs for the task that could see more than IRQ3 and IRQ4 in
        DOS as well as just COM1 and COM2.

        Hope this helps..

        Mike Luther
        [email protected]
        Mike Luther
        [email protected]


        • #5

          If you need more than 4 rs232 ports then we have found the
          Moxa Intellio C218 Turbo to be the best choice, it's an 8 port
          shielded wire isa or pci card. it comes with its own API,
          under DOS it's a small TSR. We have been using them for years,
          however they are not cheap.
          What is it you want to do with ore that 4 serial ports ???



          • #6
            Neil ..

            Does this card have any driver capability for OS/2 or do you have
            any info on how SIO could be used with it?

            I really would like to use more serial ports at the station site
            to do antenna control work for the complex HF directional arrays
            at the same time all the other stuff is going on.

            I've been using the STB card for a long time. It's a shielded
            cable card but it is only a four port card. I have three more port
            things I'd like to do in array control and so on, as well as go
            after a total remote control operation for the station that needs
            an additional phone line for modem controlled fail-safe bailout for
            the system.

            First order of business would be array control to pick up the proper
            hf directional array based on a couple of factors, then to get it
            headed in the right direction automatically for, as needed short
            path or long path. That would be, of course, driven by the ID on
            the remote station as you hear it and punch up sic 'em tiger!

            The competition gets kinda fierce at 315 countries worked on 40 CW
            I assure you! Sorta not any port in a storm, but every port in a

            Mike Luther
            [email protected]
            Mike Luther
            [email protected]


            • #7
              I am needing to collect real-time data from equipment that uses the RS-232 communication channel.

              I need these ports (six of them) to all be read real-time, and data to be logged to a data file.

              I want to use PowerBasic and Dos 6.22, because of stability over windows and the knowledge I have with PowerBasic. If I had a second choice it would be using C and Linux, but I have a way to go in my C before that is a viable alternative.