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Reading RS-232 with PC?

Discussion in 'Electronic Design' started by eromlignod, Jan 3, 2007.

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  1. eromlignod

    eromlignod Guest

    Hi guys:

    I'm an ME and I have run across a situation where I need to read what
    is coming out of an RS-232 port on a medical device. All I really need
    is to be able to literally see what bytes are coming out...even ASCII
    letters are OK. I just want to see what the data looks like so that I
    can determine what protocol is being used.

    I can make a cable to plug into the serial port on my computer that
    reads from their serial-out. What sort of software will simply display
    what is coming over the line (once I set the data settings, etc.)?
    This probably has a ridiculously simple answer...doesn't it?

    Thanks for any help you can give me.

    Kansas City
  2. Tim Wescott

    Tim Wescott Guest


    Every version of Windows that I know of since 3.0 has included a
    terminal program. For the last eight or so years this has been "Hyper
    Terminal", which can be found in Start -> "All Programs" ->
    "Accessories" -> "Communications".

    It sucks in many ways, but it's good enough that I've never been able to
    overcome my laziness enough to find a better one, and I generally use
    terminal access a lot when I write embedded applications.

    I'm sure that any Linux machine or MAC-OS would also have some sort of
    terminal programs -- probably multiple ones, and probably many that are
    better than Hyper Terminal.


    Tim Wescott
    Wescott Design Services

    Posting from Google? See

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at
  3. If you have or can get a Borland Delphi compiler, I recommend SerialNG,
    which is shareware provided by Ekkehard Domning in Germany
    ( You can start with the demo terminal programs
    and add features (such as control character translation) if you need them.

    Another useful freeware tool is "portmon", which monitors all activity on a
    serial port and gives you a log with timestamp info:

    Both of these may be overkill for your needs. The Windows Hyperterm
    suggested by others usually works very well.

  4. John B

    John B Guest

    If Hyperterminal fails you then try this:
  5. Gary Peek

    Gary Peek Guest

    Tim, I wrote Term232 for uses like this. It can display in ASCII,
    decimal values, and hex values. It can be downloaded on our web site,
    on the Resources page.

    Gary Peek, Industrologic, Inc.
  6. Guest

    I use this (free) one and have been pretty happy with it.

    Bob Stephens
  7. David Brown

    David Brown Guest

    Ignore the suggestions to try "Hyper Terminal" - even by MS standards, it
    is outstandingly bad.

    Far and away the best terminal emulator for serial port work is Tera Term
    Pro ( ), as
    mentioned by another poster.

    If you need something more, such as monitoring the status lines or better
    views for binary data, try RealTerm ( ).
    It's more powerful, but harder to use.

    These two beat anything I have seen at any price (they are both open
    source) - and terminal emulator programs have been an essential tool for
    my job for the last 13 years. If you need something beyond these, you are
    better off writing your own serial port software (it's not hard).

    Of course, if you are using linux, there are other tools like minicom, or
    just "cat /dev/tty0", for capturing serial data.
  8. Joel Kolstad

    Joel Kolstad Guest

    Hyperterminal came from Hilgraeve, and I'm amazed that (1) they got the
    contract in the first place and (2) they even managed to get Microsoft to let
    them include a "click here to upgrade to the full version!" button in some

    It really is crap.
    Agreed, although since it's somewhat dated it unfortunately only knows
    Com1-Com4 so you may end up having to shuffle ports around in Device Manager.

  9. cat /dev/ttyS0 to be pedantic.
    That other one may get you in trouble.
  10. If there is enough interest I will modify tera term to use ports
    greater than 4 (providing the author gives permission). I have had a
    look at the source and compiled it using VC2005 with no problems.
  11. vasile

    vasile Guest

    Hi Don,

    *Be sure* that you have an approved medical device with an optoisolated
    RS232 as long device is connected with the pacient.
    If you don't, then use a laptop powered only by own batteries, without
    any charger, printer, or ground connection except the RS232 medical
    device connected to your laptop.

    Real terminal could be a good choice.

  12. Arlet

    Arlet Guest

    Not necessary. Just edit the TERATERM.INI file (in the directory where
    you installed TeraTerm), and change the line that says


    into whatever number you want.
  13. Joel Kolstad

    Joel Kolstad Guest

    Thanks, I didn't even know it kept an .Ini file!

    So presumably the only real limitation would be newer serial device (e.g.,
    those that show up on USB connections) that -- on infrequent occasion -- call
    themselves, e.g., HSS1: rather than COM1:, right?
  14. Arlet

    Arlet Guest

    I guess so, but I'm not familiar with those. The ones I've worked with
    all allowed setting the COM: port in the device manager properties.
  15. Guest

    why bother, Here's a free on that better...
  16. David Brown

    David Brown Guest

    The help file describes it quite clearly. But I too used it for years
    before someone in a newsgroup pointed out the MaxComPort setting.

    The ones I have used have always come up as coms ports - any USB serial
    device that does not has bad drivers.

    If you are using a lot of these USB devices, it helps to clear the old
    ones out of the registry on occasion, as new devices keep getting higher
    numbers (assuming they have different serial numbers). Windows may
    theoretically support 255 ports, but it gets inconvenient after a while.
  17. Arlet

    Arlet Guest

    You can avoid the Windows new hardware dialog for devices that only
    differ in their serial number (but have otherwise identical
    vendor/product id).

    In order to do that, go to registry path
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\UsbFlags, and
    create a new binary entry "IgnoreHWSerNum<VID><PID>", where <VID> is
    the vendor ID, and <PID> the product ID (both 4 digit hex numbers).
  18. Guest

    I have 129 serial ports and only 16 show up in Tera Term even with
    MaxComPort set to 129. How can I get all them to show up in Tera Term?
  19. Jamie

    Jamie Guest

    look in the Registry under your devices..
    see what the table has translated too ?
    it's possible windows is not giving any more than 16 ?
    in any case, from the programming point of view you
    maybe able to use the "\\.\COM17" or something like that
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