Advice needed - How to resolve serial port conflicts Windows XP

Posted on 2005-05-01
Last Modified: 2009-12-16
I have a brand new Dell Optiplex system I am setting up as a POS.  This requires 3 serial ports so I added a 2 port serial card for a grand total of three serial ports. Although Windows XP reports no conflicts between the ports, the system sort of hangs up whenever I plug a device into a port on the serial card I added. Can somone point me in the direction of resolving this?  Im lost since XP shows that there arent any conflicts when obviously there are.  IRQs are all different for each of the three ports.  
Question by:sbcw
    LVL 31

    Assisted Solution

    A standard PC BIOS has the ability to handle 4 serial ports by itself; it scans 4 I/O ports and detects serial port hardware that way. Very often ports are set up to share IRQ's so that serial 1 and 3 share IRQ4 and serial 2 and 4 share IRQ3. This will not work if 3 ports are used simultaneously - you get an IRQ clash. Consequently, serial port hardware needs to have options for setting IRQ to other lines than 3 and 4. How you do this depends on the hardware - jumpers or a config software. I think it may be safest to allocate resources manually, if possible, not allowing windows to mess things up. You may have to check your BIOS setup so that the on-board port(s) have fixed IRQ and I/O address and then check that the add-on ports do not clash in either respect.
    LVL 5

    Accepted Solution

    A standard BIOS may support 4 ports... but windows can support up to 99 serial ports at least from my experience.  I add 4 ports to my computers all the time... serial ports will never go out of style... alto... having a cable plugged in to a serial port shouldn't do anything in itself.

    When you run serial related software, it sets up interrupt vectors so your software will be able to receive information or send information to the secified serial port and the software sets the port up for specific parameters.  If you are not running your POS software and the system still crashes when you plug your cable in to a seemingly un-used serial port... I would think something may be wrong with that port... personally, I haven't had this happen tho with 4 or more ports. Most serial ports I've had on a PC was 12.

    What brand of serial port is it?  I usually use Lava or Netmos.  The add-in board probably uses a different IRQ I would think?

    Com1 Com2 use IRQ4 but different I/O ports.
    Com2 Com4 use IRQ3 but different I/O ports as well... they all use different I/O ports but... until you start your software... those ports are closed.

    If the software is running when you test these... maybe cables are plugged in to the wrong ports?  Maybe the software is crappy? hehe.  Serial ports are pretty trivail for computers these days I would think... if windows XP says there are no conflicts... I would believe it... "unless" it's a much older PC in which there may be conflicts... i have seen Com problems on older computers... but you dont have an old PC...hmmm.

    If your POS software is crashing... try running the hyperterminal ssoftware and openning each port... you got a serial barcode scanner?? you can watch the codes come in on a certain serial port... etc.


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