How do I change the serial ports to COM1 and COM2 on this adapter when they say busy??

Posted on 2007-10-11
Last Modified: 2011-09-20
We have a compaq computer with XP pro.  It did not have any serial ports so we added a card to the machine.  It has picked up COM4 and COM6 indicating that COM1,2,,3,5 are all busy, however, I cannot find what is using them.  I need to make this card COM1 and COM2.  How can I eliminate the busy ones???
Question by:stallings123
    LVL 9

    Accepted Solution

    Check the device manager, and expand PORTS, check to see if there is any exclamation mark next to it. Also open up COM port, and make sure it is not disabled. You can also click  the resources tab and look for any conflict.

    usually COM1 and COM3 are taken up by a MODEM if so installed in the machine...
    also check the BIOS if com ports are active...
    LVL 66

    Assisted Solution


    Yes, it does state Windows 3.1 on it, but it works fine under XP. Simply launch the app, and it will ask you to forcibly close the port.

    (not sure if thats a good link, might need to google it)
    LVL 66

    Expert Comment

    I have phantom serial ports in Windows XP. How can I remove them?

    good search term online is .....

    Remove Phantom Com ports Windows
    LVL 1

    Assisted Solution

    Make sure all onboard com ports are disabled in BIOS to use this card as 1 and 2.
    There may not have been com ports on the back plane but guaranteed there are plugs for them on the base just about every mobo made in the last 15yrs has a com port onboard somewhere. (Unless it is a custom configuration or thin client setup)

    Also try disabling the LPT or Parallel port along with the modem, I have seen, specifically, Compaq, Sony and older Packard Bell (remember those?) put the darn printer on a com1 or 3 in an attempt to make their systems unique and not service friendly by anyone but them.

    If this doesnt automatically set the Com ports on the add-in to 1 and 2, try enabling everything and during post, try to catch what is assigned to 1 and 2. In XP, if they show up you can easily change port numbers and memory addresses used by windows for each port through device manager.
    LVL 6

    Expert Comment

    Ensure the IO addresses are correct for Com1 (3F8) and Com2 (2F8).

    You can also delete all the com ports listed in the device manager. Include the comport 5 & 6. Then force a hardware detection. This may put your ports to com1 & com2

    If you can not see any com ports, remember to show non present devices.

       1. Go to Start, right-click My Computer, and select Properties.
       2. In the System Properties dialog box, select the Advanced tab and click the Environment Variables button.
       3. In the Environment Variables dialog box, locate the System Variables panel and click New.
       4. In the New System Variable dialog box, type DEVMGR_SHOW_NONPRESENT_DEVICES in the Variable Name text box and type 1 in the Variable Value text box.
       5. Click OK twice.
       6. To view the non-present devices, go to Start, right-click My Computer, and select Manage.
       7. Click Device Manager, pull down the View menu, and select Show Hidden Devices.

    Also check in the BIOS to see if com ports are enabled even if you do not have the connections for them.

    LVL 31

    Assisted Solution

    As suggested, an internal modem may use one of COM 1 or COM 2; also an infrared port may use one COM port.

    If this is a desktop computer and you put in an add-on PCI card with serial ports, these should be proper hardware ports and as such recognised by computer BIOS. Standard PC BIOSs will detect up to 4 COM ports, a busy COM 5 suggests some kind of software active that wants to use that port.

    If your BIOS POST shows some sort of system summary screen, you should see all identified hardware serial ports noted there. As suggested, look around in BIOS setup and see if you find anything related to serial ports.

    Are there any jumpers on this add-on card for setting ports and addresses?

    LVL 1

    Expert Comment

    Forced accept.

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