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Troubleshooting Serial and Parallel Ports (Windows 7 and Windows Vista)

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This document applies to HP and Compaq desktop computers with Windows 7 or Windows Vista.
Use the steps in this document to fix serial and parallel issues by enabling, or resetting the serial and parallel ports.

If the computer does not have a serial or parallel port

If the computer does not have a serial or parallel port, you must install a card or external device that adds port functionallity.
  • An add-in card that has the port you need. You must install the card on the computer.
  • A USB to serial port adapter.
  • A USB to parallel port adapter.

Step 1: Enabling the ports in the BIOS

A parallel or serial port has to be enabled in the Basic Input/Output System (BIOS) before it can function properly. Many parallel devices also require that ECP mode be used. Use the following steps to enable the ports and ECP in the BIOS if they are disabled:
NOTE:These steps will work with BIOS v6 or earlier with older add-in cards. For BIOS v7, a newer Plug and Play card with IRQ sharing must be used.
  1. Turn on the computer and press the F10 key repeatedly when the first screen appears.
  2. Press the RIGHT ARROW key to select Advanced.
  3. Use the UP and DOWN ARROW keys to select I/O Device Configuration and press the ENTER key.
  4. Use the UP and DOWN ARROW keys to select the listing next to Serial Port A.
  5. If it is not already set to Enabled, press ENTER to select Enabled.
  6. If the listings next to Base I/O Address and Interrupt Request (IRQ) for Serial Port A is the same as the listing for Serial Port B, then select the Base I/O Address number and change it to a different number. The default numbers for most computers are 3F8H/IRQ 4 for serial port A and 2F8H/IRQ 3.
  7. Select and enable Serial Port B and the other Parallel ports in the same way.
    NOTE: There may be a mode setting or mode listings for the parallel port. Many parallel scanners and multifunction devices will not work unless mode is set to Extended Capabilities Port (ECP) or Bi-directional.
  8. Press the F10 key to save the settings and exit.
  9. Connect a serial or parallel device to test the serial or parallel port. If the serial or parallel device fails, go to the next step.

Step 2: Reinstall the ports

Remove and reinstall the serial or parallel ports to force Windows to reset the information for the ports. When Windows discovers the ports again it will look for open IRQ numbers and re-assign a new IRQ and Base Address for the port. Use the following steps to remove and reinstall the ports:
  1. Restart the computer and press the F8 key repeatedly, every second, until a menu is displayed.
  2. Select Safe Mode and press the ENTER key. Windows will open with Safe Mode displayed in the corners of the desktop.
  3. Click Start , and enter Device Manager into the Search field. Click Device Manager.
    Figure 1: Opening Device Manager
    Opening Device Manager from the Search field
  4. Double-click Ports (COM & LPT).
  5. Right-click a serial or parallel port, and then click Uninstall .
  6. Click OK to confirm the removal of the port.
  7. Continue removing the ports until all serial ports or all parallel ports are removed.
  8. Restart the computer.
  9. When Windows opens, it automatically finds and configures the ports.
  10. Connect a serial or parallel device to test the serial or parallel port. If the serial or parallel device still fails, try the following items:
    1. Use a different cable to connect the device.
    2. Use a different port to connect the device (serial).
    3. Check the Web site or documentation for the device that is using the port. The device may require special settings in order to operate correctly.
    4. If an extra parallel card was installed, refer to the documentation that came with the card or card manufacturer's website.

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