Sharing Serial Port


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Article ID: Q500004

The information in this article applies to:

  • Direct I/O, version 4.3, 4.4

For Direct I/O, version 4.0, 4.1, 4.2 see article Q500002.


Normally the serial port (COM) is controlled by the operating system. Software needing direct access to the serial ports registers does not run properly.
Direct I/O can be configured to grab the serial port resources and allow those programs to run successfully.


Follow the steps given below to configure your system properly:

  1. Open the Direct I/O Control Panel
  2. Identify the serial port you want to use and enter the resources in the tab I/O Ports
    COM1:   3F8-3FF
    COM2:   2F8-2FF
    COM3:   3E8-3EF
    COM4:   2E8-2EF
  3. Enter the appropriate pathname of your process in the tab Security
  4. Check if your application utilizes the serial port IRQ. If you are unsure skip this step.
    You can enter an IRQ later if your application failed to run because of a missing interrupt.
    COM1:   4
    COM2:   3
    COM3:   4
    COM4:   3
  5. Close the Control Panel

Please read article Q700007 for instructions how to determine the resources used by your operating system.

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Last modified: 2018-04-24.
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