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JSI Tip 3947. Error messages caused by incorrect serial port configuration?

Micrsoft Knowledge Base article Q112584 contains:

Error Messages Caused by Incorrect Serial Port Configuration


If you configure a serial port incorrectly in the Ports option of Control Panel (JSI NOTE: or Device Manager), there are several error messages that may appear in Event Viewer after you restart the computer. For example, you may receive the following error message:

User configuration data for parameter COM2 overriding firmware configuration data.

The specific error message that appears depends on which configuration parameter is incorrect. The three main sources of serial errors are Input Output (I/O) address conflicts, hardware interrupt (IRQ) conflicts, and configuring serial ports that do not exist.


Incorrect I/O Address

Suppose you have added a serial port or serial device to your computer since you first installed Windows NT. You can use the Advanced Settings dialog to configure the port. In the Advanced Settings dialog, you can configure a COM port number, a Base I/O Port Address, and an Interrupt Request Line (IRQ). If you assign an I/O address to the new COM port, and that I/O address is already assigned to another COM port, one of the following error message appears in Event Viewer after you restart the computer:
The Control registers for COMx overlaps with the COMy control registers.
Event ID 29
Descr: Control register for COMx overlaps with the control register for Comx.
A Conflict has been detected between two drivers which claimed two overlapping I/O port regions.

where x and y represent the number of the COM port. This error message appears even if you create a duplicate entry for the same COM port, thus making x and y the same number.

Incorrect IRQ Setting

On ISA and EISA computers, COM1 and COM3 both use IRQ 4, and COM2 and COM4 both use IRQ 3. Thus you can configure COM1 - COM4 to their respective interrupts, but if you configure one of these COM ports to an IRQ being used by any other device, an error message appears. Suppose, for example, you configured COM4 to IRQ 5, and you have a bus mouse on the system also configured to IRQ 5; the following error message appears in Event Viewer after you restart the computer:
A conflict has been detected between two drivers which claimed equivalent IRQs. Driver <driver name>, with device <\Device\device name. Translated> claimed an interrupt with level in data address <hex address>, vector in data address <hex address> and Affinity in data address <hex address>.

There will be an entry with this format in Event Viewer for each of the conflicting devices.

After identifying the IRQ conflict, Event Viewer then displays another warning about using the COM port in question:
The hardware resources for COM<X> are already in use by another device.

COM Port Doesn't Exist

An error message appears in Event Viewer if you attempt to configure a COM port that physically does not exist on the system. Suppose you went to the Ports option in Control Panel and added a COM3 port, when in fact you physically only have COM1 and COM2 on the system. The following error message appears in Event Viewer the next time you restart the computer:
While validating that COM3 was really a serial port, the contents of the divisor latch register was identical to the interrupt enable and receive registers. The device is assumed not to be a serial port and will be deleted.

This error message means that the system will delete the I/O address entry for the non-existent port in the Windows NT internal I/O port address table. The entry for this non-existent port will still exist in the Ports option of Control Panel and in the appropriate key of the Registry.


To clear these messages from Event Viewer, do one of the following:

  • Use the Advanced Settings dialog box to change the I/O, IRQ, or the COM Port Number setting


  • Delete the appropriate entry from the Windows NT Registry using Registry Editor.

Using the Advanced Settings dialog box clears the error messages in many cases, but in two cases you need to delete certain entries in the Registry:

  • If you want to change the settings for a COM port already detected at Setup by NTDETECT.


  • If the COM port in question doesn't physically exist on the system.

In the first case, the Advanced Settings option will not be available. In the second case, no facility exists in the Ports dialog box to delete the entry for the non-existent COM port.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at you own risk.

To delete the false entry from the Registry, use the Registry Editor (REGEDT32.EXE) to find the following key:


The Parameters key lists one or more subkeys listed as Serial10000, Serial10001, and so on. Check the DosDevice value to find which subkey represents the non-existent COM port. Then, highlight the subkey for the erroneous serial port and choose Delete from the Edit menu.
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