COM port changing

[helizone]

Can someone please explain why my com port changes from com port 1 to com port 3 or none when I have not physically changed it myself? Thanks

[Geek-9pm]

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First of all, I have never heard of that. The BIOS sets the COM vectors when the PC starts up. There is no good reason for a program to alter the vectors.

But more detail is needed to answer your question fully. The model # of you PC and the OS you are using. And why are you using a COM port? Nowadays everything is USB.

[jason2074]

Where did you see this information?

[helizone]

Well, my OS is XP and my computer is in an office used for managing a security gate . The mangement software controls  a system controller thru a serial port. There is a device server at a remote site to control the security gate which has an IP address. It has always worked fine until recently when the com port keeps changing from com 1 to com 3 and sometimes to none. I can set it to com 1 in the morning and everything works fine,but by afternoon it changes to com 3. Of course this causes the communication to the gate to stop which is not good. I set it back to com 1 and it works fine again for hours and maybe days,but eventually it switches to either com 3 or to none. I wish I could lock it to com 1. This would solve the problem.
Just a thought,maybe I should try a serial to USB cable adapter? Any thoughts?

[jason2074]

I am not sure if for Win XP, COM Ports 3 is the default under port settings tab in Device manager. It will display what is currently in use. There is a resource tab option to check/uncheck use automatic settings. Have you tried toggling this?