How do I query a serial com port to determine if it is already open?

[Tri_State_Port]

I would like to query a COM port to see if it has already been opened by another program and select a different Com port if the original choice was already opened.

[Dennis_Knutson · Accepted solution]

What language and api are you using? With LabVIEW and VISA, when you open a port and it's in use, you will get a specific error (I don't remember the exact error code). Look for this error code.

The VISA error is -1073807246

Message Edited by Dennis Knutson on 05-01-2009 09:47 AM

[Tri_State_Port]

You hit the nail on the head with LabView and VISA.  Thanks for the help!