check serial port availability

[jyang72211]

I would like to check is a serial port availble (not already opened by another application) without opening and closing the port.  Currently, the program opens and closes the serial port a lot.   Sometimes, an port access deny error occurs.  We suspect that after a the close command is issued, the port didn't close immediately and another application try to acces the port at the time, which generated the error.  Any idea? 

[RTSLVU]

You might want to ask yourself why your program opens and closes the serial port a lot.

You should open the serial port once at the beginning of your program, pass the VISA reference throughout, then close it once at the end of your program

[zenthoef]

Agree with suggestion to ask yourself why the port is closing and opening so much. That is going to a cause a lot of confusion.

If you still want to close and open it a lot, look at the error you get when trying to open the port. Error -1073807246 tells you that the VISA resource is valid, but it can't be accessed. That is a pretty good indicator that the port is in use somewhere else.

[jyang72211]

opening, pining, and closing is for searching through all the existing comm port to see which port I am communicating on.

[jyang72211]

The opening and closing is due by a custom .net DLL function. 

[Dennis_Knutson]

As already mentioned, you have to attempt to open the port and check the error returned.

[RTSLVU]

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@jyang72211 wrote:

The opening and closing is due by a custom .net DLL function. 

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Well without any code to look at I have two suggestions...

1. Dump the DLL and either use LabVIEW to search for the port the device is on or just tell LabVIEW what port to use.

2. Put a delay in your program every time the DLL is called to make sure it is done with the ports before LabVIEW tries to access it.