Virtual Serial Port Problem

[Mike_S]

Hi,

I just got LabVIEW 8.2 for OS X. I had the evaluation copy for Windows previously, and I had a working VI for controlling a serial device. Since I don't have any open PCI slots on the Mac, I got a USB to serial adaptor (http://serialio.com/products/adaptors/usb_serial.php). It seems to be working correctly. I see the virtual serial port in both the Mac hardware viewer and the NI_VISA configuration utility.

 I copied the VI over and fired it up and it worked great... but only once. There is no error message or anything, the command just doesn't send and I don't get a response from the device. After some fiddling around I determined that if I unplug the USB adaptor, it will work again exactly once. Exiting LabVIEW does help read again without unplugging the adaptor.

I think I'm closing the port correctly. Could this be a problem with the adaptor?

Thank you,
Mike

[Wayne.C]

Mike,

Based on what you have tried, it sure sounds like a problem with the adapter.  I personally have had no luck trying to use the cheaper USB-RS232 adapters.  ( windowsXP on PC )I seems that not all adapters/drivers are fully compatable with the serial spec. 

I personally stick with either a NI or Blackbox adapter.  If you search the forum posts you will find other adapters that have been sucessfully used with NI.

[Mike_S]

Thanks for your reply.

The main problem with getting a different adaptor is that neither one you mentioned is compatible with Mac.

I plugged the adaptor into my Windows machine and it works fine. Would that point more towards a problem with the Mac drivers?

Thank you,
Mike

[Wayne.C]

Sounds like the mac driver is a strong candidate.

Some of the higher end Black Box adapters are mac compatable.  I know that B&B electronics http://bb-elec.com/product.asp?SKU=UC232A&Trail=45&TrailType=Main makes one that is mac compatable.  I've never tried it though.

Would an ethernet serial port work for your application?

[Mike_S]

I removed everything from my VI and started adding things one at a time. The problem seems to be with closing the VI session. If I don't do a VISA Close at the end, everything seems to work. I'll let you know if I figure out what's going on exactly.

Mike

[Wayne.C]

Mike,

Your troubleshooting instincts are right on the money.  Does the VISA close return any errors or warnings?