Serial port visa conflicts with USB visa?

[folcon_zzz]

Hi,

I am working on a GUI to communicate/control two devices: one through serial port and other one through USB. I used Labview 7.1 to make the GUI. In the GUI, first I use VISA configure Serial Port, and I can read/write the device-1 through serial port. After that, the GUI closed serial port. And then I open USB port through VISA Open, and the GUI can talk to the device-2 with USB port. Then GUI close the USB port. ANd then GUI use Visa Open to open Serial Port, but read/write the device-1 no response, also no error message, then the GUI close the serial port. And then GUI uses Visa Open to open USB port, and GUI can talk/control device-2 very well. So, I am thinking USB visa has inflict with Serial port visa so that USB visa works but serial port doesn't work.

Is that true?

[Andrew_E]

What version of VISA are you using. If you have you windows xp you may want to update to 3.3.1, if you are using Vista, you may want to update to atleast Visa 4.1, but preferably 4.4. 

[folcon_zzz]

I use Windows XP, and VISA is 4.2. If just serial port, it works well, or if just USB port, it works, too. Only when both of those two present together, I got the problem.

I tried different combinations: if USB open first and then close, then configure serial port, and serial port will work; then open USB port and then close, after that, serial port will not work.

[Andrew_E]

This sunds like a problem with resource access to the com ports. Try running the VI with highlight execution and perhaps lace in some sequence structures to ensure that the resource isn't trying to be controlled at the same time by two different visa calls.