Why does VISA write vi get a clock symbol added?

[felt]

In an application, I was using the older serial I/O primitive vi's, and now that I've switched to LV 7.1, I wanted to change the older serial read and write (worked fine) vi's (not VISAs) to the VISA Read and Write. When I place a VISA write on the block diagram, it adds a little clock symbol at the upper right corner that was not on the templates.

What is this clock symbol doing there, when it wasn't on the functions panel version of the VISA write vi?

Having a lot of problems getting the VISA read and write vi's to work; they seem to be far more tricky than the old primitive serial read and write vi's.

All my VISA read vi's are getting errors, and some of them cause a severe slowdown on execution with those er
rors. Thoughts on debugging these problemsome VISA vi's. (These problems are why I used the primitive serial read and write vi's in the first place.. couldn't get the VISA vis to work.)

Thx.

[Dennis_Knutson]

The little clock symbol means to do I/O asynchronously. If you right click on the function, you'll see the option to do it synchronously. Select that and the clock will disappear.

What exactly are the errors that you're getting? One thing to try is to disable termination character detection with VISA Configure Serial Port and use VISA Bytes at Serial Port to determine how many bytes to read. If you have enabled the termination character and specify too many bytes to read, you'll get an error because VISA Read will timeout waiting for the termination character to be detected.

[JoshuaP]

Check out this KB.

http://digital.ni.com/public.nsf/websearch/ECCAC3C8B9A2A31186256F0B005EEEF7?OpenDocument

-Josh

[felt]

Thanks, Joshua ..
Looks like I need to leave it as asynchronous.

Lots of problems getting the VISA read and Write to work; seems like NI's expanding what VISA's do has further complicated using them.

I'll research this further, and/or put in another specific question on the issue.
Thx!

[felt]

Joshua and others ..
The problem was the VISA Write and Read VIs really want to be running synchronously. I dug out the Examples Write and Read VIs as suggested, rebuilt them, and if I run synchronously they work great, if I try to run them asych. they slow down with errors.
Thanks, guys!!
Dave