whats the difference between VISA and GPIB?

[BrentSchenk]

The reason i am asking this question stems from a problem i am having.

I am using an MXA N9020A to aquire Burst Power measurements and i'm using labview to automate and issue the commands.  If i connect to the device using VISA (which is how i pretty much have connected to other devices) and i issue a command :INIT:TXP it will start the burst power and then freeze the measurement disallowing me from changing channels to measure other channels' burst power.  If i use the GPIB VI instead it will not do this and I am capable of channel hopping to measure other channel powers.  I really dont have a reason to use VISA other than to keep it uniform with everything else in the application but why is this?

[TV_Enable]

Hi Brent,

Thank you for your post.  Before I can answer this question, I'll need a little bit more information from you.  Which version of VISA are you using?  Also, are you running in asynchronous or synchronous mode?  I look forward to hearing from you soon.

Regards,

Todd V. 

[BrentSchenk]

Hi, thanks for helping me out here.  I'm using LabVIEW 8.5 here and shortly i will be installing 8.6 i do believe.  I have not specified whether I'm using asynchronous or synchronous mode to send the GPIB commands so i'm assuming whatever is the default.  I also have not specified the mode in which i am sending the packets so i would assume mode zero.  thanks for any explanations!

Brent

[TV_Enable]

Hi Brent,

Thank you for your quick response.  This should not be happening, as the VISA VIs merely make calls to the NI-488.2 DLLs.  Which version of NI-VISA and NI-488.2 are you using?  Could you also attach both of your VIs (the 488.2 one that works and the NI-VISA one that doesn't)?  Also please perform one NI-Spy capture for each VI, and attach the two resulting screen shots.  If you need assistance performing the NI-Spy capture, you can find more details here.

Regards,

Todd V. 

[BrentSchenk]

I apologize for the delayed response but in the midst of doing this i had deleted anything with VISA communicating with the MXA.  When i went to recreate it all i was getting the same results that i had with GPIB which were still not favorable.  I will need some time to get back to you with all this as i will do some more investigating myself.  Thanks for the prompt replies though!

-Brent