How can I solve a GPIB/VISA compatibility problem?

[Chris_Regan]

My Labview (version 5.1 on a Macintosh) application talks to a variety of instruments over GPIB. In one mode it communicates with both 1) a LakeShore 340 temperature controler (LS340) using VISA-based drivers and 2) a Linear Research LR-700 AC resistance bridge using low-level GPIB functions. My application can query these instruments a couple of times per second, usually without trouble. However, periodically (about once an hour) the GPIB Read will cease to work with the LR700 or any of the other instruments on the same bus, returning error 6 (I/O operation aborted). GPIB Write still works fine. Querying the LS340 when the system is in this state produces the VISA error Hex 0xBFFF003C (Insufficient system resource
s to perform necssary memory allocation). Querying the LS340 a second time is successful, and thereafter GPIB Reads are also successful.
I think somehow the GPIB and VISA protocols are interfering with each other. (Although the data dependency requires that the VISA Write/Read be complete before the GPIB Write/Read begins, I am not opening/closing the VISA session with every iteration. The VISA session is opened on the first iteration and stored in a shift register.) However, the maddening infrequency of this problem makes it very difficult to troubleshoot. Any suggestions?

[Randy Solomonson]

Hello-

Try using only VISA commands. It sounds like mixing the two interfaces might be causing a memory leak of some sort.

Randy Solomonson
Application Engineer
National Instruments

[Dan_Mondrik]

Chris:

You might also try upgrading to NI-VISA 2.6. It fixed some LV/GPIB problems, although I'll be honest I don't recall hearing of one like this before.

Good luck,
Dan Mondrik
Senior Software Engineer, NI-VISA
National Instruments

[Chris_Regan]

Hi Dan,

I'm trying to follow your suggestion, but I can't get the VISA upgrade to function. I downloaded the NI-VISA 2.6 full development installer, which recommends uninstalling the prior version first. I couldn't find a good way to do this (the documentation is no help), so I ended up just reinstalling the entire Labview 5.1 without the VISA package. But even this approach (I tried several others) doesn't work - when I run VISA commands from within Labview after the VISA 2.6 install, I get 'unknown system error'. Any suggestions?

Chris

[S.D. Dharshan]

Chris,
If NI-VISA 2.6 is properly installed then

1. then System Folder > Preferences > VXIPlug&PlayAlias points to a folder with
visaconf.ini, visastat.ini and other folders/files AND
2. in the extensions folder, the following libraries must be present
VISA(PPC), NI-VISA Passports, NIGPVX

Dharshan
Staff Software Engineer, NI-VISA
National Instruments