How can a I solve and GPIB/VISA compatibility problem?

Question

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 reso
urces 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?

Answer 1

Hi Chris,
One suggestion;
Write two seperate test routines that each use only one method or the other.
Test the H*&#$ out of each to attempt to determine if the issue is associated with the high level or the the low.
Ben
Ben Rayner
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