I have run into a rather peculiar problem while testing GPIB communication and was wondering if I may be missing something regarding setup of the new NI488.2 drivers.
Background:
I am testing GPIB communication of my application by simulating GPIB commands from a terminal that is connected to the computer running my LabVIEW application. The terminal has NIMax installed and I am using the NI488.2 "Communicate with Instrument" interface screen to send all GPIB commands to my application. I also have a separate terminal connected in-line with the communication terminal and application computer with a GPIB+ card installed in it running GPIB Analyzer. GPIB Analyzer is configured to capture all data transfers and command tansfers, as well as control line transitions. My LabView application is programmed to assert the SRQ line and send a data byte to signal a separate testing computer, which I am simulating communication with via NIMax. These asserts occur multiple times while the application is running.
Problem:
On the first six asserts of the SRQ line, my application appears to function normally. The SRQ is asserted, then the NI488.2 driver un-asserts the SRQ and passes the data byte. However, when the application asserts the SRQ for the 7th time, the SRQ remains stuck on. The driver never un-asserts the SRQ and the data byte is never passed. (See attached "SRQex.jpg" screen shot of capture file.) It appears that the only way to clear the SRQ is to re-start my LabVIEW application. After doing so, everything runs fine again, until the 7th assert. This problem almost appears as if some kind of buffer is filling up in memory, as it is repeatable.
Analysis:
After running several tests to determine if this problem existed with my application or not, I was able to make the following observation: When I used a PC with NI488.2 ver 1.7 or earlier installed to communicate with my application, this problem does not appear at all. My application appears to run fine and the SRQ asserts and un-asserts as it should. This problem only surfaces when I am running NIMax on the communication computer with NI488.2 ver. 2.0 or later installed. I noticed that the GPIB properties interface window is radically different in versions 2.0 and later than that of earlier versions of NI488.2. Could there be something in the GPIB setup that I am missing here? I have tested this using several different PCs running different Windows operating systems and my results were always the same. By the way... I have verified that autopolling was checked on for every version of NI488.2 that I tested.
