I am not new to LabVIEW, but I would not call myself a GPIB expert either. We have a NI PCIE GPIB 488.2 board installed in our computer. I understand the high-level calls, but I don't know the difference between what LabVIEW VISA or GPIB calls are doing and NI MAX other than EOS and EOI which are not obvious at the higher level VISA and GPIB LabVIEW calls.
Our LabVIEW software has always worked with this external device. Recently, the vendor completely rewrote their software and now we see hang ups right after startup where we cannot communicate with this external device. We have to use NI MAX to send an *IDN? query to "wake" the external device up before we can use our software. After that all of our legacy VISA commands (including the *IDN?) work. I tried sending the *IDN? query from LabVIEW at startup, but I get a VISA Write timeout with an EABO (6) error which is not very helpful. What is strange is after I send the NI MAX *IDN? query once, the LabVIEW *IDN? query works every time.
I tried simplifying things by using just the LabVIEW GPIB and VISA examples and sending just one *IDN? query, but I get the same timeout error. I tried extending my timeout and playing with the expected read bytes, but no luck. I tried changing my Open VISA setup parameters (VISA Defaults, Loaded Configuration, etc) with no luck.
I switched from VISA to GPIB and played around with the GPIB Write Mode parameter for EOS and still had no luck. We are supposed be using the default NI 488.2 board settings with just EOI (no EOS). In case the vendor was trying to use EOS, I tried Codes Display and sending \r and \r\n with no luck.
Why does my *IDN? query always work in NI MAX, but not LabVIEW until after I run the NI MAX query ? I am using the LabVIEW examples (VISA and GPIB). I can send them, but anyone that has LabVIEW can drop a VISA Write or a GPIB Write block and right-click on them and go to the Examples to see what I am using.