I just want to clarify a few things about mixing VISA and GPIB.
If all your I/O is done on the diagram with VISA functions and GPIB
functions, you should be okay. LabVIEW has code that tries to keep the two
from stomping on each other. You have to know what you're doing--you can't
have two VIs trying to control the instrument at once, for example.
This is _not_ true for C-based instrument drivers (aka, VXIPNP,
including IVI). We have no protection between the VISA calls inside those
drivers and the builtin functions. If one is in progress and you try to use
the other, you'll get an error. One way to demonstrate this would be to
start a GPIB Read (which is asynchronous by default, meaning that LabVIEW
starts the Read and then looks for other stuff to do),
then use an
instrument driver for a device on the same bus. The instrument driver will
return an error. You just have to be using the same bus--it doesn't matter
if you use the same device.
Fortunately, this doesn't come up that often in practice. When needed,
there are workarounds--e.g., keeping all GPIB I/O in a single thread (at
least per bus) and using synchronous VISA and GPIB Reads/Writes. Yes, we're
working on ways to make this less of an issue, but I won't go into details
yet.
Brian Powell
Sr. Group Manager
LabVIEW R&D
brian@ni.com
