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vrf GPIB to LAN

Question asked by brian_vee on Apr 12, 2004
> I think your best bet would be to have GPIB added to the scope.  It is a
> $400 accessory with p/n TDS3GV.  At that point you get a supported driver.

     I'm not sure I understand what the original poster wants to do, so
there are some fundamental concepts that I think are worth mentioning.
     Most LAN-capable instruments (at least from major instrument vendors
like Agilent and Tektronix) support VXI-11.  VXI-11 has nothing to do with
VXI; it's just a protocol for how you send messages to and from instruments
over TCP/IP.  VXI-11 is very similar to GPIB in that it supports reading and
writing messages, triggering, clearing, asserting SRQ, etc.  (Can you tell
it was defined by major instrument vendors who already invested in GPIB?)
     NI-VISA and Agilent VISA both know how to talk to VXI-11 instruments.
Thus, if you write a program using VISA for a GPIB interface, it will
probably work with no modifications if you switch to a LAN interface.  (More
on the "probably" in a moment.)  You just have to open up a different
resource--instead of "GPIB0::22::INSTR", you open
"TCPIP::10.0.20.30::INSTR".
     So, I'm wondering if Jim Hetrick (the original poster) just needs to
point his existing application at the LAN device and if it will work.  You
should be able to send regular SCPI commands, or you could probably use the
existing VXIpnp driver from Tek.
     One caveat...  I have a TDS3054B with the TDS3GV option, and it speaks
VXI-11.  I have not tried removing the TDS3GV and tested whether I can still
use VXI-11.  I can't imagine that Tek would disable that, but you never
know.
     Someone else suggested you could just try to use your own socket
connections to talk to the scope.  I would suggest that this is way more
trouble than it's worth.  VXI-11 is based on Remote Procedure Calls, which
is significantly more complicated than just socket reads and writes.  Use
VISA instead.  Really.
     A note on the "probably work with no modifications"...  Be sure you get
the latest firmware from Tektronix and the latest VISA library you want to
use.  I know there were some bugs in early Tek TDS 3xxx firmware revisions
that kept SRQ from working correctly.  Also, unless you have source code to
the driver, you never know what sort of interface-specific code might be
going on inside the driver.  E.g., if the author had code that did low-level
GPIB configuration, it would return an error with VXI-11.  This sort of code
is rare (except for serial I/O), but you never know.  That's why you want
source code for your instrument drivers.
     Anyway, I hope this helps.  If you could be clearer what you are really
trying to do, I think we could provide more assistance.

Brian H. Powell
Sr. Group Manager
LabVIEW R&D
brian@ni.com



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