Detecting GPIB Instruments when an HP 37204 Extender is involved 
Author Message
 Detecting GPIB Instruments when an HP 37204 Extender is involved

Originally I had a simple VI that used the VISA FIND function to
locate required instrumentation before stepping into the test
application.  This was a reliable method until the application was
used in the test system which utilizes GPIB extenders.  The Extenders
force all 30 addresses to be handshaked as listeners before any code
is sent programmatically.

I then used unique sessions for each instrument (mostly using *IDN?,
ID?, ID, etc...whatever applies or status byte checking, and even
simple  visa reads and parsing to determine a remote status).  There
is a wide mix of instrumentation vintages.  The VI now only functions
well if most instruments can be located.  The more units that are
missing from the expected communication, the more unstable the looping
to establish communication becomes.

Is there a way, to reliably check remote status of the instruments,
(not the address status of the card)?  I dont expect to
programmatically diagnose a situation in which a lockup is inevitable,
like two instruments on a same GPIB address. I would like to diagnose
any missing, powered down, or disconnected instruments in a looping
fashion.



Sat, 13 Dec 2003 02:16:10 GMT  
 Detecting GPIB Instruments when an HP 37204 Extender is involved
Mike,

There really isn't another good way to do this other than with the
VISA Find function.  My suggestion would be to use one of our
extenders, a GPIB 140A cable, which does not cause the VISA Find
function to lose functionality.

Ryan Tamblin
Applications Engineer
National Instruments



Sun, 14 Dec 2003 23:56:07 GMT  
 Detecting GPIB Instruments when an HP 37204 Extender is involved
Ryan,

I believe the original GPIB extenders were introduced to "expand" the
instrument
load limit from 14 to a possible 28 on a single workstation.

I have been doing some further research on this issue and found the
N.I. app. note 042 to be informative as well as the "Hardware
Reference for GPIB-120A".  Am I correct in stating that the GPIB-120A
will expand our control capability without interfering with the
labview VISA-FIND results?  N.I. uses the term "Protocol Transparency"
to refer to their expander/extender performance.  In which case, it
sounds like I would get true listener results in my returned data.

Mike B.



Mon, 15 Dec 2003 02:49:17 GMT  
 Detecting GPIB Instruments when an HP 37204 Extender is involved
I have come to find out that the VISA find function CANNOT determine
what
listeners are available on the GPIB bus when extenders or expanders
are
introduced to the bus, regardless of manufacturer.

I have purchased 2 N.I. 120A expanders and they are NOT "transparent"
when
it comes to the Labview VISA FIND function.



Tue, 03 Feb 2004 03:56:22 GMT  
 
 [ 4 post ] 

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