Instrument Control (GPIB, Serial, VISA, IVI)

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How to sniff sent data over GPIB bus?


a customer is using an old MS-DOS measurement program (no sourcecode available) which is talking to an GPIB instrument.

How can i grab the SCPI data that is sent through this bus using a laptop with two GPIB-cards.

The idea is something like.




How can this be done?


Thanks for ideas or better solutions

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Message 1 of 10

I assume you could use VISA Write(s) Read(s) functions from the Labview tools palette to relay the SCPI commands. 

Message 2 of 10

In the NI Gpib card an analyzer can be present that you can use.

Or what I have done log ago but not works in your case is to have an extra layer of visa writes that log the data and then call the original routines, and and original VISA reads that are called and also write to the same logfile.

greetings from the Netherlands
Message 3 of 10

>In the NI Gpib card an analyzer can be present that you can use.


What do you mean with "analyzer in the card"? How can this be done?



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Message 4 of 10

If you have MAX installed, start it up and check your gpib card for the analyzer.

greetings from the Netherlands
Message 5 of 10

PC_Meas -> GPIB -> Instrument




PC_Log ----->GPIB


You mean i can simply start on the addidtional PC_Log the Analyzer and it will show the traffic between PC_Meas and Instrument?




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Message 6 of 10

I don't think the GPIB analyzer will help you sniff commands. I not 100% sure.


Your logging SCPI or are you logging GPIB interface?


Here's my guess to log SCPI, using your setup of PC and laptop, open NI MAX on the laptop, right click on your GPIB card, select Visa Test Panel. You may be able to set a GPIB address you want to listen/capture SCPI as you run your DOS program. 


Your not responding with commands but maybe you can observed what is Tx from the DOS program.


After further looking into this. This is not possible without writing labview code to capture scpi...

Message 7 of 10

I only want to see the sent and read SCPI commans. The rest of the GPIB protocol is not interesing.

What do you mean with "This is not possible without writing labview code to capture scpi..."? I can run Labview-code on the PC_Log of course. Oly the PC_Meas is a black box.


On the PC_Meas is the program ist using a NI LAN->GPIB-Interface.

So another solution could be to use wireshark and sniff the the LAN packets.


Does someone know if the SCPI commands are visible in clear text in the LAN packets?



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Message 8 of 10


Skippy is normally clear text, except when sending binary blocks e.g, sometimes in arbitrary waveform transfers or block data from a device. But normally you can find that in the manual of your instrument.


In very special cases a gpib command is explicitly in binary to keep a protocol secret, but normally it is an open text format.

greetings from the Netherlands
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Message 9 of 10

What instruments are you using?  If it's old MS-DOS program the instruments are likely also old.  They may pre-SCPI and just simple two character commands specific to that instrument.  If you know the instrument, the commands should be easy to find.  Starting over might be easier than trying to packet sniff with a second pc! 

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Message 10 of 10