Instrument Control (GPIB, Serial, VISA, IVI)

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I would like to ask if


1st question: Is it possible to snoop into the GPIB communication of a system (HANDLER-TESTER) by tapping another GPIB (ASIC TNT4882) setted as LISTEN MODE?


2nd Question: Is it possible to tap directly on the dataline of the GPIB? when it sends a string.... do the things that appear on the datalines is a binary representation of the string? for example A 10000001?

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Message 1 of 13



There are a couple of ways to monitor GPIB.  You can Listen to the GPIB Bus Without Interfering of Distruption Communications, or performing an NI I/O Trace.


There is also a good GPIB Programming Manual found here.


What kind of hardware and programming language are you using?


M. Whitaker
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Message 2 of 13

Hi M. Whitaker,


My Development history came from here:


My problem now is I cannot have the TNT4882 Devkit working yet, So I am still waiting for NI response about that issue

in parallel I am  trying to work out with microcontroller at tap directly to GPIB LINES


I have already tried IO trace.. but because of the fact that we have many platforms :95, 98, NT, linux, XP, WIN 7. + 100% cpu ussage when the testers program are running... NI IOTRACE became blurred to be a solution ( but i have tried it and it has worked!)


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ABout this Listen to the GPIB Bus Without Interfering of Distruption Communications,


We don't want to use this solution because... If I have to deploy it on 200 testers... meaning.. I need 200 Units of computers, 200 units of GPIB +, 200 units of OS license, 200 units of Antivirus license + network + 200 units of GPIB cables, + 200 units of devices consuming about 400watts of power.... that really costs a lot.

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Message 4 of 13

Hi M. Whitaker,


is the listen mode the  clear solution?

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Message 5 of 13

What are you looking at monitoring?  How much data are you trying to get?


There are a lot of ways to complete your desired task.  It comes down to how you would like to set it up and what works for your hardware.


Here is a KnowledgeBase Article relevant to making a GPIB TNT Board in a Listen state.


Another option would be to stream the information over a network via something like TCP or UDP.



M. Whitaker
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Message 6 of 13

Hi M. Whitaker,


What are you looking at monitoring?


I want to get a certain data for the tester-handler communication.


How much data are you trying to get?




Actually I have successfully done this with serial and parallel. Im just not sure how to do it using GPIB


hmmm are you familiar with the tnt4882 dev kit?

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Message 7 of 13

I don't think the TNT4882 Developer Kit would be appropriate for your application. This kit is intended for development of instruments which will be controlled and communicated with using GPIB and the TNT4882 ASIC (Application-Specific Integrated Circuit).


If I understand your application correctly, you're trying to monitor communications between a computer (acting as the GPIB controller-in-charge, or CIC) and an instrument performing tests. You also don't want the device monitoring the GPIB connection to participate in any handshaking or disrupt communications. This is the intent behind our GPIB+ products. These products ship with GPIB analyzer software, which will allow you to more easily capture the what is happening on the bus. It's possible that the TNT4882 (with the Developer Kit) could be configured in a way that captures the signals on 200+ separate GPIB busses, but this is not their intended use.

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Message 8 of 13

Hi Frank,


Thank you very much! I am glad you have understood me in one try.


These products ship with GPIB analyzer software, which will allow you to more easily capture the what is happening on the bus

-Unfortunately I cannot use the GPIB+ device that you have because.. If I have to deploy that on the production line.... for example 100 pcs.... it would be costly as you will include the power consume by the PCs, cost of buying the pcs, cost of os, cost of the GPIB+ + cost of antivirus, cost of network.


is it possible to tap directly to the datalines of the gpib.. as stated:


The eight data lines, DIO1 through DIO8, carry both data and command messages. The state of the Attention (ATN) line determines whether the information is data or commands. All commands and most data use the 7-bit ASCII or ISO code set, in which case the eighth bit, DIO8, is either unused or used for parity.


meaning if one of the devices will send "ABC" I WOULD SEE in my data lines in sequence





is my understanding correct?

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Message 9 of 13

In theory, that is what you would see if you read the values of each data line at the correct rate. However, the very low-level details about how these characters are transmitted (parity, clock, endian-ness, etc) would be something explained in the IEEE 488.2 specification. Another consideration is whether your devices strictly follow the standard; some do not.


As I understand it, it is cost-prohibitive to deploy GPIB+ cards to each GPIB bus? Just to make sure: you're trying to monitor many separate GPIB busses, correct? A "bus" constitutes all devices physically connected to each other using a GPIB cable. You would only need one GPIB+ card to monitor a bus with many devices.


Finally, if you can't deploy GPIB+ cards to each bus you need to monitor, would it be possible for the computers controlling each GPIB bus to report what is happening? In other words, have each PC publish the GPIB commands and data as it sends and receives them, then read this data from one server machine?



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