can i read GPIB instruments in paralel?

[ararajan]

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@Dennis_Knutson wrote:
Being in the same loop does not force simultaneous anything.

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Yeah I realized that was wrong after I had posted it.

Will do and thanks again.

[Ben]

The conflict over the GPIB rears its ugly head when doing work that reuies a lot of time. An example would be reading the trace from a scope or a curve-tracer.

I was able to avoid that complication by adding a unique GPIB adapter for each GPIB device.

For what its worth...

Ben

[ararajan]

Thanks Ben. The experiments that require these VI do run for a long time. I'll keep this in mind.

[Omar_II]

On a GPIB bus the send and receive are two distinct and separate steps.

Consider that the GPIB controller controls talkers and listeners. That is it will actually control when the instrument is allowed to reply with it data.

So if you have 2 instruments on the same bus it might go something like this (and that is a big might)

VISA Write to instrument #1 requesting data. (nothing is sent back)

VISA Write to #2 requesting data. (nothing is sent back)

VISA Read from #1 reading in data (now the data is sent)

VISA Read from #2 reading in data (now the data is sent)

In GPIB

When an instrument receives a request or a command it goes and get the data or does the command, but it DOES NOT REPLY until told to.

The controller tell everyone on the BUS that it (the controller) is going to be the TALKER and tells instrument #1 to be the LISTENER (nobody else is to listen). The controller sends the message only to instrument #1. When instrument #1 acknowledge that it has received the message, the controller tells instrument #1 to UN-LISTEN.

Then some time later, the controller tells everyone on the BUS that it (the controller) is going to be the LISTENER and that instrument #1 is going to be the TALKER and when to start talking. Then after the message the controller tell instrument to "UN-TALK"

In between that the controller can send and receive any number of messages all interlaced with one another.

BUT at any one time ONE and ONLY ONE device can be a TALKER, but you can have multiple LISTENERS. 

It is like a school teacher asking the Tom a question. Then asking Bob a question. When Tom get his answer he rises his hand. When Bob is ready, he raises his hand. But nobody speaks until the teacher points to them.

http://www.ni.com/white-paper/3389/en/

[crossrulz]

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@ararajan wrote:

Thanks Ben. The experiments that require these VI do run for a long time. I'll keep this in mind.

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I think you misunderstood what Ben was saying.  You run into problems when something takes over the bus for a "long" time, such as capturing a waveform from an oscilloscope.  It does not matter how long your experiment is.