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PFI pin transmission

A friend of mine and I were wondering, if we use different PFI pins to transmit the same triggering signal to differnent DAQ cards, does the signal leave the pin at teh same time, or is there an amount of latency that needs to be considered because each pin would send out the signal seperately.


Thanks for any replies



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Message 1 of 6

If your chassis are daisy chained together, you should be fine.  The only delay I think you might see would be due to the distance between the chassis.  It would be ideal for all of the cables between your chassis to be exactly the same length. 

Have a great day!


Applications Engineer

National Instruments

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So now after some discussion we have decided to split one of the PFI signals and output it to different DAQ cards, it's the same as Daiosy Chaining in some respects though the connection is from card to card instead of card through card.


Another inquiry that we have now is that if the signal is split would we still be able to satisfy the TTL specifications needed for clock signal scanning and transmission. I found a few specs for cable transmission but I do not know what to expect until I test for it, or if I can find any facts that help talk about split transmission.




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Message 3 of 6

You shouldn't see any problems unless you're doing something pretty complex where you'll be using a lot of voltage, and could weaken your signal too much.  I'm curious though, how exactly are you splitting this signal?  And what are you doing with it after it's split?


Applications Engineer

National Instruments

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Thats what we are going to test out today, we have old SCXI 1302 Chassis bus that has mulitple bus pins on the inside, we we are going to connect one of the DAQ card to a break out box, from that break out box we are going to extend PFI pin number 7 to cable that will connect to the one of the bus pins in the spare chassis. From that chassis connection we can split the signal into other buses and test for results.


What we hope to do with that split signal is pass it to other PFI pins, on other DAQ cards and have that signal serve as the scanning, or clock signal for the DAQ cards Data Acquisition. The challenge here connecting these cards together to have all of them share a common timed signal for simultaneous Data aquisition.


Hope that gives you an idea.


Also we are using PCI 6071E cards, that is why we are considering this method




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Message 5 of 6

Hey Ryan,

       I'd love to hear how that goes.  I'm hoping you don't run into propagation delay, but it sounds like because you guys are doing a lot with your signals you might see some of that.  Let me know what kinds of results you get.  Good luck!


Applications Engineer

National Instruments

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