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Analog triggering on PCIe-6251 using BNC-2120 on Mac Pro?

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Greetings all -


Does anyone out there know how to do analog triggering using a PCIe-6251 board connected to a BNC-2120 interface box?  I am running LabVIEW 8.6 on a Mac Pro under OS 10.5.6, and my analog data acquisition VI seems to run but hangs up waiting for a trigger.  The analog trigger signal must be applied to the APFI0 terminal, and the BNC-2120 contains no connector labeled with that name.  On M series boards, APFI0 corresponds to pin 20 on the board itself, but I have not been to locate any information that shows how the BNC-2120 connector pins connect internally to the various BNCs and spring connectors on its front panel.  The NI sales folks recommended the BNC-2120 as the correct interface box to use with the PCIe-6251, so I'm thinking that surely one of the many connectors on the front panel of the box is wired to pin 20.  Am I wrong?  I've spent hours connecting signals to the box in hope of getting a trigger, and nothing has worked yet.  To make matters worse, revising the VI to trigger a data acquisition by using a TTL signal connected to any of the PFI 0...9 connectors on the BNC-2120 just causes the VI to give the undefined error message "89136  Specified route cannot be satisfied because the hardware does not support it."  The specifications for the PCIe-6251 indicate that digital triggering should be possible through any of the PFI connectors, so it's a puzzle.  I have available a BNC-2110 interface box in case that turns out to be a solution, though nothing on it is labeled APFI0 either.  Any suggestions would be of interest.  Thanks.


- Ken1

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Greetings again -


I just solved the digital triggering problem in my original post so, oops, never mind about that.  However, my original problem with analog triggering and APF0 remains unsolved.  I'd still appreciate any help possible with it.  Thanks.


- Ken1

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Accepted by topic author Ken1

Hi Ken,


Unfortunately, the BNC 2120 does not have a connection available for the APFI line of your M series.  The BNC-2110 does have this connection available.



One possible workaround is that you may trigger off of analog input channels as well.  Here's a screenshot from the M Series User Manual that shows the analog triggering circuitry:






There are a couple caveats for triggering off of AI channels (mentioned in chapter 11 of the manual)

If using a start trigger, the analog channel to be triggered off of must be the first channel in your scan list.


If using an analog input as a reference or pause trigger, it must be the only channel in the scan list.


I hope this helps!


Best Regards,


John Passiak
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Hi John -


Thanks very much for your quick reply.  Though it is disappointing that the BNC-2120 lacks what seems like such a crucial connector, your verification that I was not overlooking something obvious is comforting.   I did look at my BNC-2110 before posting the question but found no connector labeled APFI0.  However, my unit is one of the old blue models, not the newer one that apparently does show that label next to the EXT REF connnector.  I am assuming the EXT REF connector on my old unit will also work for accessing APFI0 on my M-series board.  If so, then problem solved.  It is lucky I have the BNC-2110.  Let me take this opportunity to lobby briefly for the publication of wiring diagrams for the BNC-2110 and 2120.  Having access to that information would have told me instantly that pin 20 was not connected inside the box, which would have saved me a good many hours of frustration.  Also, there would be the possibility of opening the box myself and wiring one of the connectors to that pin (something I know NI would really prefer that users not do but that might solve a problem in an emergency).  This can be done without a wiring diagram, of course, but having one would make it a little easier.  Anyway, thanks again for your help and, if my BNC-2110 doesn't do the job for some reason, I'll investigate your suggestion of triggering from one of the other analog inputs before resorting to a soldering iron.


-  Ken

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