Having trouble figuring out how to use trigger inputs as a general purpose input.

[Rob Wright]

I'm trying to use "Trigger 1" as a general purpose input to indicate the status of external circuitry. I can't seem to get the "Read High-Speed Capture Status" to indicate anything. I'm using the "Configure High-Speed Capture" VI with the capture mode set to Inverting Digital Input, and that VI feeds into a Do-While loop which contains the "Read High-Speed Capture Status" VI, which has the Ret Vect set to 0. I see from the online help that the High-Speed Capture function is available on Servo and Closed-Loop stepper systems, which I suppose is to enable the ability to read the position of the encoders. I'm using an open loop stepper system, so are these High-Speed Capture fun
ctions unavailable even though I'm looking only for status (Trigger 1), and not concerned with reading position? Thanks in advance, Rob.

[KenSun]

Hi Rob,

You can use the trigger inputs as general purpose digital input without encoder feedback.

It sounds like you're doing everything right, except you set the RetVect to 0. (This means you don't want data to be returned) You want to wire 255 to this terminal or simply leave it unwired.

That's most likely the problem. If it still doesn't work, I have attached a VI that I made and know it works. You can try it out.

Ken Sun
National Instruments
Applications Engineering

[Rob Wright]

Thanks a bunch, Ken! You were right, with RetVect set to 0, I was getting nothing out. I also noticed that I hadn't enabled the encoder (even though I don't have one) in MAX (Measurement & Automation Explorer). Turns out, even if you don't have an encoder, it still needs to be enabled to be able to read the "Trigger" lines. I also wanted to thank you for the VI. It looked similar to the one I'd created, except I didn't have the "Start Motion" or "Set Operation Mode" VI's. Thanks for the quick response. I'm in the process of getting a 3D tester up and running. I'd programed it previously in Visual Basic on an old 386 computer, and we're trying to bring it up to date with a 933MHz computer with 7344 motion card. Fairly new at LabView, so any help is greatly appreciated
! Thanks again, Rob.

[KenSun]

No problem Rob. Glad to have helped you out. I'm really liking this Developer Exchange thing... It's a great way to share knowledge for National Instruments products. I'm sure there will be people who run into the same problem you had, and they can find the answers here.

Good luck with your application! Let me know if you run into any more problems.

[Rob Wright]

I've got one other issue, but it's more of a general LabView question. I'll ask here in the motion forum since the VI I'm having trouble with is only used with the 7344 motion card.
Problem: I am trying to create a sub VI to continually read the trigger status. It works great as a vi, but not as a sub VI. It's because the trigger status is read in a loop, and when used as a sub VI, I can't seem to find a way to pass the status out of the loop. Using local variables works to pass the status out of the loop, but for some reason the calling VI can't utilize these outputs. I'd like you to have a look at my VI & sub VI if you have a chance. I know the answer is going to be blatantly obvious to you, but I can't see the forest for the trees... How can I e
mail you these two files? TIA (thanks in advance), Rob.

[KenSun]

Hi Rob,

That's a classic LabVIEW programming problem. Because of how a subVI works, the data inside a subvi is not passed out to the main VI until it's done executing.

So, you have a few options to still make this work. First, you can try to use a global variable. This is the simplest, but not the most efficient, because globals can be slow. Or else, you can use a Queue, to pass data between your subVI and your main VI. You have to first flatten the data to string and pass it to the queue. And in your main program you can have a loop that dequeues the queue.

Ken

[Rob Wright]

Thanks for the answer Ken. I'm going to try a different workaround. The global was too slow, and I think I'll break my subVI into two parts. I'll create a sub that has all the setup stuff in it, then embed the actual "check trigger status" loop in the main VI. The loop contains only 2 or 3 nodes. Too bad LabView works this way. I can see one reason it should, but another larger reason it shouldn't. Wishlist.... Oh, speaking of wishlist, I like the improvements that 6.0 has brought, but one thing still bugs me. There's no way to have LabView remember the place to look for files when it's first started. It defaults to "My Documents", which should be, as all LabView programers know "LabVIEW6\user.lib" (or whatever). Of course, once th
ere, LabView remembers for that session. Next time it's started, back to "My Documents" again. How 'bout fixing the "Options", "Path" settings so that it will actually remember the path set? Am I missing something here, or does it have anything to do with the fact that we're using Windows 98? My buddy's using NT, and his works the same. Is there a way around this? TIA, Rob.

[Rob Wright]

OK, never mind.... Found it in the knowledge base. Have to go to the "miscellaneous" section and uncheck "use native dialog boxes". Had looked in the online help, but it left off this very important detail... Works great now. Thanks, Rob.