Generating continuous waveform while preserving properties

Question

Hello,
Thanks to all the past
posters for being so helpful.
I was unable to answer two questions:
The first concerns the maximum
triggering rate in LabVIEW. My goal is to have two trigger / gate blocks set up
working at approximately 25 Hz and 7800Hz, respectively. Is it reasonable to
expect proper trigger/gating even at the higher rate?
Secondly, how can the frequency
and duty cycle of a simulated square wave be preserved for smaller samples? I'm
trying to simulate a 25Hz square wave with 50% duty cycle at 1MHz sampling
frequency, but in 129 – sample increments. Currently, only the first 129 samples are
displayed, even on both “reset phase, seed and time stamps” and “use continuous
generation” modes. In other words, my goal is to have a waveform that is
displayed in ‘pieces’ or in ‘frames’ of the total waveform without resetting
generation.  
Your help is always
appreciated,
BME_guy

Answer 1

Hello,
One way to implement this would be to simply create 1 period of your desired waveform and hold it in an array.  Then, on each iteration of your loop, you simply take out the next 129 points.  The only catch would be that you will have to account for the rollover case.  Well, I decided to just implement this for fun, so I have attached a VI which will take the next N points from a buffer, as well as an example which illustrates how to use it.  The subVI is used like a functional global - basically it has an initialization state where you need to specify the buffer (your array of data) and the start index.  Then you can call it with the Get Next N Points state and it will get the next N points from the array - accounting for the rollover when necessary.  In fact, you can specify getting a different N on different executions of the Get Next N Points state (which is why this must be wired inside the while loop of the example VI which uses the subVI).  If you're not familiar with the functional global concept, it's the idea that you can have an uninitialized shift register hold data across executions of a subVI.  Save both attached VIs to the same location on your machine, and run the example to see how it works.  You can then use my previously attached code to generate 1 period (40000 points for your case) of your square wave, and use that array instead of the example's.  Then make N=129 and you're golden.
I hope this helps!  Admittedly the code isn't cleaned up - I literally just wrote this a few minutes ago.  But it should do the job!
Best Regards,
JLS
PS - Just to be clear, the "subVI" referred to as a functional global above is named "Circular Read Buffer Functional Global.vi" and the example which shows how to use it is named "Example Using Circular Read Buffer Functional Global.vi".
Best,
JLS
Sixclear
Attachments:
Example Using Circular Read Buffer Functional Global.vi ‏38 KB
Circular Read Buffer Functional Global.vi ‏47 KB