How to acquire samples every n samples ?

[xela75]

Hi !

I'm using 6541 card and I want to acquire 1 or 2 samples every 5 samples for instance.

Is it possible ?

I tried Pause Trigger but it does not seem to work...

Thank you.

[Keith.Shapiro]

Hi xela75,

Pause trigger should work to do exactly what you want.  Keep in mind that pause trigger is synchronous with the data (it can be thought of as the inverse of a "data valid" signal).  The pause trigger must meet the same setup and hold requirements as the data.

What sort of behavior are you seeing with the pause trigger?

Also, could you filter the unwanted data after capture, or are you concerned that you'll run out of pattern memory if you have to do that?

Thank you,

Keith Shapiro

National Instruments R&D

[xela75]

Eventually, i used the "filter the unwanted data after capture" method. It takes a lot of memory but anyway it works !

But i'm still interested in how to acquire samples every n samples. I tried Pause trigger but it does not work.

Do i have to put a start strigger and a pause trigger or just a pause trigger ?

Thank you.

[Keith.Shapiro]

I'm still not sure what you mean by "Pause Trigger doesn't work".  Can you explain the signals that you're providing (timing diagrams are always helpful), and what you expect to happen, and what actually happens?  Maybe with more information I can help you track down the trouble.

Per your question, you do NOT need a start trigger.  You can start immediately and have the system be in "pause", and then "unpause" when you have data come in.  I've done this use case before.  I'm pretty sure that you'll need to unpause at the end of your transfer for the system to register as done, but I don't remember off the top of my head.

Also, keep in mind, Pause trigger is synchronous - that means it's evaluated EVERY clock cycle.  So you'll need to hold your pause trigger asserted when you do NOT want to capture data, and deassert Pause for all the data you do want captured.