delay between 2 counters

[cig438]

I'm using the 6221 & attached is a VI where I need to adjust the
initial delay between 2 counters. I get error  50103 : specified
resource is being used. I guess it doesn't like the fact that I'm
starting 2 tasks - one with each counter ?
I based this delay code from the delay example forum.vi posted on
another post. It uses ctr0 & 1 start tasks without any problems
apparently.

How come mine is having issues ?
Is this because ctr 0 & 1 are 'paired' ?

Thanks,
ak


2 counters with delay between them.vi:
http://forums.ni.com/attachments/ni/70/6607/1/2 counters with delay between them.vi

[cig438]

Thank you - I understand. I've found a different way to incorporate the
delay - literally padding the pulse trains appropriately with zeroes.

To be honest, I'm a little perplexed at why such seemingly simple tasks
are that complicated in DAQmx.... I'm wondering if this is an inherent
DAQmx balance between versatility & ease of use, or whether my 6221
card is just a low end DIO device ?

As an example, I have another post in the DIO forum where I've given up
trying to find a solution - but the problem is amazingly simple : I
want the user to supply a digital waveform & have that continously
output together with 2 other fixed waveforms. I must have create 10
different vi's but none of them are error-free. Apparently my
particular DIO task is considered difficult & that worries me.

Right now I don't have much confidence in DAQmx as a straightforward
means of DIO & would opt for use of a microcontroller that,
compared to at least my 6221, has no limitations on signal
configuration.

ak

[Kevin Price]

The way the board's counters work requires 2 counters working together as a pair in order to generate a "finite pulse train" with a specific # of output pulses. 
DAQmx attempts to do some of the grunt work by configuring the helping counter automatically "under the hood."  However, that fact seems not to be advertised prominently enough.  Many people have posted before who didn't know why they couldn't do something with their 2nd counter when the 1st was set up for finite pulse train generation.  Somewhere, somehow, NI should emphasize this side effect.
It's most fundamentally a hardware limitation, not specifically a DAQmx issue.  The older driver also required 2 paired counters working together -- it just required more grunt work on the programmer's part.  It was both more difficult *and* more clear.
Another item about the DIO stuff.  As I recall one of the other threads, the problem arises because of wanting to have 2 separate hardware-timed DO tasks.  Again, it's the board that doesn't support that.  You can have a whole bunch of separate software-timed DO tasks, but then you may not get the precision you want due to your OS.  The board only supports 1 hardware-timed DO task at a time.
I just reviewed two other threads you had about this kind of stuff.&nbsp; I found that I was in <a href="http://forums.ni.com/ni/board/message?board.id=170&amp;message.id=237423#M237423" target="_blank">one of them</a>.&nbsp; I think the "buffer merge" idea I presented could work, though I know it isn't trivial to&nbsp;implement&nbsp;-- what problems did you have?&nbsp; I can't say much about the other thread now because I don't have LV near me to look at the posted code.
-Kevin P.

[cig438]

I've modifed the vi to use continous samples. I have a dedicated
counter that is delayed w.r.t to a 2nd counter. One waveform is written
to each digital IO line that receives it's clock from its own counter.
I get error 89137 : Specified route cannot be satisfied, because it
requires resources that are currently in use by another route.
What does this mean ?

All I want to do is to delay 2 digital waveforms a user specified amount.
A 2nd issue is that the internal while loop never exits because the
task is never done (continous samples) ! I've tried many things in the
past &amp; can't get this part to work either.
I've looked &amp; implemented examples &amp; must have at least 20 simple vis but nothing works right. I'm not having much luck :smileysad:

Any help would be greatly appreciated - specific code is best - I've been trying to implement this for a while &amp; need specific help.

ak


2 counters with delay between them II.vi:
http://forums.ni.com/attachments/ni/70/6629/1/2 counters with delay between them II.vi

[Kevin Price]

I saved the code you attached and will try to take a look later when I can get on LabVIEW.&nbsp; However, your text description sounds like you're *still* trying to simultaneously run 2 separate hw-timed digital output tasks.&nbsp; If so, then STOP!&nbsp; It can't be done!&nbsp;&nbsp; The error you describe sounds consistent with this -- if you are trying to specify a 2nd simultaneous clock signal to be mapped to the DO timing subsystem, that's sounds like the kind of error you'd get.&nbsp; The first counter output has *already* been mapped to the DO timing subsystem, so the 2nd attempt fails.
You really *do* need to merge the data so you can create it with 1 DO task.&nbsp; The job of merging the data correctly will require some careful planning ahead on your part.&nbsp; In one of your other threads, I <a href="http://forums.ni.com/ni/board/message?board.id=170&amp;message.id=237423#M237423" target="_blank">posted</a> an approach for a&nbsp;fairly simple example.&nbsp; Did you follow that?&nbsp; Do you see how you would extend that idea to your own app?&nbsp;
Sorry I can't offer specific code to help.&nbsp; This kind of merge is, in general, non-trivial and I just don't have the time.&nbsp;&nbsp; Can you describe the nature of the two patterns in more detail?&nbsp; If by chance they are a&nbsp;special case that's easier to handle, maybe&nbsp;I could&nbsp;help a bit after all.
-Kevin P.

[cig438]

Thanks Kevin. I created the delay using your suggestion. I created a
small timebase for all 3 signals that would allow me to modify a delay
between them &amp; it worked from a single task.

But wow, the 6221 bristles with inputs &amp; outputs &amp; yet only 1
hardware task can be performed at a time - my suggestion is that that
be stated in somewhere in the product description.

Also, the 6221 data sheet on the NI website doesn't seem to open
properly - I'm using Adobe Reader 7.0 &amp; get an error 'file does not
begin with %PDF-.

ak