asynchronous counter reset in DAQmxCreateCILinEncoderChan()

[DAQTech]

I am implementing a PCI-6602 counter and am using the function DAQmxCreateCILinEncoderChan() to measure linear position.  I would like to use an external pulse to reset the the counter to 0.  I would like this to be independent of phase.

Can I set this as equivalent to the ZIndex pulse?  If so can I set the argument ZindxPhase so that the reset occurs at any phase of my encoder?

or is there another way to perform an asynchronous counter reset?

Thanks

[Kevin_Price · Accepted solution]

No, you really can't reset the count independent of phase using the z-index reload feature on a 6602.  The newer X-series counters provide for a phase-independent hardware-edge-driven count reset, but I'm not certain whether it's available for modes other than simple edge counting.

I'm just piecing together an almost-workaround that'd need an M- or X- series board with digital change detection, but it's kinda convoluted and not for the faint of heart.  [Executive summary: extend the z-index pulse for 4 quad states using another counter and the change detect event signal.] 

A different pain-in-the-neck workaround would be to parallel wire your encoder to another counter and use the desired z-pulse as a sample clock.  You'd need these two encoder tasks to be "arm-start triggered" together to keep in sync.  Then neither counter uses z-indexing, but the 2nd counter keeps a record of the positions where the 1st counter *should* have been reset.  In post-processing, you can find where the 1st counter passed through those positions and apply the appropriate offsets.  See?  Told you it'd be a pain...

-Kevin P

[DAQTech]

Thanks Kevin for the prompt reply.

Your idea of a second counter may be what would work best four our app.

I will give it a try today.

[DAQTech]

Kevin,

Taking the 'parallel wire' approach... I could setup a second counter using the DAQmcCreateCILinEncoderChan() function applied to a second task.  Can I have 2 DAQmxReadCountF64() functions reading into arrays simultaneously in the same thread?

[Kevin_Price]

It may depend on what you mean by "simultaneously."

They will be separate tasks buffering at different rates and will need to be read using separate Read calls.  Within a given thread, those read calls would have to be consecutive.  However, the board & driver will be buffering their captured data simultaneously.  That's why the post-processing you'll need to do on the data will still be valid.  Just be sure to "arm-start trigger" the tasks off a common hardware signal.

-Kevin P