Timed Toop: Signal From Task with Change Detection Event

[phili]

Dear all,

I have a digital input comming from a HAL Sensor of a motor. This HAL Sensor helps me find the inital motor postition.

I used to poll the digital input to detect changes on the line. Now I found the much more elegant way of using a timed loop in combination with "Create Timing source VI" .

I would like to use the "Signal from Task" instance of the VI as the associated task has already been created.

The problem is that I keep getting the following error message:

-200452

DAQmx Create Timing Source (Signal From Task).vi<append>
<B>Property: </B>SignalFromTask.Signal <B>Task Name: </B>_unnamedTask<4A1>

I use a PXI System and the digital input is located on a PXI-6602.

Additional Question:

Later I will need to read the digital line before using it with the described loop.
The Manual tells me not to use the "DAQmx Start Task" VI to start the task as the Timed Loop starts the task automatically.

But I will have to start the Task. Otherwise reads are not possible.

Thanks in advanvce for helping me with the Problem

Viele Grüße
Phili

Message Edited by phili on 03-23-2006 06:25 AM

[RebeccaFo]

Hello Phili,

for your first question you will find the answer in link:

http://zone.ni.com/devzone/conceptd.nsf/webmain/5b71e273769cbdd286256fd200677b70

and there it is Application 6.

Hope this helps,

[phili]

Hello Rebecca,
thank you for your reply.

The given example works fine. But that is not really what I want.

The example makes the loop run each time a new sample is acquired and this is rample rate dependant.

I would like to loop to run each time a rising or falling edge is detected on my digital input.

I guess that the block diagram is somewhat similar to the one given in the example you pointed me towards but I still can't figure it out.

Any help is still very much appreciated.

Grüße
Phili

[phili]

It looks like as if the current DAQmx drivers (whatever current is) only support the 65xx Digital I/O Cards as far as change detection is concened.

Cound anybody please confirm this so that I stop digging for something it is no use to dig for.

I read that the M Series do suppoert change detection by hardware. It's just the driver that is not capable to support it yet.

How about other cards? Is there a reference that shows which cards do support change detection by hardware?

"Yet" is already a year old. Has anything changed that I am not aware of?

I still use Labview 7.1. Will I be a happy man to see "Change Detection" work with LV 8?

Liebe Grüße
Phili

[Kevin_Price]

DAQmx 8.0 began support for change detection on M-series cards -- I've tried it and can confirm it on a 6259.

However, I don't know whether M-series change detection can be used to generate a route-able timing pulse or act as a Timing Source for a Timed Loop.

-Kevin P.

[phili]

Thank you Kevin,
that is a first valuable hint.

Do you know anyrhing about the "change detection" support of other cards?

Phili

[phili]

They only support Digital and M-Series cards

http://digital.ni.com/public.nsf/allkb/8914FA5E30971E0C86256FEF005760FF

Phili

[Stuart_G]

Phili

What you want to do is not use the Signal From Task Flavor.  You can use two other timing sources depending on what your board supports

#1.  Use the Change Detection Timing Source VI.  There is an example \examples\daqmx\control\event response.llb

#2.  If your board doesn't support change detection you can also use the Digital Edge using Counter Timing source.  This example uses a counter to trigger each time a digital line goes high or low on a given PFI line.  Look at the example \examples\daqmx\control\Dig Output-digital Edge with Ctr.

I also want to encourage and remind everyone who might be reading this to use the NI example finder.   We have a ton of example programs and searching for timed loop would have yielded each of these examples.

StuartG

[phili]

Hi Stewart,
thanks for the reply.

Well, the board doen't support change detection as it is a PXI-6602.

And the problem with counter supported edge detection ist that I am short of counters.
I need to use the boad for PWM control and I have to read a quadratur encoder (6 motors total).

Hence I guess I'm stuck with polling.

Phili