Configure Timed Loop Dialog Box - what is the period?

[hshane]

In the Configure Timed Loop Dialog Box documentation we are told that:

Period—Specifies the amount of time that elapses between two subsequent iterations of the Timed Loop. The unit of the period changes depending on the timing source you select in Source Type.

But nowhere are we explicitly told what the unit of Period is. This ought to be made explicit for each of the possible Loop Timing Source Types. I'm guessing that if I select 1 kHz Clock the unit of Period is 1 millisecond. But I shouldn't have to guess!

[note: this is a cross post from the NI Discussion Forums]

[X.]

one clock cycle?

[hshane]

@X: Your question mark gets to the heart of my complaint. We're both guessing.

[X.]

Well, that's the kind of question with the answer in it!

[timtamslam]

I think the easiest way to validate the unit is by reviewing the timing attributes in the Configure Timed Loop dialog (double click on the Timed Loop Input node or right click on Input node and select "Configure Input Node")

From there, depending on which source you have used, it will show you the unit for the period and the value (if you aren't explicitely specificying it with an input) in the Loop Timing Attributes subsection. It will grey out the value if you use a terminal input. 

Another useful resource is,

http://zone.ni.com/reference/en-XX/help/371361L-01/lvconcepts/configuring_the_labview_timed_loop/#Se...

[X.]

But we agree that the period cannot be shorter than the clock period, right?

Therefore the smallest, period (1) is equal to 1 clock unit (you'll notice that the "unit"of the period, ms in the example above, cannot be edited and that the value of the period, 1000 "units", is reflected in the dialog window, which shows 1000 ms).

If you use the "Create Timing Source.vi", this becomes even clearer:

Double-clicking on the input node:

The unit is called "tick", even though it could have been set to "us" (corresponding to the period of the 1 MHz clock).

QED.

[timtamslam]

hshane, 

"But nowhere are we explicitly told what the unit of Period is. This ought to be made explicit for each of the possible Loop Timing Source Types."

Do you think that the "Period Units" (had to break out the context help for the official name) is insufficient in providing this information? If so, do you have a recommendation on how it could be made more clear?

X. ,

"But we agree that the period cannot be shorter than the clock period, right?"

I agree. For all of the timing source types usable with RT and FPGA, yes, the smallest possible unit is "ticks" which is the time duration for a single clock tick. And, as you've already pointed out, a 1MHz timing source tick is .000001 s (1 us). 

[Darren]

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