why does my min:sec timer decrement while not enabled?

[Jeff in Pleasanton]

My application uses many minute:second timers that must be displayed to the operator as mm:ss.

The attached simple vi does what I need except that the count-down-time value stored in the shift register decrements even when the timer is not enabled.  There may be a blindingly ovbious logic error that I can't see, or there may be something subtle in the way LabVIEW operates that is tripping me up.

In any case, the shaft register variable (Hi-1) begins decrementing as soon as you run the vi.  It should not.  It should hold the value set by the control called Timer until the Start button is pressed.  It should stop decrementing and revert to the Timer control value when Abort is pressed.

Can anybody see my error?

[TCPlomp]

Hello Jeff,

it seems strange to me as well. I tried to initialize the shift register but that didn't work. However if a replace the timed loop with a normal while loop and put a wait until next ms (1000) the VI functions as expected. Maybe this is a bug in the timed loop. Even terminating the loop had no succes..
Ton

[altenbach]

Very interesting... I vote for mayor bug!

Interestingly, it behaves correctly if execution highlighting is on. You can actually place a probe on the shift register wire and the value jumps depending on the execution highlighting setting while the VI is kept running.

(Still, it seems like overkill to use time loops just to run a timer. Why don't you use the system timer instead? :))

[Jonnie_5]

OK, I know diddlely about timed structures (never used one in my life), so someone else can explain the WHY, but it works if you configure the input node to Use Built-In Timing but RESET at structure start.

[tbd]

Hi Folks,

     Would some kind soul please post this in 7.1 (or post a pic)?  I wanna see tooo!

Thanks!

[TCPlomp]

tbd, here you go:


BUT when i rebuilded the vi, i did not see the same issue, but when i recompiled the Vi the issue remained, and when i converted the timed loop into a normal and back the issue was gone as well. So I think there something with this VI, have you done the 8.0.1 update?
Was there anything done special when making this VI?

Ton

Message Edited by TonP on 08-02-2006 01:11 PM

[Jeff in Pleasanton]

Dave Weisberg found the problem - somewhere along the line I had unchecked "Discard missed periods".  The timed loop is treating periods during which it is not enabled by the Start button as missed.  When you press the Start button, it "catches up".

This still seems like a bug to me.  I assumed that missed periods meant that the code was enabled to execute but there weren't any processor cycles available, so one or more loop periods failed to execute.

[tbd]

Thanks, TonP!