How do I get values into a vi from a subvi while the subvi is still running within the vi?

Question

Hello
This is my problem. I have a subvi that runs an experiment. At different point in the experiment different instruments are on or off and I have a boolean array display this info. It is updated at various points of the experiment via a local variable. That works fine. Here is the problem though. I run that subvi from a main vi program (that runs it several times for several experiment cycles). I would like to pass the status of that array onto the mainvi to display there too. The problem is that the array in the main vi is not updated until the subvi is done running and thus displays only the array status at end of experiment (instead of changing
as the status changes within the subvi). I tried using a global variable to write to it in the subvi every time there is an update, and read from it in the mainvi, but that doesn't work, it still displays just the status at the end of the subvi execution. Does anyone know how to make this work, or if there is a workaround this? Thanks.

Answer 1

If you have LabVIEW 6i, you can update indicators of a calling VI from
a SubVI, while the subVI is running.
In your case you need
1) an indicator on the main VI panel to display the boolean array
2) to pass a reference to that indicator to the subvi when you call it
3) to use this reference in the subVI, connect a property node to it and
write the values to be displayed to the 'value' property of this node
If you don't have version 6, you can write the values to be displayed to
a global and display this global in the main VI from within a while loop
which must run in the main VI in parallel to the running subVI.
It's more complicated, since you need a mechanism to gracefully shut
down the while loop after subVI finishes. You could do this with
another global control boolean which is not displayed but just connected
to the repeat terminal of the while loop. Don't forget to put a 'Wait' of,
say, 50...100 msec in that while loop.
-Franz
zkajan schrieb:
> Hello
> This is my problem. I have a subvi that runs an experiment. At
> different point in the experiment different instruments are on or off
> and I have a boolean array display this info. It is updated at
> various points of the experiment via a local variable. That works
> fine. Here is the problem though. I run that subvi from a main vi
> program (that runs it several times for several experiment cycles). I
> would like to pass the status of that array onto the mainvi to display
> there too. The problem is that the array in the main vi is not
> updated until the subvi is done running and thus displays only the
> array status at end of experiment (instead of changing as the status
> changes within the subvi). I tried using a global variable to write
> to it in the subvi every time there is an update, and read from it in
> the mainvi, but that doesn't work, it still displays just the status
> at the end of the subvi execution. Does anyone know how to make this
> work, or if there is a workaround this? Thanks.
Franz Josef Ahlers
Section Semiconductor Devices
Physikalisch-Technische Bundesanstalt
Bundesallee 100
D-38116 Braunschweig
phone: [phone]
fax: [phone]