Event Structures and Dataflow

[SercoSteveB]

The following VI is executed.  Assuming the default values for Boolean Value 1-5 are FALSE, if the user performs a left mouse press and release on the Boolean Value In 3 control, what is the value in Boolean Value Out?

a) TRUE

b) FALSE

[thinnker]

Its (b) false is the answer.

Here we used event triggered on Mouse Up not the value change.

so previous value(FALSE) will passed to boolean value out

[Anagha.G]

i think a is the answer

[Calvin_Fernandez]

hi everyone,

could someone please explain to me how this vi-works. i`d like to work it out. thanks a tonne for the help.

[SercoSteveB]

Hi Calvin.  Welcome to 'The daily CLAD'.

The box is called an Event Structure.  You can configure this type of structure to respond to events (keypresses, mouse clicks, mouse moves etc. etc).  In the question we have configured the Event Structure to respond to a Mouse Up event on any of the controls Boolean Value In 1-5. 

Because we haven't wired a value to the Timeout (egg timer shaped) Terminal, this event structure will wait forever for any of the configured events to occur.  When an event occurs the code inside the structure (for the appropriate event) is called. 

As we have not included this Event Structure within a looping structure, this VI will only respond to one event and then finish.

A little hint.  This question is not really about how an Event Structure works (although you need to know to answer the question).  This question is more about something fundamental to LabVIEW.

Hope this helps

Steve

[ROSEJ]

answer is b

[mini09]

Yeah i go with all who says B.

[Anagha.G]

yah now i too think ans is b coz value really doesnt change on mouse up and release

[Calvin_Fernandez]

thanks steve.....:-)

[JÞB]

would be interesting to put the event in a loop- declare the MA of each bool and ask again

[BenoitP.]

I agree with JeffBoher, you can't answer to this question without the type of Mechanical Action for each control. And a Timeout could be define to let people think about the main question !

[JÞB]

you can't answer to this question without the type of Mechanical Action for each control

Not quite.  As shown the event structure input tunnels will have all have a false as soon as the vi runs waiting for the event to fire. fire event and the PREVIOUS data enters the event All false OR'd = False out.

Its actually a race condition.

[SercoSteveB]

Answer: B  As JeffBohrer states, the values of the Boolean Controls 1-5 are read when the VI runs, before the left mouse press and release is performed.  When the mouse left press and release is performed, the values at the input tunnels of the event structure are all FALSE.

Nice comments guys.  As I think Jeff is indicating in his last comment; I don't think you need to know the mechanical action of the controls to work out the answer to this one.  This is a dataflow question masquerading as an event structure question. 

If we had a loop around the event structure and the terminals then it would be a different story (thanks Jeff; a future Daily CLAD question defined).

[JÞB]

Certainly, a good way to point to the caveats on using Event Structures and Latchers!  a must learn for any CLAD candidate!