The Dataflow Paradigm #7

[SercoSteveB]

The following VI is executed; exactly 2 seconds later the user performs a left mouse click on the 'Stop' control.  Assuming an initial value for the 'Stop' control of FALSE and a 'latched when pressed' mechanical action; what is the value of Numeric Value Out following activation of the 'Stop' button?

a) 11

b) 15

c) 21

d) Undefined

[SercoSteveB]

Answer: D

The While loop will iterate indefinitely.  The default value of the 'Stop' control (FALSE) is read at the start of execution and passed to the standard input tunnel of the While Loop.  Once the While loop has all required inputs the value of the standard input tunnel is read (along with that of the shift register) and begins to execute.

Once the value of the standard input tunnel has been read (on the first iteration) it is not read again; therefore a boolean FALSE is passed to the Conditional Terminal of the While loop throughout execution.  As the Conditional terminal is set to STOP on TRUE, the While loop never completes.

[Frabto]

Tricky qsn

[GSXR100038]

Hi,

I need to know whay happen if the button Stop is inside the While loop the numeric Value Out is 20 but I don't understand why. Because normally the while loop execute (2000/500 = 4) in this case the  

numeric Value Out is 15. Can you explain Why? Thanks for your answer.

[crossrulz]

GSXR100045 wrote:

                       

Hi,

I need to know whay happen if the button Stop is inside the While loop the numeric Value Out is 20 but I don't understand why. Because normally the while loop execute (2000/500 = 4) in this case the  

numeric Value Out is 15. Can you explain Why? Thanks for your answer.

                   

It is sort of a race condition.  At exactly the 2second mark, the loop has iterated 4 times.  But it hasn't stopped yet.  On the fifth iteration, the button will be read as TRUE.  So at the completion of the 5th iteration, you have a value of 15 (5+0+1+2+3+4).  You would get 20 if you were even slightly late for the 2 second mark.

[GSXR100038]

Hi

Ok, I understand it's a race condition but in the question is "exactly 2 seconds later the user performs a left mouse click on the 'Stop' control" and the reponse is 15, 20 or both ?  

[ps3fer]

download the examples please

[faisalm88]

Clever question!

[GSXR100038]

Sorry for my question is not very clear, thank you crossrulz for you explanation.

[ashwinilele]

D

Stop button doesn't change to TRUE  while WHILE loop is in running condition.  It occurs race condition . I think so.

[eleshrudra]

D

[Andreas.Bernau]

D

[M.P.Bharghavi]

Ans: D

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[ersmt444]

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