Then there are trial versions by some other manufacturers which for checking of some behavior might be perfect.

Contact me by PM if you require help with adopting the solution.

 The ELSE does not belong to an IF, but to the CASE statement itself. It is executed when #Case does not match any of the specified values.

You may benefit from reading the help article on the CASE statement. I think you'll find it answers your questions. In particular: after executing the instructions in the matched case, execution continues after the END_CASE statement. Other cases are not executed. 

steurung__

 

qwazee

 Yes. The sequence is stuck. If you do not want this, you will have to expand the condition used for the first IF-statement. The attachment makes a suggestion you can evaluate. Note that the sample is not meant to be perfect; it is meant to open discussion.

What are your thoughts?

 Hi qwazee, 

in your sample code:

 

#Check := #Press1 and #Press2 and #Press3;

// if not #Check then (* optional *)

//    #Case := 0

// end_if;

case #Case of

0:  // restart

if #Check then

#Case := 10;

end_if;

10:  // do function 1

#Case := 20;

20:  // do function 2

#Case := 30;

30:  //do function 3

#Case := 40;

40: // do function 4 & exit

// if not #Check then (* alternative *)

//    #Case := 0;

// end_if;

#Case := 0;

else

#Case := 0;

end_case;

 Assuming that #Check is TRUE: the variable #Case is never set, therefore none of the values inside the CASE function will be activated, therefore the #Case := 0; at 40 will be ignored since #Case is never set to 40. Moreover, to which IF the ELSE used in 40 refers to?

steurung__

Assuming that #Check is TRUE: the variable #Case is never set, therefore none of the values inside the CASE function will be activated, therefore the #Case := 0; at 40 will be ignored since #Case is never set to 40. Moreover, to which IF the ELSE used in 40 refers to?

@alizon already answered expertly (thanks). Allow me to add some notes.

#Case must have some value. That value is by default 0 if it is not set to something else in the definition of the tag. The ELSE inside the CASE-structure ensures that the #Case tag always have a legal value.

Do note that #Case cannot be a temporary tag, but must be either from in-out parameter (FC / FB) or static parameter (FB). This ensures that the tag has memory.

If you are not going to implement anything in a simulator or in actual hardware, what's the point? An academic exercise?  That is not a very good teacher or PLC programming.

Also, 21 day trial license allows full plcsim function so you _can_ test these types of things out for yourself. 

steurung__

jacek d

steurung__

The question is: after supposing that #Check is always TRUE upon each cycle, and according to the above code, will function 1, function 2, function 3, and function 4 will ALL be executed in a cycle?

How about getting hardware or the PLCSim and checking it by yourself ? That's good exercise to grasp the basics.

 If any of the suggested solutions (hardware/plcsim) are affordable at this point, I would not have created such post initially. 

Not as you currently provided with a being initialized to 0 every pass through the PLC logic.

If the logic is placed inside an FB, sure, it could do that, but only handle the code inside each case once per PLC scan of that FB's logic - the normal and customary approach and how you might use a case instruction to manage an FSM (finite state machine).

FYI, there's absolutely no reason you cannot call an FB 10 times per PLC scan - in case you want the FSM logic to do nothing in between - which is really generally useless since no actual outputs get activated - without special design considerations in advance of coding the PLC logic.

steurung__

Hi Einstein,

Thank you for your interest. The moral of the story goes as follow:

The usage of the CASE function, as intended to make a "virtual" program Jump, between successive cases, can NOT be done, if the procedure was following the initial pseudo-code posted, UNLESS an Else is used at its bottom: True or false? In overall, the usage of the CASE function to create program jumps, is a bad programming routine: True or false?

With thanks,