how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:28.341000Z

It is not really clear what you mean.
Static variables in functions are not available in V2.3. In V3 you can define them.
What you could do is use function blocks, or use global variables (which is not really good programming).

If you mean how you need to declare a variable you could use:
VAR
y : INT := 100;
END_VAR

VAR CONSTANT
y : INT := 100;
END_VAR

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:26.911000Z

hi,

   how to declare 100? and y 100 is not recognized as it is an integer?

Thanks

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:22.896000Z

  That means we can declare as a global variable and use that one in a function?Because function is just a machine which gives output for different recipes differently. of course memory allocation is only once even though reused.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:21.514000Z

Maybe good to know is that CoDeSys V3 will support the new variable type VAR_STAT. This feature is an extension to the IEC 61131-3 standard. This can also be used in Functions.

Your PLC should have the CoDeSys V3 runtime to be able to use this.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:17.619000Z

Yes, I agree that it is a perversion of the intention of 61131 function, the key being that a function should always return the same output with a given input, but if accessing global variables that are essentially static, then the function, possibly by design, will NOT return the same output every time for a given input.

I might be tempted to use such a function if it actually made the programming clearer and simpler. From reading a version of the 61131 spec, I assumed the above code wasn't even possible until I decided to test it.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:16.200000Z

I had forgotten also that the function is confusing to a user. A function is suppose to have action and the same input will yield the same output. If I were the end user what would I expect as the output especially if there are no inputs? How would I be aware of what the function is doing unless I had access to the internal code. What if I made a function like:

FUNCTION ADD :WORD
ADD := 1;

What would the end user think when using this function? I would like to ADD something but what, there are no inputs? In your case calling that global function will cause an action that the end user will not even know about and cause all kinds of havoc.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:14.832000Z

Interesting but I would considered it poor programming practice. As described above you can not "DECLARE a global variable". You declared global variables else where in Main so it is legal. But now you have a function that is not reusable unless you have the global variables defined in main that are referenced in the function. The only time I see a need to use a global in a function would be a GLOABL CONSTANT. Like MAX_FAULTS = 32 to define an array bound. There is a SIZEOF in CoDeSys but if you are a stickler for pure IEC61131 then sizeof is not a part of the standard.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:10.977000Z

This may be a perversion of the 'standard', and I don't know if this is a Beckhoff-ONLY implementation or standard across Codesys v2, but you use a global var in a function to achieve a static var capability. (...or cross-function comms or other dirty tricks... )

I can write one thus:

FUNCTION F_TestFunGlobals : BOOL
VAR_INPUT
END_VAR
VAR
END_VAR
IF bTest1 THEN
   iTest3 := iTest3 + 1;
ELSE
   iTest4 := iTest4 + 1;
END_IF;
bTest2 := bTest1;
F_TestFunGlobals := bTest1;
MAIN.bTest := FALSE;

Every var above is global, declared in the main global var resource, except for var_input MAIN.bTest, which is a bool in MAIN that permits the function to be called from MAIN, and the function itself resets it (another test of to what a function can write).

So if bTest1 global is true, the function outputs true, bTest2 is set true, and iTest3 is incremented. If bTest1 is false, the function outputs false, bTest2 is set false, iTest4 is incremented. Finally the function resets the bool that is used to conditionally execute the function, resulting in a single run through the function for each setting of MAIN.bTest.

Is this the path to the dark side of programming, or a useful technique?

It reminds me of why I don't like anyone using SET and RESET outputs in ladder.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:09.604000Z

you will have to tell the function what 100 is. i do it normal to make also the statics to be in a variable so hundred:=100:uint;

for example.

100 is no type.

how can I use STATIC VARIABLE in FUNCTION

2020-02-27T20:37:05.754000Z

As a very basic rule of thumb if your POU doesn't rely on saving any prior state internally then use a function, else use a FB.

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