How functions works

Hi folks….. I have question about functions in s300. Function are procedures that do not save data so I can use only temp variables in local data stack. So if I have function and I call it twice for example does cpu reserve different local data for the second instance of the function. Im asking that because I have this situation. I have function and in I set a bit (temp var)in it and on the next instance this bit is already set …. Is that mean that function safe the state of temp vars ?

fury_omen

...I have function and in I set a bit (temp var)in it and on the next instance this bit is already set ….

gre_m

Hi fury_omen!
You talk about the global data outside of a a function?

fury_omen

...(temp var) ...

Hello fury_omen

For FC’s you cannot use TEMP’s to store data, the option for you will be FB’s with Instance DB, where you can declare STAT statics variables.

The following linkDifference ... explains weell the differencesbetween FC's and FB's
Regards
Marciano

Let look that example. I have two function. The first ‘fc4’ called the second ‘fc3’ twice. In ‘fc3’ I have set coil ‘temp1’. The output of ‘fc3’ depends on two inputs var ‘in1’ and ‘in2’ and local var ‘temp1’. On second instance of function ‘fc3’ I have only to set ‘in1’ and the output ‘pass’ is on. The ‘temp1’ var is set in the second instance on function ‘fc3’. Is what mean that local data is saved? I just copied these function in STL just past them in stap7 and turn the view to LAD and test it will PLCSim. So my question is if I set tamp var in function how to know what happen with this var in second instance of this function is it will be clear, set or undefined

fc 3

in: in1 – bool; in2 – bool;

out: out1 – bool

temp: temp1 – bool

A #in1

S #temp1

A #in2

A #temp1

= #out1

fc4

in: n1 - bool; n2 - bool

out: pass – bool

temp: t1 – bool; t2 – bool

A M 10.1

= L 1.0

BLD 103

A M 10.2

= L 1.1

BLD 103

A #n1

JNB _001

CALL FC 3

in1 :=L1.0

in2 :=L1.1

out1:=#t1

_001: NOP 0

A M 10.3

= L 1.0

BLD 103

A M 10.4

= L 1.1

BLD 103

A #n2

JNB _002

CALL FC 3

in1 :=L1.0

in2 :=L1.1

out1:=#t2

_002: NOP 0

A #t1

AN #t2

= #pass

ob1

A M 20.0

= L 21.0

BLD 103

A M 20.1

= L 21.1

BLD 103

A M 1.0

JNB _001

CALL FC 4

n1 :=L21.0

n2 :=L21.1

pass:=M30.0

_001: NOP 0

You should see the TEMP as a sketch or draft , temporarily variables valid inside the block only.
Now answering your question, they are not cleared, actually they ” keep the state”., and not officially if your program have only one OB and one FC you could have your TEMP’s holding values… However because this area is shared with other blocks with same priority, the TEMP area will be constantly been updated /several updates during one single scan – so I think you can say theresult would be undefined.

Yep, my mistake is ‘in2’.

So in one OB, I do NOT have fresh instance on same function if I call it more than ones. And this happed because the local date stack is not cleared after end of function. If I want everything to be fresh I have to clear all set bit and so on before exit from function. Is that right ?