Difference between Properties and own getter/setter

2020-02-27T14:17:26.304000Z

Originally created by: scott_cunningham

Are you giving FB_C a reference to FB_A's instance of FB_B?

FB_C knows nothing about FB_B, unless you define an FB_B instance in FB_C. But, since you want to have FB_C specifically affect FB_A's instance of FB_B, then you need to setup FB_C to have a REFERENCE TO FB_B, instead of it's own instance of FB_B.

Silly example:

Create FB_B with a simple Property that maps to a local variable...

FUNCTION_BLOCK FB_B
VAR_INPUT
END_VAR
VAR_OUTPUT
END_VAR
VAR
   _Local : BOOL;
END_VAR
PROPERTY Prop1 : BOOL
Get routine:
Prop1 := _Local;
Set routine:
_Local := Prop1;

Now setup FB_C so it can take somebody else's instance (aka REFERENCE TO FB_B). You could also do POINTER TO FB_B or use an interface... I will use REFERENCE TO...

Here, FB_C will set FB_B's property "Prop1" to match "DoIt".

FUNCTION_BLOCK FB_C
VAR_INPUT
   DoIt : BOOL;
   refB : REFERENCE TO FB_B;
END_VAR
VAR_OUTPUT
END_VAR
VAR
END_VAR
refB.Prop1 := DoIt;

Now create FB_A that creates instances of both FB_B and FB_C and does something really silly...

FUNCTION_BLOCK FB_A
VAR_INPUT
END_VAR
VAR_OUTPUT
END_VAR
VAR
   MyB : FB_B;
   MyC : FB_C;
   Count : INT;
END_VAR
Count := Count + 1;
IF Count > 20 THEN
   Count := 0;
END_IF
IF Count >= 10 THEN
   MyC(DoIt:=TRUE, refB:=MyB);
ELSE
   MyC(DoIt:=FALSE, refB:=MyB);
END_IF

And call FB_A from PLC_PRG...

PROGRAM PLC_PRG
VAR
   MyA : FB_A;
END_VAR
MyA();

Difference between Properties and own getter/setter

2020-02-27T14:17:25.833000Z

Hey,

I'm struggling with the properties of a FunctionBlock in CODESYS V3.5.

I have a FB A, which instances two different FBs B and C.
Now I want to change a property from FB B in FB C.

The error message says, that the FB B is not an entry of FB A.

If I write my own setter-method in FB B for the property and call it in the FB C it works and I don't get an error message.

Can anybody explain why I'm able to call a function from the other FB but not a property?

Thank you for your help!

Fabian

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