How is the RETAIN keyword considered for function block instances?

Concerning RETAIN a nd NON_RETAIN, the →variables of →function block instances are treated as the section VAR in which the function block instance has been declared. This means:

If the keyword RETAIN is defined in section VAR, the variables of the function block instance are treated as they would have been declared with RETAIN.
If the keyword NON_RETAIN is defined in section VAR, the variables of the function block instance are treated as they would have been declared with NON_RETAIN.

The following cases are treated as exceptions:

One or more variables are explicitly declared as NON_RETAIN or RETAIN in the declaration of the appertaining function block.
If function block instances are declared again in the declaration of the appertaining function block, RETAIN or NON_RETAIN declared in the section VAR of the first function block instance is not valid for their variables (but the one in the appertaining function block).

Here an example how the above rules are applied:

ST-code that is the basis for the following table

PROGRAM Test
  VAR RETAIN
    myFB1 : FB1;
    var1  : INT; 
  END_VAR
END_PROGRAM
 
FUNCTION_BLOCK FB1
  VAR 
    var2  : INT; 
    myFB2 : FB2;
    myFB3 : FB3;
  END_VAR
  VAR NON_RETAIN
    var3    : INT; 
    myFB3_2 : FB3;
  END_VAR
  VAR RETAIN
    var7    : INT; 
    myFB3_3 : FB3;
  END_VAR
END_FUNCTION_BLOCK
 
FUNCTION_BLOCK FB2
  VAR 
    var4  : INT; 
  END_VAR
  VAR NON_RETAIN
    var5  : INT;
    myFB3 : FB3; 
  END_VAR
END_FUNCTION_BLOCK
 
FUNCTION_BLOCK FB3
  VAR 
    var6  : INT; 
  END_VAR
END_FUNCTION_BLOCK

The variable...	is treated as ...	Reason
`Test.var1`	`RETAIN`	keyword `RETAIN` in line 2
`Test.myFB1.var2`	`RETAIN`	keyword `RETAIN` in line 2 (because there is no keyword in line 9)
`Test.myFB1.var3`	`NON_RETAIN`	keyword `NON_RETAIN` in line 14
`Test.myFB1.var7`	`RETAIN`	keyword `RETAIN` in line 18
`Test.myFB1.myFB2.var4`	`NON_RETAIN`	no keyword in lines 9 and 25 (The keyword `RETAIN` in line 2 is not applied for this variable because `FB2` is declared in `FB1`.)
`Test.myFB1.myFB2.var5`	`NON_RETAIN`	keyword `NON_RETAIN` in line 28
`Test.myFB1.myFB3.var6`	`NON_RETAIN`	no keyword in lines 9 and 35 (The keyword `RETAIN` in line 2 is not applied for this variable because `FB2` is declared in `FB1`.)
`Test.myFB1.myFB3_2.var6`	`NON_RETAIN`	keyword `NON_RETAIN` in line 14 (because there is no keyword in line 35)
`Test.myFB1.myFB3_3.var6`	`RETAIN`	keyword `RETAIN` in line 18 (because there is no keyword in line 35)
`Test.myFB1.myFB2.myFB3.var6`	`NON_RETAIN`	keyword `NON_RETAIN` in line 28 (because there is no keyword in line 35)

logi.cals recommends to install and use the most current versions of logi.CAD 3 and the runtime system so that the latest features and problem fixes according to the release notes are provided in the used version.

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