SA0102: Access to program/fb variables from the outside

Function	Determines read accesses from outside to local variables of programs or function blocks.
Reason	TwinCAT determines external write access operations to local variables of programs or function blocks as compilation errors. Since read access operations to local variables are not intercepted by the compiler and this violates the basic principle of data encapsulation (concealing of data) and contravenes the IEC 61131-3 standard, this rule can be used to determine read access to local variables.
Importance	Medium

Samples:

Function block FB_Base:

FUNCTION_BLOCK FB_Base
VAR
    nLocal : INT;
END_VAR

Method FB_Base.SampleMethod:

METHOD SampleMethod : INT
VAR_INPUT
END_VAR

nLocal := nLocal + 1;

Function block FB_Sub:

FUNCTION_BLOCK FB_Sub EXTENDS FB_Base

Method FB_Sub.SampleMethod:

METHOD SampleMethod : INT
VAR_INPUT
END_VAR

nLocal := nLocal + 5;

Program PRG_1:

PROGRAM PRG_1
VAR
    bLocal : BOOL;
END_VAR

bLocal := NOT bLocal;

MAIN program:

PROGRAM MAIN
VAR
    bRead     : BOOL;
    nReadBase : INT;
    nReadSub  : INT;
    fbBase    : FB_Base;
    fbSub     : FB_Sub;
END_VAR

bRead     := PRG_1.bLocal;       // => SA0102 
nReadBase := fbBase.nLocal;      // => SA0102 
nReadSub  := fbSub.nLocal;       // => SA0102