SA0038: Read access to output variable

Detects output variables (VAR_OUTPUT) which are accessed with read permission within the POU

Justification: According to the IEC 61131-3 standard, it is prohibited to read an output within a POU. This is an indication that the output is not only used as an output but also as a temporary variable for intermediate results. This kind of dual use should be avoided.

Importance: Low

Example 48. Example

VAR_GLOBAL
    g_xGlob AT %QX0.0 : BOOL ;
    g_iGlob AT %QW1 : INT ;
END_VAR

PROGRAM PLC_PRG
VAR_OUTPUT
    xVarOut1:BOOL;
    xVarOut2:INT;
    xVarOut3:INT;
END_VAR
VAR
    iCondition : INT;
END_VAR

iCondition := iCondition + INT#1;
CASE iCondition OF
    INT#1:
        xVarOut1 := g_xGlob;
        xVarOut2 := g_iGlob;
    INT#2:
        xVarOut3 := xVarOut2;    // SA0038
    ELSE
        xVarOut1 := FALSE;
        g_xGlob := xVarOut1;    // SA0038
        xVarOut2 := INT#0;
        xVarOut3 := INT#-1;
END_CASE

Output in the Messages view:

SA0038: Read access to output variable 'xVarOUT2'
SA0026: SA0038: Read access to output variable 'xVarOUT1'