SA0037: Write access to input variable

Detects input variables (VAR_INPUT) which are accessed with write permission within the POU

Justification: According to the IEC 61131-3 standard, an input variable must not be changed within a POU. This kind of access is also a cause for errors and makes the code poorly maintainable. This is an indication that a variable is used as both an input variable and an auxiliary variable. This kind of dual use should be avoided.

Importance: Medium

VAR_GLOBAL
    g_xGlob AT %QX0.0 : BOOL;
END_VAR

PROGRAM PLC_PRG
VAR_INPUT
    xVarIn1 : BOOL;
    xVarIn2 : BOOL;
END_VAR
VAR
    iCondition : INT;
END_VAR

iCondition := iCondition + INT#1;
CASE iCondition OF
    INT#1:
        g_xGlob := xVarIn1;
    INT#2:
        g_xGlob := xVarIn2;
    ELSE
        g_xGlob := FALSE;
        xVarIn1 := FALSE;       // SA0037
END_CASE