Skip to main content

SA0004: Multiple write access on output

Detects outputs which are written to more than one location.

Justification: The maintainability is degraded when an output is written in different locations in the code. Then it is uncertain which write access is the one that actually has an effect in the process. Good practice is to calculate the output variables in auxiliary variables and assign the calculated value at one location at the end of the cycle.

Importance: High

PLCopen rule: CP12

Tip

An error is not issued when an output variable (VAR_IN_OUT) is written to in different branches of IF and CASE statements.

A pragma cannot disable this rule.

Example 17. Example
VAR_GLOBAL
    g_xVar AT %QX0.0 : BOOL ;
    g_iTest AT %QW0 : INT ;
END_VAR
PROGRAM PLC_PRG
IF g_iCondition < INT#0 THEN
    g_xVar := TRUE;
    g_iTest := INT#12;
END_IF

CASE g_iCondition OF
    INT#1:
        g_xVar := FALSE;
    INT#2:
        g_iTest := INT#11;
    ELSE
        g_xVar := TRUE;
        g_iTest := INT#9;
END_CASE

Output in the Messages view:

  • sa_icon_message.png SA0004: Multiple write access on output '%QX0.0'

  • sa_icon_message.png SA0004: Multiple write access on output '%QW0'



: