Attention

IronPLC can only run very simple programs. The steps described are accurate but many language features are not yet supported.

Retention

Retention qualifiers control whether variables preserve their values across power cycles and program restarts.

IEC 61131-3

Section 2.4.3

Support

Not yet supported

Qualifiers

Qualifier

Description

RETAIN

Value is preserved across power cycles

NON_RETAIN

Value is reset to initial value on restart

CONSTANT

Value cannot be modified after initialization

Example

PROGRAM main
    VAR RETAIN
        run_hours : DINT := 0;
    END_VAR
    VAR CONSTANT
        MAX_TEMP : INT := 150;
    END_VAR
    VAR
        current_temp : INT;
    END_VAR

    run_hours := run_hours + 1;
END_PROGRAM

See Also