Structured Text Components: Assignments

Use an assignment to change the value stored within a tag. An assignment has this syntax:
tag := expression;
where:
Component
Description
Tag
Represents the tag that is getting the new value; the tag must be a BOOL, SINT, INT, DINT, STRING, or REAL.
Tip:
The STRING tag is applicable to
CompactLogix
5380,
CompactLogix
5480,
ControlLogix
5580,
Compact GuardLogix
5380, and
GuardLogix
5580 controllers
only.
:=
Is the assignment symbol
Expression
Represents the new value to assign to the tag
If tag is this data type
Use this type of expression
BOOL
BOOL
SINT
INT
DINT
REAL
Numeric
STRING
(
CompactLogix
5380,
CompactLogix
5480,
ControlLogix
5580,
Compact GuardLogix
5380, and
GuardLogix
5580 controllers
only).
String type, including string tag and string literal
(
CompactLogix
5380,
CompactLogix
5480,
ControlLogix
5580,
Compact GuardLogix
5380, and
GuardLogix
5580 controllers
only).
;
Ends the assignment
The tag retains the assigned value until another assignment changes the value.
The expression can be simple, such as an immediate value or another tag name, or the expression can be complex and include several operators and functions, or both. Refer to Expressions for more information.
TIP:
I/O module data updates asynchronously to the execution of logic. If you reference an input multiple times in your logic, the input could change state between separate references. If you need the input to have the same state for each reference, buffer the input value and reference that buffer tag. For more information, see
Logix 5000
Controllers Common Procedures
, publication 1756-PM001.
You can also use Input and Output program parameters which automatically buffer the data during the
Logix Designer
application execution. See LOGIX 5000 Controllers Program Parameters Programming Manual, publication 1756-PM021.
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