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Safety Tags
The GuardLogix control system supports the use of both standard and safety
tags in the same project. However, the programming software operationally
differentiates standard tags from safety tags.
Safety tags have the attributes of standard tags with the addition of
mechanisms to provide data integrity at the configured SIL level (SIL 2 or
SIL 3).
Safety tags can be composed of the following:
• All primitive data types (for example, BOOL, SINT, INT, DINT,
LINT, REAL)
• Predefined types that are used for safety application instructions
• User-defined data types or arrays that are composed of the previous two
types
The Studio 5000 Logix Designer application helps prevent the direct creation
of invalid tags in a safety program. If invalid tags are imported, they cannot be
verified.
IMPORTANT Aliasing between standard and safety tags is prohibited in safety
applications.
Tags that are classified as safety tags are either controller-scoped or program-
scoped. Either standard or safety logic or other communication devices can
read controller-scoped safety tags, but only safety logic or another GuardLogix
safety controller via a consumed tag can write the controller-scoped safety tags.
Program-scoped safety tags are accessible only by local safety routines. These
routines reside within a safety program.
Tags that are associated with Safety I/O and produced or consumed safety data
must be controller-scoped safety tags.
IMPORTANT Safety input tags and safety consumed tags are readable by any standard
routine, but the update rate is based on the execution of the safety task.
These tags are updated at the beginning of the safety task execution, which
differs from standard tag behavior.
Rockwell Automation Publication 1756-RM012B-EN-P - April 2018
Characteristics of Safety Tags, the Safety Task, and Safety Programs
Chapter 5
45
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