User manual

Publication 1756-RM093F-EN-P - January 2010 51
Characteristics of Safety Tags, the Safety Task, and Safety Programs Chapter 5
Tags classified as safety tags are either controller-scoped or
program-scoped. Controller-scoped safety tags can be read by either
standard or safety logic or other communication devices, but can only
be written to by safety logic or another GuardLogix safety controller.
Program-scoped safety tags are only accessible by local safety
routines. These are routines that reside within the safety program.
Tags associated with Safety I/O and produced or consumed safety
data must be controller-scoped safety tags.
Standard Tags in Safety Routines (Tag Mapping)
Controller-scoped standard tags can be mapped into safety tags,
providing you with a mechanism to synchronize standard and safety
actions.
IMPORTANT
Any controller-scoped safety tag is readable by any standard
routine, but the update rate is based on the execution of the
safety task. This means that safety tags are updated at the
safety task periodic rate, which is different from standard tag
behavior.
ATTENTION
When using standard data in a safety routine, you are
responsible for providing a reliable means of ensuring that the
data is used in an appropriate manner. Using standard data in a
safety tag does not make it safety data. You must not directly
control a safety output with standard tag data.
This example illustrates how to qualify the standard data with
safety data.
Qualify Standard Data with Safety Data
ONS
MappedBooleanTag LatchOneShot
Node30ComboModule:O.Pt03Data
Node30ComboModule:I.Pt07Data Node30ComboModule:O.Pt03Data
Latch circuit to prevent automatic restart if the standard
input (MappedTag) is failed in a ‘stuck at 1’ state.
Safety Input Qualifier for Mapped Tag
Safety Output