Class – Rockwell Automation 1756-L7x GuardLogix 5570 Controllers User Manual
Page 85
Rockwell Automation Publication 1756-UM022A-EN-P - November 2012
85
Develop Safety Applications
Chapter 6
Controller-scoped Tags
When safety tags are controller-scoped, all programs have access to the safety
data. Tags must be controller-scoped if they are used in the following:
• More than one program in the project
• To produce or consume data
• To communicate with a PanelView/HMI terminal
• In safety tag mapping
for more information.
Controller-scoped safety tags can be read, but not written to, by standard
routines.
Tags associated with Safety I/O and produced or consumed safety data must be
controller-scoped safety tags. For produced/consumed safety tags, you must
create a user-defined data type with the first member of the tag structure reserved
for the status of the connection. This member is a predefined data type called
CONNECTION_STATUS.
Program-scoped Tags
When tags are program-scoped, the data is isolated from the other programs.
Reuse of program-scoped tag names is permitted between programs.
Safety-program-scoped safety tags can only be read by or written to via a safety
routine scoped in the same safety program.
Class
Tags can be classified as standard or safety. Tags classified as safety tags must have
a data type that is permitted for safety tags.
When you create program-scoped tags, the class is automatically specified,
depending upon whether the tag was created in a standard or safety program.
When you create controller-scoped tags, you must manually select the tag class.
IMPORTANT
Controller-scoped safety tags are readable by any standard routine. The
safety tag’s update rate is based on the safety task period.
Table 26 - Additional Resources
Resource
Description
Safety Connections on page 117
Provides more information on the
CONNECTION_STATUS member
Logix5000 Controllers I/O and Tag Data Programming Manual,
publication
Provides instructions for creating user-defined
data types