Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 23)

Designing Add-On Instructions Chapter 1
direct programmatic access to controller or program scope tags. This lets the
Add-On Instruction be a standalone component that can execute in any
application that calls it by using the parameters interface. It can be validated once
and then locked to prevent edits.
Safety Add-On Instructions
Safety Add-On Instructions are used in the safety task of GuardLogix safety
controllers. Create a safety Add-On Instruction if you need to use your instruction
in a safety application. Safety Add-On Instructions are subject to a number of
restrictions. These restrictions, enforced by Logix Designer application and all
GuardLogix controllers, are listed here for informational purposes only.
• They may use only safety-approved instructions and data types.
• All parameters and local tags used in a safety Add-On Instruction must also
be safety class.
• Safety Add-On Instructions use ladder diagram logic only and can be called
in safety routines only, which are currently restricted to ladder logic.
• Safety Add-On Instructions may be referenced by other safety Add-On
Instructions, but not by standard Add-On Instructions.
• Safety Add-On instructions cannot be created, edited, or imported when a
safety project is safety-locked or has a safety task signature.
Refer to the GuardLogix Controller Systems Safety Reference Manual , publication
1756-RM093 , for information on how to certify a safety Add-On Instruction as
well as details on requirements for safety applications, the safety task signature,
and a list of approved instructions and data types.
Instruction signature
The instruction signature, available for both standard and safety controllers, lets
you quickly determine if the Add-On Instruction has been modified. Each
Add-On Instruction has its own instruction signature on the Add-On Instruction
definition. The instruction signature is required when an Add-On Instruction is
used in SIL 3 safety-related functions, and may be required for regulated
industries. Use it when your application calls for a higher level of integrity.
Once generated, the instruction signature seals the Add-On Instruction,
preventing it from being edited until the signature is removed. This includes rung
comments, tag descriptions, and any instruction documentation that was created.
When an instruction is sealed, you can perform only these actions:
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