Safety Add-On Instructions
You can create safety Add-On Instructions to be used in safety applications. Safety Add-On Instructions enable you to put commonly used safety logic into one instruction, which makes it modular and easier to reuse. An Add-On Instruction is composed of parameters, local tags, logic routine, and optional scan-mode routines.
Safety Add-On Instructions feature a safety instruction signature for use in safety-related applications up to and including SIL 3-rated applications. The safety instruction signature is an ID number that identifies the execution characteristics of the safety Add-On Instruction. The signature is used to verify the integrity of the safety Add- On Instruction during downloads to the controller.
IMPORTANT:
You must initialize safety critical Add-On Instruction tag values in the Add-On Instruction prescan logic.
The following figure shows the steps that are required to create a safety Add-On Instruction and then use that instruction in a safety application program. The shaded items are steps unique to Add-On Instructions.
Safety Add-On Instruction Workflow
Create an Add-On Instruction Test Project
You must create a unique test project to create and test the safety Add-On Instruction. This project must be a separate and dedicated project to minimize any unexpected influences. Follow the guidelines for projects that are described in Create the Project.
Create a Safety Add-On Instruction
For guidance in how to create Add-On Instructions, see the Logix 5000 Controllers Add-On Instruction Programming Manual, publication 1756-PM010.
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