Planning Your Add-On Instruction Design (Part 2)

Local Tags

· What data is needed for your logic to execute but is not public?
· Identify local tags you might use in your instruction. Local tags are useful for items such as intermediate calculation values that you do not want to expose to users of your instruction.
· Do you want to create an alias parameter to provide outside access to a local tag?

Programming Languages

What language do you want to use to program your instruction?

The primary logic of your instruction will consist of a single routine of
code. Determine which programming language to use based on the use and
type of application. Safety Add-On Instructions are restricted to Ladder
Diagram.

Scan Mode Routines

· Do you need to provide Scan mode routines?

You can optionally define the scan behavior of the instruction in different Scan modes. This lets you define unique initialization behaviors on controller startup (Program -> Run), SFC step postscan, or EnableIn False condition.

· In what language do Scan mode routines need to be written?

Test

· How will you test the operation of your Add-On Instruction before commissioning it?
· What possible unexpected inputs could the instruction receive, and how will the instruction handle these cases?

Help Documentation

What information needs to be in the instruction help?

When you are creating an instruction, you have the opportunity to enter information into various description fields. You will also need to develop information on how to use the instruction and how it operates.