Rockwell Automation Logix5000 Controllers Add-on Instructions Programming Manual - Manual (Page 38)

Chapter 1 Designing Add-On Instructions
• 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 software programming language to use based on the use
and type of application. Safety Add-On Instructions are restricted to Ladder
Diagram.
• If execution time and memory usage are critical factors, refer to the
Logix5000 Controllers Execution Time and Memory Use Reference
Manual , publication 1756-RM087.
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.
38 Rockwell Automation Publication 1756-PM010F-EN-P - October 2014