Take time to design the Add-On instruction. Move ahead planning can recognize issues that require to be addressed. You also determine the interface when defining the instruction requirements. Keep the below factors in mind when defining your requirements of instruction and generating the Add-On Instruction.
Aimed Behavior
• What is the reason for gerating the Add-On Instruction?
• What problem/difficulty is it supposed to solve?
• How is it aimed to function?
• Do you require to advanced level of reliability on your Add-On Instruction? If so, you can create a signature of instruction as a means to validate that the Add-On Instruction has not been customized.
• Do you require utilizing safety application instructions and endorsing the safety Add-On Instruction to SIL-3 reliability?
Parameters
• What information requires to be accepted to the instruction?
• What data requires to be available outside of the instruction?
• Will parameters of alias have to be identified for data from local tags that requires to be available from outside of the Add-On Instruction?
• How will the parameters show? The parameters order identifies the instruction appearance.
• Which parameters supposed to be needed or visible?
Conventions Naming
The name of instruction will be utilized as the instruction mnemonic. Even though the name can be up to 40-characters long, you will usually desire to apply shorter, more controllable names.
Protection of Source
• What kind of protection source requires to be identified, if any?
• Who will have admission to the key of source?
• Will you require controlling protection of source and a signature of instruction?
The protection of source can be utilized to give read-only access of the Add-On Instruction or to entirely hide or lock the local tags and Add-On Instruction. The protection of source have to be useful prior to produce a signature of instruction.
Reuse Instructions - Nesting
• Are there another Add-On Instructions that you can reprocess?
• Do you require intending your instructions to allocate universal code?
Local Tags
• What information is required for your logic to perform but is not open?
• Classify tags of local you may apply in your instruction. Local tags are helpful for things for example intermediate computation values that you do not desire to share to users of the instruction.
• Do you desire to build an alias parameter to give outside access to a tag of local?