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:

· Copy the instruction signature
· Create or copy a signature history entry
· Create instances of the Add-On Instruction
· Download the instruction
· Remove the instruction signature
· Print reports

The instruction signature does not prevent referenced Add-On Instructions or User-defined Data Types from being modified. Changes to the parameters of a referenced Add-On Instruction or to the members of a referenced User-defined Data Type can cause the instruction signature to become invalid. These changes include:

· Adding, deleting, or moving parameters, local tags, or members in referenced User-defined Data Types.
· Changing the name, data type, or display style of parameters, local tags, or members in referenced User-defined Data Types.

If you want to enable project documentation or source protection on an Add-On Instruction that will be sealed with an instruction signature, you need to import the translated information or apply source protection before generating the signature. You must have the source key to generate a signature or to create a signature history entry for a source-protected Add-On Instruction that has an instruction signature.