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Rockwell Automation Publication 1756-RM093J-EN-P - April 2018
Glossary
Periodic Task
A task that is triggered by the operating system at a repetitive period of time.
Whenever the time expires, the task is triggered and its programs are executed.
Data and outputs established by the programs in the task retain their values until
the next execution of the task or until they are manipulated by another task.
Periodic tasks always interrupt the continuous task.
Primary Controller
The processor in a dual-processor controller that performs standard controller
functionality and communicates with the safety partner to perform safety-related
functions.
Recoverable Fault
A fault, which when properly handled by implementing the fault handling
mechanisms provided by the controller, does not force user logic execution to be
terminated.
Requested Packet Interval (RPI)
When communicating over a network, this is the maximum amount of time
between subsequent production of input data.
Routine
A set of logic instructions in a single programming language, such as a ladder
diagram. Routines provide executable code for the project in a controller. Each
program has a main routine. You can also specify optional routines.
Safety Add-On Instruction
An Add-On Instruction that can use safety application instructions. In addition
to the instruction signature used for high-integrity Add-On Instructions, safety
Add-On Instructions feature a SIL 3 safety instruction signature for use in safety-
related functions.
Safety Application Instructions
Safety Instructions that provide safety-related functionality. They have been
certified to SIL 3 for use in safety routines.
Safety Component
Any object, task, program, routine, tag, or module that is marked as a safety-
related item.
Safety Instruction Signature
The safety instruction signature is an ID number that identifies the execution
characteristics of the safety Add-On Instruction. It is used to verify the integrity
of the safety Add-On Instruction during downloads to the controller.
Safety I/O
Safety I/O has most of the attributes of standard I/O except it features
mechanisms certified to SIL 3 for data integrity.
Safety Network Number (SNN)
Uniquely identifies a network across all networks in the safety system. The end
user is responsible is responsible for assigning a unique number for each safety
network or safety subnet within a system. The safety network number makes up
part of the Unique Node Identifier (UNID).
Safety Partner
The processor in a dual-processor controller that works with the primary
controller to perform safety-related functions.
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