Technical Paper Abstract
CIP Safety is based on the Black Channel concept defined in IEC 61784‑3, where the communication path is treated as unknown and potentially faulty, and safety integrity is achieved through end‑to‑end mechanisms in the Safety Communication Layer (SCL). These mechanisms provide a SIL 3 compatible residual error rate independent of the underlying network and lower protocol layers. However, current applications of IEC 61508-3 standard’s non‑interference requirements can impose stringent architectural constraints when integrating SIL 3 capable CIP Safety stacks into devices whose safety functions require only SIL 1 or SIL 2 to meet application needs.
This paper examines the implications of applying mixed‑criticality non‑interference rules—originally intended to prevent interference between safety‑related and non-safety-related software elements—within a Black Channel communication model. Not only can implementing non-interference measures in both hardware and software be overly burdensome for products not requiring SIL3, but the alternative is just as burdensome. Namely, requiring Systematic Capability (SC) 3 down to the supporting software, operating systems, and hardware will effectively force a full SIL 3 design onto a platform and/or system where the system-level risk assessment simply does not justify such elevated integrity levels.
The recently adopted closed communication system option in CIP Safety resolves this tension. In closed systems where the system integrator controls the complete communication network, responsibility for achieving appropriate Systematic Capability shifts to the integrator—aligning with IEC 61508:2010 system design principles. This enables device developers to integrate CIP Safety onto platforms with SC levels proportional to their individual safety functions, while the integrator ensures overall system integrity. The paper concludes by outlining areas investigated within ODVA, including conformance policy interpretation and guidance.
Keywords
CIP Safety; IEC 61784-3; IEC 61508-3; ISO 13849-1; Non-Interference; Systematic Capability; Closed Communication System; Black Channel; Mixed Criticality
Paper and presentation from the 2026 ODVA Industry Conference & 24th Annual Meeting: to be published November 2
Arun K Guru, Systems Architect/Principal Engineer, Rockwell Automation
Steven Seidlitz, Principal Engineer, Rockwell Automation
Jim Grosskreuz, Technology Manager, Safety, Rockwell Automation
Stina Hornstrom, ABB Robotics
David Crane, Senior Staff Engineer, ODVA