Figure B.4 – One sided OA on each side is possible

Figure B.4 shows a scenario where an operator acknowledgment activated at controller A or controller B suffices for re-establishing the bidirectional connection. Both sides will cease delivering fail-safe values and continue sending process values. This is accomplished by the logic circuits shown in the safety applications.

Bibliography

1. Object Management Group, Unified Modeling Language (UML), V2.5.1, 2017, https://www.omg.org/spec/UML/2.5.1/
2. National Institute of Standards and Technology (NIST), Computer Security Resource Center, Recommendation for Random Number Generation Using Deterministic Random Bit Generators, SP 800-90A Rev. 1, June 2015
3. Anwendungshinweise und Interpretationen (AIS) 20, Functionality classes and evaluation methodology for physical random number generators. Bundesamt für Sicherheit in der Informationstechnik (BSI), 1999.
4. Anwendungshinweise und Interpretationen (AIS) 31, Functionality Classes and Evaluation Methodology for Physical Random Number Generators, Bundesamt für Sicherheit in der Informationstechnik (BSI), 2001.
5. ISO/IEC 18031 Information technology, Security techniques. Random Bit Generation, 2011
6. OPC 10010 (all parts), OPC Test Lab Specification

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