DANSK DS/EN IEC 61158-3-25 PDF

This document provides common elements for basic time-critical messaging communications between devices in an automation environment. The term “time-critical” is used to represent the presence of a time-window, within which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant and possibly human life. This document defines in an abstract way the externally visible service provided by the Type 3 fieldbus data-link layer in terms of a) the primitive actions and events of the service; b) the parameters associated with each primitive action and event, and the form which they take; and c) the interrelationship between these actions and events, and their valid sequences. The purpose of this document is to define the services provided to – the Type 3 fieldbus application layer at the boundary between the application and data-link layers of the fieldbus reference model, and – systems management at the boundary between the data-link layer and systems management of the fieldbus reference model. 1.2 Specifications The principal objective of this document is to specify the characteristics of conceptual data link layer services suitable for time-critical communications, and thus supplement the OSI Basic Reference Model in guiding the development of data-link protocols for time-critical communications. A secondary objective is to provide migration paths from previously existing industrial communications protocols. This specification may be used as the basis for formal DL-Programming-Interfaces. Nevertheless, it is not a formal programming interface, and any such interface will need to address implementation issues not covered by this specification, including a) the sizes and octet ordering of various multi-octet service parameters, and b) the correlation of paired request and confirm, or indication and response, primitives.