DIN EN 61158-4-19

Abstract

<strong>General</strong> <br>The data-link layer provides basic time-critical messaging communications between devices in an automation environment. <br>This protocol provides communication opportunities to all participating data-link entities <br>a) in a synchronously-starting cyclic manner, according to a pre-established schedule, and <br>b) in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those data-link entities. <br>Thus this protocol can be characterized as one which provides cyclic and acyclic access asynchronously but with a synchronous restart of each cycle. <br><strong>Specifications</strong> <br>This standard specifies <br>a) procedures for the timely transfer of data and control information from one data-link user entity to a peer user entity, and among the data-link entities forming the distributed data-link service provider; <br>b) the structure of the fieldbus DLPDUs used for the transfer of data and control information by the protocol of this standard, and their representation as physical interface data units. <br><strong>Procedures</strong> <br>The procedures are defined in terms of <br>a) the interactions between peer DL-entities (DLEs) through the exchange of fieldbus DLPDUs; <br>b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system through the exchange of DLS primitives; <br>c) the interactions between a DLS-provider and a Ph-service provider in the same system through the exchange of Ph-service primitives. <br><strong>Applicability</strong> <br>These procedures are applicable to instances of communication between systems which support time-critical communications services within the data-link layer of the OSI or fieldbus reference models, and which require the ability to interconnect in an open systems interconnection environment. <br>Profiles provide a simple multi-attribute means of summarizing an implementation's capabilities, and thus its applicability to various time-critical communications needs. <br><strong>Conformance</strong> <br>This standard also specifies conformance requirements for systems implementing these procedures. This part of this standard does not contain tests to demonstrate compliance with such requirements.