工业通信网络.现场总线规范.第4-14部分:数据链路层协议规范.14型元件

[中文适用范围]： The data-link layer provides basic time-critical messaging communications between devices in an automation environment. This protocol provides communication opportunities to all participating data-link entities a) in a synchronously-starting cyclic manner, according to a pre-established schedule, and b) in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those data-link entities. Thus this protocol can be characterized as one which provides cyclic and acyclic access asynchronously but with a synchronous restart of each cycle. La couche de liaison de données assure les communications de messagerie à contrainte de temps de base entre les appareils d'un environnement d'automatisation. Ce protocole offre à toutes les entités de liaison de données participantes des opportunités de communication a) de manière cyclique à démarrage synchrone, selon un ordre préétabli, et b) de manière synchrone cyclique ou acyclique, tel que requis par chacune de ces entités de liaison de données. Ainsi, ce protocole peut être caractérisé comme un protocole qui offre un accès cyclique et acyclique asynchrone, mais avec un redémarrage synchrone de chaque cycle. [外文原描述]： IEC 61158-4-14:2014 specifies 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 and 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. This third edition cancels and replaces the second edition published in 2010 and constitutes a technical revision. The main changes are: - update the Communication model; - update the Encoding of DL-management Tag for FRT applications in Subclause 6.2.3; - corrections the edit error; - update of the requirements for all conformance classes; - update of the requirements for all conformance services.