工业通信网络.现场总线规范.第4-11部分:数据链路层协议规范.11型元件

[中文适用范围]： 数据链路层在自动化环境中的设备之间提供基本的时间关键消息通信。该协议为所有参与的数据链路实体提供通信机会：a）根据预先建立的时间表，以同步启动循环方式；b）按照每个数据周期的请求，以循环或非循环异步方式-链接实体。因此，该协议的特点是异步提供循环和非循环访问，但每个周期同步重新启动。 [外文原描述]： IEC 61158-4-11:2010(E) 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; procedures for giving communications opportunities to all participating DL entities, sequentially and in a cyclic manner for deterministic and synchronized transfer at cyclic intervals up to one millisecond; procedures for giving communication opportunities available for time-critical data transmission together with non-time-critical data transmission without prejudice to the time-critical data transmission; procedures for giving cyclic and acyclic communication opportunities for time-critical data transmission with prioritized access; procedures for giving communication opportunities based on standard ISO/IEC 8802-3 medium access control, with provisions for nodes to be added or removed during normal operation; 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 second edition cancels and replaces the first edition published in 2007 and constitutes a technical revision. The main changes with respect to the previous edition are: - Introduction has been modified to add the patents related to the loop-architecture and - Addition of loop (ring) -architecture.