标准摘要
[中文适用范围]： DLL 在自动化环境中的设备之间提供基本的时间关键型数据通信。类型 21 使用内部无冲突、全双工双端口以太网交换机技术提供基于优先级的循环和非循环数据通信。为了广泛应用于各种自动化应用，Type 21 不限制 DLL 中的循环/非循环调度策略。 [外文原描述]： IEC 61158-4-21:2010 describes 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 procedures for giving communication opportunities based on standard ISO/IEC 8802-3 MAC, with provisions for nodes to be added or removed during normal operation; structure of the fieldbus data link protocol data units (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 standard cancels and replaces IEC/PAS 62573 published in 2008. This bilingual version published in 2012-01 corresponds to the English version published in 2010-08.
英文名称Industrial communication networks - Fieldbus specifications - Part 4-21: Data-link layer protocol specification - Type 21 elements