工业通信网络 - 现场总线规范 - 第4-24部分:数据链路层协议规范 - 24类元素

[中文适用范围]： 数据链路层在自动化环境中为设备之间提供基本的实时消息通信。该协议为所有参与的数据链路实体提供通信机会：a) 按照预先建立的计划以同步启动的循环方式进行；b) 由每个数据链路实体按需以非循环方式进行。因此，该协议可以被描述为提供循环和非循环访问，但每个周期都同步重启的协议。 [外文原描述]： IEC 61158-4-24:2019 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 second edition cancels and replaces the first edition published in 2014. This edition constitutes a technical revision with the following technical changes: • patent declaration in the Introduction; • corrections on transmission sequence of fixed-width time slot type in 4.3.2; • technical extension for band sharing between I/O data exchange and message communication; • spelling and grammar