IEC 61158-6-12:20 19为自动化环境中的应用程序和特定于2型现场总线的材料之间的基本时间关键和非时间关键消息通信提供了通用元素。术语“时间关键”用于表示时间窗口的存在，在该时间窗口内需要以某种定义的确定性水平完成一个或多个指定的动作。未能在时间窗口内完成指定的操作可能会导致请求操作的应用程序失败，从而给设备、工厂和可能的人的生命带来风险。 该国际标准规定了远程应用程序之间的交互，并定义了由2型现场总线应用层提供的外部可见行为。本文件的目的是定义提供给 a)定义本文档中定义的服务原语的线表示，以及 b)定义与它们的转移相关联的外部可见行为。本文件规定了符合OSI基本参考模型（ISO/IEC 7498-1）和OSI应用层结构（ISO/IEC 9545）的2型现场总线应用层协议。 与上一版相比，第四版包括以下重大技术变更: -技术更正；和 -为澄清而进行的编辑改进。

IEC 61158-6-12:2019 provides common elements for basic time-critical and non-time-critical messaging communications between application programs in an automation environment and material specific to Type 2 fieldbus. The term “time-critical” is used to represent the presence of a time-window, within which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant and possibly human life.
This International Standard specifies interactions between remote applications and defines the externally visible behavior provided by the Type 2 fieldbus application layer. The purpose of this document is to define the protocol provided to
a) define the wire-representation of the service primitives defined in this document, and
b) define the externally visible behavior associated with their transfer. This document specifies the protocol of the Type 2 fieldbus application layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure (ISO/IEC 9545).
This fourth edition includes the following significant technical changes with respect to the previous edition:
- technical corrections; and
- editorial improvements for clarification.