Deutsches Institut fur Normung e. V.

Industrial communication networks - Fieldbus specifications - Part 6-21: Application layer protocol specification - Type 21 elements (IEC 61158-6-21:2010)
 N EN 61158-6-21

Annotation

General

This standard is one of a series produced to facilitate the interconnection of automation system components. It is related to other standards in the set as defined by the three-layer fieldbus reference model described in IEC/TR 61158-1:2010.

This standard contains material specific to the Type 21 communication protocol.

Overview

The Fieldbus Application Layer (FAL) provides user programs with a means to access the fieldbus communication environment. In this respect, the FAL can be viewed as a window between corresponding application programs.

This standard provides common elements for basic time-critical and non-time-critical messaging communications between application programs in an automation environment, as well as material specific to Type 21. The term "time-critical" is used to represent the presence of a time-window, within which one or more specified actions must to be completed with some defined level of certainty. Failure to complete specified actions within the required time risks the failure of the applications requesting the actions, with attendant risk to equipment, plant, and possibly human life.

This standard defines interactions between remote applications. It also defines the externally visible behavior provided by the Type 21 application layer in terms of:

a) the formal abstract syntax defining the application layer protocol data units (APDUs) conveyed between communicating application entities;