BS EN IEC 61158-6-25:2019

1   Scope

   1.1   General 
   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 International Standard 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 25 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 document defines in an abstract way the externally visible behavior provided
     by the different Types of the fieldbus Application Layer in terms of: 
   
      
         
            

a) the abstract syntax defining the application layer protocol data units conveyed between communicating application entities,

b) the transfer syntax defining the application layer protocol data units conveyed between communicating application entities,

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