BS EN IEC 61158-6-26:2019

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 part of [IEC 61158](/search?q=IEC%C2%A061158) 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 26 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 defines in an abstract way the externally visible behavior
     provided by the Type 26 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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