BS EN IEC 61158-6-12:2019

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 12 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 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...