Industrial communication networks. Fieldbus specifications - Application layer protocol specification. Type 21 elements
Industrial communication networks. Fieldbus specifications - Application layer protocol specification. Type 21 elements
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What is BS EN 61158-6-21 - Type 21 application layer about? The Fieldbus Application Layer (FAL) provides user programs with a means to access the Fieldbus communication environment. In this respect, the FAL can be considered a window between corresponding application programs. BS EN 61158-6-21 part of IEC 61158 provides the 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 the Type 21 protocol. 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. BS EN 61158-6-21 defines the externally visible service provided by the FAL in terms of:
An abstract model for defining application resources (objects) capable of being manipulated by users via the FAL service The primitive actions and events of the service The parameters associated with each primitive action and event and the form that they take The interrelationship between these actions and events, and their valid sequences
BS EN 61158-6-21 defines the services provided to:
The FAL-user at the boundary between the user and the appli...
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