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Profibus PA/DP/FMS overview 311
14a.2.6
Fieldbus management layer (FMA 7)
This describes object and management services. The objects are manipulated locally or
remotely using management services. There are three groups here:
1. Context management: This provides a service for opening and closing a
management connection.
2. Configuration management: This provides services for the identification of
communication components of a station, for loading and reading the communi
cation relationship list (CRL), and for accessing variables, counters, and the
parameters of the lower layers.
3. Fault management: This provides services for recognizing and eliminating
errors.
14a.3
The Profibus communication model
From a communication point of view, an application process includes all programs,
resources, and tasks that are not assigned to one of the communication layers. The
Profibus communication model permits the combination of distributed application
processes into a common process, using communications relationships. This acts to unify
distributed application processes to a common process. That part of an application
process in a field device that is reachable for communication is called a virtual field
device (VFD).
All objects of a real device that can be communicated with (such as variables, programs,
data ranges) are called communication objects. The VFD contains the communication
objects that may be manipulated by the services of the application layer via Profibus.
14a.4
Relationship between application process
and communication
Between two application processes, one or more communication relationships may exist;
each one having a unique communication end point as shown in Figure 14a.5:
Figure 14a.5
Assignment of communication relationships to application process