10. Appendix A
10.1. Fieldbus Technology
R400 Experion PKS Series A Fieldbus Interface Module User's Guide 379
July 2010 Honeywell
Layer Functional Description Associated Terms
Fieldbus Access
Sublayer (FAS)
Defines the types of services used to pass
information to the Fieldbus Message
Specification layer. The types of services are
defined as Virtual Communication
Relationships (VCR).
The VCR types are Client/Server, Report
Distribution, and Publisher/Subscriber. The
Client/Server type handles all operator
messages. The Report Distribution type
handles event notification and trend reports.
The Publisher/Subscriber type handles the
publishing of User Application function block
data on the network.
Virtual
Communication
Relationship (VCR)
Fieldbus Message
Specification (FMS)
Defines how fieldbus devices exchange User
Application messages across the fieldbus
using a set of standard message formats. It
uses object descriptions that are stored in an
object dictionary (OD) to facilitate data
communication. The OD also includes
descriptions for standard data types such as
floating point, integer, Boolean, and bitstring.
A Virtual Field Device (VFD) mirrors local
device data described in the OD. A physical
device may have more than one VFD.
Provides these communication services to
standardize the way the User Applications
such as function blocks communicate over the
fieldbus - Context Management, Object
Dictionary, Variable Access, Event,
Upload/Download, and Program Invocation.
Uses a formal syntax description language
called Abstract Syntax Notation 1 (ASN-1) to
format FMS messages and applies special
behavioral rules for certain types of objects.
Object Dictionary
(OD)
Virtual Field Device
(VFD)
Network
Management
Information Base
(NMIB)
System Management
Information Base
(SMIB)
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