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10. Appendix A
10.3. Device Descriptions and Block Parameters
10.3 Device Descriptions and Block Parameters
About Device Descriptions
Device Descriptions (DD) are critical to the interoperability of fieldbus devices. They
define the data needed to establish communications between different fieldbus devices
from multiple vendors with control system hosts. The DD provides an extended
description of each object in the User Application Virtual Field Device (VFD).
The Fieldbus Foundation provides Device Descriptions for all standard Function Blocks
and Transducer Blocks on a CD-ROM and on its web site. Manufacturer's may provide
an "Incremental" DD that references the standard DDs and describes manufacturer
specific features such as calibration and diagnostic procedures added to their devices.
Device Description Language
The Device Description Language (DDL) is a structured text language used to write a
DDL source file. A DDL source file describes each device function, parameter, and
special feature as well as how a field device can interact with a host application and other
field devices. A completed DDL source file is converted into a binary formatted DD
output file. The DD output file information can be provided in object form in the device
itself, or on a removable storage media delivered with the device. A field device's Object
Dictionary (OD) can be transferred from a device to a host using standard Fieldbus
Message Specification services.
Device Description infrastructure
The Fieldbus Foundation defines a four-level infrastructure for Device Descriptions for
the sake of consistency. See the following illustration for a graphical representation of
the DD infrastructure.
416
Experion PKS Series A Fieldbus Interface Module User's Guide
Honeywell
R400
July 2010
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