Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 41)

Publication 1757-UM006A-EN-P - May 2002
The Fieldbus Communication Model 1-27
Device Descriptions and
Block Parameters About Device Descriptions
Device Descriptions (DD) are absolutely critical to the interoperability
of fieldbus devices. They define the data needed to establish
communications among different fieldbus devices from multiple
vendors and 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.
Manufacturer's 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.