5/12/2017
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Device Description
A key objective for Foundation Fieldbus is interoperability—the ability to build systems
comprised of devices from a variety of manufacturers to take full advantage of both the
standard and unique capabilities of every device.
Instead of requiring that device manufacturers use only a given set of functions in a device to
ensure that a system can always communicate with a new device, Foundation Fieldbus uses
device descriptions, which describe all the functions in a device using a specific programming
language called DDL.
The FF DDL is a language used to describe the information and procedures available through
the fieldbus interface in a general and extensible way. It is a human readable structured text
language designed to express how a field device can interact with a host application and
other field devices.
The basic elements of the EDD language (DDL) are: blocks, variables, menus, edit displays,
methods, unit relations, refresh relations, write as one relations, records, arrays, variable
lists, response codes, programs, domains, item arrays, collections, axes, charts, files, graphs,
grids, images, lists, sources and waveforms.
Each of these elements has a set of attributes associated with them. For example, a menu
has two attributes: items and label. For instance, the menu label can be “Calibration” and an
item of the “Calibration” menu can be a block parameter like the “CALIBRATION
COMMANDS”.
Although the FF Device Description (DD) and the enhanced version (EDD) source files are
defined by the device manufacturer to best represent its device’s objects, the host system is
responsible to render the graphics and other objects using its own graphic interface standard
or conventions. FF has specified how to build and distribute the EDD, using standard EDD
files. However, each host has a proprietary mechanism to use or import the EDD files
according to the host requirements.
The DD and EDD files are generally supplied in a set containing three files: A binary file
(extension .ffo or .ff5), a symbol file (extension .sym or .sy5) and a so called capability file, or
just CF file for short (extension .cff). The full name of these files is actually the revision of the
EDD and CF
Also, there are two versions of DDs: The legacy DD version 4 and the current version, the EDD
version 5. These versions are related to the EDD specification, as defined by IEC standards
and not to the EDD revision number of a certain device. To differentiate a legacy DD from the
current EDD specification, the DD file extension was modified. The extensions used for the
legacy DD version 4 are .ffo and .sym. The extensions used for the current EDD version 5 are
.ff5 and .sy5.
Also the EDD file name is specified in a way that it is uniquely defined in the system.
he convention used to name the file is: aabb.ff5, aabb.sy5 and aabbcc.cff, where
•
aa = Device revision (DEV_REV)
•
bb = DD / EDD revision (DD_REV)
•
cc = CF revision.
For more information about Device Description Language, see Reference (FOUNDATION™
Specification, Device Description Language – FF-900, Rev 5.1).
