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F
Fieldbus
™
OUNDATION
December 2022
8.1.4
Device descriptions
Device descriptions are specified tool definitions that are associated with the
function blocks. Device descriptions provide for the definition and description of
the function blocks and their parameters.
To promote consistency of definition and understanding, descriptive information,
such as data type and length, is maintained in the device description. Device
descriptions are written using an open language called the Device Description
Language (DDL). Parameter transfers between function blocks can be easily
verified, because all parameters are described using the same language. Once
written, the device description can be stored on an external medium, such as a
CD-ROM or diskette. You can then read the device description from the external
medium. The use of an open language in the device description permits
interoperability of function blocks within devices from various vendors.
Additionally, human interface devices, such as operator consoles and computers,
do not have to be programmed specifically for each type of device on the bus.
Instead, their displays and interactions with devices are driven from the device
descriptions.
Device descriptions may also include a set of processing routines called methods.
Methods provide a procedure for accessing and manipulating parameters within
a device.
8.1.5
Instrument-specific function blocks
In addition to function blocks, Fieldbus contains two other block types to support
the function blocks. These are the resource block and the transducer block.
The resource block contains the hardware specific characteristics associated with
a device. Transducer blocks couple the function blocks to local input/output
functions.
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