Rockwell Automation 1788-FFCT NI-FBUS Configurator User Manual - Manual (Page 13)

Publication 1788-UM052B-EN-P - April 2002
Fieldbus Overview 1-5
Device Description Files
The vendor supplied Device Description (DD) files describe the
function and transducer blocks contained in a device. A DD file
includes symbolic information (such as names and help strings) and
functional information (such as menus and methods that you can use
with the device). DDs are used with the NI-FBUS Configurator to
configure a device.
Identifying Blocks
Blocks are uniquely identified on the fieldbus network by a character
string name, or tag, similar to the device tag. The block tag is an
attribute of a block that usually describes the purpose and location of
the block. You can change the block tag, but block tags must be
unique to each block on a fieldbus network.
Linkages
The function blocks configured to control a process are linked, or
connected by configuration objects inside the devices. These linkages
allow you to send data from one block to the other. A linkage is
different from a link, in that a link is a physical wire pair that connects
devices on a fieldbus network, and a linkage is a logical connection
that connects two function blocks.
A block parameter that is written to the bus is referred to as a
published parameter. A block parameter that is receiving data is
referred to as a subscribed parameter. Figure 1.4 shows an example of
a linkage between blocks. In this example, the output parameter in
block A is the published parameter and the input parameter in block
B is the subscribed parameter. The blocks can be in the same device
or in different devices.
Figure 1.4 Linkage Between Function Blocks
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