Device Descriptions - Emerson Rosemount 5600 Series Reference Manual

Rosemount 5600 Series
Figure 2-1. Function Block
Internal Structure

Device Descriptions

2-2
Figure 2-1 illustrates the internal structure of a function block. When execution
begins, input parameter values from other blocks are snapped-in by the block.
The input snap process ensures that these values do not change during the
block execution. New values received for these parameters do not affect the
snapped values and will not be used by the function block during the current
execution.
Input Events
Input
Input
Snap
Parameter
Linkages
Status
Once the inputs are snapped, the algorithm operates on them, generating
outputs as it progresses. Algorithm executions are controlled through the
setting of contained parameters. Contained parameters are internal to
function blocks and do not appear as normal input and output parameters.
However, they may be accessed and modified remotely, as specified by the
function block.
Input events may affect the operation of the algorithm. An execution control
function regulates the receipt of input events and the generation of output
events during execution of the algorithm. Upon completion of the algorithm,
the data internal to the block is saved for use in the next execution, and the
output data is snapped, releasing it for use by other function blocks.
A block is a tagged logical processing unit. The tag is the name of the block.
System management services locate a block by its tag. Thus the service
personnel need only know the tag of the block to access or change the
appropriate block parameters.
Function blocks are also capable of performing short-term data collection and
storage for reviewing their behavior.
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.
Reference Manual
00809-0100-4025, Rev AA
Output Events
Execution
Control
Processing
Output
Algorithm
Snap
Status
May 2003
Output Parameter
Linkages