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Instruction Manual
IM-106-880C, OI
September 2009
7-3
Hazardous Area OCX 8800
Once the inputs are snapped, the algorithm operates on them, generating
outputs as itprogresses. Algorithm executions are controlled through the
setting of containedparameters. Contained parameters are internal to function
blocks and do not appear asnormal input and output parameters. However,
they may be accessed and modified remtely, as specified by the fundtion
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.
Figure 7-1. Function Block Internal Structure
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
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. Users 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,