Array Data Structures - Allen-Bradley 1756-IF8I User Manual

Appendix A Analog I/O Module Tag Definitions

Array Data Structures

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Fast digital I/O modules use an array data structure. In this type of structure, all
the tags for a particular point are organized under that point. For example, in
Figure 33, all of the tags that appear under point 0 also appear under points 1...15
for the input module in slot 1. With this structure, you can copy or access all of
the data for a particular point by simply referencing or copying the point or alias
for the point, such as Pt[3] or PressureValveTank3.
Figure 33 - Array Data Structure
Other digital I/O modules use a flat data structure. In this type of structure, only
one instance of a tag exists for a module. For example, in
instance of each tag appears under the input module in slot 3. To reference or
copy data for an individual point, you specify the tag name followed by a bit
number, such as Data.0 or EventOverflow.3. Unlike an array structure where all
the data for a point can be accessed via a single tag reference, a flat structure
requires multiple tag references to access all the data for a point.
Figure 34 - Flat Data Structure
The 1756-OF8I module uses either type of data structure depending on how you
configure the module. For more information, see
Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Figure 34, only one
page 204.