Rockwell Automation Publication 1756-RM100F-EN-P - October 2018
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Standard Application Conversion
Chapter 5
Data Structures
The Logix Designer application has requirements for data type use. The
requirements differ based on the Logix Designer application version that
you use.
The Logix Designer application manages the requirement automatically, and
the change has no effect on individual LINT tags, regardless of
application version.
The requirement change between Logix Designer application, version 26, and
version 27 is fundamental to the application and applies to all Logix 5000
controllers. The fact that the requirement was changed does not alone require
action on your part.
Conditions can exist within which the change between Logix Designer
application, versions 26, and version 27 contributes to the need for action on
your part.
If you migrate a Logix Designer project, version 26 or earlier, to a Logix
Designer project, version 27 or later, LINTs inside a UDT can be misaligned.
Additional pad bytes are added to the data structure to account for the
misalignment. The pad bytes can cause an increase in the size of the UDT.
The possible effects of data structure changes, and subsequent actions that you
can take as a result, are described in the rest of this section.
Logix Designer Application Version
Requirement
Version 26 or earlier
Logix 5000 controllers require all data types to be placed on 4-byte
address boundaries in RAM.
Version 27 or later
Logix 5000 controllers require 8-byte (64-bit) data types (LINTs) to be
placed on 8-byte address boundaries in RAM.
IMPORTANT
You must act when in the following conditions:
• You migrate a project, version 26 or earlier, to project, version 27 or later,
and you have LINT tags inside a UDT.
• Your application includes Logix 5000 controllers, version 26 or earlier,
that communicate with Logix 5000 controllers, version 27 or later.