Rockwell Automation Publication 1756-RM100F-EN-P - October 2018 41
Replacement Considerations with ControlLogix 5580 and GuardLogix 5580 Systems Chapter 2
Because the controllers have 32-bit data integrity, this only applies to data 
structures larger than 32 bits. If word-level integrity is your primary concern, 
the 32-bit data integrity does not impact your data use.
Good programming practice dictates the use of two unique words at the 
beginning and the end of data. The controller validates the words to assure the 
entire structure has data integrity. We recommend that the handshake data is 
changed and the application code validates it every transaction before the 
controller application code or higher-level system reading controller data acts 
on it.
Download the Program to 
the Controller
The first time that you download a program, it can take longer than subsequent 
downloads. These situations can affect download/compile times:
• The capability of the personal computer or laptop.
• You download the project immediately after a project import or upload, 
but before Logix Designer has compiled the project once.
• You edit a User Defined Tag (UDT), Add-On Instruction (AOI), or an 
object that is used in many places.
• Increased load when Logix Designer compiles and generates code.
Build Button
The new Build button in Logix Designer creates binary files that are compiled 
from user subroutines, and caches them in the project .ACD file.
If these files are present in the project during a download, then Logix Designer 
does not have to recompile them, and saves time during the download process. 
Every download requires that only the changed subroutines must be 
recompiled. You can perform a build offline, save the project .ACD file, and 
later distribute it to many controllers without recompilation.
This manual build step is optional. If you do not use the build button, Logix 
Designer builds all necessary files when you initiate a download.
An imported project requires a complete rebuild, and extends the download 
process the first time you attempt a download.
Downloading Workflow Change on page 42
 provides an explanation of the 
download changes.