Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 155)

Rockwell Automation Publication 1756-UM535D-EN-P - November 2012 155
Program the Redundant Controller Chapter 7
Group Data Types Together in User-Defined Data Types
When you create a User-Defined Data Type for use in your redundancy program,
group like data types together. Grouping like data types compresses the data size
and helps reduce the amount of data transferred during a crossload.
Figure 41 - Example of Bytes Saved by Grouping Like Data
Group Data into Arrays of User-Defined Data Types by Frequency of Use
To update the secondary controller, the primary controller divides its memory
into blocks of 256 bytes. Anytime an instruction writes a value, the primary
controller crossloads the entire block that contains the value. For example, if your
logic writes only 1 BOOL value to a block, the controller crossloads the entire
block (256 bytes).
To minimize crossload time, group your data by how frequently your program
uses it.
Figure 42 - Data Types Grouped
Figure 42 - Data Types