152 Rockwell Automation Publication 1756-UM535D-EN-P - November 2012
Chapter 7 Program the Redundant Controller
Program to Minimize Scan
Times
Because your system switchover time is impacted by your total program scan
time, there are several aspects of your program that must be as efficient as possible
to facilitate the fastest possible switchover. The sections that follow indicate
methods of making your program more efficient to minimize your program scan
time.
These methods make your program more efficient and minimize program scan
times:
• Use a 1756-L7x Controller with a 1756-RM2/A Redundancy Module
• Use Multiple Controllers
• Minimize the Number of Programs
• Manage Tags for Efficient Crossloads
• Use Concise Programming
Use a 1756-L7x Controller with a 1756-RM2/A Redundancy Module
Beginning with enhanced redundancy system revision 19.053, you can use
1756-L7x controllers in your application. Relative to the redundancy module
being used, the 1756-L7x controllers scan the controller program faster than
1756-L6x controllers. The 1756-L7x controllers also scan the controller program
fastest if the enhanced redundancy system uses the 1756-RM2/A redundancy
module.
If your application needs better controller performance, we recommend that you
update from 1756-L6x controllers to 1756-L7x controllers and use 1756-RM2/
A redundancy modules.
Use Multiple Controllers
When possible, use multiple controllers in your redundant system. If you use
multiple controllers, you can strategically program between the controllers so the
program execution and scan times are faster.
For more information about controllers that can be paired in redundant chassis,
see Components of an Enhanced Redundancy System on page 24
.
Only the 1756-L72, 1756-L73, 1756-L74, and 1756-L75 controllers can be used
in conjunction with the 1756-RM2/A redundancy modules and revision
19.053. See Components Available for Use in a Redundant Chassis Pair on
page 24.
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