76 Rockwell Automation Publication 1756-RM100F-EN-P - October 2018
Chapter 3 Replacement Considerations with CompactLogix and Compact GuardLogix Systems
Local I/O Module Performance
Local I/O module performance is significantly improved in 5380 systems
when compared to 5370 systems. The improved performance results from the
following:
• A high-performance, multi-core processor architecture
• High-speed Compact 5000 I/O system backplane supports faster
transfer rates
In 5370 systems, local I/O module updates are transferred to the controller via
the 1769 CompactBus at the specified requested packet interval (RPI). The
controller uses a dedicated I/O task to update internal I/O tag data. The task is
internally set to a priority of level 6. You must carefully arrange user task
priorities so that important local I/O updates are not interrupted by scanning
of lower-level tasks in the controller.
With the high-performance 5380 controller, you are no longer required to
arrange task priorities around the dedicated I/O task. The I/O tag data is
updated as part of an internal task on its own processor core and does not affect
the user tasks running on the controller processor core.
System performance is also improved because you can configure much faster
RPI rates with Compact 5000 I/O modules. For example, you can configure
the RPI to occur as fast as every 200 μs. You cannot use the same rate with the
1769 Compact I/O modules that are used in 5370 systems.
Finally, the backplane is optimized to move larger amounts of data in one
packet than is possible on the 1769 CompactBus backplane.
Logix 5000 controllers still scan for I/O updates at the RPI asynchronously to
the program scan. The 5380 system handles controller multi-tasking and I/O
updates more efficiently and faster than 5370 systems, though. The enhanced
performance results from improvements to the architecture, hardware, and
system backplane.
When you use 5380 systems, there are fewer configuration considerations and
a much better screw-to-screw I/O performance compared to 5370 systems that
use local 1769 Compact I/O.
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