218 Rockwell Automation Publication 1769-UM021G-EN-P - October 2015
Chapter 8 Use I/O Modules with CompactLogix 5370 L2 Controllers
Validate I/O Layout
You must validate the layout of I/O modules in your CompactLogix 5370 L2
control system. Consider these points when validating I/O layout placement:
• Estimate Requested Packet Interval
• Module Fault Related to RPI Estimates
• System Power Availability
• Power Supply Distance Rating
Estimate Requested Packet Interval
The requested packet interval (RPI) defines the frequency at which the
controller sends data to and receives data from I/O modules. You set an RPI rate
for each I/O module in your system, including embedded I/O modules, local
expansion modules, or distributed I/O modules over an EtherNet/IP network.
The CompactLogix 5370 L2 controllers attempt to scan an I/O module at the
configured RPI rate. The controller scans distributed I/O modules at the
configured RPI rates.
With embedded I/O modules and local expansion modules, however, some
system configuration parameters determine the actual rate at which the controller
scans the modules. That is, the controller can be configured to scan an I/O
module at one rate but actually scan the module at another rate.
For individual I/O modules, a Module RPI Overlap
minor fault occurs if there is
at least one I/O module that cannot be serviced within its RPI time.
The configuration parameters for a system determine the impact on actual RPI
rates. These configuration factors can affect the effective scan frequency for any
individual embedded or local expansion module:
• Rates at which RPI values are set for embedded I/O modules
• Number of embedded I/O modules that are used in the system
• Types of embedded I/O modules that are used in the system
• Rates at which RPI values are set for Compact I/O modules
• Number of Compact I/O modules in the system
• Types of Compact I/O modules in the system
• Application user task priorities
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