242 Rockwell Automation Publication 1769-UM021G-EN-P - October 2015
Chapter 9 Use I/O Modules with CompactLogix 5370 L3 Controllers
Validate I/O Layout
After you have selected your I/O modules, you must validate the system that you
want to design. Consider these points when validating I/O layout placement:
• Estimate Requested Packet Interval
• Module Fault Related to RPI Estimates
• Calculate System Power Consumption
• Power Supply Distance Rating
• Physical Placement of I/O Modules
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.
The CompactLogix 5370 L3 controllers attempt to scan an I/O module at the
configured RPI rate. For individual I/O modules, a Module RPI Overlap
minor
fault occurs if there is at least one I/O module which 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 module:
• Rates at which RPI rates are set for other Compact I/O modules
• Number of other Compact I/O modules in the system
• Types of other Compact I/O modules in the system
• Application user task priorities
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