164 Rockwell Automation Publication 1769-UM021I-EN-P - May 2018
Chapter 7 Use I/O Modules with CompactLogix 5370 L1 Controllers
• If multiple contiguous modules are removed under power, connections
to all modules in the contiguous missing module set are disallowed until
all modules are replaced. The controller cannot detect an empty base.
Therefore, it does not know the physical positioning of the modules
until all missing modules are replaced.
• If a module that separates two sets of contiguous missing modules is
removed, the two sets merge into one set. All modules must be replaced
before connections are permitted to any module in the set.
• If modules of different types are removed and returned to the wrong
locations, attempts to connect to these modules fail during verification
of Electronic Keying.
• If modules of the same type are removed and returned to the wrong
locations, they accept connections from the controller. The modules also
reconfigure with the correct data once they pass their electronic keying
check.
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 L1 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 are enough I/O modules with RPI rates set too fast
that they cannot all be serviced in the allotted interval.
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:
• Other 1734 POINT I/O module RPI rate settings
• Number of other 1734 POINT I/O modules in the system
• Types of other 1734 POINT I/O modules in the system
• Application user task priorities
IMPORTANT If Electronic Keying is set to Disable Keying, no verification of
electronic keying occurs and unintended control can occur.
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