220 Rockwell Automation Publication 1769-UM021G-EN-P - October 2015
Chapter 8 Use I/O Modules with CompactLogix 5370 L2 Controllers
Module Fault Related to RPI Estimates
When following the guidelines described in Tab le 24, most CompactLogix 5370
L2 control systems operate as expected. Some systems that follow the guidelines
can experience a Module RPI Overlap minor fault that is described in the
following table.
System Power Availability
An embedded 24V DC Input, nonisolated power supply powers all components
in a CompactLogix 5370 L2 control system.
The embedded power supply provides the following power to the CompactBus:
• 1769-L24ER-QB1B controller:
– 1.54 A @ 5V DC
– 0.95 mA @ 24V DC
• 1769-L24ER-QBFC and 1769-L27ERM-QBFC1B controllers:
– 1 A @ 5V DC
– 0.8 mA @ 24V DC
The embedded power supply can power any combination of controller,
embedded I/O modules, and local expansion modules that are used in your
application.
Name Fault
Information
Condition in Which Fault Occurs
Module
RPI
Overlap
(Type 03) I/O fault
(Code 94) Module
RPI overlap
detected
Module Slot = x,
where x is the slot
number of the I/O
module in the I/O
Configuration
section
This fault is logged when the current RPI update of an I/O module overlaps with its
previous RPI update. The Minor Faults tab in the Controller Properties dialog box
indicates in which module the RPI overlap occurs.
If multiple I/O modules experience the fault, the application indicates that the fault
occurred on the first such I/O module. Typically, it is an I/O module with a large
Input/Output array sizes. Example modules that use large Input/Output array sizes
include the 1769-SDN and 1769-HSC modules. In these cases, we recommend that
you adjust the RPI of the module to eliminate the fault.
Once the fault is cleared from the first I/O module, the application indicates the
next module that experiences the fault. This pattern continues until the fault is
cleared from all affected I/O modules.
To avoid this fault, set the RPI rate of the I/O modules to higher numerical values.
We recommend you use an RPI value that is not a common multiple of other
module RPI values, such as 2.5 ms, 5.5 ms, or 7 ms:
• We recommend that you do not run CompactLogix 5370 L2 control systems with
Module RPI Overlap faults.
• A system that experiences many Module RPI Overlap faults cannot operate
optimally because I/O data is not sampled at the expected rate that RPI settings
determine.
• When the project is downloaded or the RPI value of a module is adjusted, it is
expected to have a minor fault. Faults under these conditions are transitionary.
Clear the fault and wait for the fault to reappear before adjusting the RPI value
or the task priorities.
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