148 Rockwell Automation Publication 1756-UM001M-EN-P - February 2012
Chapter 8 I/O Modules
• Analog I/O modules can be added only as direct connections.
• Disable the Change of State (COS) feature on digital input modules
because it can cause inputs to be sent more quickly than the RPI.
• If you plan to add large amounts of I/O to the ControlNet network,
dedicate one ControlNet network for I/O. For the dedicated ControlNet
network, verify that there is little or none of the following:
– HMI traffic
– MSG traffic
– Programming workstations
• If the module has a Real Time Sample (RTS), it should be disabled or set
to a rate that is greater than the RPI.
• You can add I/O modules until you reach these limits:
– 80% of CPU utilization of the 1756-CN2, 1756-CN2R, or
1756-CN2RXT communication module.
– Less than 400,000 unscheduled bytes per second are displayed in
RSNetWorx for ControlNet software after the network has been
scheduled.
Online Additions - EtherNet/IP Considerations
When you add I/O modules to the EtherNet/IP network, make these
considerations:
• The EtherNet/IP I/O modules you add can be added as these connection
types:
– Rack-optimized connections, including new and existing connections
– Direct connections
• You can add I/O modules until you reach the limits of the communication
module.
For EtherNet/IP module limitations, see the EtherNet/IP Modules in
Logix5000 Control Systems User Manual, publication ENET-UM001
.
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