Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 38)

38 Rockwell Automation Publication 1756-UM535D-EN-P - November 2012
Chapter 2 Design an Enhanced Redundancy System
ControlNet Networks with
Redundant Systems
ControlNet networks are used to connect redundant control chassis to remote
I/O and to other devices in the system.
ControlNet Network Requirements
If you use a ControlNet network in your enhanced redundancy system, you
must take these considerations into account when using ControlNet networks in
your enhanced redundancy system:
• Use at Least Four ControlNet Network Nodes
• Assign Lowest Node Numbers to Remote ControlNet Modules
• Set Partnered ControlNet Module Switches to the Same Address
• Reserve Consecutive Node Addresses for Partner Modules
Use at Least Four ControlNet Network Nodes
With redundant systems, at least four ControlNet network nodes are required.
This is because two or more ControlNet nodes must be used in addition to the
two ControlNet modules used in the redundant chassis. One of the two nodes
outside of the redundant chassis must be at a lower node address than the
ControlNet modules in the redundant chassis.
If your ControlNet uses less than four nodes, in the event of a switchover,
connections can be dropped and outputs connected to that node can change state
during the switchover.
You can include these ControlNet modules in addition to redundant
ControlNet nodes:
• ControlNet bridge modules in remote chassis
• Any other ControlNet devices on the ControlNet network
• A workstation running RSLinx Classic communication software that is
connected via a ControlNet network
IMPORTANT A remote chassis can be accessed over a ControlNet network using any
ControlNet module that works in a nonredundant chassis with no additional
firmware requirement.