Publication 1756-UM523F-EN-P - December 2006
16 ControlLogix Redundancy System Overview
Network Access Port
To connect a device to the network access port (NAP) of a
1756-CNB/D/E or 1756-CNBR/D/E module, use an NAP that is outside
of a redundant chassis.
Bump in Outputs During a
Switchover
Depending on how you organize your RSLogix 5000 project, outputs
may or may not experience a change in state (bump) during a
switchover.
• During the switchover, outputs controlled by the highest priority
task experience a bump-free switchover. For example, outputs
do not revert to a previous state.
• Outputs in lower priority tasks may experience a change of
state.
The switchover time of a redundant system depends on the type of
failure and the network update time (NUT) of the ControlNet network.
For a NUT of 10 ms, the switchover time is approximately 80...220 ms.
Keep the Second Controller
Up to Date
To take over control, the secondary controller requires the same
project as the primary controller. It also requires up-to-date tag values.
These terms describe the process of communication between the two
controllers.
IMPORTANT
Use of the Network Access Port (NAP)
Do not connect any device to the network access port (NAP) of
a 1756-CNB/D/E or -CNBR/D/E module in a redundant chassis.
• If you connect a device to the NAP of a CNB module in a
redundant chassis, a switchover will fail to occur if the
CNB module is disconnected from the network. While
the CNB module is disconnected from the network, the
controller will be unable to control any I/O devices
through that CNB module.
• If you connect a workstation to the NAP of a CNB
module in a redundant chassis, the workstation will be
unable to go online after a switchover.
To connect a device to a ControlNet network via a NAP, use a
NAP that is outside of a redundant chassis.
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