18 Rockwell Automation Publication 842E-UM001C-EN-P - September 2016
Chapter 3 EtherNet/IP Overview
Specifying the Requested
Packet Interval
The requested packet interval (RPI) is the update rate that is specified for a
particular piece of data on the network. This value specifies how often to
produce the data for that device. For example, if you specify an RPI of 50 ms, it
means that every 50 ms the device sends its data to the controller or the
controller sends its data to the device.
RPIs are only used for devices that exchange data. For example, a
ControlLogix® EtherNet/IP bridge in the same chassis as the controller does
not require an RPI because it is not a data-producing member of the system; it
is used only as a bridge to remote modules.
EtherNet/IP Topologies
The 842E encoders can be connected in any of three network topologies: star,
linear, or Device Level Ring (DLR).
Star Topology
Figure 4
The star structure consists of a number of devices that are connected to a
central switch.
IMPORTANT Rockwell Automation recommends that you use no more than 50 nodes on
one DLR or linear network. If your application requires more than 50 nodes,
we recommend that you segment the nodes into separate, but linked, DLR or
linear networks.
IMPORTANT When this topology is used, make the Ethernet connection on the 842E
encoder to the Link 1 connection. The Link 2 Ethernet connection must
remain unused.
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