Rockwell Automation 842E EtherNet/IP Absolute Encoder User Manual - Manual (Page 18)

10 Rockwell Automation Publication 842E-UM001A-EN-P May 2012
Chapter 3 EtherNet/IP overview
Specifying the requested
packet interval The requested packet interval (RPI) is the update rate 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 module 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
The star structure consists of a number of devices connected to a central switch.
IMPORTANT
Rockwell Automation recommends that you use no more than 50 nodes on a
single 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.