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Kepware Knowledge Base: Solution

Ethernet Connection Limits on ControlLogix PLCs

Last Update: 11/7/2018

In general, the limit on the number of Ethernet connections that can be made to a ControlLogix PLC is high. The server opens one TCP socket or connection to the PLC's Ethernet module for each channel that is defined in the server. For example, if a user created a single channel with 15 devices that were configured to connect to the same PLC, then a single TCP socket connection would be made. Many KEPServerEX applications only have one channel with one device connecting to the PLC. In theory, if the PLC's Ethernet module had a limit of 64 simultaneous TCP sockets, then users could connect 64 copies of the server at the same time to the PLC.

Note: As more connections are made to a controller, the communications performance will begin to degrade based on the amount of data being acquired and the rate of acquisition. To refine the ratio of CPU time spent on processing and communications, refer to the PLC's System Overhead Time Slice (SOTS) parameter description (located in Rockwell's documentation).