Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C | Page 188ALLEN-BRADLEY CONTROLLOGIX AND COMPACTLOGICS PLC FOR VIPER SYSTEMThis guide is intended to assist with Allen-Bradley CompactLogix and ControlLogix communication setup betweenmaster PLC and remote PLC using AB Ethernet/IP TCP protocol between PLCs.PLC communication via serial lines or serial terminal server is not covered here, nevertheless some information may beapplicable.Note: Please consult the Viper General PLC setup, earlier in this appendix for important information about setting upsystems with PLCs.ALLEN BRADLEY COMPACTLOGIX AND CONTROLLOGIX PLCSFollowing are important settings recommended to improve communications when used with a limited bandwidth Vipernetwork. This provides more specific information that supplements the general PLC communication informationpresented earlier in this appendix.Note: When required, contact your PLC provider or Allen-Bradley or Rockwell Automation support.PLC Ladder Logic On Restart Opens All Connections At Once Instead Of SequentiallyWhen the PLC ladder program is set up to have at startup all write message rungs set to true, all TCP connections aretriggered “simultaneously.” This creates an overload of TCP SYNs and somewhat could congest the on-air trafficdepending on the system.It is recommended to setup the ladder write message rungs not to start up simultaneously. Write messages should besetup to open the TCP connection sequentially. For more information it may be required to contact your PLC provideror Allen-Bradley or Rockwell Automation support.Allen-Bradley CompactLogix and ControlLogix Series PLCs Ethernet IP Connection Timeout(Setting Timeout Too Short Can Cause Problems!)When using the Ethernet IP with Allen-Bradley CompactLogix or ControlLogix (Logix series), the TCP Connectiontimeout is set on a per-message instruction basis using Message Configuration rather than Channel Configuration –Channel 1 of the MicroLogix series that was shown in the previous section.When messages are defined using Message Configuration and using path, for example, LocalENB,2,192.168.1.9:1,0, inthis example:– TCP connection is opened when the first message is sent.– The TCP connection timeout is set by default to 120 seconds, since the inactivity default setting is 120 seconds.– While connection is established with the same remote IP and same port (in this example, 192.168.1.9) othermessages will use the same TCP connection and therefore resetting the timeout count for each message sent.– When all messages are using the same default inactivity time (120 seconds) the TCP connection stays open as longas the next message is sent within the inactivity timeout period.– The TCP connection is closed after the last message plus the inactivity period (default 120 seconds).– The TCP connection can also be terminated based on network connection problems.The message configuration for this example will look similar to the following figure.
