Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
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ALLEN-BRADLEY CONTROLLOGIX AND COMPACTLOGICS PLC FOR VIPER SYSTEM
This guide is intended to assist with Allen-Bradley CompactLogix and ControlLogix communication setup between
master 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 be
applicable.
Note:
Please consult the Viper General PLC setup, earlier in this appendix for important information about setting up
systems with PLCs.
ALLEN BRADLEY COMPAC TLOGIX AND CONTROLLOGIX PLCS
Following are important settings recommended to improve communications when used with a limited bandwidth Viper
network. This provides more specific information that supplements the general PLC communication information
presented 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 Sequentially
When the PLC ladder program is set up to have at startup all write message rungs set to true, all TCP connections are
triggered “simultaneously.” This creates an overload of TCP SYNs and somewhat could congest the on-air traffic
depending on the system.
It is recommended to setup the ladder write message rungs not to start up simultaneously. Write messages should be
setup to open the TCP connection sequentially. For more information it may be required to contact your PLC provider
or 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 Connection
timeout 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, in
this 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) other
messages 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 long
as 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.