Allen-Bradley Rockwell Automation 1734-4IOL - Second Data I;O connection rejected; Controller goes to fault when enabling;disabling Unicast; Generic device with zero length input and output accepted by Add-on Profile

Rockwell Automation Publication 1734-UM020B-EN-E - August 2019 65
Troubleshooting Appendix C
Troubleshooting Scenarios
The following are scenarios you may encounter while using the modules.
Second Data I/O connection rejected
The 1734-4IOL module does not support a Listen-Only or Input-Only
connection. A connection attempt from a second Logix controller will be
rejected.
Controller goes to fault when enabling/disabling Unicast
If you check the “Major Fault on Controller if Connection Faults While in Run
Mode” check box and uncheck the “Use Unicast Connection over EtherNet/IP”
check box while online and apply the changes, the Logix controller will fault.
The work-around is to first inhibit the connection, make the changes to the two
check boxes, then uninhibit the connection.
Generic device with zero length input and output is accepted by
the Add-on Profile
The input and output length for a generic device can both be set to zero. These
settings will cause the communication fault bit to be set for the channel.