Rockwell Automation 1769-L23E-QB1B_L23E-QBFC1B_L23-QBFC1B CompactLogix Packaged Controllers Quick Start and User Manual - Manual (Page 187)

Publication IASIMP-QS010B-EN-P - October 2009 187
Network Communication Chapter 2
If you are configuring a 1769-L23-QBFC1B controller, click the system
protocol tab that corresponds to the serial port you configured in
step 2
(for example, CH0-System Protocol).
8. From the Protocol pull-down menu, choose DH485.
1769-L23E
1769-L23