Allen-Bradley MicroLogix 1400 User Manual page 328

Appendix F MicroLogix 1400 Distributed Network Protocol (DNP3)
314
After you write your ladder program, select "Save As ..." from the File menu of
RSLogix 500/RSLogix Micro. Select the save type as "RSLogix IMG Files
(*.IMG)"
After saving the file, you can see the file "ML1400A_DNP3S.IMG". This is the
file to be used for download.
RSLogix 500/RSLogix Micro v8.10.00 and the MicroLogix 1400 Series
IMPORTANT
A controller do not support the opening of *.IMG files. Be sure to
store your ladder program in the RSLogix Files (*.RSS) format before
generating RSLogix IMG Files (*.IMG). Otherwise, you may lose the
latest modifications to your ladder program.
Rockwell Automation Publication 1766-UM001I-EN-P - June 2015