Rockwell Automation 1756-Mxxxx ControlLogix SERCOS interface Module Installation Instructions - Manual (Page 7)

ControlLogix SERCOS interface Module 7
Publication 1756-IN572G-EN-P - May 2005
2. Insert each fiber optic cable into the appropriate port and screw on
finger tight. The cable that emits light is the transmitter.
Any break in the ring disables the SERCOS network and creates a warning a
on the SERCOS Ring Status LED.