SLC-5/02 is Data Highway-485 ONLY
That RJ-45 modular connector on the SLC-5/02 controller is for A-B's Data Highway 485 network only.
DO NOT plug an Ethernet cable into it.
Connection alternatives include the old 1747-PIC interface to RS232, the new 1747-UIC interface to USB, or a 1784-PCM4 cable for your 1784-PCMK card (get Series A or Series B cable to match your card).