How are you trying to connect? (hardware, cables, what port on the SLC)
Have you tried the SLC's serial port? (RS232 DF1 devices driver and a null-modem cable)
For the DH485 port you will need a 1747-UIC ( USB to DH485 converter) or an old 1747-PIC ( need a real serial port for this)
Someone might have used a 1784-KTX card and named it KT500-1 to connect to the DH485 port.
If you can get connected with RSLinx with one of the above methods, then open RSLogix500 and the SLC's program. Then click on "Comms" select "Who Active Go Online" then select the controller in the who active window and go online.