The 1747-PIC will convert the info from your com port to the DH485 protocol.
If you only have an RJ45 connector on the front of your SLC500, then you have a 500 (fixed unit)5/01 or 5/02 processor and you will have to use the PIC or another DH485 converter.
If you also have a 9 pin serial...
I'm perhaps plagerizing this, I was sent this as an explanation of the PIC's problems with USB. I hope it helps.
"unofficial" PIC fact (v1.0)
The PIC was designed in the early 90's. Since memory was expensive, it was given a very small communications buffer. To account for this, the...
Be aware that AB is offering their 10 I/O MicroLogix (1761-L10BXB) for $99, and a limited edition RSLogix starter to program it as a free download. Having worked with both the SLC / Micro controllers, I'd lean this way rather than the Pico controller (also from AB)since the Pico's programming is...