Thanks for your note. The BitsyXb doesn't have 485 support as part of its feature set. You could probably implement 485 by connecting Serial 2 (3.3V logic level) to an external differential transceiver and controlling the TX and RX enable lines with the RTS line.
Another option is to use a product like the GCX, which has RS-485 functionality built in.
Feel free to email us with details of your objectives and we'll be glad to advise. Let us know how we can help.
p.s. I've moved your post from the Linux Open Discussion forum to Hardware.