Hi, first post so forgive me if I lack correct etiquette. I don't think I can legally give you their document, but if you google "weller Application Note: WAN12-0006" that's what you are after. I spoke with their AMAZING tech support and they sent it right over - such awesome people at that company IMO.
What I don't yet know, but have asked, is if you can interface via the USB bus or have to use the RJ11 on the back of most units - which is what the serial chip is attached to. IIRC it is an analog devices ADM3251E or similar.
If you do anything interesting with the comms do post it as I'd love to know what you learn.