Makaron‘s author Deunan has posted a tutorial on his blog on how to make a cheap connector to link your Dreamcast with a PC, especially for those coders who can’t get a hold of a BBA.
Deunan wrote:
So, does it work? Hell yes, on 3 Dreamcasts already. Same technique in every case. Works like a charm up to 1.5Mbps too. Just keep the wires to FT chip as short as possible (already long board traces and protective RC elements not helping any). If you have problems with higher speeds you can try using 5V instead of 3.3V for I/O. I belive this to be pretty safe (run it for hours on my Dreamcasts) but make no guarantees.
You can find detailed steps on how to make your own here.