That Homelynk thing sure has a lot of hardware for needing a bidirectional port. The
Freewing interface (probably the nibble mode interface mentioned in the Homelynk doc) only needs two more 74xx circuits, works with unidirectional ports, and has some software already written for it (the Caetla tools for PSX, and I think SSLINK for Saturn supports it too). It's probably a bit slower though, since it multiplexes the return byte. If you want to write some Saturn-side software that uses the cable, keep in mind that the commslink addresses are in different places on the Datel and EMS AR units. I'd say what the addresses are, but that info is on my main PC which is dead at the moment.
If someone really wants to know, let me know and I'll figure it out again; hopefully my memory is good enough to make it relatively easy...