>>>>> "Jonathan" == Jonathan Vaughn <biosehn@airmail.net> writes:

  Jonathan> I don't think it needs microcode, only, we just need to know what the
  Jonathan> registers
  Jonathan> that control it are. After all, it IS a hardware modem.

Since the advent of V32 (9600 bps) modems, there have been no real
"hardware modems".  They are all based on some DSP core, which needs
firmware.  All the code runs on the DSP, so it is not a "software
modem" in the "winmodem" sense, but there is need for some software.
Normally, this is provided in a flash rom or something, and is loaded
automatically when the modem is powered on.  In the case of the DC
modem, I have been led to believe that there is no such rom and that
the firmware has to be uploaded from the CPU bus.  I can't verify this
of course, as the register map is not documented as you say.
Inspection of the modem circuit board only reveals two chips though;
the modem chip itself (Rockwell RP336LD in the case of my Japanese
modem) and the SEGA G2 bus glue chip.


  Jonathan> And there are docs available for the hardware interface,

The docs for the hardware interface are of course utterly useless
unless you plan to make your own PCB.  (Yes, I have read them.)


  // Marcus