[Coco] Color Computer cart addresses / CoCo PSG

RETRO Innovations go4retro at go4retro.com
Thu Dec 22 19:38:54 EST 2016

On 12/22/2016 2:00 PM, Zippster wrote:
> Ah, ok..
> I think I have a pretty clear picture now between the Lomont doc and something Jim
> sent me that appears to possibly be based on it (but different).
Yeah, I know I dloaded it from somewhere.  It's a Word Doc, called "Coco 
Registered Port Addresses and Devices", authored by Galapas.
> *SCS is active for $FF40-$FF5F if I understand correctly (R&W).  I think if I place
> the 5 addresses I need at the upper end of this I should be ok staying out of the way
> (and have the help of *SCS in doing so).
5 addresses?  I thought the YM and the AY needed 16 addresses?  Are you 
doing indirect addressing?
> I had it at the lower end of the *SCS region, but it looked like the SDC modifies a reg
> on it’s initial search for other disk controllers (just a guess, I don’t know the procedure used).
> Not a big deal as it can easily be corrected in software once running, but if I can stay
> completely clear I’d rather.
> So I’m thinking $FF5B-$FF5F in conjunction with *SCS will be ok for decoding register
> access.  Easy to change if an issue crops up at least.  :)
You're OK in an MPI, but with a Y cable, FDC underdecodes all of *SCS, 
so you'll conflict.

Not saying you should move, just noting it so you're aware.


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