Re: Ultima 3 "Mockingboard" version.

[Rubywand <rubywand@swbell.net>]

"Michael J. Mahon" writes ...
> 
> Rubywand wrote:
> 
> >Linards Ticmanis writes ...
> >>
> >> Rubywand wrote:
> >>
> >> >      Mockingboard uses off-the-shelf chips....
> >>
> >> Cool. The 6522 should still be available I guess, since it's a really
> >> common chip for any 65xx thing. As for the PSG, maybe they still make
> >> one that's compatible, I'll see...
> >>
> >> It sounds like a fun summer project. Don't know yet if I'll find the
> >> time to do it. You don't happen to have any schematics, do you?
> >>
> >
> >     No; have never come across such a diagram. Maybe I'll pull our
> >Mockingboard "Sound II" and try diagraming the circuit.
> 
> Actually, it's simplicity itself.  Each PSG is controlled by a parallel
> port of an associated 6522 VIA.  As Linards notes in a later post,
> the PSG is pretty easy to control, and the Mockingboard does nothing
> but interface it to the Device Select addresses on the Apple.
>

     With the 6522 to handle interfacing it is a pretty simple circuit.

 
> FWIW, there is a design omission in the Mockingboard which is
> worth correcting:  Reset on the Apple is not propagated to the
> PSG's which can leave them "sounding" after the machine is
> reset.  A diode between the reset line and the PSG reset will
> fix this.  (A wire is not a good idea, since the 6522's can reset
> the PSG, too, and you don't want them resetting the Apple!)
>

     A connection to the system Reset seems like a very good idea. When we
expanded the Monitor ROM on our II+, one of the first new routines was one to
shut down Mockingboard sound upon a Reset. Doing it in hardware is a lot
simpler.


 
> (And, Ruby, although you are absolutely correct that software
> can modulate the envelopes of the PSG, I know of no software
> ever written for the Mockingboard that does this, while virtually
> all Commodore SID software uses full ADSR control, since it
> is trivial, and does not require constant housekeeping.  So in
> this case, "Turing equivalent" is not nearly so useful.  ;-)
> 
 ....

     Well, mainly, the idea is that it's possible.



Rubywand