Re: YMZ284? Re: My Mockingboard Clone

[Eric Rucker <bhtooefr@gmail.com>]

On Aug 21, 8:59 pm, Michael J. Mahon <mjma...@aol.com> wrote:
> Ralph <rwh...@gmail.com> wrote:
> > On Aug 3, 4:59 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> >> On 8/3/2010 12:30 PM, Linards Ticmanis wrote:
> >>> On 08/03/2010 03:00 PM, Polymorph wrote:
>
> >>>> I just completed implementing my most challenging hardware project
> > > > > to
> >>>> date - a Mockingboard clone!
>
> >>> Also, if you do your own programming for the card and don't just
> > > > want to
> >>> use it with existing games, it makes sense to connect PB6 to PB7 on
> > > > each
> >>> of the VIAs (kudos to Michael Mahon, IIRC, for that idea).
>
> >> It's also worth noting that a Mockingboard has two mostly unused
> > > ports
> >> on the two 6522s (six bits on each), and four completely unused ports
> >> on the AY-3-8910s (16 bits on each).  The AY ports are much less
> >> versatile than the 6522's and an extra bit fiddle away (accessed
> > > through
> >> the 6522s) but they are there, and completely unused.  It could have
> >> supported a pretty flashy LED display!  ;-)
>
> >> -michael
>
> > Since the AY-3-8910s ports are unused, could you replace them with a
> > variant
> > of the 8910 without the extra I/O pins?  I'm thinking of using a 6522
> > and the
> > YMZ284D chip, which is supposed to have the same registers as the
> > YM2149, but
> > without the I/O pins.  It has the 8-bit parallel input, but no digital
> > I/O
> > ports (just the three sound channels merged into a single Audio output
> > pin)
>
> That should work fine.
>
> -michael  -  NadaNet 3.1:  http://home.comcast.net/~mjmahon

If the I/O ports are unused, then there's another possibility for FM,
as well - the YMF288. It's essentially a YM2608, albeit with the PCM
channel gone (but the noise and rhythm "channels" still implemented,)
a few FM functions that weren't used removed, and no I/O ports... in a
MUCH smaller package.