On Fri, 28 May 1999, MkII wrote:
> > Some Sega Master System games do use the 5.5 bits trick, but the
> >PSG of the Master isn't a true AY-3-8190. Instead, it is a SN-something,
> >slower than our one (and also it doesn't have envelopes...)
>
> But compatible?
>
Nearly. The main difference between their PSG and ours is the
number of i/o ports. The SMS chip has only one i/o port dedicated to the
psg, the number of the channel and the frequency/volume has to be sent
encoded in two consecutives writes to the same port. Another difference is
the way you set the volume, in our one 15=maximum volume and in theirs
15=maximum attenuation.
Leonard, I believe this the reason to choose this chip... This way
you can simplify the i/o decoder...
----------------------------------------------------------------
Ricardo Bittencourt http://www.lsi.usp.br/~ricardo
[EMAIL PROTECTED] "Ricardo is subtle, but malicious he is not"
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