On Wed, 30 Jun 1999, Richard Atkinson wrote:
Oh dear, here I go again, answering my own emails and rabbiting on about
that silly old Sound Expander ;)
> Well the idea of a compatible implementation would be that there would
> already be at least some software, Commodore's own software for the YM3526
> OPL, which would be upwards-compatible with the hacked Soundblaster
> interface.
Hmm. now that I have worked out the bizarre implementation of the FM sound
chip on the 65xx bus, I doubt very much that a Soundblaster card could be
grafted onto the Commodore bus without at least some modifications on the
Soundblaster pcb.
> Anyway, time for an update: I've succeeded in finding one YMF262 chip, in
> the sound card in this computer, but unfortunately it's SMT. There is also
> a YAC512 and an 071 quad op-am in SMT. Ideally I need another YAC512 and
> 071 to make a four channel system, but the biggest problem is desoldering
> them.
..... and Yamaha won't give me any YAC512 documentation, saying that
they're discontinued parts..... :(
> Anyway, to sum up I should say that the finished OPL3 card will have 5
> registers not 4 as in the PC implementation for much the same reason that
> the current Sound Expander has 3 registers rather than the PC's two. (to
> do with the seperate /READ and /WRITE lines) Does anyone know of any good
> OPL3 music software? (with source) The easiest thing to do would be a port
> from PC to C64.
Here's the proposed software interface ('supported' register addresses):
$DF40 Primary index register write only (220 on PC)
$DF48 Secondary index register write only (222 on PC)
$DF50 Primary data register write only (221 on PC)
$DF58 Secondary data register write only (223 on PC)
$DF60 Status register read only (220 on PC)
The two registers labelled 'Secondary' are new. Of course, in actual fact
there are mirrors all over the DFxx address range, just as there are in
the original Sound Expander.
Expect scanned-in copies of hand-drawn schematics tomorrow at an ftp site
near you ;)
Richard
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