SFX Sound Expander cartridge and .... Plus/4?

Hi All,

When I have some free time, I'm still working on the SFX player stuff. Since
I've discovered that VICE can emulate the cartridge for VIC20 and 128 too (I
am not sure however it would work in C128 mode, or just in C64? Is there any
difference, with/without 2MHz mode?), so I've decided to have multi-platform
solution, not just C64.

It was also easy this way to support Plus/4 too (my program has the "target
dependent" parts separated, so support another CBM machine this way only
requires some minutes of work - so why not then?), at least on the level
that the program would run it.  However, AFAIK this hw does not exist for
Plus/4, so it's quite useless; the program would run, but no sound for sure
because of the lack of cartridge (and also the emulation by VICE, since I
use emulator).

My question: is there anything like that cartridge for Plus/4 that it's
worth to support by me? If there is, can someone give me information how to
program it (I/O addresses)? Anyway, even if such a thing does not exist, it
would be great to build then, if we forget about the "keyboard" for that
cartridge, it's about basically an YM3812 OPL2 chip (well, the older OPL
only version for the "real" cartridge, but OPL2 is nicer, and it seems many
people replaced it anyway?) interfaced to Plus/4.

Of course, eg C16 is also targeted, afaik it's compatible with Plus/4, just
having less memory, no +4 softwares (I don't care anyway), and hmm user
port, or so, as far as I remember?

- Gábor

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