Paprium and it's sound engine

Ask anything your want about Megadrive/Genesis programming.

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Re: Paprium and it's sound engine

Post by Sik » Wed Apr 19, 2017 1:37 am

How does the 32X output audio? Also if I recall correctly, there are differences even between FM and PSG depending on the board revision (not sure how big though), so I don't know if there's much that can be done about this at all.
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Re: Paprium and it's sound engine

Post by TmEE co.(TM) » Wed Apr 19, 2017 8:17 am

32X sends audio through cart to MD. AV in to AV out is just a passthrough.
The loading is very easy to take care of. Something like this is able to drive even 2 ohm speakers without drop (assuming you use transistors with right current rating and don't go overboard with emmiter resistors) in level and it only needs couple additional parts compared to just opamp :

You could also use some video opamp as they have no problem with 75ohm loading on their own but their performance in audio range tends to be poor, but perhaps it isn't a problem since stock circuits in MDs already suck and probably mask any problems nicely, leaving you with a nice drop in solution. Keeping those opamps from oscillating might be a problem though.

Now as far as identifying models goes, you can identify MD2 VA4 + Genesis3 VA1 (315-5690) and Genesis 3 VA2 (315-6123) by just looking at how many times you can access ROM from Z80 side in some timeframe. Those machine have differing timings there compared to all earlier things. Identifying MD2 from MD1 is another problem, but there's one Z80 bug that can be exploited to some extent. MD2s have CMOS Z80 in them, while all MD1s apart from VA7 have NMOS. Here's e-mail from TotoOnTheMoon about it :

I don't know if you remember your problem of exchanging the CPC Z80 by using a CMOS version?
I think that I got an answer... It is a Z80 bug!

NMOS = OUT (C), 0 ; out 0.
CMOS = OUT (C), 0 ; out 255!!!

An other difference is:

NMOS = LD A,R/LD A,I ; P/V flag is cleared if interrupt is received during the execution of these commands.

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