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Richard Atkinson
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YM2413 OPLL MSX-MUSIC adaptor schematic
 Posted: Thu Jan 17, 2002 4:07 pm
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As promised, here is the schematic of the MSX-MUSIC adaptor I am going to build for the SMS expansion port. I ordered the parts from my local Maplin today, but (of course) they didn't have any of them in stock. Anyway, here is the design - tell me what you think of it! :)
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Richard Atkinson
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Re: YM2413 OPLL MSX-MUSIC adaptor schematic (link fixed)
Posted: Thu Jan 17, 2002 4:09 pm
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Blah. Silly http prefix...
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Richard Atkinson
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Re: YM2413 OPLL MSX-MUSIC adaptor schematic (link fixed)
Posted: Thu Jan 17, 2002 4:39 pm
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Argh. I give up. You can edit the URL yourself...
Anyway, I thought I'd share some thoughts on the design of this thing. The MSX has two write only I/O ports at 7Ch/7Dh for the YM2413 OPLL, whereas the Master System expects the chip at F0h/F1h with an extra detection latch at F2h. As there is no way to read from the chip in the MSX cartridge, the latch has to be implemented in the adaptor, which is what the 74LS374 U4 is for. U1 and U2A decode the address range F2h/F3h for I/O accesses and U3A and U3B produce the OE# (read) and CLK (write) signals for the latch.
To map F0h/F1h onto 7Ch/7Dh I swap some of the address lines round and invert one of them using U2B. The mapping is as follows:
SMS Address bus
A7 A6 A5 A4 A3 A2 A1
1 1 1 1 0 0 0 (F0/F1)
Remap
A3 A6 A5 A4 A7 A1# A2
0 1 1 1 1 1 0
MSX Address bus
A7 A6 A5 A4 A3 A2 A1
0 1 1 1 1 1 0 (7C/7D)
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