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[kazmat]

I have 8M MGD1 with MD I/O & PCE I/O.

I would like to build SFC I/O.

Is it possible to make SFC I/O from SFC 8M+64K Sram cart ?

Anyone knows pin assignment of 40pin MGD I/O ?

[kyuusaku]

Yes, it's possible, I don't know the MGD pin assignment though. It will be difficult to modify an existing cartridge because you must add in a tristate buffer chip and IDC connector.

You can figure out the pins if you open your PCE I/O, it is the same as SFC because both are 8-bit ROM consoles. All you have to do is adapt the Hucard to SFC and add in SRAM. SRAM in early LoROM games is decoded using a 74LS139 chip. I have made this diagram for you to show the decoding:



Remember, "PCE /OE" is "MGD /OE"; For SFC, "ROM /OE" is "MGD /OE" because of the decoder.

To make a LoROM cartridge (like Bung original), connect MGD A0-A14 to SFC A0-A14, then connect MGD A15-A19 to SFC A16-A20; A15 is not used for LoROM.

For HiROM connect MGD A0-A19 to SFC A0-A19 (but you must change SRAM decoder), I don't think there are many good 8M HiROM games anyway.

You can make a DUAL LoROM and HiROM I/O by adding 2x 74LS157 multiplexer chips to select address lines. This way you can use one cartridge with a switch to select either Lo/HiROM mapping.

If you want AUTO Lo/HiROM switch you can use this equation: A22 AND A23 = HiROM.