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Sega Master System mapper and cartridge pinout
Posted: Thu Apr 27, 2023 4:02 pm
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Hi, reading the SMS docs I found that an internal mapper is already present (correct?).
I saw the cartridge pinout but I didn't see any A16-A19 pins. Did I make some assumption wrong or is there no mapper? |
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Posted: Thu Apr 27, 2023 4:16 pm |
Hi siriokds, there is no internal mapper, only the Z80 bus. Mappers are implemented by cartridges. |
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Posted: Thu Apr 27, 2023 5:18 pm |
Thanks a lot to clarify it.
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Posted: Fri Apr 28, 2023 11:46 am |
note that the SMS BIOS(es) assumes that a SEGA mapper is present into the connected cartridge/card if the ROM size is reported to be >= 64 KiB in the SEGA ROM 'signature'... | |
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Posted: Fri May 05, 2023 8:19 am |
Is the signature the only requirement? How about custom mappers? |
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Posted: Fri May 05, 2023 8:52 am |
I guess the point is that you should assume that the Bios might write values to $fffc, $fffd, $fffe and $ffff so your mapper should continue to function in that case. | |
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Posted: Fri May 05, 2023 9:02 am |
a correct signature IS required on export SMS (US/Eur/Bra/AUS...) but you can report the size of the ROM as 32 KiB and the BIOS won't try to communicate to any mapper. check this. You probably want to write $4C at $7FFF - note that the checksum will be then calculated on the first 32 KiB minus 16 bytes of your ROM data. |
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Posted: Sat May 06, 2023 11:51 am |
Nice thanks. So I can put into the header the 32KB dimension but I can page swap the 8000-BFFF range. Btw, what's the /CE signal of cartridge connector? It's like /MEMREQ of Z80? |
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Posted: Mon May 08, 2023 5:48 pm |
This might be useful for you @siriokds: https://www.smspower.org/Development/BusSignals |
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