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  • Joined: 10 Dec 2009
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Sega Master System mapper and cartridge pinout
Post Posted: Thu Apr 27, 2023 4:02 pm
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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Post Posted: Thu Apr 27, 2023 4:16 pm
siriokds wrote
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?

Hi siriokds, there is no internal mapper, only the Z80 bus. Mappers are implemented by cartridges.
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Post Posted: Thu Apr 27, 2023 5:18 pm
Thanks a lot to clarify it.


willbritton wrote
siriokds wrote
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?

Hi siriokds, there is no internal mapper, only the Z80 bus. Mappers are implemented by cartridges.
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Post 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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Post Posted: Fri May 05, 2023 8:19 am
sverx wrote
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'...


Is the signature the only requirement?
How about custom mappers?
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Post 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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Post Posted: Fri May 05, 2023 9:02 am
siriokds wrote
Is the signature the only requirement?
How about custom mappers?


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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Post Posted: Sat May 06, 2023 11:51 am
sverx wrote
siriokds wrote
Is the signature the only requirement?
How about custom mappers?


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.


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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Post Posted: Mon May 08, 2023 5:48 pm
siriokds wrote
Btw, what's the /CE signal of cartridge connector? It's like /MEMREQ of Z80?

This might be useful for you @siriokds: https://www.smspower.org/Development/BusSignals
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