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Is it possible to change to a 256kb built-in game using the 315-5235 mapper?
Posted: Mon May 16, 2016 2:46 pm
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Hi guys, I'm new to the forum and I've been reading about the BIOS replacement these last days and I want to do it on my Tec Toy Master System I with the Safari Hunt/Hang-On BIOS.
I wanted to change the original bios to one that doesn't check the header so I can play SG-1000/Mark III cartridges with homemade adapter and also japanese Sega My Card games. I know I can just flash Bock's SMS Boot Loader or the Japanese Bios to a eeprom and that would work, but since I'm already changing the bios I wanted to know if it is possible to use the US/European BIOS that have Sonic the Hedgehog 1 installed using a 315-5235 mapper from a After Burner chip and a 256kb EEPROM. Is it possible to change the built-in game for a Sonic the Hedgehog with FM Hack? I patched the FM hack in the bios file and it played with FM music file on my emulator, I would now need to hack the bios to not check for the header and correct checksum. Is this possible? |
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Posted: Thu May 11, 2017 8:56 am |
Hello everyone! Haven't been around for a while :)
A friend of mine asked me to change his Alex Kidd (128kb) bios in his SMS II into the one with Sonic (256kb). So I searched and found this topic. I was doing the multibios stuff few years back so I hope since I left here, you guys found out some way to easily do this :) So does anybody know if this is possible and provide a solution? Thanks a lot!! |
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Posted: Sun May 14, 2017 1:09 pm |
Bump!
Does any of you guys know where is the difference between 128k and 256 k bios? How the mapping works? Is the bios a special combined-function chip with rom+mapper or is the mapper on board in case of the 256k SMS II pcb? In case of that multi IC, I'm going to say: WTB Sonic built in Bios :) |
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Posted: Sun May 14, 2017 4:02 pm |
Both are combined mappers and ROM, this is actually good because it means the interface is the same - if they have the same number of pins. If not, it's trickier. I haven't done it myself, so I can't give any specifics. | |
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Posted: Mon May 15, 2017 12:50 pm |
The AKMW and Sonic BIOSes do not have the same number of pins. The former has 28 while the latter has 32. | |
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Posted: Wed May 17, 2017 7:28 am |
It should be not so complicated to find out where to connect the excess pins, since I have both type systems at home so I can trace those.
The main problem is the mapping. It's a shame no one has done more research in this matter, I have not such skills to do it myself. As the first post suggest, a mapper should be used, maybe it can be done by simply comnecting an afterburner cart pins to the bios pins. I must check the pinout... |
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Posted: Wed May 17, 2017 8:44 am |
I think I'm misunderstanding - what's unknown about the mappers?
To swap the BIOS ROM (with integrated mapper) is fairly easy except for the pinout differences. Inserting a cartridge ROM (with integrated mapper) is a problem because it has no BIOS (or, more correctly, IPL) code so it will never boot anything else. To add a custom ROM (requiring mapping) means adding a mapper chip along with a EPROM, which I don't think anyone has done yet, but it's mostly a matter of pinouts again. One hackier option is to stack the chips and have a hardware switch on the /CE lines. Game ROMs may not boot reliably though, as they may rely on some of the work done by the BIOS. |
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Posted: Tue Mar 08, 2022 10:19 am |
Hello,
I'm very interested in switching my Sonic integrated game with an Alex Kidd one (I have a working Sonic-integrated SMS II and a dead Alex Kidd one). Did anyone succeed doing so ? Is there any guide somewhere I could use ? Thank you :) |
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Posted: Wed Mar 09, 2022 6:46 am |
Going from a sonic bios to an alex the kidd one should be easy as you dont have to add any extra signals. Im fairly sure the sonic bios will have the same pinout as a 27c010. The alex the kidd one matches a 27c512.
I would remove the bios rom and put a 32 pin socket on the board first as that will make it easier to reverse or change later if needed. We can make a simple adapter to go from 32 pin down to 28 pin so you dont have to modify the master system pcb itself. Get a second 32 pin socket and bend pin 30 out to the side. Solder a wire from the bent pin 30 to the very top of pin 32 on the socket. Put the alex the kidd bios rom into this adapter socket but leaving the first 2 rows of pins empty. So pin 1 of the rom would go into pin 3 on the socket. Then you can put it into the socket on the pcb... pin 1 to pin 1. All being well that should work. |
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Posted: Thu Mar 17, 2022 1:13 pm |
Thanks for the reply :)
I've ordered a IC adapter, it comes from China so it will take some time to be here. I'll keep you posted about this mod. Regards, Benjamin |
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Posted: Sun Mar 27, 2022 9:56 am |
\ may i advise against this? I've owned probably 100 model 2's and had ONE with sonic built in, which i kept. I only knew about it because my mums friend had an SMSII with that built in back when i was 10 or 11 years old , maybe younger :) They're definitely harder to find. |
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Posted: Sun Apr 10, 2022 3:52 pm |
Alex Kidd game is even harder to find at reasonable price. I will use a chip socket and of course keep the original BIOS in case I have to sell it :) |
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Posted: Sun Apr 10, 2022 6:45 pm |
It works ! Thank you very much for your help :) |
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Posted: Mon Apr 11, 2022 10:11 am |
Excellent work! Glad you got it going :) | |