My UV eraser died so while im waiting on a new one to get here I wanted to experiment with burning some hack roms for genesis, i know this is nes board but it's same concept.
1. anyway if the hacked rom is bigger than the original rom, example a 1M rom and a hacked version that is 1.2M or something, can I burn it to a 2M eprom and do I need to pad out the remaining space with FF or just random junk, or is this not possible.
2. have a wilywars rom and patched it, it's 2M, i have a 3M eprom, same question slightly different, pad out the rest? If I had a 4M eprom could I double the rom up?
I would try it myself but I'm down to a few eproms and dont wanna waste anymore till eraser gets. I've researched on Google and dev sites and cant find info on it although i've seen some repros done of hacked roms and the file sizes were not correct.
thanks all
You have a 3M EPROM? Like 3 Megabytes? I don't think those exist, do they?
If your EPROM is bigger than the game you are programming the proper thing to do would be to mirror the data. Meaning if it's 2M on a 3M chip, you'd place the first 2M at the front/beginning, and then put another copy of the first 1M after it. However it's unlikely but still possible that a game would depend on this mirroring behavior on Genesis. On NES it may be more important.
And yes if you have a 2M game and a 4M eprom, just double it up.
Be aware of endianness (big or small) when propgramming 16bit eproms! When I first tried to put Eproms in a Genesis cartridge it turned out the endianness was incorrect and it didn't work.
Hi MottZilla, the guy that patched megaman wilywars, great work btw
I burned one hack, sonic 2 the lost worlds, the endian is different but you can just do a byte swap of the rom before burning
You are right, no 3M roms, i dont know why my brain was thinking that, probably because of the label, M27C322, it's only a 4M (2Mx16), I also have some 1M and 2M chips
The main question I have is the hacked roms that go over the standard rom size limit, normal rom 1024, 2048, 4096 etc, hacked rom that is 1129 or something in size, how would i burn that to a 2M rom? I can mirror the data but not sure if that matters on genesis. Do i just pad out the rest of the bytes?
If the game is hacked and not a multiple of 1 megabit size, it's very unlikely the game cares what comes after it. Just leave it be, put garbage, mirror, it likely doesn't matter which you do. For real games, some are 10 megabit, (1.25mbytes?) some are 12 megabit (1.5mbytes) and you may or may not want to mirror the beginning of the ROM to the unused portion on a 16 megabit eprom.
So with that ROM in theory that is between a 1024 and a 2048, you would just pad it up to 2048 for any hacked ROMs as it's unlikely data beyond is ever accessed though if you have problems you should try mirroring.
On Genesis, you can usually FFFF-pad the ROM to the next larger power of two.
Thanks guys, that is the answer I needed. I will give it a try.
One last question on the genesis carts. Is there any specific carts to use with burned eproms. I read there is only 2 different types but after pulling them apart I have many layouts. Is there a list somewhere like the list for the NES donor carts? I have a bunch of crap sports games i've got ready for eproms.
On the Genny/MD, the Sega header and 68k pointers are at the beginning (pointers from 0 to 0xFF and Sega header is from 0xFF to 0x1FF), so you can pad with anything (00s, FFs or random garbage)
I'm interested too in the Megadrive, because it's simpler to use: no mapper/mirroring things and 32-bit integer support, and (for me) the mnemonics from the 68k are simpler than those from the 6502
Most Sega Genesis cartridges will use either 40pin DIP 4mbit chips, 42pin 16mbit, or 42pin 32mbit. You can find out by looking up the ROM size of whatever game's PCB you are going to use. Some games do use two 8bit ROM chips to simulate a 16bit ROM.
right, but will the other pcb layouts change anything with game compatibility, for example EA game pcb vs acclaim etc, can i put any game on any board assuming the chip i add is for the correct rom size? Can i for example put a sonic 2 eprom on an nba jam cart?
The only consideration you need to make besides what type of EPROM the PCB wants is SRAM and EEPROM types of saving. Some games use SRAM (8kb usually) and a battery for saving. Others with a Serial EEPROM for saving. I think NBA Jam is like this. There are two other special PCBs, Virtual Racing which has the SVP and Super Street Fighter 2 which has a memory mapper for its 40 megabits of ROM.
Games that use EEPROM saving are more complicated by the fact that not all are the same. So generally if you stay away from those games, and note which use SRAM, you should have no problems.
what would happen if I was to put a generic non-saving type game, like sonic 2 on a cart with sram. Would it work or would I have to rewire it so that the sram chips are bypassed? I have a bunch of craptacular sports games im destroying for better games.
If a game is 2 megabytes or smaller it should not matter if SRAM is present. For larger games it may have issues, I'm not sure. You really shouldn't waste a SRAM PCB on a game without SRAM though.
interesting, does the sram just ignore it then? Im not worried about wasting them, I have about 40 sports games i scored on ebay awhile back
sleepy9090 wrote:
interesting, does the sram just ignore it then? Im not worried about wasting them, I have about 40 sports games i scored on ebay awhile back
I've never had an issue using a game with battery backed SRAM as a donor for a game that does not need it. Also, I've never had an issue using a game that uses a serial EEPROM (like College Slam) as a donor for a game which does not use it.
No idea why it works as I definitely don't have the hardware knowledge that most people on here have, but I learned a lot from trial and error.
I've yet to find any MD game that actually cares what comes after it. Does not matter if you pad, mirror or fill with garbage the game will work.
mrmark0673 wrote:
sleepy9090 wrote:
interesting, does the sram just ignore it then? Im not worried about wasting them, I have about 40 sports games i scored on ebay awhile back
I've never had an issue using a game with battery backed SRAM as a donor for a game that does not need it. Also, I've never had an issue using a game that uses a serial EEPROM (like College Slam) as a donor for a game which does not use it.
No idea why it works as I definitely don't have the hardware knowledge that most people on here have, but I learned a lot from trial and error.
It works well with games with 2MB (16 megabit) or less, because the SRAM is mapped at 200000-3FFFFF.
Usually, if the game is 2MB or less, in that 200000-3FFFFF space, there's just a mirror or the game at 000000-1FFFFF, so the game ignores it
mrmark0673 wrote:
I've never had an issue using a game with battery backed SRAM as a donor for a game that does not need it. Also, I've never had an issue using a game that uses a serial EEPROM (like College Slam) as a donor for a game which does not use it.
No idea why it works as I definitely don't have the hardware knowledge that most people on here have, but I learned a lot from trial and error.
The reason it works is because the game doesn't behave oddly. However it is possible for it to do so. It just seems that on the Genesis no one did anything fishy, atleast with official software. On SNES the existing SRAM was often checked as a means of copy protection. Games like Donkey Kong Country (I think), Super Metroid (definite), and Killer Instinct (definite) would check not only if SRAM existed but how much of it is there. If it doesn't match the original cartridge it would give you a screen about don't copy games.
Genesis didn't seem to have any such protections in games. However it certainly could have been done.
MottZilla wrote:
On SNES the existing SRAM was often checked as a means of copy protection. Games like Donkey Kong Country (I think), Super Metroid (definite), and Killer Instinct (definite) would check not only if SRAM existed but how much of it is there.
And for one of the most triumph example,
Mother 2 (or Earthbound if you want).
OH man I remember that one, truly an evil copy protection