Replacing ROM's in MegaDrive games

Discussion in 'Modding and Hacking - Consoles and Electronics' started by Bearking, Mar 6, 2011.

  1. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
    For a long time now I've been wanting to replace a few ROM's in my EU MegaDrive games with the US ones, for those games that won't run in anything but 50Hz.
    I'm guessing some kind of EEPROM burner will be needed but I have no experience with any of that. I do have the basic soldering skills to remove the old ROM chip's and installing the new ones.

    How many types of ROM chips does MegaDrive cartridges use? The easiest thing would be if I could just get a bunch of the largest needed and for the small games fill the remaining space up with 0's or something :) As said I have never worked with these things before :)

    [​IMG]

    In the above picture it's pretty easy to spot what needs changing in the Mega Turrican cartridge ;) The Soleil on the other hand might be more complicated? Soleil does work fine in 60Hz I just used it to show a difference between cartridges.

    Another thing that would be nice is getting RPG's like Langrisser 2 from Japan and replace the ROM with the fan translation. Or simply buy the cheaper and prettier Japanese versions of, for example, the Phantasy Star series and replace the ROM's with the English ones.
    Any chance that the Japanese cartridges will differ so much that simply replacing the ROM won't work?

    I have an EverDrive cartridge on the way so I could just use that to play the preferred versions of the games I already own, but it would be nice to use the original cartridges if possible.

    Is this a retarded idea and are there any downsides in doing this?
     
    Last edited: Mar 6, 2011
  2. ASSEMbler

    ASSEMbler Administrator Staff Member

    Joined:
    Mar 13, 2004
    Messages:
    19,394
    Likes Received:
    995
    No downside, just that most eproms of the same size as the rom in the cart will require modifications to the board for various reasons.

    I'm no expert on it, but if you look up how people have made sonic beta carts might be a start until more knowledgeable people chime in.
     
  3. retro

    retro Resigned from mod duty 15 March 2018

    Joined:
    Mar 13, 2004
    Messages:
    10,354
    Likes Received:
    822
    Of course there are downsides.

    • Decent EPROM burners are expensive.
    • You may not have the correct adapter for the EPROM you want to burn by default.
    • If you want to burn several kinds of EPROM, you may find you need two (or more) adapters (although I don't see that this should be an issue if you're just doing MD games).
    • You may have to do a bit of rewiring to make the EPROM work on the board.

    You'll want series 27 CMOS EPROMs. You might want to take a look at this:

    http://devster.monkeeh.com/sega/segarom.png

    Yes, the EverDrive will be a LOT less hassle!
     
  4. Alchy

    Alchy Illustrious Member

    Joined:
    Apr 6, 2004
    Messages:
    6,216
    Likes Received:
    19
    For the amount of cash you'll spend it'll almost certainly be cheaper to buy the American carts instead.
     
  5. MottZilla

    MottZilla Champion of the Forum

    Joined:
    Feb 1, 2006
    Messages:
    5,063
    Likes Received:
    102
    Rewiring is not true. Sega Genesis/MegaDrive MaskROMs are JDEC (I think that is what it's called) standard and are EPROM compatible. Just get a FlashROM or EPROM of the same size and have at it. It is just a matter of desoldering the MaskROM and soldering in an EPROM.

    The programming of the chip is a much bigger deal since you need to have the correct Endianness of the 16bit ROM. Also you need a programmer that can handle 16bit chips.

    Really it's dead simple once you can manage to get your ROM file onto an EPROM or FlashROM.
     
  6. Twimfy

    Twimfy Site Supporter 2015

    Joined:
    Apr 10, 2006
    Messages:
    3,570
    Likes Received:
    32
    Seconded.

    You're also fucking up existing carts, labels etc. I'd never damage an original game when there are plenty alternatives (overdrive etc.)
     
  7. Calpis

    Calpis Champion of the Forum

    Joined:
    Mar 13, 2004
    Messages:
    5,906
    Likes Received:
    21
    I don't really condone this stuff but might as well chime in. Yeah the ROMs are JEDEC-compliant.

    4M - 27C4096
    8M - 27C800
    16M - 27C160
    32M - 27C322

    I would suggest getting the correct ROM sizes for what you're working on. If you do need to pad the game up to the next ROM size, use a tool such as uCON64 as it should generate the correct mirroring on non-power-of-2 ROMs. If you are padding a power-of-2 ROM like 4M game to 8M or 8M to 16M (both are really wasteful), you can just "double-up" the ROM until you get the desired size. Padding with 0s may be problematic with some games.
     
  8. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
  9. retro

    retro Resigned from mod duty 15 March 2018

    Joined:
    Mar 13, 2004
    Messages:
    10,354
    Likes Received:
    822
    I think Elnec's SmartProg2 supports up to 40 pin devices natively, and should support 27C EPROMs:

    http://www.elnec.com/products/universal-programmers/smartprog2/

    That's their cheapest device.

    Dataman's MEMPro should do, also:

    http://www.dataman.com/WebPages/ProductView.aspx?pid=622

    Like I said, they're not cheap. Cheap programmers (e.g. Willem) are horrible.
     
  10. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
  11. retro

    retro Resigned from mod duty 15 March 2018

    Joined:
    Mar 13, 2004
    Messages:
    10,354
    Likes Received:
    822
    If it stops you from buying a poor programmer, surely it's not a waste of time? ;-)

    I don't know about that one - have a google and see what you can come up with. Arcade forums might be a good place for reviews.

    Willem programmers can be pretty ropey (and they come as bare PCB). Other cheap Chinese devices aren't much cop, either.

    The American brand Xeltek are very good, but I don't know whether they have any cheap solutions. Probably not!
     
  12. Calpis

    Calpis Champion of the Forum

    Joined:
    Mar 13, 2004
    Messages:
    5,906
    Likes Received:
    21
    I dunno, I would go with something cheap if all you're going to do is program EPROM. I had a Willem and it served me well for a couple years before I damaged it with the wrong power supply. They aren't the most reliable since they use discrete components and a charge pump to generate VPP, but they're certainly suitable for EPROM and small flash. My revision was from 2002 so if anything the maintainers have probably improved the design since then.

    Even the best programmers available today which cost a small fortune only offer marginally better support for MCU, larger flash and PLDs. In most cases their legacy algorithms are hit or miss (mostly miss) so you'll need legacy programmers anyway for ancient SPLD/EPLD and MCU, and the way more recent MCU and CPLD are handled through ISP and JTAG makes it cheaper to go with dedicated vendor programmers for those devices, you even get more functionality too.
     
    Last edited: Mar 9, 2011
  13. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
  14. Calpis

    Calpis Champion of the Forum

    Joined:
    Mar 13, 2004
    Messages:
    5,906
    Likes Received:
    21
    I have no experience with these new enhanced USB Willem. To me that one seems expensive since mine was ~$40 including international shipping, but you are getting USB and an enclosure. Anyways, that model by itself is NOT suitable for programming 16-bit ROMs >4M, you'll need some kind of adapter. Maybe it supports the original Willem 16-bit adapter (~$20), you'll have to look into it and decide. Other USB programmers in this $120 price range definitely cannot directly support large 16-bit ROMs either (nor can that entry level Elnec) so this one might be the way to go.
     
    Last edited: Mar 10, 2011
  15. MottZilla

    MottZilla Champion of the Forum

    Joined:
    Feb 1, 2006
    Messages:
    5,063
    Likes Received:
    102
    The EverDrive is supposed to be able to load other Sega CD BIOS roms for you. No need to do some kind of mod to your Sega CD then. You might need a region mod on your actual Console to change region though but that is just switches to control jumpers.
     
  16. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
    The ROM chips I need for MegaDrive and MegaCD Bios are 40-pin DIL types and should fit into the burner. But you say it won't work, is that because these chips are wired differently than the socket on the burner?

    Please remember that I have no experience with these things. Sorry if this is a stupid question :)

    Yes good suggestion, but that way I wouldn't be able to use my MegaCD memory card :)
    I do already have a Multi bios in my MegaCD but it's the old kind that requires switches to switch between regions. I would much rather have one that plays everything with no switches :)
     
    Last edited: Mar 11, 2011
  17. Calpis

    Calpis Champion of the Forum

    Joined:
    Mar 13, 2004
    Messages:
    5,906
    Likes Received:
    21
    If you only need to program 40 pin 4M ROMs it's probably fine, 8M and larger are 42 pin.
     
  18. Bearking

    Bearking Konsolkongen

    Joined:
    Aug 2, 2010
    Messages:
    855
    Likes Received:
    100
    I didn't know the chip had different number of pins. That makes perfect sense then :)
     
  19. l_oliveira

    l_oliveira Officer at Arms

    Joined:
    Nov 24, 2007
    Messages:
    3,879
    Likes Received:
    245
    40 pin MEGA DRIVE MASK ROMs are non JEDEC. They use the same pinout as the 27C160 but at that capacity (512KB) the pinout is non JEDEC.

    You can fit a 27C160 on a 512KB SEGA ROM board but there's pin lifting involved on the EPROM. (You're supposed to lift pins 1 and 42 then connect them to GND or to the Mega Drive bus... Maybe make a multi cart with 4 512KB games ? lol)

    Edit:

    Bugmenot, 68000 is a BIG ENDIAN CPU... You want the game rom to look like this on hex editor:

    Definitely NOT like this:
    This process is called "byteswap". And if you use .BIN files that are suitable for emulation they're certainly swapped because x86 is little endian.
     
    Last edited: Feb 8, 2014
  20. chrholder2

    chrholder2 Member

    Joined:
    Feb 9, 2014
    Messages:
    5
    Likes Received:
    0
    Hi. Okay, then my problem is how to program the 42 Pin Chip. Do I need an adaptor. I have this programmer: http://www.ebay.com/itm/USB-MiniPro...PROM-FLASH-8051-AVR-GAL-PIC-SPI-/221092473435. There exist 40Pin to 42Pin adaptor but even if I had this adaptor I don't know which Chip to select because the 27C160 is not listed. Is there anotherprogrammer for this kind of Chip?

    The Rom seems to be correct (Olympic Gold), see picture imag2.JPG
     

Share This Page