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Thread: [GUIDE] Make a Reprogrammable Genesis Cart

  1. #136
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    Thanks for the info. So it seems like every game so far that I want to make is 2Mbytes unfortunately.

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    Ok, that's fine. What we should do is figure out how they are being mapped.
    Lets start by choosing one board, looking at the 74hc00 IC and trace back all of the inputs and outputs. Please look at that diagram I posted above and write down where each pin goes:

    1 - GND
    2 -
    3 -
    4 -
    5 -
    6 -
    7 -
    8 -
    9 -
    10 -
    11 -
    12 -
    13 -
    14 - VCC

    Then we can determine which ones to lift and rewire. It should be pretty simple if you have a multimeter with continuity checker. Some of the inputs may be bridge together and connected to address pins on the cart edge. Some may simply be connected to either vcc or gnd with the outputs floating, but we won't know until you check.

    Do you know what a truth table is? It looks like so:
    http://sub.allaboutcircuits.com/imag...z/02772x02.png

    we will make one of our own that pertains to our project once you trace those pins for us.

  3. #138
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    So what two points am I checking for continuity for? between the 74HC00 and the sram, board connections or eprom?

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    Quote Originally Posted by Lotaphi View Post
    So what two points am I checking for continuity for? between the 74HC00 and the sram, board connections or eprom?
    I would like to know where all of the pin on the 74hc00 go:

    1 - GND
    2 -
    3 -
    4 -
    5 -
    6 -
    7 -
    8 -
    9 -
    10 -
    11 -
    12 -
    13 -
    14 - VCC

    This will tell us how the board is mapping the locations of ROM and RAM, then we can modify the map for 2MBytes of ROM and keep the RAM after it.

    I assume you will find cart edge pins like A21 and ~CE connecting to some of the inputs of the 7400. Some of the outputs from the 7400 will connect to ~CE of ROM and ~CE of RAM.

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    updated photos in original post.

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  7. #141
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    Hello there.. Thanks for all the info, it has been very useful. Can I buy a Japanese phantasy star IV cartridge and put the English version on it ? Are the PCB the same? I understand there is 2 mask ROMs so how do I go about splitting the ROM to put it on 2 EPROMS? Any help would be much appreciated

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    Quote Originally Posted by wal666 View Post
    Hello there.. Thanks for all the info, it has been very useful. Can I buy a Japanese phantasy star IV cartridge and put the English version on it ? Are the PCB the same? I understand there is 2 mask ROMs so how do I go about splitting the ROM to put it on 2 EPROMS? Any help would be much appreciated
    You could do that if you wanted to. It is likely that you could use most any cartridge that you could find for much cheaper. Lets have a look at the game in question. According to uCON64:

    uCON64 2.0.0 Win32 (MinGW) 1999-2005
    Uses code from various people. See 'developers.html' for more!
    This may be freely redistributed under the terms of the GNU Public License

    C:\Users\Jordan\Desktop\Phantasy Star IV (USA).md

    Magicom/BIN/RAW

    00000100 53 45 47 41 20 47 45 4e 45 53 49 53 20 20 20 20 SEGA GENESIS
    00000110 28 43 29 53 45 47 41 20 31 39 39 34 2e 4e 4f 56 (C)SEGA 1994.NOV
    00000120 50 48 41 4e 54 41 53 59 20 53 54 41 52 20 54 68 PHANTASY STAR Th
    00000130 65 20 65 6e 64 20 6f 66 20 74 68 65 20 6d 69 6c e end of the mil
    00000140 6c 65 6e 6e 69 75 6d 20 20 20 20 20 20 20 20 20 lennium
    00000150 50 48 41 4e 54 41 53 59 20 53 54 41 52 20 54 68 PHANTASY STAR Th
    00000160 65 20 65 6e 64 20 6f 66 20 74 68 65 20 6d 69 6c e end of the mil
    00000170 6c 65 6e 6e 69 75 6d 20 20 20 20 20 20 20 20 20 lennium
    00000180 47 4d 20 4d 4b 2d 31 33 30 37 20 2d 30 30 05 cb GM MK-1307 -00..
    00000190 4a 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 J
    000001a0 00 00 00 00 00 2f ff ff 00 ff 00 00 00 ff ff ff ...../..........
    000001b0 52 41 f8 20 00 20 00 01 00 20 3f ff 20 20 20 20 RA. . ... ?.
    000001c0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
    000001d0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
    000001e0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
    000001f0 34 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 4

    Genesis/Sega Mega Drive/Sega CD/32X/Nomad
    PHANTASY STAR The end of the millennium
    Sega
    Brazil
    3145728 Bytes (24.0000 Mb)

    Padded: Maybe, 46572 Bytes (0.3553 Mb)
    Interleaved/Swapped: No
    Backup unit/emulator header: No
    Japanese game name: PHANTASY STAR The end of the millennium
    Date: 1994.NOV
    Internal size: 24.0000 Mb
    ROM start: 00000000
    ROM end: 002fffff

    Cartridge RAM: Yes, 15 kBytes (backup)
    RAM start: 00200001
    RAM end: 00203fff

    Product type: Game
    I/O device(s): 3 Button Pad
    Modem data:
    Memo:
    Product code: MK-1307
    Version: 1.00
    Checksum: Ok, 0x05cb (calculated) == 0x05cb (internal)
    Checksum (CRC32): 0xfe236442
    The information above shows that the game seems pretty typical. 24MegaBits, or 3MBytes starting at address 0x00000000 to 0x002fffff and has SRAM. However, SRAM is located at 0x00200001 to 0x00203FFF. You'll notice that SRAM overlaps with the ROM, so you'll need a slightly different cart. One such cart is descirbed in detail here:
    http://forums.nesdev.com/viewtopic.p...11615&start=15
    So the Japanese copy would probably be easiest to mod. I don't see many carts like that one. In fact I don't have any as far as I know. if you come across another cartridge with two ROMs, one SRAM a 74ls74 and 74ls139, let me know. We can rewire it if need be.

  9. #143
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    Wow thanks for the reply. I'm not home at the moment but I'm pretty sure I have one similar (2 mask ROMs, SRAM and a couple of other chips). I will take pics when I can. Its a baseball game I think

    The Story Of Thor and Phantasy Star 4 are the only 2 that have this board apparently

    [ATTACH=CONFIG]48174[/ATTACH

    Attachment 48175

    That is world series baseball 95. According to my ROMs list this is 3mb, could this possibly be reworked?
    Attached Images Attached Images
    Last edited by Cookie Monster; 15th-January-2016 at 12:34. Reason: multiple posting in a row isn't allowed, use the EDIT POST BUTTON

  10. #144
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    Reworking any cart for 3MBs with no RAM is easy. Reworking a random cart to "hide" the RAM location within the ROM location is the hard part unless it has the RAM already mapped to the right location with logic.
    Lets look at World Series Baseball '95 in uCON64. This time I will remove the useless info:

    Internal size: 24.0000 Mb
    ROM start: 00000000
    ROM end: 002fffff
    Cartridge RAM: Yes, 63 kBytes (backup)
    RAM start: 00200001
    RAM end: 0020ffff
    Comparing this game to PS4, we can see that the ROM and RAM are in fact mapped to the same locations. The SRAM included in the baseball game is much larger, but that is not a bad thing since the extra room will just be ignored.

    tl;dr

    Yes, I think so. It looks like the lower ROM is the first 2MBytes and the higher ROM is the third MByte. Does the back of your cart look like this:
    http://forums.nesdev.com/download/fi...1966&mode=view

  11. #145
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    IMG_20160115_205427.jpg

    Yes they are the same except my board has an extra chip in the top left
    Last edited by wal666; 16th-January-2016 at 00:25.

  12. #146
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    That extra chip should be a low power reset circuit. It disabled ram when the power is turned off so it doesn't lose save data. I think the picture I showed had the chip removed.

  13. #147
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    Awesome! So all I need to do is split the ROM into 2mb and 1mb and use a 27c160 and 27c800?
    I'm confident writing the chips with gq4x. Just not sure how or where to split the ROM

  14. #148
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    Quote Originally Posted by wal666 View Post
    Awesome! So all I need to do is split the ROM into 2mb and 1mb and use a 27c160 and 27c800?
    I'm confident writing the chips with gq4x. Just not sure how or where to split the ROM
    Thats easy. You could use a hex editor (my fav is HxD) or you can download and configure uCON64 to do it. uCON64 is hard to configure but I still suggest it.

    For using HxD, open the file and click Extras > File Tools > split...
    Where it says "Base name for partial files" just click on the ... button and choose your desktop and name it something. (the file (.bin) type isn't necessary since it will put numbers at the end of it)
    Choose the dot for "Number consecutively"
    Then use the drop down to choose MB and put in 2. Since its only 3MBs, the first file will be 2 and the last will be 1.
    hit "OK"

    nifguy654r7u6yg.PNG

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    Updated step 6 in the first post for those using the GQ-4x programmer instead of the Old Willem.
    EDIT: Added a very short list of "hidden" sram games to OP.
    Last edited by Jazzmarazz; 17th-January-2016 at 02:02.

  16. #150
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    An observation and a question here,
    It seems the music is stored on the bottom ROM. I forgot to put the top ROM in and I got music and no video haha!
    I used 2 27c160 eproms because that's all I had and this works!
    I tried to make the image region free but wrecked it every time so I must be doing something wrong.
    I entered JUE in the correct spot but how do I check checksum?

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