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Thread: [GUIDE] Make a Reprogrammable Genesis Cart

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    Hey there Jazz!

    I wanted to point out something that I found out today. Not all larger boards are compatible with smaller chips. I opened a copy of College Slam and tried it with a 512, 1mb, and 2mb eprom and none worked even with several modifications. They all worked in other boards no problem. College Slam would still work in it's own PCB after being zif socketed so it wasn't the solder or the chips. I think the flash rom messes it up. I thought the game was a saving game until I realized it just gives you a password on save. However the game still works on a battery saving 2mb board.

    I successfully created a NTSC repro today. I thought it wouldn't work until I realized it was just the board itself and swapped it to a 2mb saving cart and it works fine. Changing the region code at the 01f0 offset did it for me. I noticed the game runs a hair fast but that's all, seems to play level to level, load, and the controls work fine. Will report back if there's any problems though.

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    I know whats wrong. College slam is a 4MB board and therefore, A20 is connected to B9 on the pcb. If you are using a chip other than 27c322, then there is no A20. Instead of A20, the pin is the BYTE line which must be connected to VPP. It is the second pin from the left on the back of each pcb: http://gendev.spritesmind.net/mirror...ter_2_back.jpg

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    Ah ok, that makes some sense. Each chip is pinned for the appropriate board and such, that's why it's better to use donors of the same size. I can live with that.

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    Quote Originally Posted by deusexvindicare View Post
    Ah ok, that makes some sense. Each chip is pinned for the appropriate board and such, that's why it's better to use donors of the same size. I can live with that.
    It is better to use boards of the same size, but it is also good to know that you can modify all of the others to work just in case you don't have a board of the same size.

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    Soon I am going to update this thread with a bank switching tutorial that allows for you to program multiple games onto a single cartridge and switch between them with the reset button! It only requires one more IC and is relatively simple to complete!

    Until I test this myself, attempt at your own risk. The reset button will switch between each 1MB bank, so make sure to program four ROMs that are exactly 1MB each. If the games you want are smaller than 1024KBs, then use a program to expand them.
    Requires:
    1x 27c322 16bit EPROM
    1x 74xx93 4bit ripple type counter IC
    1x 100nF cap
    1x 1K ohm resistor

    B27 is on the cartridge but will not be labeled, so count the pins on the front of your cartridge pcb until you find it.
    Right now, it is all theoretical, but if it works I will also write up how to do smaller banks.

    EDIT:
    Now here is a method to switch between two 512KB banks on a 27c800 (middle picture)
    and a method to switch between four 256KB banks on a 27c800 (right picture)

    A simple way to expand a ROM image is to add "FF" in a hex editor at the very end of your ROM. Add "FF" until offset 0007FFFF for a 512KB file or offset 000FFFFF for a 1MB file. Then copy your other games starting at 00080000 or 00100000.

    Also note that you must not connect the Address lines (A17, A18, A19 or A20) to the board if you plan on hooking them to a switch. By adding the switch, you are deciding for the console which Address Line to activate or to deactivate and connecting them to the cartridge pcb would be counter productive.
    Attached Images Attached Images
    Last edited by Jazzmarazz; 7th-May-2012 at 18:56.

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    Bank Switching works without any problem! As you can see from these pictures, I have one with the switch up and one with the switch down (1 and 0). by changing these address bits, the data sent to the console is split between the upper 512KBs and the Lower 512KBs. Pretty simple.

    (switch down)

    (switch up)

    (chip wired)


    I had to focus on capturing the switch itself, so the television image suffered. you get the picture though.
    Soon adding this to the tutorial above.

    For anyone not grasping the concept of bank switching, it allows for people to put an entire series of games onto a single cartridge.
    Last edited by Jazzmarazz; 14th-May-2012 at 20:33.

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    Reopened.

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    I will be expanding on this wiring so that we can manipulate our cartridge to hold 2, 4, 8, 16, etc. ROMs. This IC is essentially the digital version of the second schematic, so there would be no need to cut holes to mount switches:
    ova6qpmr.png
    When I get the chance that is...

    And to further explain what we see here:
    4switcher.png

    In the current state, each bank or ROM file is referred to as a 2 bit binary number because there are two switches; more switches means more possible bits. Because there are 2 combinations for each bit: 0 and 1, the number of ROMs is be calculated as follows:
    2^(switches), where each following switch must be connected to the next highest Address pin (ie A16...A15...A14 and so on). Each switch you add will cut the size of the banks in half but double the number of available banks.

    For example:

    4 switches, connected to A19, A18, A17 and A16 will yield:
    2^4 = 16 banks of 128KBs each. Not many good games are less than 128KBs, so less switches will limit the number of available banks, but increase the size of each one.
    For the same example, you may also create a truth table like so:

    A19 A18 A17 A16 Bank
    0 0 0 0 0
    0 0 0 1 1
    0 0 1 0 2
    0 0 1 1 3
    0 1 0 0 4
    0 1 0 1 5
    0 1 1 0 6
    0 1 1 1 7
    1 0 0 0 8
    1 0 0 1 9
    1 0 1 0 10
    1 0 1 1 11
    1 1 0 0 12
    1 1 0 1 13
    1 1 1 0 14
    1 1 1 1 15

    An alternative to these large switches that I used are DIP switches. But these may introduce another problem for you to solve. These have only two pins for each switch, so at one state, the pin would be "floating" - neither 0 or 1. A solution may be to have the pins hard wired directly to 1 (+5v) and the switch wired to 0 (ground). That way, all Address pins are 1, but will be grounded to 0 once the switch is flipped.
    Last edited by Jazzmarazz; 19th-November-2012 at 17:42.

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    Nice updates

    P.S. do you want me to move this out of the now hidden section of the forum to Everything Console - Sega systems??

    It would make it easier to get to and find

    Any others aswell I am happy to move for you
    Last edited by Zorlon; 19th-November-2012 at 17:56.

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    Quote Originally Posted by Zorlon View Post
    Nice updates

    P.S. do you want me to move this out of the now hidden section of the forum to Everything Console - Sega systems??
    Hidden!? ...yes
    Are my other guides there too?

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    Just point me to any of your guides you want shifting out of here I will do it

    EDIT - This one is now moved

    The index stickies still have the guides linked but it's still nice to be able to get to them easier
    Last edited by Zorlon; 19th-November-2012 at 18:00.

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    Quote Originally Posted by Zorlon View Post
    Just point me to any of your guides you want shifting out of here I will do it

    EDIT - This one is now moved

    The index stickies still have the guides linked but it's still nice to be able to get to them easier
    Thanks, I'll get back to you with the other guides soon. As for what I posted here, it is more of a lesson than an update.
    Professor jazz teaching ICs and the binary counting system.

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    This thread has really helped me out, and I was wondering if you had any insight. I can't get the pocket monsters game working
    (got the second one, the first ones giving me issues) I've tried every rom of it I can find. I get the licensed by Sega screen, then nothing.

    Edit: Using a GQ-4X programmer + adapter and M27C160 EPROMs

    Edit 2: It took 2 days but I finally found a good rom
    Last edited by SnesGuy; 22nd-September-2013 at 17:44.

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    Wanted some feedback. I have a copy of Flicky which is a 1MB (128kb) rom, no battery backed save. This cartridge doesn't work for some reason and I figured a good solution would be swapping the ROM chip on a functional board - I thought donor of Barney Hide & Seek 8MB (1mb) rom, no battery, would be suitable but I thought it might be incompatible because of the alloted ROM size. I see here that some PCBs can support larger ROM sizes, is the reverse possible (donor having larger max ROM size tolerance swapped with a lower ROM size).
    Here are the respective PCB photographs.
    Last edited by fahlim003; 6th-February-2014 at 21:43.

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    It should work perfectly, if that is what you want to do. you will notice that Barney has a 42-pin mask ROM while flicky has a 40-pin mask ROM.
    Just like the picture below, place Flicky all the way to the right, leaving pins 1 and 42 open.



    The only problem I can think of is that the mask ROM in Flicky may be broken. Before removing it, make sure the golden contacts are clean and check all of the traces on the board for cuts or corrosion. You could also replace the capacitors (or swap them from one board to the other) in case they are causing the problems. Electrolytic capacitors can cause wild things when they dry up or leak. Since they are cheapest and easiest to remove, start with those.

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