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Thread: Any way to underclock the Super GameBoy?

  1. #1
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    Question Any way to underclock the Super GameBoy?

    I got myself a Super GameBoy today, but I noticed that the sound pitch is notably higher than an original GameBoy(CPU clock frequency doesn't match between the Super GameBoy and GameBoy "Brick," 4.194304 MHz for the "Brick" and 4.295454 MHz for the Super GameBoy. I'm looking to underclock the thing, but I have no clue where the clock frequency is supposed to be hooked up on the CPU. The guide I've found for the GameBoy "Brick"(this one: http://gieskes.nl/underclocking_or_o...ssic_tutorial/) involves replacing a crystal that is nowhere to be found on the Super GameBoy, and I can't retrace the connections from the crystal to the processor of my GameBoy "Brick"(that may be useless anyways, as I don't think the Super GameBoy and GameBoy "Brick" processors are 100% pin-for-pin compatible. Anyone know how to underclock the Super GameBoy?
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  2. #2
    ding-doaw Raging in the Streets tomaitheous's Avatar
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    Quote Originally Posted by Ace View Post
    I got myself a Super GameBoy today, but I noticed that the sound pitch is notably higher than an original GameBoy(CPU clock frequency doesn't match between the Super GameBoy and GameBoy "Brick," 4.194304 MHz for the "Brick" and 4.295454 MHz for the Super GameBoy. I'm looking to underclock the thing, but I have no clue where the clock frequency is supposed to be hooked up on the CPU. The guide I've found for the GameBoy "Brick"(this one: http://gieskes.nl/underclocking_or_o...ssic_tutorial/) involves replacing a crystal that is nowhere to be found on the Super GameBoy, and I can't retrace the connections from the crystal to the processor of my GameBoy "Brick"(that may be useless anyways, as I don't think the Super GameBoy and GameBoy "Brick" processors are 100% pin-for-pin compatible. Anyone know how to underclock the Super GameBoy?
    Chris Covell did a lot of stuff with the SGB unit. You can do fun stuff like cut the clock speed in half, etc. He talked about it on IRC, but I'm not sure if he made a page about it or not.

  3. #3
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    I'd REALLY need to know what pin on the CPU chip takes the clock frequency in so I can put a proper clock on the cartridge.
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    Mastering your Systems Shining Hero TmEE's Avatar
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    There is a crystal somewhere, just look where its signals end up.... I am quite positive there is no regular oscillator or a PLL unit.
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    Found a schematic: http://fms.komkon.org/GameBoy/Tech/SuperGameBoy.gif

    Seems like the CLK line is on pin 75 according to that, but it seems like that may not be the case, as it's written as "CLK?". Anyone have a spare Super GameBoy to test that on?
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    ESWAT Veteran Chilly Willy's Avatar
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    The XO and XI pins are for a crystal. They've done like a lot of designs and leave the XO unconnected, inputting the clock on XI alone. The CLK? line is a clock quadrature signal output to the cart port. Such signals are rarely used, but could be handy for things using a pipeline (FIFO, shift reg, etc) to feed data to the port.

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    So XI is the pin that the clock frequency goes in? If so, it's time to get an oscillator at 4.194304 MHz to replace the faster clock on the Super GameBoy, complete with a video guide on my YouTube account.
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  8. #8
    ESWAT Veteran Chilly Willy's Avatar
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    That's the CPU clock input, but you'll notice that it's generated by ICD2-R. It probably has to be synchronous between the two chips or the whole thing won't work. Given that a number of inputs to ICD2-R come from the SNES cart port through some passive components (resistors/caps), perhaps the source of the clock does as well.

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    Slightly off-topic...

    Why exactly would you want to double or half how fast your games go?

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    Quote Originally Posted by lilmul123 View Post
    Slightly off-topic...

    Why exactly would you want to double or half how fast your games go?
    He doesn't. Read the OP again - he wants it to be EXACTLY GB speed so that the sound has the proper pitch. It was someone else who mentioned someone else who did things like double or halve the the speed.

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    Right, but that's what that tutorial posted above was all about. It tells you how to double, triple, or half the speed without ever really explaining why you want to do that.

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    Yeah, but that's for a GameBoy "BRICK", not a Super GameBoy. The hardware isn't made the same way; there is absolutely no crystal to be found anywhere on the Super GameBoy. The mod job would involve, comparing a schematic of the GameBoy "Brick" and a Super GameBoy, 2 capacitors linked in parallel to ground on a 4.194304 MHz crystal connected between pins 73 and 74 of the Super GameBoy CPU. Compare:

    GameBoy "Brick": http://fms.komkon.org/GameBoy/Tech/GameBoy.gif
    Super GameBoy: http://fms.komkon.org/GameBoy/Tech/SuperGameBoy.gif

    The XI pin gets a frequency that's higher than it's supposed to be for a B&W GameBoy on the Super GameBoy. As the processor is pin-for-pin compatible between the "Brick" and Super GameBoy, I might be able to replicate the circuitry around the crystal that's found on the "Brick," cut the trace on ICD2-R pin 3(that pin delivers a frequency that's about .1-something MHz too fast, and it causes a NOTABLE increase in sound pitch, as well as a VERY SLIGHT(but still noticeable) acceleration in gameplay), and install it between the Super GameBoy CPU pins 73 and 74.
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  13. #13
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    SUCCESS!

    My Super GameBoy is now running at the proper speed of a GameBoy "Brick." Expect a video guide to be uploaded on YouTube.
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  14. #14
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    Hey Ace,

    I would be very happy to see a sound comparison of the Super Gameboy vs the original Brick video. I never realized there was a difference, as i usually play my games in the Gameboy player for gamecube, or a GBA unit.

    i have a question... do all the gameboy games sound higher pitched while playing in anything other than an original old "brick" gameboy? or is it just the SNES super gameboy that has this problem?


    - Retromangia

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    The Super GameBoy is the only system with that problem.

    This is the GameBoy hardware I own:

    GameBoy "Brick"
    GameBoy Pocket
    GameBoy Color
    Super GameBoy
    GameBoy Player

    Out of all these(and my friend's backlit GameBoy Advance SP), ONLY the Super GameBoy has the sound pitch that's too high. In the videos, the GameBoy Player is used to demonstrate how a GameBoy game is supposed to sound like(Gradius - well, Nemesis and Tetris are used to compare). And you can also rig a switch if you like the slightly accelerated speed and slightly higher sound pitch of the Super GameBoy(which I don't like).

    A proper and highly-detailed explanation of the increased speed and sound pitch will be given in the video(it should be called "Ace's Modding Session - make your Super GameBoy sound like an original GameBoy" - keep an eye out for that video to show up on my YouTube account, Ace9921).

    EDIT: Looks like the video will take a while. The Super GameBoy is pulling off a Sega MegaDrive on me: when the solder on the Super GameBoy's CPU is fresh, it works just fine, but after a few minutes, it dies until I resolder the crystal. I'm going to take a different approach and use a 4.194304 MHz oscillator with the Super GameBoy CPU's pin 74 taken off the board.
    Last edited by Ace; 04-01-2009 at 10:38 PM.
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