9MHz Overclock

Discussion in 'Mega Everdrive / Everdrive MD' started by lnx64, Dec 26, 2012.

  1. MottZilla

    MottZilla Champion of the Forum

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    Maybe if you overclocked it by changing the divider it wouldn't have that problem?
     
  2. lnx64

    lnx64 Robust Member

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    Not really, besides, you can't actually change the divider. It's built into the glue logic. Un----modifiable.
     
  3. MottZilla

    MottZilla Champion of the Forum

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    That's not true. The clock going to the CPU is exposed. The source clock is available somewhere too I'm sure. You just have to add your own divider and hook it up the CPU and the original source clock. Just because the original divider can't be changed doesn't mean you can't add a new one, just like how you'd added a new oscillator.
     
    Last edited: Jan 1, 2013
  4. lnx64

    lnx64 Robust Member

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    That's more work than needs to be and I'm sure it won't work either.
     
  5. smf

    smf mamedev

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    There is no integer divide of the main crystal that can get you 8mhz, that is why they run the cpu at 7.6mhz.
    Similar to why the 68000 in the Amiga doesn't run at 8mhz.
     
    Last edited: Jan 2, 2013
  6. smf

    smf mamedev

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    If the divider in the genesis doesn't already have the output you want then adding another chip would do it. That other thread seems to be a bit of a kludge but is probably the simplest way of doing it. Adding a new crystal is definitely the wrong way of doing it and is very unlikely you'll ever get it stable. You always want to divide down from one crystal or you run into problems with Synchronicity.

    "Synchronicity requires that either (1) a central clock be distributed across the circuit, (2)
    independent clocks local to circuit components be frequency locked, or (3) a low frequency
    reference clock be distributed across the circuit and multiplied up to the data rate at each
    component"

    clock skew can also be a problem, signal lengths can be important to make sure everything works right.
     
    Last edited: Feb 9, 2013

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