Why cant a scn chip overclock

[Hashmire420]

ive got two model one genesis's and both have the
SCN68000CBN64 cpu i looked at the pinouts online for these and they are they same as the motorola/hitachi so am i missing somthing or did the guy just not try it on a scn one?

[oompa loompa]

ic's made by different manufacturers of the same chip are not all the same. different designs make your chip different than others. it will still operate the same as other 68k's within a certain spec, but when you go out of that spec and overclock it, things may not work, which should be normal anyways

[Hashmire420]

would it destroy my genny to try the overclock or would gettin a new chip be the only way either way i really want an oc'd genesis cause its just so ...........1337

[oompa loompa]

you can get a new chip, but there's no guarantees that it will run overclocked, or run very stable. you can just get a new genesis too, they're not very expensive at all, although you don't know whether it carries the cpu you want

[GiGaBiTe]

If you have the first genny model (the one with the elongated MC6800P8) there are other P series models that have the same pinouts at a higher clock speed.

I have seen 10, 12 and 16 MHz models of the MC68000P around the internet, and rather cheap too. It would require some solder skill, but since it's not a surface mount chip, it will be alot easier to change out.

But, I would put a socket in there so you could swap processors without having to de-soldering it again.

[Epicenter]

Upon deeper analysis, such an early revision of the board just seems to have .. issues. I like to call that board "Revision 0", the one with the Signetics 68000 and EXT port, and 2 part GLU chip, also note the lack of TMSS display. If you swap the CPU for a Motorola or Hitachi part, it won't overclock correctly-- there will still be weird instability, crashes, and the VDP/Z80 will miss lots of writes leading to weird graphical and audio glitches. Generally with ANY processor these boards don't make it past 9 MHz, and they are glitchy even THERE.

This is also the board revision with a major VDP bug that leads to some ugly unnecessary disappearing-sprite action in the foreground.

It's my personal theory Sega revised the MD because Sonic ran like ass on it. It was extremely slow-- Cyan Helkaraxe's theory is that they added wait states in the hardware to slow the 68000 so the rest of the hardware, like the very slow RAM, could keep up-- so Sonic ran terribly laggy. Also there was mad sprite flicker especially in stages like Marble Zone with the big pillars of lava that shot up .. then half of their sprites would blink and vanish. Less than ideal when you're trying to sell Sonic as the MD's killer app.

[evildragon]

epicenter said:

Upon deeper analysis, such an early revision of the board just seems to have .. issues. I like to call that board "Revision 0", the one with the Signetics 68000 and EXT port, and 2 part GLU chip, also note the lack of TMSS display. If you swap the CPU for a Motorola or Hitachi part, it won't overclock correctly-- there will still be weird instability, crashes, and the VDP/Z80 will miss lots of writes leading to weird graphical and audio glitches. Generally with ANY processor these boards don't make it past 9 MHz, and they are glitchy even THERE.

This is also the board revision with a major VDP bug that leads to some ugly unnecessary disappearing-sprite action in the foreground.

It's my personal theory Sega revised the MD because Sonic ran like ass on it. It was extremely slow-- Cyan Helkaraxe's theory is that they added wait states in the hardware to slow the 68000 so the rest of the hardware, like the very slow RAM, could keep up-- so Sonic ran terribly laggy. Also there was mad sprite flicker especially in stages like Marble Zone with the big pillars of lava that shot up .. then half of their sprites would blink and vanish. Less than ideal when you're trying to sell Sonic as the MD's killer app.

i've been researching that VDP bug, and EVERY genesis model I have, including the model 2 genesis, have flickering sprites in the same spot as my Rev 0.. are you 100% sure on this? because why would every model have the same VDP sprite limit in the same exact spot?

not to mention, the Sonic 1 title screen relies on the sprite limit, as without it working the way it should, sonic appears to be in FRONT of the thing he's supposed to be behind...

[GiGaBiTe]

epicenter said:

...very long post...

Like oompa loompa said, clones of the 68000 are not the same as having the original 1st party chip made by Motorola. Even within spec, the chips may not perform the same as the original Motorola processor.

But as for the VDP, it was a bad chip in general. I don't know why Sega chose to use that trashy TI chip, it would have been much better if they used a better GPU like from the neo-geo. You would have had far better looking games.

[Tiido]

I overclocked my MD1 with Signetics chip to 12MHz and it worked nicely, anything above and it goes crazy. I've got the same model with Motorola chip and it overclocks to 12MHz too, and anything beyond results in madness. My damn MD2 goes crazy after 11MHz ...