NES Under Clocking and Circuit Bending

NES Under Clocking and Circuit Bending
by pivotman on 2010-02-10 (#56411)

I want to make my NES a different

I want to under clock it to maybe 3/4 speed or half the speed,
how fast is the crystal in the nes? any crystal that would make it 3/4 speed or half?

And does anyone know where I can get some info on nes circuit bending?

Thanks!

by tokumaru on 2010-02-10 (#56412)

You know that this might cause problems with existing games, right? NES games perform video updates during a period called Vblank, which is the time it takes from the end of a video frame to the start of the next one.

Attempts to perform video updates outside of this period result in graphical corruption. If you underclock the CPU, the game will not be able to do as much during this window of time, so the updates will spill into the rendered frame, corrupting the display.

Might I ask why the hell you want to do this?

by pivotman on 2010-02-10 (#56415)

well will the same problem happen with over clocking?

and why not do!

by tokumaru on 2010-02-10 (#56416)

pivotman wrote:
well will the same problem happen with over clocking

Overclocking has been done, and it works up to a certain point. It seems that past this point the video memory can't keep up, and this also results in graphical glitches.

Also keep in mind that all games that rely on timed code for visual effects (lots of 3D racing games, for example) will be completely broken, with overclocking or underclocking. So if you can, make your mod with a switch that allows switching back to the normal clock when you need to.

by pivotman on 2010-02-10 (#56417)

OK but do you no what speed crystal the NES use so that I can find one that will over clock it?

by MottZilla on 2010-02-10 (#56418)

The NTSC NES uses a 21.477272MHz clock. The CPU and PPU operate off that with different dividers.

by Dwedit on 2010-02-10 (#56420)

Won't it stop displaying correctly on a TV if you mess with the PPU's timing?

by tokumaru on 2010-02-10 (#56422)

Dwedit wrote:
Won't it stop displaying correctly on a TV if you mess with the PPU's timing?

I guess so. The last person that overclocked the NES probably found a way to mess only with the CPU.

EDIT: Found the thread.

EDIT: Oh yeah, overclocking the CPU screws up the music notes, because the CPU is responsible for generating sound.

EDIT (again!): The page with the mentioned guide is gone, but it seems to be archived here.

by kyuusaku on 2010-02-10 (#56424)

Info on circuit bending? Isn't that oxymoronic?

by tepples on 2010-02-10 (#56427)

kyuusaku wrote:
Info on circuit bending? Isn't that oxymoronic?

OK, then "info on common patterns in circuit bending." Or is your point that "patterns in circuit bending" is itself a contradiction?

by Memblers on 2010-02-10 (#56428)

I wonder how fast that thing can go, or how hot it can get.

I was a little surprised to see on the VS Unisystem board (arcade version of NES) that the PPU has a heatsink on it.

by MottZilla on 2010-02-10 (#56436)

Maybe it had a heat sink due to the tight enclosed poorly ventilated living space.

by hyarion on 2010-02-10 (#56437)

Memblers wrote:
I wonder how fast that thing can go, or how hot it can get.

just one way to find out

by kyuusaku on 2010-02-11 (#56451)

tepples wrote:
kyuusaku wrote:
Info on circuit bending? Isn't that oxymoronic?

OK, then "info on common patterns in circuit bending." Or is your point that "patterns in circuit bending" is itself a contradiction?

My understanding of circuit bending has been "do first, determine results/consequences later" so I'm just being pretentious over the (modification) culture.