An SNES hardware question about the PPUs

Discussion of hardware and software development for Super NES and Super Famicom.

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overlordmanny
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An SNES hardware question about the PPUs

Post by overlordmanny » Tue Dec 04, 2018 9:06 am

Hi all, I know this is more of a software forum, but I though maybe an emulator/game developer may know the answer to this. I have a Super Famicom that is having the odd issue of not setting sprite priority correctly. On SMW Mario and Yoshi appear perfectly on the screen but walk behind the immediate background (Bushes, etc), jumping plants which should jump up from behind the ground are visible in front of the ground before they jump. I figure I have a bad PPU or video ram. I have a donor SNES but I'd rather not stress the chips with hot air unless I have to.

Does anyone know which PPU handles sprite priority?

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Drew Sebastino
Formerly Espozo
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Re: An SNES hardware question about the PPUs

Post by Drew Sebastino » Wed Dec 05, 2018 8:17 pm

There really doesn't seem to be much knowledge of what roles each PPU have specifically, but I thought I remember PPU2 deals with later graphics related functions? Does PPU2 ever communicate with VRAM, for example?

lidnariq
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Re: An SNES hardware question about the PPUs

Post by lidnariq » Wed Dec 05, 2018 8:38 pm

What we know for certain:
* PPU1 controls the address bus for both RAMs
* PPU2 contains the palette RAM and RAMDACs
* PPU2 manages fine X scrolling; PPU1 manages coarse X and fine Y scrolling
* PPU2's EXT pins are how mode 7's EXTBG mode gets its data

Given that some of the bus between PPU1 and PPU2 is called "PRIOrity" I also wouldn't be surprised if the problem is the drivers/inputs on that bus instead.

Ziggy587
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Re: An SNES hardware question about the PPUs

Post by Ziggy587 » Thu Dec 06, 2018 7:29 am

overlordmanny wrote:I have a donor SNES but I'd rather not stress the chips with hot air unless I have to.
FWIW, you can use ChipQuik with a relatively low temperature. It really only effects the legs and pads without having to apply heat to the chip itself or the rest of the board. And even then, you can use a fairly low temperature. I've used it a few times now, and even in more fragile situations it seems to always work out great.

https://youtu.be/UmD7F0--7Lc?t=545

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