8k to 32k SNES VRAM schematic

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nintendo2600
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8k to 32k SNES VRAM schematic

Post by nintendo2600 » Fri May 29, 2020 5:20 am

Hey All,

Where would the extra address lines need to be routed to expand the VRAM from 8k to 32k? Would
it be different on lorom VS hirom? The 8k footprint being 28pin is nice and a little easier for placement
but I was also considering if a 2k could be replaced with a 32k as well? I have a 1a1m lorom with 2k
that I would like to beef up and a 1j3m with 8k that I would like to beef up as well. I already know
how to rewire 2k to 8k but I've never seen, nor do I understand how to go higher than that for sram
as large as 32k in the VRAM slot. Hope everyone is healthy and well during this trying time in the world.

Thanks,

Shawn

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dougeff
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Re: 8k to 32k SNES VRAM schematic

Post by dougeff » Fri May 29, 2020 6:12 am

Are you sure you mean SNES?

SNES has 64kB VRAM, and is not expandable.

Edit... Oh, you mean 0x8000. That still doesn't make sense. That's 32768 decimal. Although there are 0x8000 word addresses, which is 64k bytes.
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Re: 8k to 32k SNES VRAM schematic

Post by nocash » Fri May 29, 2020 8:34 am

dougeff wrote:
Fri May 29, 2020 6:12 am
Are you sure you mean SNES?
I think the post is about SRAM in SNES cartridges... but...
VRAM is short for Video RAM.
But there is no video memory in SNES cartridges (unlike NES cartridges).
SNES cartridges that do contain SRAM are using it for saving game positions.
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tepples
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Re: 8k to 32k SNES VRAM schematic

Post by tepples » Fri May 29, 2020 5:25 pm

The closest thing to "video memory" in a Super NES Game Pak is the work RAM used by the Super FX GSU to hold the frame buffer that it renders, which the S-CPU copies to VRAM through DMA once the frame is done. And even this is already much bigger than 8 KiB (0x2000 = 8192 bytes).

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Re: 8k to 32k SNES VRAM schematic

Post by lidnariq » Fri May 29, 2020 6:43 pm

Assuming, for the moment, that you mean "cart save RAM" when you wrote "VRAM" ...

LoROM carts connect extra address lines in order, skipping A15. (So a 2KiB RAM is connected to A0 through A10; 8 KiB to A0-A12; 32 KiB to A0-A14; 128 KiB to A0-A14 and then A16 and A17)
HiROM carts connect address lines in order, skipping A13 through A15. (So a 2KiB RAM is connected to A0-A10; 8 KiB to A0-A12; 32 KiB to A0-A12 and then A16 and A17)

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