SNES Parallel port RAM cart

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Oziphantom
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SNES Parallel port RAM cart

Post by Oziphantom » Wed Feb 03, 2021 7:23 am

Before I go down the path of reinventing the wheel. Does anybody know of a RAM cart that has a Parallel port on it that enables you to communicate to a host computer to send data to/from the SNES?

secondsun
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Re: SNES Parallel port RAM cart

Post by secondsun » Wed Feb 03, 2021 7:40 am

Maybe. The Zelda 3 Randomizer community has a multiworld mode that uses the USB port on the SD2SNES to let different games communicate with each other. Here's their setup guide with more information : https://docs.google.com/document/d/19Fo ... xrKoI/edit

It isn't what you asked for at all, but it is the closest thing that came to mind.

Screwtape
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Re: SNES Parallel port RAM cart

Post by Screwtape » Sat Feb 06, 2021 5:22 pm

It's not exactly the same thing, but the 21FX Near designed is a circuit-board that attaches to the expansion port on the bottom of the SNES unit, with a DB25 serial port. Reading/writing to $21FF receives/sends data over the serial port.

Oziphantom
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Re: SNES Parallel port RAM cart

Post by Oziphantom » Sat Feb 06, 2021 11:45 pm

So its able to inject code from the expansion port? Where do you get an expansion port socket from?

qwertymodo
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Re: SNES Parallel port RAM cart

Post by qwertymodo » Sun Feb 07, 2021 12:02 am

Oziphantom wrote:
Sat Feb 06, 2021 11:45 pm
So its able to inject code from the expansion port? Where do you get an expansion port socket from?
Working on it.

https://twitter.com/qwertymodo/status/1 ... 36928?s=19

nocash
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Re: SNES Parallel port RAM cart

Post by nocash » Sun Feb 07, 2021 8:21 am

Console mod to upload and execute code in internal WRAM:
http://problemkaputt.de/fullsnes.htm#sn ... adwramboot
Wiring parallel data lines to WRAM with auto-increasing addresses is ways faster and much cheaper than anything else.
I guess the reception does range from "Why didn't we do that in 1990's?" to "Why would anybody do that today?"

The extended circuit with SRAM isn't too useful. I had installed a huge 512Kbyte SRAM, which turned out to be still too small for average SNES homebrews. The extended circuit's wiring for OUT2 and /PARD can be useful (when intending to send reply data from SNES to PC).
The whole thing is more intended for running tests on hardware, not for gaming.
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Oziphantom
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Re: SNES Parallel port RAM cart

Post by Oziphantom » Sun Feb 07, 2021 8:41 am

Yeah I'm looking for a Stock SNES -> Parallel port and a for the main purpose I guess 128K would actually be enough. But it would be nice to be able to go full devkit with it and add MBs.

Is it safe to write the bus while reset is lo, or would I need to pull the whole cart off the bus as well?

nocash
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Re: SNES Parallel port RAM cart

Post by nocash » Sun Feb 07, 2021 10:28 am

It's an internal mod for the console, it can disable /RD and /ROMSEL so there will be no conflict with the cart databus even when having a cartridge inserted (but the circuit can activate the cart memory after upload). The other issue are address/data signals from CPU during upload, that's solved by lifting and rewiring the RDY pin on the CPU. As far as I remember just holding /RESET low didn't work.

With a lot more components you could do something similar externally, eg. SRAM with increasing address counter, and logic for swapping the address/databus. I guess most or all not too crappy flashcarts are supporting that, via USB or the like (except they usually won't allow to plug-in a retail cart simultaneously).
homepage - patreon - you can think of a bit as a bottle that is either half full or half empty

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