DIYing a plug that fits the PlayStation's parallel port to boot from a ROM

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prochazkaml
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PlayStation Model: SCPH-7502
Discord: prochazkaml#4853
Location: Czech Republic
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Post by prochazkaml » August 6th, 2022, 8:46 pm

Alright. Bit of an insane idea:

DigiKey appears to be the only store where the correct 68-pin connector is available, but their shipping rates to the Czech Republic are astronomical (1300 CZK ? 54 USD!!). Of course, they give you free shipping when your shopping cart value is over 1300 CZK (without VAT, so you actually have to buy over 1573 CZK to get free shipping), but I couldn't care less.

In contrast, Farnell has way better shipping rates (around 200 CZK including VAT), but they only stock a 50 pin version of the same connector (they're identical in every other way). So I thought that I could buy 2 of these, chop them up, join them together and end up with a bit flaky, but hopefully functional 68 pin connector. Each one costs 74 CZK, which is less than half of the 68 pin connector sold on Digikey (154 CZK), so overall, it's actually cheaper. If it ends up working, that is.

Image

So I ordered 2 pieces (along with some other stuff, including a 512 kB 3.3 V parallel flash chip for the final cart). We'll see how it goes.
Development Console: SCPH-7502 with 2MB RAM, some random modchip and a custom 2.54 mm (0.1") pin header for easy access to the serial port using my Propeller Plug.

PlayStation Development PC: Arch Linux, Ryzen 5 3500U at up to 3700MHz, 20GB SDRAM, no dedicated PSX dev hardware, 19" Fujitsu Siemens X19, some cheap composite to VGA adapter, Hitachi GP60NB60 CD/DVD burner and an integrated chiclet keyboard.

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MottZilla
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Post by MottZilla » August 14th, 2022, 1:35 pm

prochazkaml wrote: August 1st, 2022, 7:08 pm Hey, that's really neat!

If I wanted to do something like that (which I might, don't get me wrong), I would skip all of that patching work and I would just get rid of the stock shell altogether (as IMHO the colour paint splash-aesthetic looks like garbage anyway) and add some extra features - I was thinking of XA audio/STR video playback, loading .EXEs via the serial port/a multisession CD, and do not forget to mention booting unlicensed discs. And I would replace the UI with something less vomit-inducing, of course.

...

Till then, I'll patiently wait for your project's release.
The project is out now. https://www.psxdev.net/forum/viewtopic.php?f=66&t=3966

There will be an update coming for Japanese console CDDA audio fix for early versions of the console (cdrom firmwares vC0 and vC1 [a] ) as well as an Anti-Mod patch for playing protected games without patching.

You could of course make your own Shell program if you wanted. But re-implementing everything is far more work than just patching the existing Shell that is loaded from the BIOS ROM. It means also that the expansion ROM can be very small. I think it's currently under 8 kilobytes. While those features like loading .EXE via serial port would be very cool to have, it's significant work re-implementing the wheel.

It would be possible to add to my project some button combinations that could be held when powering up/resetting to load some programs from ROM to do things like Serial Upload which would be cool. I may seriously consider that as I find the ability to do that extremely useful.

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prochazkaml
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Posts: 28
Joined: Jan 22, 2021
I am a: Student & Programmer
PlayStation Model: SCPH-7502
Discord: prochazkaml#4853
Location: Czech Republic
Contact:

Post by prochazkaml » August 24th, 2022, 6:46 am

Dude, if you could somehow add the support for booting user-uploaded .EXEs (compressed, ideally) via some button combination and a simple selection menu before the shell even loads, that would be super-awesome. I'd solder the ROM directly to the mainboard as an internal mod then! :D

Anyway, my connectors have arrived, I chopped them up and they fit quite well inside the console. Checked the connections, and all pins are making contact and none are shorting with each other! Which is great.

However, I'm currently struggling with programming my new 512k Flash chip, as it only runs on 3.0-3.6 V, whereas my Arduino Mega (on which I built my programmer upon) runs on 5 V. I tried powering the board with an external 3.3 V supply, but then (for whatever reason) upon attaching my Propeller Plug to the board (as I cannot use the integrated CH340 serial converter), I simply cannot connect to it properly, it drops out after sending a few kB of read data to the PC (I have not tried writing to the memory chip, as it is way too unreliable at the moment). I also have another USB-to-Serial converter, this time based on the same CH340 as the one on-board, so I'll try using that instead, perhaps that might work. If not, then I'll try to make a programmer out of a Raspberry Pi Pico, which runs at the correct voltage to begin with. But we'll see.
Development Console: SCPH-7502 with 2MB RAM, some random modchip and a custom 2.54 mm (0.1") pin header for easy access to the serial port using my Propeller Plug.

PlayStation Development PC: Arch Linux, Ryzen 5 3500U at up to 3700MHz, 20GB SDRAM, no dedicated PSX dev hardware, 19" Fujitsu Siemens X19, some cheap composite to VGA adapter, Hitachi GP60NB60 CD/DVD burner and an integrated chiclet keyboard.

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Post by MottZilla » August 27th, 2022, 7:00 am

If there is a smaller PS-EXE program available than the UniROM Boot CD version I could include that possibly in a future ROM to be loadable via a button combination on power up so that Serial Cable uploads could be done from the same ROM. The UniROM EXE though is quite large if I want to fit in under 128KB. Although I'm not sure if there are cheat carts out there that have a 128KB EEPROM. And maybe some compressed EXE loader would help out with that.

I do definitely like the idea of having both the Stealth Unlocker features but also Serial Uploading for testing, homebrew, memory card download/upload, etc. I have also been considering implementing a GameShark style cheat menu that could be entered before the game starts, since you lose that capability when you flash your GameShark. I know you could use a CD based one instead, but that is another disc to load and also wouldn't work on the Japanese/Asian consoles that rely on the swap trick. We'll see though.

Looking forward to see how your new connectors look in pictures.

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