Pseudo Saturn Kai + Action Replay Plus in 1 via bank switch.

[darknezz19]

Found out if you open your ARP and if you have sst29ee020 flash chips you can have both Kai and ARP in one cart. You can also remove the original chips and replace them with the larger 256k chips as well. Check if A17 has no connection(lift the pin if it does,) then put a jumper between the two flash chips on this address line. Now get a switch and tie ground to one side and Vcc to the other and have A17 in the middle. Boot Pseudo Saturn Kai iso and flash an image to either the low(gnd) or high(vcc) bank. You can then use the switch to boot one or the other. Pretty simple and no more having to swap carts around to get more save space.

Here is a long unnecessary video with a lot of jibberish(was late) showing that it works.


Now I'm wondering if we can use 512kb flash chips in place and tie a17 and the extra a18 from the chips to the proper cart connector pins and flash the full 1mb image of Kai.

Edit: I want to try to get the bank switching done with a binary ripple counter via the reset button. I looked at the Saturn schematic and did not see a pin labeled as /reset but am wondering if it might be labeled something else. Anyone else maybe know?

http://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:saturn_schematic_va0_pal_-_main-6_of_7.png

Actually after looking at it again just now it looks like it might be pin A3, SYSRES.

 

[cafe-alpha]

Nice mod ! The pin you're looking for is A3 (/SYSRES), but please not that it will also trigger when doing software reset (typically when entering multiplayer screen) too.
From what I know, there's no pin triggering only when pushing reset button.

 

[darknezz19]

Thanks for the help cafe-alpha. That's something to consider then. So using the in game reset function that was recently added to Kai would trigger the reset pin?

Wonder if something could be added to only trigger the ripple counter if reset is held for more than 1.5 seconds for example.

 

[cafe-alpha]

Thanks for the help cafe-alpha. That's something to consider then. So using the in game reset function that was recently added to Kai would trigger the reset pin?

Yes : both soft reset methods (default one going to multiplayer screen, and patched one requesting SMPC to do a system reset) would generate a pulse on /SYSRES pin.

Wonder if something could be added to only trigger the ripple counter if reset is held for more than 1.5 seconds for example.

IIRC, pulse width on /SYSRES pin doesn't changes with reset button push duration. It was (= IIRC) always around 0.5 seconds at low state whatever the way reset button was pushed.
If you have an oscilloscope or a digital analyzer, please connect a probe on this pin, and see by yourself : this will be more helpful than my confused explanations 🙂


A workaround in order to detect if bank needs to be swapped or not would be to monitor /SYSRES pin, flash chips select pin (let's call it /CE) pin and a properly selected pin (let's call it Ax) on address bus, and add logic like "if Ax pin is high and /CE is low, then swap bank on next /SYSRES pulse".
Selection of which address pin to use may probably need some tuning since Saturn BIOS checks cartridge ROM first bytes (in order to see is a cartridge is inserted or not), and some games/third party utilities (example : Panzer Dragoon Saga) may access cartridge ROM too. Maybe A7 is a good candidate for testing ?
Note : it shouldn't cause problem when flasher utility is used if you swap bank during /SYSRES pulse. But if you swap bank without checking /SYSRES, then firmware will be written here and there on your both ROMs 🙂

Additionally, it would be good to add a LED in order to see which firmware will be used on next reset, and this will be useful for testing too.