Using SOROM to make SNROM not saving?

A place that you can discuss reproduction of classic titles or "licensed-for-reproduction" homebrew for personal use.

Moderators: B00daW, Moderators

Forum rules
1. NO BLATANT PIRACY. This includes reproducing homebrew less than 10 years old, with the exception of free software.
2. No advertising your reproductions, with the exception of free software.
3. Be nice. See RFC 1855 if you aren't sure what this means.
Post Reply
guitarzombie
Posts: 164
Joined: Sat Dec 07, 2013 6:18 pm

Using SOROM to make SNROM not saving?

Post by guitarzombie » Mon Jul 20, 2015 11:57 am

Hey all, just a quick 2 cents in here. Im making a Sweet Home translated from an SOROM. SNROM and SOROM are identical except SOROM usings WRAM ontop of another WRAM for battery. For some reason the game isnt saving. I changed the battery and its still not saving.

Is there some sort of issue with the other WRAM? Im thinking I could just desolder it out.

lidnariq
Posts: 9301
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Using SOROM to make SNROM not saving?

Post by lidnariq » Mon Jul 20, 2015 12:09 pm

SOROM is not quite a superset of SNROM: SOROM uses CHR A15 to select between PRG RAM banks, while SNROM uses CHR A16 to disable PRG RAM.

tepples
Posts: 21946
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Re: Using SOROM to make SNROM not saving?

Post by tepples » Mon Jul 20, 2015 12:30 pm

lidnariq wrote:SOROM uses CHR A15 to select between PRG RAM banks
Where false selects the non-battery-backed chip and true selects the battery-backed one. So the quickest, dirtiest way to make it always use the battery-backed chip is to cut the MMC1's CHR A15 output trace (pin 10) and connect the trace to +5 V on the far side of the cut. Another way is to hack the game's init code to write values to $A000 (and possibly $C000) with bit 3 (CHR A15) set to true.

guitarzombie
Posts: 164
Joined: Sat Dec 07, 2013 6:18 pm

Re: Using SOROM to make SNROM not saving?

Post by guitarzombie » Mon Jul 20, 2015 12:35 pm

Ahhh fiddlefuck. Ok learned something new! Itll just be easier to get a new donor. Thanks peeps.

FrankWDoom
Posts: 217
Joined: Mon Jan 23, 2012 11:27 pm

Re: Using SOROM to make SNROM not saving?

Post by FrankWDoom » Mon Jul 20, 2015 2:34 pm

SOROM only battery powers the top 8K of ram. IIRC you can swap the /CE connection from the first chip to the second chip and disable the first chip.

Looking at the docs you might get away with it as long as the game isn't trying to disable ram and then write to ram with the expectation of being protected or writing the 8K chr ram select bits.

User avatar
HVC-Man
Posts: 41
Joined: Wed Nov 25, 2015 7:54 pm

Re: Using SOROM to make SNROM not saving?

Post by HVC-Man » Mon Aug 01, 2016 1:33 am

I came across this thread with the same issue. I utilized the info here and at the NesDev Wiki to come up with a method of converting SOROM to SNROM. It's probably sloppy but it works good, SNROM games boot and they save.

SOROM -> SNROM Conversion (mapper 1):
Bend up pins 1, 2, 24, 30 and 31
Solder pin 2 to hole 24 (A16)
Solder pin 24 to GND (OE)
Solder pin 30 to hole 1 (A17)
Cut track from MMC1 pin 10 to WRAM /CE control
Solder WRAM /CE control to VCC
Solder MMC1 pin 11 to WRAM 1 pin 20 (/CE)
(WRAM 0 goes unused)

Here's a pic the help better describe what's going on.

Image

baddflash
Posts: 13
Joined: Thu Jun 30, 2016 11:19 pm

Re: Using SOROM to make SNROM not saving?

Post by baddflash » Wed Dec 07, 2016 1:56 pm

Worked just fine for me, thanks saved me a lot of time.

Post Reply