Want to build an SNES repro cart

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Want to build an SNES repro cart

Postby qwertymodo » Sun Apr 08, 2012 3:16 pm

I'm interested in creating an SNES repro cart, but the info for doing so is rather spread out and most places I find someone attempting it, they just get told it's not worth the effort and that's the end of it. Yes, I know I could buy a flashcart. Yes, I (think) I understand the amount of work involved. I still want to do it. I found http://nintendoallstars.w.interia.pl/romlab/cart2epr.htm which details how to modify the cart for an EPROM or FLASH ROM, but I have a few questions. First of all, I don't want to have to use a UV eraser, so I'm more interested in the option of a flash ROM, but the ones on that page are only up to 4Mbit, and I'd like something larger, perhaps 32Mbit (what's the largest SNES game size, anyway?). What considerations (if any) need to be made besides the pinout changes for the extra address lines? Also, can anyone recommend a 32Mbit chip that would be compatible for this purpose? I'm looking for a TSOP package that I can build an adapter for like the one mentioned here http://www.snescentral.com/article.php?id=0909. I may have more questions as I progress, but for now, that should get me started...
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Re: Want to build an SNES repro cart

Postby Haunted360 » Tue Apr 10, 2012 8:21 pm

Dont use Flash ROM. Get the same megabit they reccomend in an EEPROM DIP package.
This job isn't for people new to electronics. It is quite a long process to make such a device.

I would offer to make one for you, but I dont own a SNES :/


By the way, who ever did this soldering, really needs help.
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Re: Want to build an SNES repro cart

Postby qwertymodo » Tue Apr 10, 2012 9:41 pm

I'm not new to electronics, I'm a 4th year software and embedded systems engineering dual major and am more than capable of doing this, I just need a place to start. Why do you suggest against flash ROM? I'm open to any suggestions as long as it can be erased by a programmer rather than requiring a UV eraser. Also, I do want a larger ROM if it can be acquired in a single chip (I'm don't want to use the DIP piggybacking method I've seen), and I do want a TSOP package, since it will give me a much cleaner result than a DIP with bent pins and rats-nest rewiring.
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Re: Want to build an SNES repro cart

Postby Haunted360 » Wed Apr 11, 2012 2:50 am

You can go with Flash ROM if you want. Programming it will be harder than an EPROM / EEPROM though. I just think for the SNES an EEPROM is best suited.
Well, as I can see, the SNES is a 16-bit console. So, you will need a 16 bit wide chip (that is, 16 data lines). http://nesdev.parodius.com/bbs/viewtopic.php?t=5367
If you go with a TSOP package, then you will have to make your own PCB (or get the correct header to place it in). Either way, as long as you design the trace path fine, you will not have a rats nest.
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Re: Want to build an SNES repro cart

Postby qwertymodo » Thu Apr 12, 2012 12:14 am

It seems like all of the chips that I find >4Mbit are 2.7-3.6v, whereas the SNES cart provides 5v. Would, say this chip http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en549546 work, using a 3.3v regulator? I'm looking for an EEPROM that would fit the bill but so far, no luck (most of what I can find are serial EEPROMs).
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Re: Want to build an SNES repro cart

Postby Ashen » Thu Apr 12, 2012 7:12 am

Your best bet is probably going to be to contact Doug or Drakon from the MBB forums. They specialize in this kind of thing and will most likely gladly help you along.

http://www.made-by-bacteria.com/viewtop ... =177&t=611
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Re: Want to build an SNES repro cart

Postby Haunted360 » Fri Apr 13, 2012 4:25 am

qwertymodo wrote:It seems like all of the chips that I find >4Mbit are 2.7-3.6v, whereas the SNES cart provides 5v. Would, say this chip http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en549546 work, using a 3.3v regulator? I'm looking for an EEPROM that would fit the bill but so far, no luck (most of what I can find are serial EEPROMs).


Thats why I suggested a EEPROM.
They use voltage levels of 5 volts which is the standard TTL voltage level - same as the SNES, where as Flash ROM uses the 3.3 volt CMOS or RTL levels. I didn't want to explain it to you, since you say you are in your 4th year software and embedded systems engineering dual major, and you are more than capable of doing this :wink:

EEPROM is a lot more cheaper than Flash ROM, and it is easier to work with. As I said, sure, you can use Flash ROM, but should the SNES use a high speed bus for its cartridges, you will need a high speed voltage divider (actually called an active level-shifter) like this: http://www.ti.com/product/sn74alvc164245

... and yes. That Flash ROM should work imo http://ww1.microchip.com/downloads/en/DeviceDoc/S71384.pdf
Just remember: 32 megabits = 4 megabytes.
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Re: Want to build an SNES repro cart

Postby qwertymodo » Tue Apr 17, 2012 8:41 pm

What's the easiest way to determine the capabilities required by a specific game? I mean, ROM and save sizes are easy, but how can I tell what expansion chips, if any, are required by a specific game? I know the main way to do it would be opening up an original of that game, but I'm thinking of unreleased games such as Star Fox 2 or the fan-translated Seiken Densetsu 3. Or N-Warp Daisakusen... that would be fun to have on a cart, but I have no idea what capabilities the game relies upon. Does BSNES or any other emulator have some indication of what coprocessors are being emulated during gameplay?
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Re: Want to build an SNES repro cart

Postby Reubensupernerd » Wed Apr 18, 2012 1:08 am

Starfox 2 uses a super fx2 chip (gsu-2 I think, should be the same as in doom). In the past overclocked super fx1 chips have been used. In terms of fan translations and larger RPGs you might have a ton of difficulty. The reason I say this is that star ocean is something like ~141Mbits and the cartridge has a rare decompression coprocessor. Now people with flash carts have been able to decompress the rom and run it from the expanded eeprom equivalent, but this is probably going to exceed the capacity of any easily obtainable chip. The following links might be slightly better than peripherally relevant: http://www.assemblergames.com/forums/sh ... f430343375 , http://www.super-nes.com/oceancart.htm , http://snesdev.romhack.de/sf2.htm
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Re: Want to build an SNES repro cart

Postby qwertymodo » Thu May 10, 2012 5:13 pm

Haunted360 wrote:
qwertymodo wrote:It seems like all of the chips that I find >4Mbit are 2.7-3.6v, whereas the SNES cart provides 5v. Would, say this chip http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en549546 work, using a 3.3v regulator? I'm looking for an EEPROM that would fit the bill but so far, no luck (most of what I can find are serial EEPROMs).


Thats why I suggested a EEPROM.
They use voltage levels of 5 volts which is the standard TTL voltage level - same as the SNES, where as Flash ROM uses the 3.3 volt CMOS or RTL levels. I didn't want to explain it to you, since you say you are in your 4th year software and embedded systems engineering dual major, and you are more than capable of doing this :wink:

EEPROM is a lot more cheaper than Flash ROM, and it is easier to work with. As I said, sure, you can use Flash ROM, but should the SNES use a high speed bus for its cartridges, you will need a high speed voltage divider (actually called an active level-shifter) like this: http://www.ti.com/product/sn74alvc164245

... and yes. That Flash ROM should work imo http://ww1.microchip.com/downloads/en/DeviceDoc/S71384.pdf
Just remember: 32 megabits = 4 megabytes.


Actually, TTL logic should be 0V-0.8V for low and 2.0V-5V for high (assuming 5V Vcc), and the datasheet for that flash ROM indicates Vol of 0.2V and Voh of 2.8V, so I shouldn't need a logic shifter, since the logic levels seem to be in valid ranges regardless. So from the looks of things, all I really need to do is step VCC down from 5V to 3.3V.

EDIT: I got slightly different numbers from a different source, but they still work.
Code: Select all
           TTL SST39VF800A/320XB
Vil(max)   0.8         0.8
Vih(min)   2.0         2.5
Vol(max)   0.5         0.2
Voh(min)   2.7         2.5


EDIT2: Dangit... I totally forgot about that pesky TTL Voh(max) 5V... so I suppose depending on the actual voltage it gets, it *might* or might not work. I'll give it a try, and I suppose I'll find out.

EDIT3: A quick multimeter check on the address lines on the cart edge is reading ~2.8V for high, so it might actually work. I didn't test the level coming out of the MAD-1 or any of the non-address input lines though
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