If you've hacked up a rom and want to play the new version on a console instead of an emulator, you can write the data to a couple of EPROM chips and then replace the chips on a cartridge. However, the EPROM chips have slightly different configs than the original chips which means you need to bend back some of the pins or sodder together some of the points. So, my question is how do you figure out where the new EPROM pinouts should map to?

For specifics, I'm trying to do this for the game Tecmo Super Bowl which is composed of a 256k PRG and 128k CHR rom and the game itself uses a MMC3 mapper. (This is also the same for Super Mario Bros. 3)

Any help would be appreciated along the lines of pointing me in the right direction to figure it out or even point by point instructions if you're feeling saucy. BTW, in order to be more specific, let's say I'm using a 27c020 and 27c010 EPROM. (that's 256k and 128k, respectively)

Wiring up the memory is not that difficult. Memory is memory, and it's interface to the processor is an address bus, a data bus, and a chip enable line or two. In general, hook up suppy voltage pins to V+ ground pins to V- and the data pins should map 1 to 1. For example, solder address line 0 of your eprom to the pad where address line 0 of the original part went, A1 to where A1 used to be etc. I could tell you exactly what to do if you can provide me with a pinout of the original part, and a pinout of the replacement eprom.

Ok, then it basically comes down to figuring out the pinouts to a MMC3 cartridge, specifically one with a 256k prg and 128k chr chip in it.

If you weren't interested in changing the graphics, could you just replace the 256k chip with an EPROM?

Not without some rewiring. On the other hand, I believe a 32k EPROM requires no rewiring.

Wouldn't you just have to worry about wiring the one Eprom that you replaced? I would guess that the graphics shouldn't matter either way.

Yeah, only the replaced one. And if you use a board that uses CHR-RAM, you'd only need to replace one chip. Those are mostly UNROM (mapper #2) games though.

I just built a mapper 0 cartridge with 32K/8K EEPROMS soldered to it for my semester project, along with a parallel port eeprom programmer. I used a SMB+DH cart which is mapper 66, and even though it is set to horizontal mirroring, both mirroring modes work great..i tested kung-fu, ice hockey (both vertical mirroring), and of course SMB with no probs. According to the solar wars website, u swap pins 1 and 27 (27 is WE' on the 28 pin eeproms im using) and that's it.

---U---
CHR A17 - |01 32| - +5V
CHR /RD - |02 31| - CHR /A13
CHR A15 - |03 30| - +5V
CHR A12 - |04 29| - CHR A14
CHR A7 - |05 28| - CHR A13
CHR A6 - |06 27| - CHR A8
CHR A5 - |07 26| - CHR A9
CHR A4 - |08 25| - CHR A11
CHR A3 - |09 24| - CHR A16
CHR A2 - |10 23| - CHR A10
CHR A1 - |11 22| - GND
CHR A0 - |12 21| - CHR D7
CHR D0 - |13 20| - CHR D6
CHR D1 - |14 19| - CHR D5
CHR D2 - |15 18| - CHR D4
GND - |16 17| - CHR D3
-------


+--()--+
VPP | 1 32| VCC
A16 | 2 31| PGMB
A15 | 3 30| A17
A12 | 4 29| A14
A7 | 5 28| A13
A6 | 6 27| A8
A5 | 7 26| A9
A4 | 8 25| A11
A3 | 9 24| OEB
A2 |10 23| A10
A1 |11 22| CEB
A0 |12 21| DQ7
Q0 |13 20| DQ6
DQ1 |14 19| DQ5
DQ2 |15 18| DQ4
VSS |16 17| DQ3
+------+

Let's say my top diagram is the chip, and the bottom is the replacement. What pinouts would have to be changed?