Game Genie Conversion Tutorial

[Kyle]

I wanted to start doing simplified tutorials for Game Genie to hex conversions. A mixture of GGCCC and Lazy Bastard's guides:

http://www.videogamesource.com/genie...andbk/p12.html
http://gamehacking.org/library/114

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NES 6 Characters

Code - SXIOPO

Run each character through this cipher:

A = 0000
P = 0001
Z = 0010
L = 0011
G = 0100
I = 0101
T = 0110
Y = 0111
E = 1000
O = 1001
X = 1010
U = 1011
K = 1100
S = 1101
V = 1110
N = 1111

Transposed - 110110100101100100011001

Rearrange the characters using this pattern:

9, 14-17, 22-24, 5, 10-13, 18-20, 1, 6-8, 21, 2-4

Was: 110110100101100100011001
Now: 000100011101100110101101

Take 1-16 and convert to hex for the address:
0001000111011001
11D9

Take 17-24 for the replace value:
10101101
AD

If the file size divided by 1024 has a remainder then add 10 for the header

If the file is bigger than 48 KB then repeat the patch every 2000

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NES 8 Characters

Code - SKSOPOVK

Run each character through this cipher:

A = 0000
P = 0001
Z = 0010
L = 0011
G = 0100
I = 0101
T = 0110
Y = 0111
E = 1000
O = 1001
X = 1010
U = 1011
K = 1100
S = 1101
V = 1110
N = 1111

Transposed - 11011100110110010001100111101100

Rearrange the characters using this pattern:

9, 14-17, 22-24, 5, 10-13, 18-20, 1, 6-8, 29, 2-4, 25, 30-32, 21, 26-28

Was: 11011100110110010001100111101100
Now: 10010001110110011100110111001110

Take 1-16 and convert to hex for the address:
1001000111011001
91D9

Take 17-24 for the compare value:
11001101
CD

Take 25-32 for the replace value:
11001110
CE

If the file size divided by 1024 has a remainder then add 10 for the header

If the file is smaller than 48 KB then subtract 4000
This allows smaller games like Excite Bike to work

If the file is larger than 48 KB then subtract C000
This allows codes for SMB3 to Zelda to seek earlier in the rom

Seek through the rom in intervals of 2000
When you find the compare value replace it

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SNES

Code - C9CF-CFBF

Run each character through this cipher:

D = 0
F = 1
4 = 2
7 = 3
0 = 4
9 = 5
1 = 6
5 = 7
6 = 8
B = 9
C = A
8 = B
A = C
2 = D
3 = E
E = F

Transposed - A5A1A191

The replace value is the first two characters (A5)

Make a binary number of what's left (A1A191)
101000011010000110010001

Rearrange the characters using this pattern:

11-14, 19-22, 1-4, 23-24, 9-10, 5-8, 15-18

Was: 101000011010000110010001
Now: 100001001010011000010110

Convert back to hex for the cpu address:
84A616

With replace value - 84A616:A5

If the file size divided by 1024 has a remainder then add 200 for the header

We now convert the cpu address to a rom address to know where to patch

Check for HiROM/LoROM rom in header:

Seek in the rom to FFD5 (101D5 if headered)
If the value is 21 or 31 then it's a HiROM
Otherwise we'll assume LoROM (most are)
For LoROM we take our binary value and shift bits again: (HiROM skips this)

0 + first 8 characters of binary + last 15 characters of binary

Was: 100001001010011000010110
Now: 010000100010011000010110

Converted back to hex:
422616

Run the address through this lovely uCON64 math to find the solution:

If the address is >= 400000 and <= 7FFFFF then subtract 400000
If the address is >= 800000 and <= BFFFFF then subtract 800000
If the address is >= C00000 and <= FFFFFF then subtract C00000

422616 - 400000 = 22616

Final address with replace value 22616:A5

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Genesis/Mega Drive

Code - GJ6A-CA7A

Run each character through this cipher:

A = 00000
B = 00001
C = 00010
D = 00011
E = 00100
F = 00101
G = 00110
H = 00111
J = 01000
K = 01001
L = 01010
M = 01011
N = 01100
P = 01101
R = 01110
S = 01111
T = 10000
V = 10001
W = 10010
X = 10011
Y = 10100
Z = 10101
0 = 10110
1 = 10111
2 = 11000
3 = 11001
4 = 11010
5 = 11011
6 = 11100
7 = 11101
8 = 11110
9 = 11111

Transposed - 0011001000111000000000010000001110100000

Rearrange the characters using this pattern:

17-24, 9-16, 33-40, 30-32, 25-29, 1-8

Was: 0011001000111000000000010000001110100000
Now: 0000000100111000101000000110000000110010

Take 1-24 and convert to hex for the address:
000000010011100010100000
138A0

Take 25-40 for the two replace values:
0110000000110010
6032

1-2 are is the first value and 3-4 is the second

At 138A0 write 60
At 138A1 write 32

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GB 6 Characters

Code - 21C-53E

The address is character 6 XOR with F, 3-5:
1C53

The replace value is 1-2:
21

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GB 9 Characters

Code - 18A-B1E-2AA

The address is character 6 XOR with F, 3-5:
1AB1

The replace value is 1-2:
18

For the compare value take 7, 9 (drop 8):
2A

Convert to binary:
101010

Left pad it to 8 characters:
00101010

Rearrange as 7-8, 1-6:
10001010

XOR with BA for the compare value:
30

Seek through the rom in intervals of 2000
When you find the compare value replace it

[rimsky82]

This information should already be in our Wiki, in the Enhacklopedia section.

If there is anything missing from there, feel free to add it.

[Kyle]

I'll go check it out thanks. I think I'm going for something more accessible. Like I can sit here and do this with notepad and calculator.

[dlevere]

I've already added it to the Wiki

http://gamehacking.org/wiki/SNES_Game_Genie_Handbook

I've added a link to my site because the formatting is messed up on the wiki when I try to copy and paste.

[Kyle]

I got them all up now.

I like the tutorial you linked to a good deal. There's stuff in it like this that reads like it's magic. You can get Hi/LoROM from the header assuming it hasn't been tampered with. Most of these guides also assume a header which newer roms are getting away from.

"Before you proceed any further towards decoding your Game Genie code to an actual address in the game's ROM, you need to know what kind of game you're dealing with -- HiROM or LoROM. This information is usually within the ROM itself, though it can be hard to locate. Some emulators, such as the old, Windows-based SNES97, will display the HiROM / LoROM information upon the opening of a ROM image to play (note: neither the author nor the GGCCC endorses the use of emulators, which are, in most cases, illegal)."