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Every cartridge that runs on a Gameboy has a header of 50h bytes that starts at memory location
100h. This header is used to let the gameboy know what sort of cartridge is plugged in, the
name of the cartridge and which gameboy it is compatible with. The following table is a
brief description of this header, ill go into each byte in more detail following it.
| MEMORY ADDRESS |
CONTENTS |
| 014F |
Checksum LSB |
| 014E |
Checksum MSB |
| 014D |
Complement Checksum |
| 014C |
Mask ROM Version |
| 014B |
Old Licensee Code |
| 014A |
Destination Code |
| 0149 |
Cartridge RAM Size |
| 0148 |
Cartridge ROM Size |
| 0147 |
Cartridge Type |
| 0146 |
GB/SGB Function |
| 0145 |
New Licensee Code LSB |
| 0144 |
New Licensee Code MSB |
| 0143 |
Colour Compatibility |
| 0134 |
Game Title |
| 0104 |
Nintendo Logo |
| 0101 |
JP ????h |
| 0100 |
NOP |
The first 4 bytes of the header, starting at 0100h, are a NOP followed by a JP command.
The jump is usually to 0150h which is just after the header. Following this is 30h bytes of
the nintendo logo, these bytes must be : -
CD, ED, 66, 66, CC, 0D, 00, 0B, 03, 73, 00, 83, 00, 0C, 00, 0D
00, 08, 11, 1F, 88, 89, 00, 0E, DC, CC, 6E, E6, DD, DD, D9, 99
BB, BB, 67, 63, 6E, 0E, EC, CC, DD, DC, 99, 9F, BB, B9, 33, 3E
This is the graphic data for the Nintendo logo that is shown on the
startup of a gameboy game. Before you get any ideas of changing this to be a logo of your
own, it is compared with an internal copy and if found to be different the cartridge will not boot.
The next 15 bytes are the title of the game in uppercase ASCII, if the name is less than
15 characters the rest of the name must be padded with 00h bytes. The byte at 0143h
is used to tell whether the game is a colour gameboy game or not. If this byte is
set to 80h then this is a colour gameboy game else it is a normal gameboy game.
As to the licensee codes I am a bit blank, if anyone can provide some documents on this I
will add it to this section.
At offset 0146h is the Super gameboy function byte, set this byte to 03h will enable super
gameboy functions, anything else and they are disabled.
The next byte is used to tell what sort of cartridge is installed. The following
table gives the byte and what facilities the cartridge has.
| BYTE |
DESCRIPTION |
BYTE |
DESCRIPTION |
| 00 |
ROM |
12 |
ROM + MBC3 + RAM |
| 01 |
ROM + MBC1 |
13 |
ROM + MBC3 + RAM + BATTERY |
| 02 |
ROM + MBC1 + RAM |
19 |
ROM + MBC5 |
| 03 |
ROM + MBC1 + RAM + BATTEY |
1A |
ROM + MBC5 + RAM |
| 05 |
ROM + MBC2 |
1B |
ROM + MBC5 + RAM + BATTERY |
| 06 |
ROM + MBC2 + BATTERY |
1C |
ROM + MBC5 + RUMBLE |
| 08 |
ROM + RAM |
1D |
ROM + MBC5 + RUMBLE + SRAM |
| 09 |
ROM + RAM + BATTERY |
1E |
ROM + MBC5 + RUMBLE + SRAM + BATTERY |
| 0B |
ROM + MMMO1 |
1F |
POCKET CAMERA |
| 0C |
ROM + MMMO1 + SRAM |
FD |
BANDAI TAMA5 |
| 0D |
ROM + MMMO1 + SRAM + BATTERY |
FE |
HUDSON HuC 3 |
| 0F |
ROM + MBC3 + TIMER + BATTERY |
FF |
HUDSON HuC 1 |
| 10 |
ROM + MBC3 + TIMER + RAM + BATTERY |
|
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| 11 |
ROM + MBC3 |
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The byte at 0148 is the size of the ROM, for a ROM bigger than 32k the second 16k of
the ROM can be paged to any 16k chunk of the larger ROM. On all but MBC5 cartridges
paging in bank 0 to the upper 16k is the same as paging in bank 1, it is only the MBC5
cartridges that allow you to page in bank 0 to the upper ROM memory. Byte 0149 is
the amount of RAM the cartridge has, this memory is banked into locations A000 - BFFF
(8k). The following tables show the different values for these two bytes and the
amount of ROM/RAM they corrispond to.
BYTE |
ROM SIZE (in kilobits) |
ROM SIZE (in kilobytes) |
ROM SIZE (in banks) |
| 00 |
256Kbit |
32KByte |
2 banks |
| 01 |
512Kbit |
64KByte |
4 banks |
| 02 |
1Mbit |
128KByte |
8 banks |
| 03 |
2Mbit |
256KByte |
16 banks |
| 04 |
4Mbit |
512KByte |
32 banks |
| 05 |
8Mbit |
1MByte |
64 banks |
| 06 |
16Mbit |
2MByte |
128 banks |
| 52 |
9Mbit |
1.1MByte |
72 banks |
| 53 |
10Mbit |
1.2MByte |
80 banks |
| 54 |
12Mbit |
1.5MByte |
96 banks |
BYTE |
RAM SIZE (in kilobits) |
RAM SIZE (in kilobytes) |
RAM SIZE (in banks) |
| 00 |
None |
None |
None |
| 01 |
16Kbit |
2KByte |
1 banks |
| 02 |
64Kbit |
8KByte |
1 banks |
| 03 |
256Kbit |
32KByte |
4 banks |
| 04 |
1Mbit |
128KByte |
16 banks |
The value at offset 014A is the destination code, this is either 00 for Japanese or 1 for
non-Japanese. Following it is he old licensee code, for Super gameboy functions to work
this needs to be 33h. The Mask ROM version number is usually 00h. The complement
check and checksums are used to make sure that the header is valid, although the Nintendo
logo is checked seperately. Using a program such as RGBFix will calculate and set the
checksum values for you.
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