From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokémon in the Pokémon Ruby and Sapphire, FireRed and LeafGreen, and Emerald Versions are all stored the same way in a 100-byte structure.
The personality value controls many things, including gender, Unown's letter, Spinda's dots, any Pokémon's Nature, and more.
The Original Trainer's ID number. This number is part of the XOR encryption key for the data section, and is also used in Shiny determination and the lottery.
The Pokémon's nickname, limited to 10 characters. The characters represented by each byte are determined by the proprietary character set.
The language of the game the Pokémon comes from. Valid values are:
The name of the Pokémon's Original Trainer. The characters represented by each byte are determined by the proprietary character set.
The markings seen in the storage Box. These markings serve only to aid in organizing large collections of Pokémon.
The checksum for the 48-byte data section of this structure. It is computed by adding all of the unencrypted values of that section one word at a time. If the computed sum and the stored checksum do not match, the Pokémon is interpreted as a Bad Egg.
Unknown, possibly simply padding (not used and usually set to either 0 or -1, depending on the data type).
Certain data pertaining to the Pokémon that is stored in a special and encrypted format.
The Pokémon's status condition is stored as follows:
|| Bad Poison
The three sleep bits are used to indicate turns of sleep. So 1112 = 7 turns of sleep, 1012 = 5 turns, et cetera.
|| This section is incomplete.|
Please feel free to edit this section to add missing information and complete it.
Reason: Are the addresses below only for US games?.
A Trainer's party starts at the following addresses in the GBA's RAM.
An opponent's party, or a wild Pokémon, starts at the following addresses.
The 600 bytes following these addresses describe a whole team of 6 Pokémon.
The full 100-byte structure for a Pokémon is only used to describe Pokémon being held in the player's party. When Pokémon are stored in the PC, their data is recorded using only the first 80 bytes of this structure, stopping after the data field. The last 20 bytes (excepting status condition) can all be recalculated from data in the data substructure when a Pokémon is withdrawn (level being derived from experience). This also explains why Pokémon suffering a status condition are "cured" when put in the PC.
This means there are also 33,600 bytes (80 bytes * 30 per Box * 14 Boxes) elsewhere in the GBA's RAM describing Pokémon in the PC. When the GBA's saved state (including memory contents) is unzipped into a 740,000+ byte file and viewed, the 14 Boxes of 420 Pokémon are stored in the general region of $038000 and $040000.