Pokémon data structure (Generation I)
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This article is incomplete. Please feel free to edit this article to add missing information and complete it. |
The Pokémon data structure in the Generation I games stores most information about the current state of a player's caught Pokémon. It has a length of 44 bytes for Pokémon in the player's party and 33 bytes for Pokémon in boxes on Bill's PC. The information lost when depositing a Pokémon in Bill's PC is its level and its HP, Attack, Defense, Special and Speed; this allows the box trick to work by recalculating the lost information upon withdrawing the Pokémon again.
The structure
| Offset | Contents | Size |
|---|---|---|
| 0x00 | Index number of species | Byte |
| 0x01 | Remaining HP | Word |
| 0x03 | Level? | Byte |
| 0x04 | Status ailments | Byte |
| 0x05 | Unknown | 3 bytes |
| 0x08 | Index number of first move | Byte |
| 0x09 | Index number of second move | Byte |
| 0x0A | Index number of third move | Byte |
| 0x0B | Index number of fourth move | Byte |
| 0x0C | Original trainer ID number | Word |
| 0x0E | Experience | 3 bytes |
| 0x11 | HP stat experience | Word |
| 0x13 | Attack stat experience | Word |
| 0x15 | Defense stat experience | Word |
| 0x17 | Speed stat experience | Word |
| 0x19 | Special stat experience | Word |
| 0x1B | Individual values | Word |
| 0x1D | PP of first move | Byte |
| 0x1E | PP of second move | Byte |
| 0x1F | PP of third move | Byte |
| 0x20 | PP of fourth move | Byte |
| 0x21 | Level | Byte |
| 0x22 | Maximum HP | Word |
| 0x24 | Attack | Word |
| 0x26 | Defense | Word |
| 0x28 | Speed | Word |
| 0x2A | Special | Word |
Notably missing from this structure are the Pokémon's nickname and the original trainer's name, which are stored elsewhere.
Pokémon stored in Bill's PC use a form of this structure that stops after the PP data for the fourth move, at 0x20.
The Pokémon box data consists only of the currently open Pokémon box, which explains the need for the player to save the game before switching the open box. In Pokémon Yellow for the US, this data starts at 0xDA95 in volatile RAM and continues for 660 bytes (33 bytes each for 20 Pokémon).
Explanation of fields
Species
The index number for the Pokémon's species.
Remaining HP
The number of HP left on the Pokémon. This value may not be greater than the Maximum HP field's value.
Level
Though it appears to be the level of the Pokémon, it seems effectively redundant: it exists as a Pokémon's level when said Pokémon is stored in a PC box, yet is overwritten as part of the recalculation that takes place when the Pokémon is withdrawn. If the Pokémon is deposited back into a box, this value is set to the Pokémon's level again. This value's purpose is currently unknown.
Status ailments
The status ailments of the Pokémon, as a bit field.
| Bit | Value | Status ailment |
|---|---|---|
| 3 | 0x04 | Asleep |
| 4 | 0x08 | Poisoned |
| 5 | 0x10 | Burned |
| 6 | 0x20 | Frozen |
| 7 | 0x40 | Paralyzed |
Since being badly poisoned is a temporary condition in battles, it is not stored here. Confusion is also not stored here. 0x00 means that the Pokémon is not affected by any major status ailment.
Original trainer ID number
The ID number of the trainer who caught the Pokémon.
Experience
The number of EXP. Points accumulated by the Pokémon. The level of the Pokémon should correspond with this value according to the growth formula for the Pokémon species.
Stat experience
- Main article: Effort values
The stat experience accumulated by the Pokémon in each of the 5 permanent stats after battling or receiving vitamins.
PP
- Main article: Power points
The PP for each move the Pokémon knows. The lowest 6 bits of each of these values is the current amount of PP for the move, and the highest 2 bits are the number of PP Ups applied to the move.
This explains the behavior of Hyper Beam and other such multi-turn moves when they glitch: the game subtracts 1 from the entire byte, and 0x00 rolls over to 0xFF, which applies 3 PP Ups to the move and makes its current PP 63. However, if one or more PP Ups are already applied to the move, the byte does not roll over in this way, so one PP Up is removed from the move. For example, if the move has 2 PP Ups applied, the byte is 0x80, which becomes 0x7F, which specifies 63 PP and one PP Up.
Maximum HP
The HP that the Pokémon has when at full health.
Attack, Defense, Speed, Special
The values of the Pokémon's Attack, Defense, Speed and Special stats, as they were last calculated from the base stats of the species, the Pokémon's individual values and its stat experience. This occurs at level-up and when the Pokémon is withdrawn from Bill's PC.
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