View source for Pokémon data structure (Generation I)

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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 ===

{| style="border: 1px solid #88a; background: #f8f8ff; padding: 0.5em; border-collapse: collapse; margin: 0 0 0.5em 0.5em;" cellspacing="1" cellpadding="2"
|- 
! style="text-align: center; background: #ccf;" | '''Offset'''
! style="text-align: center; background: #ccf;" | '''Contents'''
! style="text-align: center; background: #ccf;" | '''Size'''
|-
| 0x00 || [[List of Pokémon by index number (GB)|Index number of species]] || Byte
|-
| 0x01 || Remaining HP || {{tt|Word|2 bytes, with Remaining HP / 256 stored first}}
|-
| 0x03 || Level? || Byte
|-
| 0x04 || [[Status_ailment|Status ailments]] || Byte
|-
| 0x05 || Unknown || 3 bytes
|-
| 0x08 || [[List of moves#Generation I|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 || [[Trainer ID number|Original trainer ID number]] || {{tt|Word|2 bytes, with Trainer ID number / 256 stored first}}
|-
| 0x0E || [[Experience]] || {{tt|3 bytes|Experience / 65536, then Experience / 256 mod 256, then Experience mod 256}}
|-
| 0x11 || [[HP]] [[stat experience]] || {{tt|Word|2 bytes, with HP stat experience / 256 stored first}}
|-
| 0x13 || [[Attack]] stat experience || {{tt|Word|2 bytes, with Attack stat experience / 256 stored first}}
|-
| 0x15 || [[Defense]] stat experience || {{tt|Word|2 bytes, with Defense stat experience / 256 stored first}}
|-
| 0x17 || [[Speed]] stat experience || {{tt|Word|2 bytes, with Speed stat experience / 256 stored first}}
|-
| 0x19 || [[Special]] stat experience || {{tt|Word|2 bytes, with Special stat experience / 256 stored first}}
|-
| 0x1B || [[Individual values]] || {{tt|Word|4 bits for each IV excluding HP}}
|-
| 0x1D || [[PP]] of first move || {{tt|Byte|6 bits for current PP, 2 bits for applied PP Ups}}
|-
| 0x1E || [[PP]] of second move || {{tt|Byte|6 bits for current PP, 2 bits for applied PP Ups}}
|-
| 0x1F || [[PP]] of third move || {{tt|Byte|6 bits for current PP, 2 bits for applied PP Ups}}
|-
| 0x20 || [[PP]] of fourth move || {{tt|Byte|6 bits for current PP, 2 bits for applied PP Ups}}
|-
| 0x21 || [[Level]] || Byte
|-
| 0x22 || Maximum HP || {{tt|Word|2 bytes, with Maximum HP / 256 stored first}}
|-
| 0x24 || Attack || {{tt|Word|2 bytes, with Maximum HP / 256 stored first}}
|-
| 0x26 || Defense || {{tt|Word|2 bytes, with Maximum HP / 256 stored first}}
|-
| 0x28 || Speed || {{tt|Word|2 bytes, with Maximum HP / 256 stored first}}
|-
| 0x2A || Special || {{tt|Word|2 bytes, with Maximum HP / 256 stored first}}
|}

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 Version|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 [[List of Pokémon by index number (GB)|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 ailment|status ailments]] of the Pokémon, as a bit field.

{| style="border: 1px solid #88a; background: #f8f8ff; padding: 0.5em; border-collapse: collapse; margin: 0 0 0.5em 0.5em;" cellspacing="1" cellpadding="2"
|- 
! style="text-align: center; background: #ccf;" | '''Bit'''
! style="text-align: center; background: #ccf;" | '''Value'''
! style="text-align: center; background: #ccf;" | '''Status ailment'''
|-
| 3 || 0x04 || Asleep
|-
| 4 || 0x08 || Poisoned
|-
| 5 || 0x10 || Burned
|-
| 6 || 0x20 || Frozen
|-
| 7 || 0x40 || Paralyzed
|}

Since [[Toxic (move)|toxic poison]] is a temporary condition in [[Pokémon battle|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 [[Trainer ID number|ID number]] of the [[trainer]] who [[caught Pokémon|caught]] the Pokémon.

=== Experience ===

The number of [[Experience|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|Effort values}}
The stat experience accumulated by the Pokémon in each of the 5 permanent stats after battling or receiving [[vitamin|vitamins]].

=== PP ===

{{main|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 Up|PP Ups]] applied to the move.

This explains the behavior of [[Hyper Beam (move)|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.

{{data structure}}