Constants Reference

Overview

Constants in the Pokémon Red/Blue disassembly provide symbolic names for game data, making the code more readable and maintainable. All constant definitions are located in constants/*.asm files. The disassembly uses the const_def macro system to automatically enumerate sequential values, reducing errors and making it easy to add or remove entries.

How Constants Work

Constants are defined using RGBDS assembler syntax with helper macros:

; Start enumeration at 0
const_def
const NO_MON         ; $00
const RHYDON         ; $01
const KANGASKHAN     ; $02

; Start enumeration at a specific value
const_def 1
const STAT_HEALTH    ; $01
const STAT_ATTACK    ; $02

The const_def macro initializes a counter, and each const increments it automatically.

Pokémon IDs

File: constants/pokemon_constants.asmPokémon IDs index multiple data tables including names, evolutions, moves, cries, and Pokédex entries.

const_def
const NO_MON             ; $00
const RHYDON             ; $01
const KANGASKHAN         ; $02
const NIDORAN_M          ; $03
const CLEFAIRY           ; $04
const SPEAROW            ; $05
const VOLTORB            ; $06

Special Constants:

DEF NUM_POKEMON_INDEXES EQU const_value - 1

; Starter Pokémon
DEF STARTER1 EQU CHARMANDER
DEF STARTER2 EQU SQUIRTLE
DEF STARTER3 EQU BULBASAUR

; Ghost Marowak in Pokémon Tower
DEF RESTLESS_SOUL EQU MAROWAK

Pokémon IDs in Red/Blue are in internal order, not Pokédex order. For example, Rhydon is

01 while Bulbasaur is

99.

Item IDs

File: constants/item_constants.asmItem IDs are used for inventory management, shops, and the bag menu.

const_def
const NO_ITEM       ; $00
const MASTER_BALL   ; $01
const ULTRA_BALL    ; $02
const GREAT_BALL    ; $03
const POKE_BALL     ; $04
const TOWN_MAP      ; $05
const BICYCLE       ; $06
const SURFBOARD     ; $07

Badge Constants:Badges use item IDs with special handling:

const BOULDERBADGE  ; $15
DEF SAFARI_BAIT EQU BOULDERBADGE ; overload
const CASCADEBADGE  ; $16
DEF SAFARI_ROCK EQU CASCADEBADGE ; overload
const THUNDERBADGE  ; $17
const RAINBOWBADGE  ; $18

TM/HM Constants:The game uses macros to define TMs and HMs with multiple related constants:

DEF NUM_TMS EQU 50
DEF NUM_HMS EQU 5

; HMs start at $C4
add_hm CUT          ; $C4
add_hm FLY          ; $C5
add_hm SURF         ; $C6
add_hm STRENGTH     ; $C7
add_hm FLASH        ; $C8

; TMs start at $C9
add_tm MEGA_PUNCH   ; $C9
add_tm RAZOR_WIND   ; $CA

Each TM/HM gets three constants:

TM_<move> or HM_<move>: The item ID
<move>_TMNUM: Learnable flag index (1-55)
TM##_MOVE or HM##_MOVE: Alias for the move ID

Move IDs

File: constants/move_constants.asmMove IDs index the moves data table, names, animations, and sound effects.

const_def
const NO_MOVE      ; 00
const POUND        ; 01
const KARATE_CHOP  ; 02
const DOUBLESLAP   ; 03
const COMET_PUNCH  ; 04
const MEGA_PUNCH   ; 05
const PAY_DAY      ; 06

Special Move Constants:

DEF NUM_ATTACKS EQU const_value - 1
DEF CANNOT_MOVE EQU $ff

; Moves double as animation identifiers
const SHOWPIC_ANIM
const STATUS_AFFECTED_ANIM
const ENEMY_HUD_SHAKE_ANIM
const TRADE_BALL_DROP_ANIM

Map IDs

File: constants/map_constants.asmMap constants use a special map_const macro that defines the map ID along with width and height:

MACRO map_const
    const \1
    DEF \1_WIDTH EQU \2
    DEF \1_HEIGHT EQU \3
ENDM

; Towns and cities
const_def
map_const PALLET_TOWN,      10,  9 ; $00
map_const VIRIDIAN_CITY,    20, 18 ; $01
map_const PEWTER_CITY,      20, 18 ; $02
map_const CERULEAN_CITY,    20, 18 ; $03

Map Categories:

DEF NUM_CITY_MAPS EQU const_value
DEF FIRST_ROUTE_MAP EQU const_value
DEF FIRST_INDOOR_MAP EQU const_value

; Special return value
DEF LAST_MAP EQU $ff  ; Returns to last outdoor map

Indoor Map Groups:Indoor maps are organized by location:

map_const OAKS_LAB,         5,  6 ; $28
end_indoor_group PALLET_TOWN

map_const VIRIDIAN_POKECENTER, 7, 4 ; $29
map_const VIRIDIAN_MART,       4, 4 ; $2A
map_const VIRIDIAN_GYM,       10, 9 ; $2D
end_indoor_group VIRIDIAN_CITY

Battle Constants

File: constants/battle_constants.asmMove Structure:

rsreset
DEF MOVE_ANIM   rb
DEF MOVE_EFFECT rb
DEF MOVE_POWER  rb
DEF MOVE_TYPE   rb
DEF MOVE_ACC    rb
DEF MOVE_PP     rb
DEF MOVE_LENGTH EQU _RS

Stat Constants:

const_def 1
const STAT_HEALTH
const STAT_ATTACK
const STAT_DEFENSE
const STAT_SPEED
const STAT_SPECIAL
DEF NUM_STATS EQU const_value - 1

DEF MAX_LEVEL EQU 100
DEF NUM_MOVES EQU 4
DEF MAX_STAT_VALUE EQU 999

Type Effectiveness:

; Scaled by 10
DEF SUPER_EFFECTIVE    EQU 20
DEF MORE_EFFECTIVE     EQU 15
DEF EFFECTIVE          EQU 10
DEF NOT_VERY_EFFECTIVE EQU 05
DEF NO_EFFECT          EQU 00

Status Conditions:

DEF SLP_MASK EQU %111 ; 0-7 turns
const_def 3
const PSN ; 3 - Poisoned
const BRN ; 4 - Burned
const FRZ ; 5 - Frozen
const PAR ; 6 - Paralyzed

Battle Status Flags:

; wPlayerBattleStatus1 / wEnemyBattleStatus1
const_def
const STORING_ENERGY           ; 0 - Bide
const THRASHING_ABOUT          ; 1 - Thrash, Petal Dance
const ATTACKING_MULTIPLE_TIMES ; 2 - Double Kick, Fury Attack
const FLINCHED                 ; 3
const CHARGING_UP              ; 4 - Solar Beam, Fly
const USING_TRAPPING_MOVE      ; 5 - Wrap, Bind
const INVULNERABLE             ; 6 - Fly/Dig charge turn
const CONFUSED                 ; 7

Type IDs

File: constants/type_constants.asmTypes are split into physical and special categories:

const_def

DEF PHYSICAL EQU const_value
const NORMAL       ; $00
const FIGHTING     ; $01
const FLYING       ; $02
const POISON       ; $03
const GROUND       ; $04
const ROCK         ; $05
const BIRD         ; $06
const BUG          ; $07
const GHOST        ; $08

; Skip to 20 for special types
const_next 20

DEF SPECIAL EQU const_value
const FIRE         ; $14
const WATER        ; $15
const GRASS        ; $16
const ELECTRIC     ; $17
const PSYCHIC_TYPE ; $18
const ICE          ; $19
const DRAGON       ; $1A

DEF NUM_TYPES EQU const_value

The gap between physical and special types (9-19) is unused space in the type system.

Usage Examples

Checking Pokémon Species

ld a, [wCurSpecies]
cp PIKACHU
jr z, .isPikachu

Adding Item to Bag

ld hl, wNumBagItems
ld a, MASTER_BALL
ld [wcf91], a
ld a, 1  ; quantity
ld [wItemQuantity], a
call AddItemToInventory

Teaching a Move

ld a, THUNDERBOLT
ld [wMoveNum], a
ld [wcf91], a
call IsTMHMMove

Map Warps

ld a, OAKS_LAB
ld [wDestinationMap], a
call LoadMapData

Common Patterns

const_skip

Skips values in the enumeration (used for unused or reserved slots):

const TANGELA            ; $1E
const_skip               ; $1F
const_skip               ; $20
const GROWLITHE          ; $21

const_next

Jumps to a specific value (cannot go backwards):

const_next $C4
add_hm CUT               ; $C4

shift_const

Creates bit flag constants:

const_def
shift_const FLAG_BIT_0   ; 1 << 0 = $01
shift_const FLAG_BIT_1   ; 1 << 1 = $02
shift_const FLAG_BIT_2   ; 1 << 2 = $04

Reference Tables

Key Constant Files

File	Purpose	Count
`pokemon_constants.asm`	Pokémon species IDs	190
`item_constants.asm`	Items, TMs, HMs	250+
`move_constants.asm`	Move IDs	165
`map_constants.asm`	Map IDs	248
`type_constants.asm`	Type IDs	16
`battle_constants.asm`	Battle mechanics	Many
`sprite_constants.asm`	Sprite IDs	100+
`event_constants.asm`	Event flags	Many
`text_constants.asm`	Text IDs	500+

Exported Constants

DEF NUM_POKEMON_INDEXES EQU 190
DEF NUM_ITEMS EQU 83
DEF NUM_TMS EQU 50
DEF NUM_HMS EQU 5
DEF NUM_TM_HM EQU 55
DEF NUM_ATTACKS EQU 165
DEF NUM_MAPS EQU 248
DEF NUM_TYPES EQU 26

Best Practices

Use Symbolic Names

Always use constant names instead of hardcoded numbers for better readability and maintainability.

Check const_value

Use const_value to get the current enumeration value for array sizing and validation.

Document Skips

Add comments explaining why values are skipped with const_skip.

Group Related Constants

Keep related constants in the same file and section for easy reference.

Macros Reference - Learn about the macro system
Data Structures - Understand how constants index data
Engine Modules - See constants in action

Get Started

Architecture

Game Systems

Code Reference

Development

Overview

How Constants Work

Pokémon IDs

Item IDs

Move IDs

Map IDs

Battle Constants

Type IDs

Usage Examples

Checking Pokémon Species

Adding Item to Bag

Teaching a Move

Map Warps

Common Patterns

const_skip

const_next

shift_const

Reference Tables

Key Constant Files

Exported Constants

Best Practices

Use Symbolic Names

Check const_value

Document Skips

Group Related Constants

Build docs developers (and LLMs) love

Get Started

Architecture

Game Systems

Code Reference

Development

​Overview

​How Constants Work

​Pokémon IDs

​Item IDs

​Move IDs

​Map IDs

​Battle Constants

​Type IDs

​Usage Examples

​Checking Pokémon Species

​Adding Item to Bag

​Teaching a Move

​Map Warps

​Common Patterns

​const_skip

​const_next

​shift_const

​Reference Tables

​Key Constant Files

​Exported Constants

​Best Practices

Use Symbolic Names

Check const_value

Document Skips

Group Related Constants

​Related Pages

Build docs developers (and LLMs) love

Overview

How Constants Work

Pokémon IDs

Item IDs

Move IDs

Map IDs

Battle Constants

Type IDs

Usage Examples

Checking Pokémon Species

Adding Item to Bag

Teaching a Move

Map Warps

Common Patterns

const_skip

const_next

shift_const

Reference Tables

Key Constant Files

Exported Constants

Best Practices

Related Pages