Part III: Object System

How objects are defined, behave, and interact in The Sims

This part covers everything that makes objects work: definitions, behaviors, interactions, routing, and the virtual machine that executes it all.

Document Navigation

Part	Focus	Status
I. Foundations	Architecture & Concepts
II. Containers	FAR & IFF Formats
III. Object System	OBJD, BHAV, VM	📍 You are here
IV. Graphics & Animation	Sprites, Meshes, Animation
V. Game Content	Characters, Careers, Strings
VI. Tools & Workflows	IFFSnooper Guides

Key Terms

Term	Definition
OBJD	Object Definition — master resource defining object properties
OBJf	Object Functions — entry point table for behaviors
BHAV	Behavior — VM subroutine containing executable code
BCON	Behavioral Constants — tunable integer values
TTAB	Tree Table — interaction definitions (pie menu)
GLOB	Global — reference to shared semi-global file
SLOT	Slot — character routing and approach positions
Opcode	Instruction code specifying VM operation
Primitive	Built-in VM operation (opcodes 0-63)

Chapter 1: OBJD Object Definition

Overview

OBJD is the master resource defining an object — nearly 100 fields control identity, appearance, behavior, pricing, and categorization.

Property	Value
Type code	`OBJD`
Version	138 (documented)
Size	216 bytes (108 × 2-byte fields)
Byte order	Little-endian

Object Roles

Configuration	master_id	sub_index	Usage
Single-tile	`0`	ignored	Most objects
Master (multi-tile)	non-zero	`0xFFFF` (-1)	Object-wide settings
Slave (multi-tile)	non-zero	`(y<<8)\|x`	Per-tile settings

⚠️ Multi-tile objects: Each tile needs its own OBJD. The master holds shared settings (price, categories); slaves hold tile-specific data (sprites, positions).

Key Field Groups

Identity (Offsets 0-4)

Offset	Field	Description
0-1	version	Format version (138)
2	initial_stack_size	Stack allocation (4 typical)
3	base_graphic	First DGRP resource ID
4	num_graphics	DGRP count for object states

GUID (Offsets 14-15)

Offset	Field	Description
14-15	guid	32-bit globally unique identifier

⚠️ GUID Uniqueness: Every object across all installed content must have a unique GUID. Conflicts cause objects to disappear from the catalog.

Object Type (Offset 9)

Code	Type	Description
0	unknown	Undetermined
2	person	Character/NPC
4	normal	Buyable object
7	sim_type	System objects
8	portal	Stairs, doors, windows
34	food	Food items

Pricing (Offsets 18, 34-38)

Offset	Field	Description
18	price	Purchase price (Simoleans)
34	sale_price	Current depreciated value
35	initial_depreciation	First-day loss
36	daily_depreciation	Per-day loss
38	depreciation_limit	Minimum resale floor

Catalog Categories (Offsets 39-40)

Room Sort Flags (Offset 39):

Mask	Category
0x01	Kitchen
0x02	Bedroom
0x04	Bathroom
0x08	Family room
0x10	Outside
0x20	Dining room
0x40	Miscellaneous
0x80	Study

Function Sort Flags (Offset 40):

Mask	Category
0x01	Seating
0x02	Surfaces
0x04	Appliances
0x08	Electronics
0x10	Plumbing
0x20	Decorative
0x40	General
0x80	Lighting

Motive Ratings (Offsets 82-88)

These values appear in the object's catalog description:

Offset	Rating
82	Hunger
83	Comfort
84	Hygiene
85	Bladder
86	Energy
87	Fun
88	Room

Skill Flags (Offset 89)

Mask	Skill
0x01	Cooking
0x02	Mechanical
0x04	Logic
0x08	Body
0x10	Creativity
0x20	Charisma
0x40	School

Build Mode Types (Offset 69)

Code	Tool
1	Door
2	Window
3	Stair
4	Plant
5	Fireplace
6	Wall/Fence
7	Pool

Expansion Sort Fields

Offset	Field	Expansion
94	function_subsort	Hot Date+
95	downtown_sort	Hot Date
97	vacation_sort	Vacation
99	community_sort	Unleashed
103	studiotown_sort	Superstar
104	magictown_sort	Makin' Magic

Complete Field Index

From Behavior.iff STR# 204:

Index	Name	Index	Name
0-1	version_1/2	39-40	room/function_sort
2	initial_stack_size	41	catalog_strings_id
3-4	base_graphic/num	42	is_global_sim_object
7	tree_table_id	46	wall_style
8	interaction_group	49	object_version
9	type	61	front_direction
10-11	master_id/sub_index	63	mt_lead_object
14-15	guid_1/2	64-65	dynamic_sprites
16	disabled	69	build_mode_type
18	price	70-73	original/suit_guid
19	body_strings_id	75	thumbnail_graphic
20	slots_id	81	wall_style_sprite_id
34-38	depreciation fields	82-88	motive ratings

Chapter 2: OBJf Object Functions

OBJf Overview

OBJf provides a vtable-like entry point table for object behaviors, replacing deprecated OBJD "old tree ID" fields.

Property	Value
Type code	`OBJf`
Typical count	31 entry pairs

Structure

Header (16 bytes):

Offset	Size	Field	Value
0	4	Reserved	0
4	4	Version	0
8	4	Identifier	`fJBO` (little-endian)
12	4	Entry count	Number of pairs

Entry Pairs (4 bytes each):

Offset	Size	Field
0	2	Guard BHAV ID
2	2	Action BHAV ID

Guard vs Action Functions

Function	Purpose	Returns
Guard	Check if action available	True/False
Action	Execute the interaction	(executes)

Entry Point Index

Index	Entry	Index	Entry
0	init	16	cook
1	main	17	eat_food
2	load	18	dispose
3	cleanup	19	fire
4	queue_skipped	20	burn_down
5	allow_intersection	21	wash_hands
6	wall_adjacency_changed	22	wash_dishes
7	room_changed	23	use_toilet
8	dynamic_multitile_update	24	use_tub
9	placement	25	sit
10	pick_up	26	stand
11	user_placement	27	lie_in
12	user_pickup	28	place_on_surface
13	level_info_request	29	pickup_from_slot
14	move_in	30	garden
15	move_out

💡 Precedence: When OBJf is present, OBJD "old tree ID" fields are ignored.

Chapter 3: BHAV Behaviors

BHAV Overview

BHAV resources are the executable code of The Sims — VM subroutines that drive all gameplay operations.

Property	Value
Type code	`BHAV`
Header size	12 bytes (13 for TSO)
Instruction size	12 bytes (fixed)
Max instructions	253
Byte order	Little-endian

Core Architecture Truth

The Sims 1 is 100% event-driven. There are NO inter-BHAV function calls.

Engine owns the main loop, not BHAVs
BHAVs execute, return control to engine, engine calls next BHAV
Communication via state variables, not call stacks
OBJf chunk maps lifecycle events → BHAV IDs

This is proven by the absence of opcode 0x0001 (BHAV Call) in actual game files.

BHAV Classification

Analysis of 2,712 BHAVs across 126 objects reveals four behavioral types:

Type	%	Entry Point	Structure	Purpose
ROLE	52.4%	OBJf Main	Polling loop + yields	Autonomy core (owns Sim)
FLOW	45.0%	Internal	Conditional branches	Decision routing
ACTION	1.6%	TTAB action	Linear, no loops	User interaction outcome
GUARD	1.1%	TTAB test	Predicate, no yields	Permission check (sync)

⚠️ No UTILITY type exists — utilities require a call hierarchy, which the event-driven model doesn't support.

Physical Structure

BHAV Layout
┌─────────────────────────┐
│ Header (12 bytes)       │
├─────────────────────────┤
│ Instruction 0 (12B)     │
│ Instruction 1 (12B)     │
│ ...                     │
└─────────────────────────┘

Header (12 bytes)

Offset	Size	Field	Description
0-1	2	Signature	Version marker (0x8000–0x8003)
2-3	2	Count	Instruction count (1–253)
4-5	2	Type	Usually 0
6-7	2	Args	Parameter count (0–4)
8	1	Locals	Local variable count (0–12)
9	1	Flags	Behavior flags
10-11	2	Reserved	Always zero

Signature Versions:

Signature	Count	Notes
0x8000	90	Deprecated
0x8001	26	Deprecated
0x8002	8,896	Standard
0x8003	—	TSO only

Instruction Format (12 bytes)

Offset	Size	Field	Description
0-1	2	Opcode	Primitive or subroutine call
2	1	Addr1	Next instruction on success
3	1	Addr2	Next instruction on failure
4-11	8	Operands	Instruction-specific data

Flow Control Addresses

Address	Name	Effect
254	TRUE	Return true to caller
255	FALSE	Return false to caller
253	ERROR	Terminate with error
0–252	—	Next instruction index

💡 Two-address flow: Instructions specify both success and failure paths. Code doesn't need to execute sequentially.

Operand Interpretation

The 8-byte operand field has flexible interpretation depending on opcode:

Individual bytes as single-byte operands
Aligned pairs as 2-byte little-endian integers
Complex references to external data containers

Example operand structures:

Instruction	Operand[0-3]	Operand[4-7]
Expression	Expression code	Variable refs
Goto Slot	Slot ID	Flags
Animate	Animation ID	Duration/Flags
Create Object	Object GUID/ID	Placement flags

Subroutine Address Ranges

When an instruction has an opcode ≥ 256, it's a subroutine call to another BHAV. The address space is divided into four regions:

Range	Hex	Scope	Ownership
0-63	0x0000-003F	—	Primitives only
256-4095	0x0100-0FFF	Global	Global.iff (all objects)
4096-8191	0x1000-1FFF	Local	Same IFF file (object)
8192+	0x2000+	Semi-global	GLOB reference file

Key concept: The address region determines where to look for the target BHAV:

Global (256+): Always in Global.iff
Local (4096+): In the same IFF file as the calling BHAV
Semi-global (8192+): In the shared semi-global file referenced by GLOB

⚠️ Scope violations: Calling outside valid address ranges causes undefined behavior.

Key Primitives (Opcodes 0-63)

The VM provides ~50 built-in primitives covering simulation operations. Expression (opcode 2) dominates: 57% of all executed instructions.

Complete Opcode Reference

Op	Hex	Name	Category	Purpose
0	0000	Sleep/Yield	Control	Pause N ticks
2	0002	Expression	Math	Arithmetic/comparison (57%!)
4	0004	Grab	Object	Pick up object
5	0005	Drop	Object	Put down object
6	0006	Change Article	Sim	Change suit/accessory
7	0007	Refresh	Looks	Redraw graphics
8	0008	Random	Math	Generate random number
11	000B	GetDistanceTo	Position	Calculate distance
12	000C	GetDirectionTo	Position	Calculate heading
13	000D	PushInteraction	Control	Queue interaction
14	000E	FindBestObject	Control	Search lot for object
17	0011	IdleForInput	Control	Wait for user
18	0012	RemoveObject	Object	Delete from world
22	0016	LookTowards	Sim	Face direction
23	0017	PlaySound	Looks	Audio effect
25	0019	TransferFunds	Sim	Move money
26	001A	Relationship	Sim	Modify sim relationship
30	001E	AnimateSim	Sim	Play animation
42	002A	CreateObject	Object	Instantiate object
45	002D	GotoRoutingSlot	Position	Walk to position
46	002E	Snap	Position	Teleport to position

Opcodes by Category

Flow Control: Sleep(0), PushInteraction(13), FindBestObject(14), IdleForInput(17)

Math: Expression(2), Random(8), GetDistanceTo(11), GetDirectionTo(12)

Object: Grab(4), Drop(5), RemoveObject(18), CreateObject(42)

Sim: ChangeArticle(6), LookTowards(22), Relationship(26), AnimateSim(30)

Position: GotoRoutingSlot(45), Snap(46)

Looks: Refresh(7), PlaySound(23)

Virtual Machine Threading Model

Multi-threaded Execution:

Each object maintains its own execution thread
Threads yield voluntarily per game tick (yield via opcode 0)
Tick rate: 15 ticks = 1 simulated minute
Display refresh: 15 Hz (66ms per frame)

Data Scope Hierarchy:

Scope	Lifetime	Visibility
Per-invocation	Call stack frame	Parameters, locals, temp
Per-thread	Object lifetime	My object ID, stack ID
Per-object	In-world lifetime	Temps, state, attributes
Per-file (IFF)	Game session	BCON, BHAV, STR#, GLOB ref
Global (shared)	Always	Global.iff constants

Execution Model

Polling Loop Pattern (ROLE BHAVs)

ROLE BHAVs (52% of all behaviors) follow this execution pattern:

loop:
  Check state variables
  If changed → recompute decisions
  Check for user interaction → return to engine if pending
  Animate/idle (YIELDS control back to engine)
  Loop back (max ~10,000 iterations)

Yield Points

Opcodes that pause execution and return control to the engine:

Opcode	Name	Purpose
0x002C	Animate	Display animation
0x0042	Route	Pathfinding
0x0043	Idle	Stand idle
0x0024	Sleep	Wait N frames

When BHAV yields:

Execution pauses at yield point
Engine renders frame, handles other objects
Engine resumes BHAV at yield point
Polling loop continues

State Communication

Objects communicate via attributes (state variables), not function calls:

Engine SETS state (user click, game event)
ROLE BHAV READS state, decides action
ACTION BHAV WRITES state, returns
No call stack needed

Chapter 4: BCON & TRCN Constants

BCON: Behavioral Constants

BCON stores tunable integer values that behavior code references instead of hard-coded literals.

Property	Value
Type code	`BCON`
Max entries	65
Entry size	2 bytes (signed)

Structure:

Offset	Size	Field
0	1	Count (N)
1	1	Flags (0x00 or 0x80)
2	2×N	Constants (little-endian signed)

TRCN: Trait Constants (Labels)

TRCN provides human-readable labels and valid ranges for BCON constants.

Property	Value
Type code	`TRCN`
Relationship	Same resource ID as paired BCON
Required	No (optional for tools)

Header (16 bytes):

Offset	Size	Field
0	4	Reserved (0)
4	4	Version (0, 1, or 2)
8	4	Identifier (`TRCN`)
12	4	Entry count

Entry:

Field	Size	Description
Disable flag	1	0 = enabled, 1 = disabled
Unknown	7	Purpose unclear
Label	var	Null-terminated + 0xA3 padding
Comment	var	Null-terminated + 0xA3 padding

Version 1+ adds range validation:

Field	Size	Description
Range enabled	1	0 = no, 1 = yes
Low range	2	Minimum legal value
High range	2	Maximum legal value

Chapter 5: TPRP Trait Properties

TPRP provides human-readable labels for BHAV parameters and local variables.

Property	Value
Type code	`TPRP`
Relationship	Same ID as paired BHAV
Required	No (optional for tools)

Header (20 bytes):

Offset	Size	Field
0	4	Reserved (0)
4	4	Version (2, 3, or 4)
8	4	Identifier (`TPRP`)
12	4	Param count (N1)
16	4	Local count (N2)

Label Data:

Parameter labels (N1): Null-terminated, 0xA3-padded
Local labels (N2): Same format
Parameter flags (N1 bytes): 0 = enabled, 1 = disabled

Chapter 6: TTAB Interactions

TTAB Overview

TTAB (Tree Table) defines object interactions — generating pie menus and controlling autonomy.

Property	Value
Type code	`TTAB`
Versions	2–9 (V9 most common)
Related	TTAs (menu text strings)

Header

Offset	Size	Field
0-1	2	Interaction count
2-3	2	Version (2–9)
4	1	Compression code (V9: 1)

Core Fields Per Interaction

Field	Size	Description
Action function	2	BHAV ID to execute
Guard function	2	Condition check BHAV ID
Motive count	2-4	Always 16
Flags	2-4	Behavior control bits
String table index	4	TTAs menu text (V5+)
Attenuation code	4	Distance fade (V7+)
Autonomy	4	Autonomy eligibility (V5+)
Join index	4	Group interaction ID (V5+)

Flags Bitfield

Bit	Meaning
0	Accessible to visitors
1	Joinable (group interaction)
3	Allow consecutive repeats
4	NOT accessible to child
6	NOT accessible to adult
9	Enable for cats (Unleashed)
10	Enable for dogs (Unleashed)

Motive Entries (16 per interaction)

Index	Motive	Index	Motive
3	Mood	9	Bladder
5	Energy	13	Room
6	Comfort	14	Social
7	Hunger	15	Fun
8	Hygiene

Motive Entry Fields (V7+):

Field	Size	Description
Minimum	2	Threshold value
Delta	2	Change amount claimed
Character type	2	Personality modifier

💡 Objects lie: Objects often claim motive benefits they don't actually deliver.

Attenuation Settings

Setting	Effect
None	Always visible in menu
Low	Moderate distance fade
Medium	Medium distance fade
High	Quick distance fade

Guard & Action Pattern

Each TTAB interaction follows a "guard + action" pattern:

Guard BHAV (Condition Check):

Type: Hard reference (required)
Scope: Object-local (addresses 4096-8191)
Executed: Every frame (visibility determination)
Returns: True = show in menu, False = hide
Efficiency: Guard runs frequently; action only on selection

Action BHAV (Execution):

Type: Hard reference (required)
Scope: Object-local (addresses 4096-8191)
Executed: Once per interaction selection
Returns: Completion status
Purpose: Perform the actual game action

⚠️ Design implication: Missing guard or action BHAV causes interaction to fail at runtime.

Reference Types Generated

Each TTAB entry generates references to three resources:

Reference Type	Size	Purpose	Optional
Guard BHAV	2	Condition check (show/hide)	No
Action BHAV	2	Interaction behavior	No
TTAs Index	4	Menu text localization (V5+)	Yes

Reference Scope:

All references are OBJECT-LOCAL (addresses 4096-8191)
Each object's interactions are isolated
Interactions cannot reference global or semi-global BHAVs

Typical Reference Counts:

Object Size	Interactions	References
Small	1–3	2–6
Medium	4–8	8–16
Large	10–15	20–30+

💡 Example: AlarmClock with 4 interactions generates 5 references (4 action + 1 TTAs).

Chapter 7: GLOB Semi-Globals

GLOB Overview

GLOB references a shared semi-global IFF file containing common resources.

Property	Value
Type code	`GLOB`
Limit	One per IFF file
Common ID	128

GLOB Structure

Offset	Size	Description
0	var	Semi-global filename (various formats)
var	opt	Filler (0xA3 padding)

String Encoding Formats

Format	Detection	Structure
1	Resource size = string	Raw string, no terminator
2	First byte ≥ 48	Null-terminated + padding
3	First byte < 48	Count byte + string + padding

Examples:

"CarGlobals" → carglobals.iff
"CybernauticsGlobals" → cybernauticsglobals.iff

The reference is case-insensitive.

Chapter 8: SLOT Routing Positions

SLOT Overview

SLOT defines character routing and approach positions for objects — where Sims stand, sit, or navigate to when using an object.

Property	Value
Type code	`SLOT`
Versions	4, 6, 7, 8, 9, 10
Unit	1/16 of a tile

Header (16 bytes)

Offset	Size	Field
0	4	Reserved (0)
4	4	Version
8	4	Identifier (`TOLS` little-endian)
12	4	Slot count

Slot Types

Type	Frequency	Purpose
0	24.7%	Support slots (non-routing)
1	1.6%	Specialized (rare, elevated)
3	73.5%	Routing (character navigation)

Core Slot Descriptor

Offset	Size	Field	Description
0	2	type	0, 1, or 3
2	4	xoffset	X position (float)
6	4	yoffset	Y position (float)
10	4	altoffset	Z/height (float)
14	4	standing	Standing preference
18	4	sitting	Sitting preference
22	4	ground	Lying preference
26	4	rsflags	Routing/facing flags
30	4	snaptargetslot	Target slot (-1 = none)

Additional fields by version:

Version	Bytes	Added Field
4	34	snaptargetslot
6	54	flags
7	58	gradient
8	62	height
9	66	facing
10	70	resolution

rsflags Bit Definitions

Bit	Value	Meaning
0	1	N (0°)
1	2	NE (45°)
2	4	E (90°)
3	8	SE (135°)
4	16	S (180°)
5	32	SW (225°)
6	64	W (270°)
7	128	NW (315°)
8	256	Allow any rotation
9	512	Absolute coordinates
11	2048	Ignore rooms
12	4096	Snap to direction
13	8192	Random scoring

Preference Values

Value	Meaning
0	Disabled
1	Weak preference
10	Moderate
100, 1000	Strong preference

Example:

standing=1, sitting=1000, ground=0
→ Character strongly prefers sitting
→ Will not lie down
→ Standing is low priority

Coordinate System

Axis	Direction	Unit
X	Positive = left	1/16 tile
Y	Positive = back	1/16 tile
Z	Height	1/16 tile

Reference point is object center (0, 0, 0).

Chapter 10: Reference Semantics

Overview

Objects define behavior through resource references — pointers to BHAV code, string data, graphics, and constants. This chapter documents which fields contain references and how the system resolves them.

Reference Types

Type	Byte Size	Purpose	Scope
BHAV ID	2	Subroutine address	Addresses 0-8191+
Resource ID	2	Graphics, animation, text	Per-file ID
STR Index	2–4	String table lookup	Per-file IFF
GLOB Ref	Variable	Semi-global IFF filename	File system

OBJD Reference Fields

OBJD contains 30+ reference fields driving object behavior:

Entry Points (6 core fields)

Field	Offset	Size	Target	Purpose
`BHAV_Init`	16	2	BHAV	Object initialization
`BHAV_MainID`	18	2	BHAV	Main loop behavior
`BHAV_Load`	20	2	BHAV	Household load
`BHAV_Cleanup`	22	2	BHAV	Shutdown cleanup
`BHAV_QueueSkipped`	24	2	BHAV	Queue skip response
`BHAV_AllowIntersectionID`	26	2	BHAV	Multi-tile intersection

Lifecycle Events

Field	Offset	Size	Target	Purpose
`BHAV_Place`	28	2	BHAV	Object placement
`BHAV_Portal`	30	2	BHAV	Door/portal activation
`BHAV_LevelInfo`	32	2	BHAV	Level information request
`BHAV_RoomChange`	34	2	BHAV	Room changed (moved)
`BHAV_DynamicMultiTileUpdate`	36	2	BHAV	Tile update

Slot & Graphics

Field	Offset	Size	Target	Purpose
`SlotID`	20	2	SLOT	Routing positions
`BaseGraphicID`	3	1	DGRP	Default state graphics
`NumGraphics`	4	1	DGRP	Total animation states
`ThumbnailGraphic`	75	2	SPR	Catalog thumbnail

String Resources

Field	Offset	Size	Target	Purpose
`BodyStringID`	19	2	STR#	Character string table
`CatalogStringsID`	41	2	STR#	Catalog description

Constants & Tables

Field	Offset	Size	Target	Purpose
`TreeTableID`	7	2	TTAB	Interactions (pie menu)
`AnimationTableID`	(OBJf)	—	TTAB	Animation control
`InteractionGroup`	8	2	BCON	Interaction categorization

BHAV Reference Patterns

Subroutine Calls (Opcodes ≥ 256)

When a BHAV instruction has opcode ≥ 256, it's a call to another BHAV:

Call Pattern:

Instruction opcode = target_BHAV_ID + 256

Example:
  Opcode 4096 = BHAV ID 3840 (local range)
  Opcode 256  = BHAV ID 0 (global range)

Address Decoding:

Range	Call Type	Computation
256–4095	Global call	target = opcode - 256
4096–8191	Local call	target = opcode - 4096
8192+	Semi-global	target = opcode - 8192 (in GLOB file)

Operand References (Opcode < 256)

Some operands encode references to external resources:

Primitive Opcode	Operand Encoding	Reference Type
2 (Expression)	Operand[4-7]	BCON constant ID or literal
44 (Animate)	Operand[0-3]	Animation group ID
42 (Create Object)	Operand[0-3]	Object GUID or instance
41 (Set Balloon)	Operand[4-7]	STR# index

Reference Classification:

Hard references: BHAV subroutine calls (required to exist)
Soft references: BCON/STR lookups (may fail gracefully)
Conditional references: Created objects (instantiation-time)

TTAB Reference Extraction

TTAB defines pie menu interactions with embedded BHAV references:

Per-Interaction References:

Field	Bytes	Purpose	Scope
`Guard Function`	2	Condition check	Local BHAV (4096+)
`Action Function`	2	Interaction exec	Local BHAV (4096+)
`String Table Index`	4	Menu text (V5+)	TTAs string IDs

Reference Generation:

Per interaction: 2 BHAV references (guard + action) + optional TTAs
Typical object:  4–8 interactions = 8–16 BHAV refs + 4–8 TTAs refs

SPR/DGRP Reference Extraction

SPR/SPR2 graphics resource reference PALT (palette):

SPR → PALT Mapping:

Field	Purpose	Reference Type
Palette ID	Color table for sprite	Hard reference

DGRP → Sprite Mapping:

Field	Purpose	Reference Type
Image ID	SPR/SPR2 resource ID	Hard reference

Graphics Extraction Priority:

OBJD.BaseGraphicID → DGRP (default state)
DGRP entries → SPR/SPR2 (animation frames)
SPR/SPR2 entries → PALT (color palette)

STR# Reference Extraction

String resources are scattered throughout object definitions:

STR# Reference Sources:

Source	Field	String Type	Purpose
OBJD	BodyStringID	Character strings	Sim descriptions
OBJD	CatalogStringsID	Catalog description	Buy mode display
TTAB (V5+)	String Table Index	Menu text	Pie menu options
TPRP	Label entries	Property labels	Tuning tool display

Expected Frequencies:

Every object: 1–2 STR# references (catalog)
Interactive objects: +1 STR# per 2–4 interactions (menu text)
Tuned objects: +1 TPRP (optional)

GLOB Semi-Global Resolution

GLOB references a shared semi-global IFF file:

GLOB Resolution Chain:

GLOB raw name
  ↓
Lowercase + ".iff" extension
  ↓
Search path: [Custom files] → [Expansions] → [Base game]
  ↓
Loaded file in memory (cached)
  ↓
Semi-global BHAV/BCON available to all objects

Common Semi-Globals:

Filename	Scope	Contents
GlobalGlobals.iff	Game-wide	Universal functions
CarGlobals.iff	Vehicle behaviors	Car interaction code
CybernauticsGlobals.iff	Maid robot	Robot-specific routines
PetsGlobals.iff	Pets	Animal AI

Reference Validation Rules

Hard Reference Rules:

Must exist in scope: Dangling pointers = object doesn't work
Scope matching: Local TTAB entries must call local BHAV (4096–8191)
No circular dependencies: Call graphs must be acyclic (runtime limit)
GUID uniqueness: Only one OBJD per GUID globally (silently hides duplicates)

Soft Reference Rules:

Optional BCON: Missing constant = literal 0 (silent failure)
Optional STR#: Missing string = blank text (graceful fallback)
Optional GLOB: Missing file = function unavailable (logged)

Reference Scope Diagram

OBJECT REFERENCE SCOPES

┌──────────────────────────────────────────────────────────┐
│                     OBJECT FILE (IFF)                    │
│  ┌────────────────────────────────────────────────────┐  │
│  │                   LOCAL SCOPE                       │  │
│  │         (Addresses 4096–8191)                       │  │
│  │  ┌──────────────────────────────────────────────┐  │  │
│  │  │ BHAV 4096: Init (called from OBJD)           │  │  │
│  │  │ BHAV 4097: Main                              │  │  │
│  │  │ BHAV 4098: Guard (called from TTAB)          │  │  │
│  │  │ BHAV 4099: Action (called from TTAB)         │  │  │
│  │  └──────────────────────────────────────────────┘  │  │
│  │                       │                             │  │
│  │         ┌─────────────┴─────────────┐              │  │
│  │         ▼                           ▼              │  │
│  │  ┌──────────────────────┐  ┌─────────────────┐    │  │
│  │  │ BCON 0-65            │  │ STR# Index 0-N  │    │  │
│  │  │ (Constants)          │  │ (Menu text)     │    │  │
│  │  └──────────────────────┘  └─────────────────┘    │  │
│  │                                                     │  │
│  │  ┌──────────────────────────────────────────────┐  │  │
│  │  │ TTAB Interaction Table                       │  │  │
│  │  │ ┌────────────────────────────────────────┐  │  │  │
│  │  │ │ Interaction 0: Guard=4098, Action=4099│  │  │  │
│  │  │ │ Interaction 1: Guard=4100, Action=4101│  │  │  │
│  │  │ └────────────────────────────────────────┘  │  │  │
│  │  └──────────────────────────────────────────────┘  │  │
│  └────────────────────────────────────────────────────┘  │
│                                                          │
│  ┌────────────────────────────────────────────────────┐  │
│  │ GLOBAL REFERENCES (Addresses 256–4095)             │  │
│  │  ↓ Global.iff                                      │  │
│  │  BHAV 256: SetComfort (shared)                     │  │
│  │  BHAV 261: SetEnergy (shared)                      │  │
│  └────────────────────────────────────────────────────┘  │
│                                                          │
│  ┌────────────────────────────────────────────────────┐  │
│  │ SEMI-GLOBAL REFERENCES (Addresses 8192+)           │  │
│  │  ↓ GLOB reference → CarGlobals.iff                │  │
│  │  BHAV 8192: CarEntry (shared across cars)         │  │
│  │  BHAV 8193: CarExit (shared across cars)          │  │
│  └────────────────────────────────────────────────────┘  │
│                                                          │
│  ┌────────────────────────────────────────────────────┐  │
│  │ PRIMITIVES (Opcodes 0–63)                          │  │
│  │  Built-in VM operations (no external refs)         │  │
│  └────────────────────────────────────────────────────┘  │
└──────────────────────────────────────────────────────────┘

Chapter 11: Virtual Machine

VM Overview

The SimAntics Virtual Machine executes BHAV subroutines to drive all gameplay — a multi-threaded engine managing every object's behavior.

Property	Value
Architecture	Multi-threaded, cooperative
Tick rate	15 ticks = 1 simulated minute
Scheduling	Per-object threads, yield-based

Core Architectural Principle

Event-driven, not call-driven. The engine owns execution, BHAVs respond to events.

This means:

No inter-BHAV function calls exist in actual game files
BHAVs communicate via state variables (attributes)
OBJf maps lifecycle events to BHAV entry points
The polling loop pattern dominates (52% of all BHAVs)

OBJf Entry Points

The OBJf chunk is THE entry point mechanism — it maps lifecycle events to BHAV IDs:

Event	ID	When Called	Purpose
Init	0	Object creation	Setup state variables
Main	1	Every frame	Primary controller
Cleanup	2	Object deletion	Free resources
Load	3	Save file loaded	Restore state
Reset	4	State reset	Clear temp flags

💡 To understand any object: Find OBJf Event 1 (Main) → that BHAV ID is the autonomy core.

Threading Model

Property	Description
Threading	Each object has its own thread
Cooperation	Threads yield voluntarily per tick
Display rate	15 Hz update

Subroutine Address Ranges

Range	Hex	Type
0–63	0x0000–003F	Primitives (built-in)
256–4095	0x0100–0FFF	Global (Global.iff)
4096–8191	0x1000–1FFF	Local (object file)
8192+	0x2000+	Semi-global (GLOB file)

Data Scopes

Per-Invocation (Call Stack):

Literals, parameters, locals, array index

Per-Thread (Object Context):

My object ID, stack object, neighbor ID

Per-Object (Instance):

Temps, definition, attributes, motives, slots

Per-File (IFF Scope):

Constants, subroutines, strings, semi-global ref

Global (Shared):

Global.iff constants and subroutines

Key Primitives (Opcodes 0-63)

Core:

Op	Hex	Name	Purpose
0	0000	Yield	Sleep/yield thread
1	0001	Generic Sim Call	VM sub-operation
2	0002	Expression	Arithmetic/comparison (55%)
3	0003	Find Best Action	Select optimal action
4	0004	Grab	Acquire object
5	0005	Drop	Release object
8	0008	Random	Random number

Animation & Display:

Op	Hex	Name	Purpose
6	0006	Change Article	Change suit/accessory
7	0007	Update	Refresh display
22	0016	Look Towards	Change facing
41	0029	Set Balloon	Thought/speech bubble
44	002C	Animate	Play animation

Navigation:

Op	Hex	Name	Purpose
11	000B	Distance To	Calculate distance
12	000C	Direction To	Calculate heading
45	002D	Goto Routing Slot	Move to position
46	002E	Snap	Align to position

Object Management:

Op	Hex	Name	Purpose
18	0012	Remove Instance	Delete object
42	002A	Create Object	Instantiate object
43	002B	Drop Onto	Place on surface

Instruction Statistics

Category	Count	Percentage
Expression	55,088	57%
Animate	4,694	5%
Play Sound	4,050	4%
Routing	749	1%
Other	31,006	33%
Total	95,487	100%

Expression (arithmetic/comparison) dominates — over half of all instructions.

Key Parsing Insights

Every instruction has TWO exit paths (true/false pointers) — code is a graph, not linear
Opcode ≥ 256 = subroutine call — the opcode value IS the BHAV ID
Operand field (8 bytes) is context-dependent — interpretation varies by opcode
0xFE/0xFF pointers = return — special flow control values (254=true, 255=false)
No opcode 0x0001 (BHAV Call) in actual TS1 files — proves no function calls

Global Subroutines (Samples)

ID	Name	Purpose
256	Set graphic	Display change
261	SetComfort	Increase comfort
266	SetEnergy	Increase energy
280	Idle	Standard waiting
370	Animated idle for	Timed pause
419	Wander	Autonomous movement

Cross-Reference Diagram

OBJECT SYSTEM ARCHITECTURE

┌─────────────────────────────────────────────────────────────┐
│                         OBJD                                 │
│              (Object Definition - Master)                    │
│  ┌─────────────────────────────────────────────────────┐    │
│  │ GUID │ Price │ Categories │ Graphics │ Type        │    │
│  └───────────────────────┬─────────────────────────────┘    │
│                          │                                   │
│          ┌───────────────┼───────────────┐                  │
│          ▼               ▼               ▼                  │
│    ┌──────────┐    ┌──────────┐    ┌──────────┐            │
│    │   OBJf   │    │   TTAB   │    │   SLOT   │            │
│    │  Entry   │    │ Interact │    │ Routing  │            │
│    │  Points  │    │  Menus   │    │ Positions│            │
│    └────┬─────┘    └────┬─────┘    └──────────┘            │
│         │               │                                   │
│         ▼               ▼                                   │
│    ┌──────────┐    ┌──────────┐                            │
│    │   BHAV   │    │   TTAs   │                            │
│    │ Behavior │    │Menu Text │                            │
│    │   Code   │    │          │                            │
│    └────┬─────┘    └──────────┘                            │
│         │                                                   │
│         ▼                                                   │
│    ┌──────────┐    ┌──────────┐                            │
│    │   BCON   │◀───│   TRCN   │                            │
│    │Constants │    │  Labels  │                            │
│    └──────────┘    └──────────┘                            │
│                                                             │
│    ┌──────────┐                                            │
│    │   GLOB   │───▶ Semi-global IFF (shared resources)     │
│    └──────────┘                                            │
└─────────────────────────────────────────────────────────────┘

VIRTUAL MACHINE EXECUTION

┌─────────────────────────────────────────────────────────────┐
│                    VM SCHEDULER (15 Hz)                      │
│  ┌─────────┐  ┌─────────┐  ┌─────────┐  ┌─────────┐        │
│  │ Thread  │  │ Thread  │  │ Thread  │  │ Thread  │  ...   │
│  │ (Obj 1) │  │ (Obj 2) │  │ (Obj 3) │  │ (Obj N) │        │
│  └────┬────┘  └────┬────┘  └────┬────┘  └────┬────┘        │
│       │            │            │            │              │
│       └────────────┴────────────┴────────────┘              │
│                          │                                   │
│                          ▼                                   │
│  ┌─────────────────────────────────────────────────────┐    │
│  │              SUBROUTINE ADDRESS SPACE                │    │
│  │  0x0000-003F: Primitives (64 built-in opcodes)      │    │
│  │  0x0100-0FFF: Global subroutines (Global.iff)       │    │
│  │  0x1000-1FFF: Local subroutines (object file)       │    │
│  │  0x2000+    : Semi-global subroutines (GLOB ref)    │    │
│  └─────────────────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────────────┘

Part III Complete — Continue to Part IV: Graphics & Animation

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Part III: Object System

Document Navigation

Key Terms

Chapter 1: OBJD Object Definition

Overview

Object Roles

Key Field Groups

Identity (Offsets 0-4)

GUID (Offsets 14-15)

Object Type (Offset 9)

Pricing (Offsets 18, 34-38)

Catalog Categories (Offsets 39-40)

Motive Ratings (Offsets 82-88)

Skill Flags (Offset 89)

Build Mode Types (Offset 69)

Expansion Sort Fields

Complete Field Index

Chapter 2: OBJf Object Functions

OBJf Overview

Structure

Guard vs Action Functions

Entry Point Index

Chapter 3: BHAV Behaviors

BHAV Overview

Core Architecture Truth

BHAV Classification

Physical Structure

Header (12 bytes)

Instruction Format (12 bytes)

Flow Control Addresses

Operand Interpretation

Subroutine Address Ranges

Key Primitives (Opcodes 0-63)

Complete Opcode Reference

Opcodes by Category

Virtual Machine Threading Model

Execution Model

Polling Loop Pattern (ROLE BHAVs)

Yield Points

State Communication

Chapter 4: BCON & TRCN Constants

BCON: Behavioral Constants

TRCN: Trait Constants (Labels)

Chapter 5: TPRP Trait Properties

Chapter 6: TTAB Interactions

TTAB Overview

Header

Core Fields Per Interaction

Flags Bitfield

Motive Entries (16 per interaction)

Attenuation Settings

Guard & Action Pattern

Reference Types Generated

Chapter 7: GLOB Semi-Globals

GLOB Overview

GLOB Structure

String Encoding Formats

Chapter 8: SLOT Routing Positions

SLOT Overview

Header (16 bytes)

Slot Types

Core Slot Descriptor

rsflags Bit Definitions

Preference Values

Coordinate System

Chapter 10: Reference Semantics

Overview

Reference Types

OBJD Reference Fields

Entry Points (6 core fields)

Lifecycle Events

Slot & Graphics

String Resources

Constants & Tables