Sonic the Hedgehog 2 (16-bit)/RAM Editing

Sonic Community Hacking Guide Sonic the Hedgehog 2 (16-bit)
Art
Uncompressed art Nemesis format art Kosinski format art Palette editing Pattern load requests
Objects
Sounds and objects Object Pointer list Sprite mappings Dynamic PLCs
Levels
Object placement Ring placement Level layout 16x16 block mappings 128x128 block mappings Level specific info
Text
Two-player mode text Options text Level select text © 1992 SEGA text Credits/iIntro text Title card text
Music
Pointer format Header format DAC samples Master playlist and compression Music pointers
RAM
Main system memory locations Object status table format
Miscellaneous
Game configuration Cheats editings Debug mode Demo recording

Main System Memory locations

This is a map of 68k memory as used by the main gameplay engine. Note that any numbers entered (for example, score or number of rings) will have to be converted to hex first.

These are the offsets in RAM. To convert them to Genecyst savestate offsets, add $2478.

RAM offset	Git label	Description
$0000 - $7FFF	Chunk_Table	Metablock table
$8000 - $8FFF	Level_Layout	Level layout
$9000 - $A9FF	Block_Table	Block table
$AA00 - $A?FF	Decomp_Buffer	Decompression buffer
$AC00 - $AFFF	Sprite_Table_Input	Sprite table input. Intermediate storage for sprite attribute table data destined for $DD00 or $F800.
$B000 - $D5FF	Object_RAM	Object attribute table
$D600 - $D8FF	Primary_Collision	Primary collision index
$D900 - $DBFF	Secondary_Collision	Secondary collision index
$DC00 - $DCFB	VDP_Command_Buffer	VDP command buffer. Stores up to 18 sets of queued up VDP commands to be issued later.
$DCFC - $DCFF	VDP_Command_Buffer_Slot	VDP command buffer free slot. Stores the address of the first available empty place in the VDP command buffer.
$DD00 - $DF7F	Sprite_Table_2	Sprite attribute table buffer for the bottom split screen in 2-player mode.
$E000 - $E3FF	Horiz_Scroll_Buf	Horizontal scroll buffer
$E400 - $E4FF	Sonic_Stat_Record_Buf	Sonic's statistic recording buffer, used by Tails' AI.
$E500 - $E5FF	Sonic_Pos_Record_Buf	Sonic's invincibility star position table
$E600 - $E6FF	Tails_Pos_Record_Buf	Tails' invincibility star position table
$E800 - $EDFF	Ring_Positions	Ring Layout
$EE00-$EE01	Camera_X_pos	Camera's X position, as measured from the top left corner of the Act.
$EE04-$EE05	Camera_Y_pos	Camera's Y position from the same point.
$EE06-$EE0B		Unknown
$EE0C-$EE0D	Camera_BG_Y_pos	Variable used by the software scroll managers. Its exact purpose is not known.
$EE0E-$EEC5		Unknown
$EE20-$EE21	Camera_X_pos_P2	Camera's X position, as measured from the top left corner of the Act, for player 2.
$EE24-$EE25	Camera_Y_pos_P2	Camera's Y position from the same point, for player 2.
$EEC6-$EEC7	Camera_Max_Y_pos	Screen Y end location for Sonic; the maximum value for camera Y position.
$EEC8-$EEC9	Camera_Min_X_pos	Screen X start location for Sonic; minimum value for camera X position. Should be 0.
$EECA-$EECB	Camera_Max_X_pos	Screen X end location for Sonic; should be at least $30 less than the end of the level, otherwise, Sonic will fall off the screen.
$EECC-$EECD	Camera_Min_Y_pos	Screen Y start location. Note that if $FF00 is placed in both the start and the end, the screen will be Y wrapped. Y wrapping should not be used on levels with water - note what happened in the beta's Hidden Palace Zone.
$EECE-$EECF	Camera_Max_Y_pos_now	Screen Y end location for Sonic; the maximum value for camera Y position. Like $EEC6, but changes slowly instead of instantly when the level Y boundary changes.
$EED2-$EED3	Sonic_Pos_Record_Index	Index into Sonic's statistics recording buffer and invincibility star position table.
$EED6-$EED7	Tails_Pos_Record_Index	Index into Tails' invincibility star position table.
$EED8	Camera_Y_pos_bias	Camera Y position bias.
$EEDA	Camera_Y_pos_bias_P2	Camera Y position bias for Tails.
$EEDF	Dynamic_Resize_Routine	Routine counter for Dynamic Screen Resizing. (Dynamic Level Events)
$EEF8-$EEF9	Tails_Min_X_pos	Screen X start location for Tails; minimum value for camera X position. Should be 0.
$EEFA-$EEFB	Tails_Max_X_pos	Screen X end location for Tails; should be at least $30 less than the end of the level, otherwise, Tails will fall off the screen.
$EEFE-$EEFF	Tails_Max_Y_pos	Screen Y end location for Tails; the maximum value for camera Y position.
$F000-$F07F	Underwater_target_palette	Underwater target palette.
$F080-$F0FF	Underwater_palette	Underwater palette.
$F100-$F5FF		Unused
$F600	Game_Mode	Master level trigger. Tells the game what it should be doing. Values: $00 - GameModeID_SegaScreen - Sega logo $04 - GameModeID_TitleScreen - Title screen $08 - GameModeID_Demo - Demo (return to title screen at 27 seconds) $0C - GameModeID_Level - Normal level (Level loop, when it has been loaded) $10 - GameModeID_SpecialStage - Special stage $14 - GameModeID_ContinueScreen - Continue screen $18 - GameModeID_2PResults - 2P vs. result $1C - GameModeID_2PLevelSelect - 2P vs. level select $20 - GameModeID_EndingSequence - Game end sequence $24 - GameModeID_OptionsMenu - Options menu $28 - GameModeID_LevelSelect - Level select The MSB is a loading routine flag. It only matters for some game modes. It won't have any effect when changing modes because it's filtered out, but the corresponding routine does pay attention to it...
$F602	Ctrl_1_Held_Logical	In-game Controller 1 held state. Same as F604, but it only updates during the main game loop, and not while paused, or a cutscene is running.
$F603	Ctrl_1_Press_Logical	In-game Controller 1 pressed state. Same as F602, but only tells which buttons are being pressed newly this frame.
$F604	Ctrl_1_Held	This bitfield tells which button(s) on Controller 1, if any, are currently pressed. Format is: Bit 0 - Up Bit 1 - Down Bit 2 - Left Bit 3 - Right Bit 4 - B Bit 5 - C Bit 6 - A Bit 7 - Start This is updated every frame.
$F605	Ctrl_1_Press	Same as $F604, but only tells which buttons are being pressed newly this frame.
$F606	Ctrl_2_Held	Same as $F604, but for Controller 2.
$F607	Ctrl_2_Press	Same as $F606, but only tells which buttons are being pressed newly this frame for Controller 2.
$F614	Demo_Time_left	Demo time left & Time until demo starts from title screen.
$F624-$F625	Hint_counter_reserve	Always contains a VDP command consisting of a write to register $0A (H-Int register). This controls which line H-Int occurs on, and is executed every V-Int.
$F62A	Vint_routine	V-Int routine to run. Goes in units of 2, like most other routine counters.
$F636	RNG_seed	RNG seed (used for pseudo-random number generation).
$F63A-$F63B	Game_paused	Game paused flag.
$F640	DMA_data_thunk	DMA data thunk: every final DMA command word gets written here and copied back out, as required by the Megadrive hardware.
$F648-$F649	Water_Level_2	Current water level. Should be a valid Y-axis value. Remember, the top of the level is $0000.
$F64C	Water_on	Water on: seems to be a copy of $F730.
$F64D	Water_routine	Water routine counter
$F64E	Water_fullscreen_flag	Flag which is set when Sonic is fully submerged in water and the underwater palette has to be displayed throughout the entire screen
$F64F	Do_Updates_in_H_int	Flag which is set when H-Int is set to occur at a line above line $5C. The only effect this has is that DemoTime is called from inside H-Int instead of from inside V-Int
$F650-$F651		The level that the water should be at. If this is different than the value above, the water will move until they are the same.
$F652		Water level change speed. If set to $00, the water level won't change.
$F65E	Palette_timer	Super Sonic palette counter. Decremented with every frame. How it works, exactly, is not known.
$F65F	Super_Sonic_palette	Sets the rotating palette for Super Sonic.
$F66A	Ctrl_2_Held_Logical	In-game Controller 2 held state. Same as $F602, but for controller 2
$F66B	Ctrl_2_Press_Logical	In-game Controller 2 pressed state. Same as $F66A, but only tells which buttons are being pressed newly this frame.
$F66C-$F66D	Sonic_Look_delay_counter	Sonic looking up/ducking counter. Starts off at 0 and is incremented each frame Sonic is looking up/ducking. When this reaches $78, the camera starts to scroll. Reset to 0 upon release of the up/down button.
$F66E-$F66F	Tails_Look_delay_counter	Same as above, only for player 2.
$F670-$F671	Super_Sonic_frame_count	Super Sonic ring drain counter. This is set to 60 ($3C). After each frame, the code subtracts 1. One ring is removed when this counter reaches zero; in other words, each second.
$F680-$F6DF	Plc_Buffer	A buffer for pattern loading cues (requests). Each entry in this consists of one longword followed by one word, the longword being the location in ROM of the compressed art, and the word being the VRAM location to decompress to. Can store a maximum of 16 entries, but a coding error in the clearing routine means that storing a PLC in the last slot screws everything up, so effectively only 15 requests can be stored at one time.
$F6E0-$F6E3	Plc_Buffer_Only_End	The address in ROM of the decompression routine to be used for the art
$F6E4-$F6F7	Plc_Buffer_Reg4	Used by the PLC routines using decompression. No idea what their function is, although it seems they get passed in as parameters to the decompression routine, and are stored updated when the routine returns.
$F6F8-$F6F9	Plc_Buffer_Reg18	The total number of tiles left to be decompressed for the current piece of art
$F6FA-$F6FB	Plc_Buffer_Reg1A	The number of tiles left to be decompressed in the current frame
$F700-$F701		Seems to be set to $0001 when in a Sonic & Tails game. Set to $0000 when not a Sonic & Tails game.
$F702-$F703	Tails_control_counter	Tails control counter. Counts how long until the CPU takes control.
$F704-$F705	Tails_respawn_counter	Tails respawn counter.
$F708-$F709	Tails_CPU_routine	Tails CPU routine.
$F70A-$F70B	Tails_CPU_target_x	Tails CPU target X position. Tells Tails where Sonic's X position is so he can fly back to him.
$F70C-$F70D	Tails_CPU_target_y	Tails CPU target Y position. Tells Tails where Sonic's Y position is so he can fly back to him.
$F70E-$F70F	Tails_interact_ID	Tails interact ID. Object ID of last object Tails stood on.
$F710	Rings_manager_routine	Routine counter for the rings manager.
$F711	Level_started_flag	Level started flag. Set to 1 as soon as the player first gets control in the level.
$F712	Ring_start_addr	Address (inside the ring layout table) of the first ring whose X position is greater than or equal to the current camera X value.
$F714	Ring_end_addr	Address (inside the ring layout table) of the first ring whose X position is greater than or equal to the current camera X value + $150
$F716	Ring_start_addr_P2	$F712 for Player 2.
$F718	Ring_end_addr_P2	$F714 for Player 2.
$F72C	Dirty_flag	Dirty flag. Setting this causes the whole screen to redraw (once) instead of only the part that's scrolling into the screen.
$F730	Water_flag	Water flag. Must be set for any of the other water variables to have any effect. Note that levels without water don't have an underwater palette; you must set one or everything below the water level will be black.
$F732-$F733	Demo_button_index_2P	Demo button index for Player 2.
$F734	Demo_press_counter_2P	Frames remaining until next button press in a demo for Player 2.
$F760-$F761	Sonic_top_speed	Sonic's top speed
$F762-$F763	Sonic_acceleration	Sonic's acceleration
$F764-$F765	Sonic_deceleration	Sonic's deceleration
$F766	Sonic_LastLoadedDPLC	Sonic's current mapping frame number.
$F76C	Obj_placement_routine	Object placement function's subroutine counter
$F76E-$F76F	Camera_X_pos_last	Unknown
$F770-$F773 $F774-$F777 $F778-$F77B $F77C-$F77F	Obj_load_addr_right	Sprite loading addresses. Tells the game where in the ROM to get sprite info.
$F780-???	unk_F780	Something
$F78C-$F78D	Camera_X_pos_last_P2	Unknown
$F790-$F791	Demo_button_index	Demo button index for Player 1.
$F792	Demo_press_counter	Frames remaining until next button press in a demo for Player 1.
$F796-$F799	Collision_addr	Pointer to primary collision data in RAM.
$F7A7	Boss_defeated_flag	Boss defeated flag. Set to $1 once boss is defeated.
$F7AA	Current_Boss_ID	Seems to be clear during normal play, but set to some value during a boss fight.
$F7CC	Control_Locked	Controller lock. Normally the player object overwrites $F602 with the actual controller state, but setting this flag will prevent that. Used when the game will supply its own movement script.
$F7D0-$F7D1	Chain_Bonus_counter	Bonus counter. Increments upon destruction of a destroyable object, and is used to determine how many points the destruction should give. Resets when the player touches the ground.
$F7D2-$F7D3	Bonus_Countdown_1	Time bonus counter at the end of level result screen/Player 1 ring bonus counter at the end of special stage result screen
$F7D4-$F7D5	Bonus_Countdown_2	Ring bonus counter at the end of level result screen/Player 2 ring bonus counter at the end of special stage result screen
$F7D6	Update_Bonus_score	Flag determines if the bonus counters need to be updated.
$F7DA-$F7DB	Camera_X_pos_coarse	Counts the number of times the camera has scrolled to the right by one full screen width from its previous position - initial value is $FF80 and then counts up like: $FF80,$0000,$0080,$0100,$0180,etc.
$F800-$FA7F	Sprite_Table	Sprite attribute table buffer.
$FA80-$FAFF		Unused (although due to the way Sonic 2's BuildSprites is designed, it is possible for the sprite attribute table buffer to spill over into this area)
$FB00-$FB7F	Normal_palette	Palette.
$FB80-$FBFF	Target_palette	Target palette.
$FC00 - $FCFF	Object_Respawn_Table	Object respawn table
$FE00	System_Stack	Start of the system stack. Note that the stack grows up rather than down. This means that when something is pushed onto the stack, the SP is decremented, and when something is popped from it, the SP is incremented.
$FE02-$FE03	Level_Inactive_flag	Level restart flag.
$FE04-$FE05	Timer_frames	Level frame timer.
$FE06	Debug_object	Object currently selected in debug mode.
$FE08-$FE09	Debug_placement_mode	Object placement mode flag.
$FE10	Current_Zone	The current Zone. This is the value assigned to the Zone, not its position in the level list.
$FE11	Current_Act	Act number
$FE12	Life_count	Number of lives.
$FE16	Current_Special_Stage	Current special stage.
$FE17	Current_Special_Act	Current segment in special stage.
$FE18	Continue_count	Number of continues.
$FE19	Super_Sonic_flag	Super Sonic flag. Setting this will load the Super Sonic tiles, adjust Sonic's jump height, and start draining rings, but it will not load the rotating palette, change acceleration, max speed, or deceleration, or make him invincible.
$FE1A	Time_Over_flag	Flag which is set when Player 1 has a time over
$FE1B	Extra_life_flags	This bitfield tells the game if the player has collected extra lives from rings. Bit 0 - 100 rings life collected Bit 1 - 200 rings life collected Bit 2 - Unused Bit 3 - Unused Bit 4 - Unused Bit 5 - Unused Bit 6 - Unused Bit 7 - Unused
$FE1C	Update_HUD_lives	Flag determines if the lives counter needs to be updated
$FE1D	Update_HUD_rings	Flag determines if the rings counter needs to be updated
$FE1E	Update_HUD_timer	Flag determines if the timer needs to be updated
$FE1F	Update_HUD_score	Flag determines if the score counter needs to be updated
$FE20-$FE21	Ring_count	Ring count. This is also applied in Special Stages.
$FE23	Timer_minute	Minutes on clock. Should not go above $09, or the clock will look like shit.
$FE24	Timer_second	Seconds. This one shouldn't go above $3B, for the same reason.
$FE25	Timer_frame	Frames. I don't know what'll happen if this goes out of range, but it's probably not good.
$FE26-$FE29	Score	Score (divided by 10)
$FE30	Last_star_pole_hit	Greatest reference number of passed star poles
$FEA0	Logspike_anim_counter	Log-spike animation counter.
$FEA1	Logspike_anim_frame	Log-spike animation frame.
$FEA2	Rings_anim_counter	Rings animation counter.
$FEA3	Rings_anim_frame	Rings animation frame.
$FEA6	Ring_spill_anim_counter	Spilling rings animation counter.
$FEA7	Ring_spill_anim_frame	Spilling rings animation frame.
$FEC0-$FEC1	Tails_top_speed	Tails' max speed
$FEC2-$FEC3	Tails_acceleration	Tails' acceleration
$FEC4-$FEC5	Tails_deceleration	Tails' deceleration
$FEC6	Life_count_2P	Tails' lives in 2P mode
$FEC7	Extra_life_flags_2P	This bitfield tells the game if the player has collected extra lives from rings. Used for Tails in 2P mode. Bit 0 - 100 rings life collected Bit 1 - 200 rings life collected Bit 2 - Unused Bit 3 - Unused Bit 4 - Unused Bit 5 - Unused Bit 6 - Unused Bit 7 - Unused
$FEC8	Update_HUD_lives_2P	Flag determines if the lives counter needs to be updated. Used for Tails in 2P mode.
$FEC9	Update_HUD_rings_2P	Flag determines if the rings counter needs to be updated. Used for Tails in 2P mode.
$FECA	Update_HUD_timer_2P	Flag determines if the timer needs to be updated. Used for Tails in 2P mode.
$FECC	Time_Over_flag_2P	Flag which is set when Player 2 has a time over.
$FED0	Ring_count_2P	Tails' rings in 2P mode.
$FED3	Timer_minute_2P	Minutes on clock for Player 2. Should not go above $09, or the clock will look like shit.
$FED4	Timer_second_2P	Seconds for Player 2. This one shouldn't go above $3B, for the same reason.
$FED5	Timer_frame_2P	Frames for Player 2. I don't know what'll happen if this goes out of range, but it's probably not good.
$FED6-$FED9	Score_2P	Score for Player 2 (divided by 10).
$FEF0-$FEF1	Rings_Collected	Rings collected since level load. Resets if you enter a Special stage. Starts recounting from 0 when level is reentered. Unknown use.
$FEF8	Loser_Time_Left	Seconds remaining for level completion in 2P versus mode.
$FEF9		Centiseconds remaining for level completion in 2P versus mode.
$FF10	Results_Screen_2P	The type of 2P versus results screen being displayed: 0 is end of act results screen 1 is end of zone results screen 2 is end of game results screen (that is when all the zones are completed) 3 is end of special stage results screen 4 is end of all three special stages results screen
$FF20-$FF39	Results_Data_2P	2P results array. The format is 6 bytes per zone (2 per act, the 3rd act is the special stage). The first byte for each act is the number of "wins" for Player 1, while the second byte is the number of "wins" for Player 2. The special stage uses 2 extra bytes: the first is the number of special stages won by Player 1, the second is the number of special stages won by Player 2.
$FF40-$FF41	Perfect_rings_left	Number of rings to collect before a perfect is scored
$FF70-$FF71	Player_mode	Player in game (at the start of the game, $FF72 is copied over to $FF70, so they're mostly identical)
$FF72-$FF73	Player_option	Player option (Sonic and Tails - 0, Sonic alone - 1, Tails alone - 2)
$FF74-$FF75	Two_player_items	2P mode items (all kinds items - 0, teleport only - 1)
$FF80-$FF81	LevSel_HoldTimer	Timer which regulates the speed at which the level select selection changes if up or down is held down. The timer is initialized to $B, and 1 is subtracted from it every frame. If the timer is positive, and the up or down button is being held down, the level select screen selection will not be changed. Only when the timer reaches $FFFF (i.e. -1) is the selection changed. The timer is reset to $B in case of it becoming negative or if up/down is released and pressed again.
$FF82-$FF83	Level_select_zone	Item in level select menu that's selected (set to 16 to see the HPZ picture)
$FF84-$FF85	Sound_test_sound	Sound currently selected in sound test; value retained when options menu is exited
$FF86	Title_screen_option	Selection on Title Screen
$FF88	Current_Zone_2P	Selection on 2 Player Level Select Menu
$FF89	Current_Act_2P	Act number in 2P versus mode
$FF8A-$FF8B	Two_player_mode_copy	Copy of $FFD8 (no idea why there are 2 copies)
$FF8C	Options_menu_box	Box slected in options menu
$FF8E-$FF8F	Total_Bonus_Countdown	Total bonus counter at the end of level result screen/emerald bonus counter at the end of special stage result screen
$FF90-$FF91	Level_Music	Zone music currently playing. Used for quick access when switching music.
$FF92-$FF93	Bonus_Countdown_3	Perfect bonus counter at the end of level result screen
$FF98-$FF99	Game_Over_2P	2P versus mode restart game flag. Set when a game over occurs in 2P versus mode, causes 2P versus results for the current session (from $FF20 to $FF37, last two bytes of result data are skipped) to be wiped, resetting the entire session.
$FFB0	Got_Emerald	Special stage completed flag
$FFB1	Emerald_count	Number of emeralds collected so far
$FFB2-$FFB8	Got_Emeralds_array	Array of finished special stages. Each byte represents one stage.
$FFC0-$FFC3	Next_Extra_life_score	Next score at which an extra life will be awarded to Player 1.
$FFC4-$FFC7	Next_Extra_life_score_2P	Next score at which an extra life will be awarded to Player 2.
$FFC8-$FFC9	Level_Has_Signpost	Level signpost flag.
$FFD0	Level_select_flag	Level select flag
$FFD1	Slow_motion_flag	Slow motion flag
$FFD4-$FFD5	Correct_cheat_entries	Number of correct sounds that have been played for the level select or debug codes
$FFD6-$FFD7	Correct_cheat_entries_2	Same as $FFD4, except it's for the 14 continues or 7 emeralds codes
$FFD8-$FFD9	Two_player_mode	2P mode flag
$FFE1	SFX_to_play	Play specified sound effect. Not sure how it works.
$FFE4	Music_to_play_2	Play specified music. These are the actual playlist values, NOT the sound test values. To convert from sound test to playlist, add $80 to the sound test value. For example, putting in $96 here will play the Super Sonic music; putting in $97 will play the invincibility music.
$FFF0-$FFF1	Demo_mode_flag	Demo mode flag
$FFFA	Debug_mode_flag	Debug mode flag
$FFFC-$FFFF	Checksum_fourcc	Set to 'init' (69 6E 69 74) once the checksum routine has run.

Object Status Table format

The starting offset in RAM for this list is $B000. The first object is always player 1, the second is always player 2. The next few slots are reserved for certain special objects (e.g. title cards), and the slots available for general use start from $B400. Each object is allocated a block of $40 bytes. The beginning of a block is used as a reference point. Note that many of these variables are object-specific - for example, some of them only make sense for Sonic, and some only work on badniks.

Offset	Git label	Description
$00	id	Object number. See the IDs at the object pointer list. Writing an ID over an empty object's memory requests that object to be loaded.
$01	render_flags	Render flags. The bitfield looks like this: Bit 0 is the horizontal mirror flag. If set, the object will be flipped on its horizontal axis. Bit 1 is the vertical mirror flag. Bits 2 and 3 are the coordinate system flags. If both bits are clear, the object will be positioned by absolute screen coordinates. This is used for things like the HUD and menu options. If either bit is set, the object will be positioned by the playfield coordinates, i.e. where it is in a level. Bit 4 is the assume pixel height flag. If clear, the pixel height of each object is assumed to be 32 pixels, otherwise the y-radius of the object (byte $16 of its status table) is also taken to be its pixel height. Bit 5 is the static mappings flag. If set, this indicates that the mappings pointer for this object points directly to the pieces data for this frame, and implies that the object consists of only one sprite piece. Bit 6 is the compound sprites flag. If set, this indicates that the current object's status table also contains information about other child sprites which need to be drawn using the current object's mappings, and also signifies that certain bytes of its status table have different meanings: Byte $B is the mapping frame to display. Byte $E is the pixel width of the object. Byte $14 is the pixel height of the object. Byte $F is the number of child sprites to draw. From byte $10 onwards is the actual data for each child sprite. The format is six bytes per sprite: the first word is the base X position, the next word is the base Y position, the next byte is ignored and the last byte is the mapping frame to display. Bit 7 is the on-screen flag. It will be set if the object is on-screen, and clear otherwise.
$02-$03	art_tile	The lower 11 bits of this represent the starting art block. This is an index into an array of cells; to get the actual address, multiply by $20. Bits 14 and 13 are used to specify the default palette line the sprite uses, and bit 15 is the priority flag - if this is set, the sprite will be given high priority.
$04-$07	mappings	Object's mappings offset
$08-$09	x_pos, x_pixel	If the object is Sonic or Tails, this is the X playfield coordinate. Otherwise: If in playfield positioning mode, it is the X playfield coordinate. If in screen postioning mode, it is the X screen coordinate.
$0A-$0B	x_sub, y_pixel	If the object is Sonic or Tails, this is the X subpixel playfield coordinate. Otherwise: If in playfield positioning mode, it is unused. If in screen positioning mode, it's the Y screen coordinate.
$0C-$0D	y_pos	If the object is Sonic or Tails, this is the Y playfield coordinate. Otherwise: If in playfield positioning mode, it is the Y playfield coordinate. If in screen positioning mode, it is unused.
$0E-$0F	y_pixel	If the object is Sonic or Tails, this is the Y subpixel playfield coordinate. Otherwise: It's unused.
$10-$11	x_vel	X speed
$12-$13	y_vel	Y speed
$14-$15	inertia	Potential speed (inertia).
$16	y_radius	Height/2
$17	x_radius	Width/2
$18	priority	Sprite priority (00 = front).
$19	width_pixels	Width of the object, in pixels
$1A	mapping_frame	Current animation frame to display.
$1B	anim_frame	Current frame in animation script.
$1C	anim	Animation number.
$1D	next_anim	Restart animation flag (when $1D is not equal to $1C, animation restarts)
$1E	anim_frame_duration	Animation frame duration (time until next frame).
$20	collision_flags	Collision response bitfield. Tells what the object will do if hit by the character. The bitfield is in the format TTSS SSSS. TT is the type of collision - 00 is enemy, 01 sets the routine counter to $4, 10 is harm, and 11 seems to be a special thing for the starpole. SSSSSS is the size, lifted from a lookup table in the collision response routine.
$21	collision_property	Custom collision property, for special interaction with Sonic. This is used by bosses, badniks, bumpers and other objects. The way in which this byte is used is different for each object. Bosses use this byte as a hit counter.
$22	status	Status bitfield. Counting from the least significant bit: Bit Hex Description 0 $01 X Orientation. Clear is left and set is right. 1 $02 Y Orientation. Clear is right-side up, and set is upside-down 2 $04 Unknown or unused. 3 $08 Set if Sonic is standing on this object. 4 $10 Set if Tails is standing on this object. 5 $20 Set if Sonic is pushing on this object. 6 $40 Set if Tails is pushing on this object. 7 $80 Unknown or unused. Note that these bits have different meanings for Sonic (see below).
$23	respawn_index	Respawn index reference number, used by badniks, rings and monitors. Each destroyable object is assigned an index number (01, 02, 03 etc.) which refers to a list at $FC00 in the RAM.
$24	routine	Routine counter.
$25	routine_secondary	Second routine counter. This is used for some of the more complicated objects.
$26	angle	Angle.
$27	flip_angle	Second angle (different axis).
$28	subtype	Object subtype. For example, the current monitor selected. See the Object List above for values. Has a different meaning for Sonic and Tails.
$3E-$3F	parent	Parent. Address of the object that spawned this one. Has a different meaning for orphans like Sonic and Tails.
Sonic and Tails-specific variables
Offset	Hg label	Description
$22	status	Special bitfield. Counting from the least significant bit: Bit Hex Description 0 $01 Orientation. Clear is right and set is left. 1 $02 Set if Sonic/Tails is in the air (jump counts). 2 $04 Set if jumping or rolling. 3 $08 Set if Sonic/Tails isn't on the ground but shouldn't fall. (Usually when he is on a object that should stop him falling, like a platform or a bridge.) 4 $10 Set if jumping after rolling. 5 $20 Set if pushing something. 6 $40 Set if underwater. 7 $80 Unused. You can add the hex values together to use multiple settings at once. Also notice that bits 1 and 2 are used in the character object as a second routine counter.
$28	air_left	Seconds of air left. Usually $1E; it decrements every second while the player is underwater. Beeps on $18, $13, and $0E. Countdown starts on $0B.
$29	flip_turned	Invert flipping flag.
$2A	obj_control	Object control flag. Set to 1 if Sonic is under control of another object but can jump out (e.g. flippers), and set to $81 if Sonic is under control of another object and cannot jump out (e.g. CPZ tubes).
$2B	status_secondary	Another bitfield. Bit Hex Description 0 $01 Shield flag. Can be set to create the effect of having a shield, though the graphics will not be loaded. 1 $02 Sets invincibility. Behaves like you would expect. No graphics are loaded when set manually. 2 $04 Speed Shoes flag. (Doesn't have visible effect in game) 3 $08 Unused 4 $10 Unused 5 $20 Unused 6 $40 Unused 7 $80 Sets infinite inertia. While Sonic is in collision with the ground, he will continue moving in the same direction and at the same speed that he was moving before (even if that speed was zero). You can still jump and control him in midair. (A few movement routines are skipped if it's set, which produces this effect).
$2C	flips_remaining	Number of flip revolutions remaining.
$2D	flip_speed	Number of flip revolutions per frame divided by 256.
$2E-$2F	move_lock	Horizontal control lock. Counts down to 0, left and right control on the ground is locked unless it's 0. Used for springs and bumpers and falling down slopes.
$30-$31	invulnerable_time	Remaining invunerability time. Starts at $0078 after Sonic is hit, and seems to decrement every frame until it reaches $0000.
$32-$33	invincibility_time	Remaining time of invincibility.
$34-$35	speedshoes_time	Remaining time of Speed Shoes.
$36	next_tilt	Angle on ground in front of sprite.
$37	tilt	Angle on ground under sprite.
$38	stick_to_convex	Stick to convex surfaces flag (unused in Sonic 2 but fully functional).
$39	spindash_flag	Set if charging a Spin Dash.
$3A-$3B	spindash_counter	Spin Dash counter. Cleared when the Spin Dash is started. After each subsequent "rev", $200 is added to the counter, which then rapidly decreases (the algorithm is to logically shift the value right by five bits and subtract the results from the original). It maxes out at $800. The game looks at the high-order byte to determine how fast the character should move after the dash is released.
$3C	jumping	Set if jumping.
$3D	interact	RAM address of the last object Sonic stood on, minus $B000 and divided by $40.
$3E	top_solid_bit	The bit in the 16x16 entries in the 128x128 block mappings to check for top solidity. Is either $C (for the default collision layer), or $E (for the alternate collision layer).
$3F	lrb_solid_bit	The bit in the 16x16 entries in the 128x128 block mappings to check for left/right/bottom solidity. Is either $D (for the default collision layer), or $F (for the alternate collision layer).