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SCHG:Sonic the Hedgehog 3 & Knuckles/RAM Editing

From Sonic Retro

(Redirected from SCHG:Sonic 3 & Knuckles/RAM Editing)
SCHG: Sonic the Hedgehog 3 & Knuckles
Main Article
Art Editing
Editing Art
Uncompressed Art
Nemesis Format Art
Kosinski Format Art
Palette Editing
Palette Locations
Pattern Load Requests
Object Editing
Editing Objects
Object Pointers
Object Pointer List #1
Object Pointer List #2
Objects not in either list
Sprite Mappings
Dynamic PLCs
Level Editing
Editing Levels
Object Placement
Ring Placement
Level Layout
16x16 Block Mappings
128x128 Block Mappings
Music Editing
Editing Music
Pointer Format
Header Format
DAC Samples
Universal Voice Bank
Music Pointers (Sonic & Knuckles)
Music Pointers (Sonic 3)
RAM Editing
Editing RAM
Main System Memory Locations
Object Status Table Format

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 Description
$0000-$7FFF 128x128 chunk mappings
$8000-$8FFF Level layout
  • $8000-$8001 - Number of chunks for each foreground row
  • $8002-$8003 - Number of chunks for each background row
  • $8004-$8005 - Number of foreground rows
  • $8006-$8007 - Number of background rows
  • $8008-$BFFF - List of pointers to each row, interleaved between foreground and background, following the actual chunk data for each row.
$9000-$A9FF 16x16 block mappings
$AA00-$ABFF Nemesis decompression buffer
$AC00-$AFFF Sprite table input. Consists of 8 different priority levels, each level taking up $80 bytes. The first word of each level is the number of objects currently in that priority level multiplied by 2, and the next $3F words are the addresses in RAM (inside the object RAM space) of the objects on that priority level. The information in this table is processed by BuildSprites to create the actual sprite table
$B000-$CFCB Object attribute table
  • $B000-$B049 - Reserved object SST for Player 1 in levels, miscellaneous purpose otherwise.
  • $B04A-$B093 - Reserved object SST for Player 2 in levels, miscellaneous purpose otherwise.
  • $B094-$B0DC - Reserved object SST for an object, which clears the number of objects in collision response list ($E380).
  • $B0DE-$CAE1 - Dynamic object SST (Level objects are loaded here).
  • $CAE2-$CFCB - Reserved object SST (Various important objects, such as Sonic, shields, invincibility stars, and title cards, are loaded here).
$CFCC-$CFDF Unused
$CFE0-$CFEE Array of flags used by the HCZ conveyor belts to avoid loading them more than once. The size of the array depends on the highest object subtype used.
$CFEF-$CFFF Unused
$D000-$DFFF Kosinski decompression buffer
$E000-$E37F Horizontal scroll buffer
$E380 Number of objects currently in collision response list, multiplied by 2.
$E382-$E3FF Collision response list. The format is one word per object, where the word is the starting address of the object's status table. Only objects in this list are processed by the collision response routine.
$E400-$E4FF In 1-player mode, this is Sonic's statistic recording buffer, used by Tails' AI. In 2-player mode, this is player 2's position table.
$E422-$E423 Player position X in Special Stage, with each checkerboard field having a size of $100.
$E424-$E425 Player position Y in Special Stage, with each checkerboard field having a size of $100.
$E426-$E427 Player direction in Special Stage.
$E428-$E429 Current player movement speed in Special Stage. Negative if walking backwards.
$E42A Direction change at the next checkerboard corner in Special Stage. Can be either -4, 0 or 4.
$E42B, $E42C, $E42F, $E430 Unknown in Special Stage.
$E431 This flag is set to 1 while going forward in Special Stage.
$E432, $E433, $E434-$E435, $E436-$E437 Unknown in Special Stage.
$E438-$E439 The number of blue spheres remaining to be collected in a Special Stage.
$E43A-$E43B The number of rings collected in a Special Stage.
$E43C Unknown in Special Stage.
$E43D Special Stage ring collection flags. Bit 0 is set when 50 rings have been collected, bit 1 is set for 100 rings, bit 2 for 200 rings, and bit 7 is set when the rings display needs to be refreshed.
$E43E-$E43F Number of frames remaining till the speed of a Special Stage increases. Initial value is 1800 (i.e. 30 seconds in 60Hz mode) for regular special stages and 2700 (i.e. 45 seconds in 60Hz mode) for Blue Spheres

special stages.

$E440 Unknown in Special Stage.
$E442-$E443 Total rings remaining to be collected in a Special Stage. A 50000 points perfect bonus is awarded for collecting all the rings.
$E444-$E445 Special Stage speed. Starts off at $1000 and is incremented by $400 every time the speed increase timer expires until it reaches $2000.
$E436-$E439 Unknown in Special Stage.
$E44A-$E44B Height of spheres when they get fly up after collecting the last blue sphere in Special Stage.
$E44C, $E44D, $E44E-$E44F, $E450 Unknown in Special Stage.
$E500-$E5FF Position table for player 1
$E600-$E653 Saved competition mode data
$E654-$E65F Unused
$E660-$E663 Long pointer to the currently-playing save slot's data in memory. Set to $FFFFE6AC when playing save slot 1, $FFFFE6B6 when playing save slot 2, etc.
$E664-$E663 Unused
$E666-$E667 Unknown
$E668-$E6AB Unused
$E6AC-$E6FF Variables for each save slot. The format is $A bytes long:
Hex Value Description
$00-$01 Word Slot State
$8000 New Game
$0000 Game in Progress
$0100 Game Complete
$0200 Game Complete with all Chaos Emeralds
$0300 Game Complete with all Super Emeralds
$02 Byte Current Character
$00 Sonic And Tails
$10 Sonic
$20 Tails
$30 Knuckles
$03 Byte Current Level
$0C Last level for knuckles
$0D Last level for Sonic without chaos/super emeralds, or Tails
$0E Last level for Sonic with at least all Chaos Emeralds
$04 Byte Unknown
$05 Byte Something with Special Stages Array
$06 Byte Something with Collecting a Chaos Emerald
$07 Byte Something with Collecting a Super Emerald
$08 Byte Current Number of lives
$09 Byte Current Number of Continues
  • Note that byte $02 also keeps a record of special stages played through, whether you won or lost it. It updates by $01's.
$E700-$EAFF Ring status table. The format is two bytes per ring, these bytes being 0000 while the ring has yet to be consumed, serving as a ring destruction timer while the ring is being consumed, and being set to FFFF when the ring has been fully consumed.
$EB00-$EDFF Object respawn table. Each object which is part of a level's object placement gets an entry in this table, and whenever the objects manager creates a new object, it sets bit 7 of the object's entry in the object respawn table. While bit 7 is set, the object will not be loaded again by the objects manager. The other seven bits of the entry are free for use by the object - for example, monitors set bit 0 to signify a broken monitor. Since every object which is part of the level's object placement has an entry in this table, the maximum number of objects any level can have in its object placement is 768, although the only level that gets close to that number is AIZ 2, with 751 objects.
$EE00-$EE01 Variable set by the horizontal scroll manager to the difference between the old and new camera X positions, multiplied by 256
$EE02-$EE03 Variable set by the vertical scroll manager to the difference between the old and new camera Y positions, multiplied by 256
$EE04-$EE05 Variable set by the horizontal scroll manager to the difference between the old and new camera X positions for player 2, multiplied by 256
$EE06-$EE07 Variable set by the vertical scroll manager to the difference between the old and new camera Y positions for player 2, multiplied by 256
$EE08 Unused, but cleared when the level starts.
$EE09 Unused
$EE0A Scroll lock for player 1 - if this is set, scrolling routines won't be processed.
$EE0B Scroll lock for player 2 - if this is set, scrolling routines won't be processed.
$EE0C-$EE0D Level's target left boundary (Unused)
$EE0E-$EE0F Level's target right boundary (Unused)
$EE10-$EE11 Level's target upper boundary (Unused)
$EE12-$EE13 Level's target lower boundary.
$EE14-$EE15 Level's left boundary.
$EE16-$EE17 Level's right boundary.
$EE18-$EE19 Level's upper boundary.
$EE1A-$EE1B Level's lower boundary.
$EE1C-$EE1D Level's left boundary for player 2.
$EE1E-$EE1F Level's right boundary for player 2.
$EE20-$EE21 Level's upper boundary for player 2.
$EE22-$EE23 Level's lower boundary for player 2.
$EE24-$EE25 Horizontal scroll delay. If this is nonzero, the upper byte is the offset into the player 1 position table, which is used to calculate camera position. Used for example by the Spin Dash and fire dash.
$EE26-$EE27 Index into Player 1's statistics recording buffer and position table.
$EE28-$EE29 Horizontal scroll delay for player 2.
$EE2A-$EE2B Index into Player 2's position table.
$EE2C-$EE2D Screen Y-offset to center the camera to. This is used for looking up or down, which changes the camera Y-offset to show more of the screen.
$EE2E-$EE2F Screen Y-offset to center the camera to for player 2.
$EE30 Deform lock flag. If this flag is set, camera will not be scrolled and level resize events are not processed.
$EE31 Unused
$EE32 Flag that is set, if camera is going to scroll vertically this frame, because the target bottom boundary was changed. This seems to only be used for the camera scrolling.
$EE33 Routine counter for screen resize routines.
$EE34-$EE38 Unused
$EE39 Fast vertical scrolling flag. If set, screen can be scrolled up to $18 pixels per frame, as opposed to 6 pixels.
$EE3A-$EE3B Copy of the foreground vertical scroll position for player 2. Seems to be used for the competition mode (Change camera position mid-screen).
$EE3C-$EE3D Copy of the background vertical scroll position for player 2. Seems to be used for the competition mode (Change camera position mid-screen).
$EE3E-$EE3F This is the difference between the foreground horizontal position and background horizontal position. Used for various things, such as collision with the background layer.
$EE40-$EE41 This is the difference between the foreground vertical position and background vertical position. Used for various things, such as collision with the background layer.
$EE42-$EE45 Address (in the ROM) of the next ring to the left. Used to more efficiently load unloaded rings when the camera is moved.
$EE46-$EE49 Address (in the ROM) of the next ring to the right. Used to more efficiently load unloaded rings when the camera is moved.
$EE4A-$EE4B Address (in the ring status table) of the next ring to the left. Used to more efficiently load unloaded rings when the camera is moved.
$EE4C-$EE4D Unused
$EE4E Apparent current zone. This is identical to $FE10.
$EE4F Apparent current act. Unlike $FE11, this is only incremented by the actual end of act score tally, so it differs from $FE11 in levels like AIZ, where $FE11 is set to 1 as soon as the first cutscene is over, while this is incremented only after the end of act points tally.
$EE50-$EE51 Animated palette timer. When set to a negative value, no palette cycling occurs. When set to 0, normal palette cycling occurs. When set to above 0, palette is either faded from black or white, depending on the level.
$EE52-$EE55 Address of the demo playback data.
$EE56-$EE59 Unknown
$EE5A Unknown, maybe competition mode related.
$EE5B Unused
$EE5C-$EE5D Unknown, maybe competition mode related.
$EE5E Flag used to indicate we started act 3. This flag disables the title cards.
$EE5F Unused
$EE60-$EE63 Plane A X-position for player 2 in 2p mode.
$EE64-$EE67 Plane A Y-position for player 2 in 2p mode.
$EE68-$EE6B Copy of plane A X-position for player 2 in 2p mode.
$EE6C-$EE6F Copy of plane A Y-position for player 2 in 2p mode.
$EE70-$EE71 Unknown
$EE72-$EE73 Unused
$EE74-$EE75 Unused, only referenced in dead code.
$EE76-$EE77 Unused
$EE78-$EE7B Plane A X-position.
$EE7C-$EE7F Plane A Y-position.
$EE80-$EE81 Copy of plane A X-position.
$EE82-$EE83 Unused
$EE84-$EE85 Copy of plane A Y-position.
$EE86-$EE87 Unused
$EE88-$EE89 Rounded plane A X-position. The position is rounded down to the last full block ($10 pixels).
$EE8A-$EE8B Rounded plane A Y-position. The position is rounded down to the last full block ($10 pixels).
$EE8C-$EE8D Copy of plane B X-position.
$EE8E-$EE8F Unknown
$EE90-$EE91 Copy of plane B Y-position.
$EE92-$EE93 Unknown, possibly unused
$EE94-$EE95 Rounded plane B X-position. The position is rounded down to the last full block ($10 pixels).
$EE96-$EE97 Rounded plane B Y-position. The position is rounded down to the last full block ($10 pixels).
$EE98-$EE99 Unknown
$EE9A-$EE9B Unknown, possibly unused
$EE9C-$EE9F, $EEA0-$EEA1, $EEA2, $EEA3 Unknown
$EEA4 Plane double update flag. This is set, when the plane has moved by more than $10 pixels this frame. It is used temporarily to remember to update the next row or column of the plane.
$EEA5 Unused
$EEA6-$EEA7 Special V-int routine. This flag is used to control various special functions that occur during the vertical interrupt. This is mainly used for the LBZ2 ship sequence.
$EEA8-$EEA9 Plane X-wrap value. This flag is used to wrap the horizontal position of the level. It looks like, that this was never used for anything.
$EEAA-$EEAB Plane Y-wrap value. This flag is used to wrap the vertical position of the level. This is used to create infinitely looping levels.
$EEAC-$EEAD Unknown
$EEAE-$EEAF Layout row mask. It is unclear why this flag is necessary and how it is used.
$EEB0-$EEB1 Unknown
$EEB2-$EEB3 Special events routine counter.
$EEB4-$EEB5 Various meanings for screen events routines.
$EEB6-$EEB7 Unknown
$EEB8-$EEB9 Unknown
$EEBA-$EEBB Unused
$EEBC-$EEBD X-position offset for various objects this frame. Used mainly for looping parts of the level, to make the illusion of constant forwards movement.
$EEBE-$EEBF Unknown
$EEC0-$EEC1 Screen event routine counter. Each routine is 4 units, so this counter can only contain multiples of 4. Affects AIZ2, FBZ2, LBZ2, MHZ2, SOZ2, SSZ1, SSZ2, DEZ2, DDZ, the slot machine bonus stage, the LRZ boss act, the DEZ boss act and the ending sequence.
$EEC2-$EEC3 Trigger event routine counter. Each routine is 4 units, so this counter can only contain multiples of 4. Affects all levels except for the bonus stages, DDZ, and MHZ1. For some reason, the ICZ1 screen event routine also uses this counter, so both the screen and trigger event routines are linked in that act.
$EEC4-$EEC5 Used to trigger various level events or scrolling events. This varies for each level.
$EEC6-$EEC7 Similar to $EEC4, used for different events. Level property (like killer wall in HCZ2 or avalanche in ICZ1). The high byte is set when an Act 1 signpost stops spinning, to signal the code that loads Act 2 into memory. This doesn't happen for AIZ and ICZ since they load Act 2 before the midboss.
$EEC8-$EEC9 Used for drawing the entire plane across multiple frames. It is a counter of sorts, to remember which plane row the draw next.
$EECA-$EECB Used for drawing the entire plane across multiple frames. This determines how many rows are left to draw.
$EECC-$EECD Screen shaking flag. If zero, screen is not shaking. If negative, screen is shaking for an earthquake and will continue indefinitely. If positive, screen is shaking from a bomb impact or the like, and the value will be decremented each frame until it reaches zero, then shaking will stop.
$EECE-$EECF Screen shaking offset: the difference between the "true" camera Y position and what appears on screen that frame. Most acts' screen events add this to $EE84 each frame. AIZ1, HCZ1, CNZ1, FBZ1, ICZ2, MHZ1 and DEZ ignore this value, so you'll need to edit the screen events if you want to add shaking effects in those acts. MHZ2 uses it as an X offset instead of a Y offset (when Robotnik hits the tree) so adds it to $EE80 instead of $EE84. ICZ1 uses it for both, depending on where in the level you are.
$EED0-$EED1 Stores the value that $EECE had during the previous frame.
$EED2-$EED3 Secondary screen event routine counter, used by some acts.
$EED4-$EED5 Various meanings in level events, used for example as the X-position for destroying blocks in the CNZ miniboss.
$EED6-$EED7 Various meanings in level events, used for example as the Y-position for destroying blocks in the CNZ miniboss.
$EED8-$EEEB Various meanings in level events and sometimes other game modes. Every word usually has different meaning.
$EEEA-$EF39 V-Scroll buffer. The buffer contains 20 entries, where an entry is a word for foreground vertical position, and a word for background vertical position. Each 16 pixel column of the screen can be scrolled a different amount as per contents of this buffer. This effect is used only in rare occasions (examples are: MGZ 2 level collapse when boss fight starts, LBZ 1 building breakdown before boss).
$EF3A-$EF3B Various meanings in level events and sometimes other game modes.
$EF3C-$EF3D If set, an alternate address is used for the sprite attribute table data.
$EF3E-$EF3F Flag that if set, changes the state of $EF3C
$EF40-$EF43 Unknown, seems to have various functions.
$EF44-$EF47 Unknown
$EF48 Unknown
$EF49 Flag which determines whether the second player in a 2P versus game is player-controlled or just a "ghost" of the first player.
$EF4A, $EF4B, $EF4C-$EF4D, $EF4E Unknown
$EF4F Unused
$EF50 Unknown, something to do with demos.
$EF51 Unused
$EF52-$EF55 Unknown
$EF56-$EF57 Flag that if set, SRAM save and load routines will disable interrupts while SRAM is enabled. This is likely done to avoid interrupts firing while SRAM is enabled, that could crash the processor.
$EF58-$EF59 Unused
$EF5A-$EF5D There are 2 object lists; Sonic 3 list, and Sonic & Knuckles list. This flag points to either one depending on the level ID.
$EF5E-$EF5F Used to temporarily store ring count, while transitioning to act 3.
$EF60-$EF63 Used to temporarily store level timer value, while transitioning to act 3.
$EF64-$EF65 Position Y of the window of active objects. Only actually used in glowing spheres bonus stage. Objects with Y coordinate lower or at least $280 higher than that will despawn.
$EF66-$EF67 Background screen shaking flag. If zero, screen is not shaking. If nonzero, the value will be decremented each frame until it reaches zero, then shaking will stop.
$EF68-$EF69 Unknown
$EF6A-$EF6B Unknown
$EF6C-$EF6D Flag which is set to $FF00 when a Super Emerald special stage is newly completed. This stops the HPZS initalizer from repeating the "beam" effect that you see when you go to HPZ from a giant ring to pick the special stage in the first place.
$EF6E Unknown
$EF6F Unused
$EF70 Unknown
$EF71 Unused
$EF72-$EF73 Flag which is set to $FF00 if an ending is running. The only thing this seems to do is prevent the game from being able to pause.
$EF74-$EF77 Address of secondary plane buffer. If set to 0, it is ignored.
$EF78 Unknown
$EF79 Unknown
$EF7A-$EF7B Currently running demo ID.
$EF7C-$EF7F Unused
$EF80-$EF81 The number of rings inside the ring consumption table.
$EF82-$EFFF Ring consumption table. Contains the RAM addresses (inside the ring status table) of rings which are currently being consumed. Once consumed, the rings are deleted from this table.
$F000-$F07F Target underwater palette. Used to fade the underwater palette slowly.
$F080-$F0FF Current underwater palette.
$F100-$F57F Plane buffer. During the normal level processing period, display update routines decide which tiles need to be updated and write the results here, and then in V-int a routine processes this and updates the planes accordingly. The first word of each entry in this buffer is the address in VRAM to write to - if this is 0, the buffer processing routine terminates. The second word is the number of 16x16 tiles to be written - 1, and the sign bit of this word being set indicates that the constituent 8x8 tiles are to be written column-by-column rather than row-by-row. Following this is the actual data to write. Warning: Some levels can, on some occasions, overflow from this buffer, inevitably causing a crash! This can be fixed by carefully rearranging RAM.
$F580-$F5FF VRAM buffer. Used to temporarily hold data while it is being transferred from one VRAM location to another.
$F600 Game mode flag. This flag is used to determine what game mode to go to next. This only takes effect when the last game mode ends (some game modes check for this flag specifically).

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... Known meanings of certain values of the lower 7 bits:

  • $00 - Game initialization or restart e.g. after Game Over
  • $04 - Show SEGA logo, which leads to the title screen
  • $08 - Load a level, and start the demo there
  • $0C - Load a level
  • $10 - Reset game mode to $00
  • $14 - Go to the continue screen
  • $18 - Reset game mode to $00
  • $1C - Go to level select
  • $20 - Does nothing.
  • $24 - Go to level select
  • $28 - Go to level select
  • $2C - Go to blue spheres challenge screen
  • $30 - Show blue spheres challenge results screen
  • $34 - Go to special stage
  • $38 - Go to competition mode menu
  • $3C - Go to competition mode player select menu
  • $40 - Go to competition mode level select menu
  • $44 - Go to competition mode results screen
  • $48 - Show special stage results
  • $4C - Go to data select screen
  • $50 - Go to time attack records screen
$F601 Unused
$F602 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 In-game Controller 1 pressed state. Same as $F602, but only tells which buttons are being pressed newly this frame.
$F604 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 Same as $F604, but only tells which buttons are being pressed newly this frame.
$F606 Same as $F604, but for Controller 2.
$F607 Same as $F606, but only tells which buttons are being pressed newly this frame for Controller 2.
$F608-$F60D Unused
$F60E-$F60F VDP command for mode register 2
$F610-$F613 Unused
$F614-$F615 Demo time left & Time until demo starts from title screen.
$F616-$F617 Foreground vertical scroll position.
$F618-$F619 Background vertical scroll position.
$F61A-$F61D Unused, but cleared in various places.
$F61E-$F61F Foreground vertical scroll position for player 2.
$F620-$F621 Background vertical scroll position for player 2.
$F622 Teleport timer (leftover from Sonic 2).
$F623 Teleport active flag (leftover from Sonic 2).
$F624-$F625 VDP register $A (H-INT counter) cache.
$F626 Number of bytes from the palette start to be ignored in screen fading routines.
$F627 Number of palette entries minus one to be affected in screen fading routines. The first affected palette entry index is half of the value in $F626.
$F628-$F629 Number of lag frames per level loop. Displayed in the place of the minutes counter in the debug HUD.
$F62A V-INT routine ID.
$F62B Unused
$F62C Number of sprites rendered on screen.
$F62D Unused
$F62E-$F631 Address to a list of offsets, used in various horizontal interrupt routines, to load the water palette gradually. These are offsets are offsets to either water palette, or the normal palette, and target CRAM locations. 3 colors are loaded each scanline, and for each scanline, new offset is read.
$F632-$F635 Counters used for palette cycling.
$F636-$F639 Random number generator seed & result.
$F63A-$F63B Game paused flag.
$F63C-$F63F Unused
$F640-$F641 Used to hold the low word of a DMA transfer command, which is then sent to the VDP control port, to get around a hardware bug.
$F642-$F643 Unused
$F644-$F645 H-int enable flag. This flag is used to make sure the horizontal interrupt code is never run twice in a single frame unintentionally. If set, the next H-int will be enabled.
$F646-$F647 Same as $F648.
$F648-$F649 Current water level. Should be a valid Y-axis value. Remember, the top of the level is $0000.
$F64A-$F64B Target water level. If this differs from $F648, the water level will move up or down $F64C lines per frame until they match.
$F64C The rate at which water rises or falls during a change in water level.
$F64D Incremented each time a player enters water.
$F64E Set to 1 if water covers the entire visible screen; clear otherwise.
$F64F If set, H-int routines will also update the HUD numbers, process the Nemesis queue, and update the demo timer flag.
$F650, $F652-$F65B Counters used for palette cycling.
$F651 Seems unused
$F65C-$F65D Offset into the Super/Hyper color array, determines which set of colors we are currently on. Each palette entry is 2 bytes and there are 3 entries per set, so this is always a multiple of 6.
$F65E Number of frames remaining until the next set of Super/Hyper colors are loaded into the palette.
$F65F The current state of Super/Hyper palette rotation. 0 means disabled, 1 means the character is newly transforming to Super/Hyper, -1 ($FF) means the player is fully transformed, 2 means the character was Super/Hyper and is transforming back to normal.
$F660-$F661 Unknown
$F662-$F663 Unused, but cleared.
$F664 Dual collision plane flag. Set to -1 ($FF) when there are two collision planes active (Examples: HCZ 2 wall chase, MGZ 2 partial level collapse, SOZ 2 rising sand).
$F665 When set to -1 ($FF), hitting the lower level border won't lead to death.
$F666 Hyper Sonic Dash screen flash timer. Usually zero, except while the screen flash is visible. Starts at 4 and decreases by one each frame.
$F667 Tails super flag, same as $FE19, just for Tails.
$F668 Same as $F65C, but for Tails. So this variable is used to control Tails' colors, and $F65C is used to control the Super Sonic flickies.
$F669 Same as $F65E, but for Tails. So this variable is used to control Tails' colors, and $F65E is used to control the Super Sonic flickies.
$F66A In-game Controller 2 held state. Same as $F602, but for controller 2.
$F66B In-game Controller 2 pressed state. Same as $F66A, but only tells which buttons are being pressed newly this frame.
$F66C Unknown
$F66D-$F66F Unused
$F670-$F671 Super Sonic ring drain counter. This is updated each frame, so the counter is set to 60 ($3C) on consoles operating in 60Hz mode, or 50 ($32) in consoles operating in 50Hz mode. After each frame, the code subtracts 1. One ring is removed when this counter reaches zero; in other words, each second.
$F672-$F675 Unused
$F676 Follow custom position flag. If this flag is set, this frame player 1's position is substituted for custom positions. This is used to focus scrolling on certain objects in the game.
$F677 Unused
$F678-$F679 Follow custom position X-position.
$F67A-$F67B Unused
$F67C-$F67D Follow custom position Y-position. Must come 4 bytes after the X-position.
$F67E-$F67F Unused
$F680-$F6DF Pattern load queue. 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 The address in ROM of the decompression routine to be used for the art
$F6E4-$F6F7 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 The total number of tiles left to be decompressed for the current piece of art
$F6FA-$F6FB The number of tiles left to be decompressed in the current frame
$F6FD-$F6FF Unused
$F700-$F701 Unknown
$F702-$F703 Tails control counter. Counts how long until the CPU takes control.
$F704-$F705 Tails respawn counter.
$F706-$F707 Unused
$F708-$F709 Tails CPU routine.
$F70A-$F70B 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 position. Tells Tails where Sonic's Y position is so he can fly back to him.
$F70E-$F70F Tails interact ID. Object ID of last object Tails stood on.
$F710 Routine counter for the rings manager.
$F711 Level started flag. Set to 1 as soon as the player first gets control in the level.
$F712-$F72D Unknown, seems to be unused however.
$F72E Flag used to determine which animated palette AIZ1 uses.
$F72F Unused
$F730 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.
$F731-$F73D Unused
$F73E Tails carrying flag. Set to 1 whenever Tails carries Sonic.
$F73F Number of frames until Tails can catch Sonic again. Used to avoid immediate catching after Sonic jumpss off.
$F740-$F741 Unknown, something to do with the software scaler used by MGZ2 boss and SSZ badniks.
$F742-$F743 Unused
$F744-$F745 Unknown
$F746 Unknown
$F747 Unused
$F748 Same as $F604, but for the title screen.
$F749 Same as $F605, but for the title screen.
$F74A, $F74B, $F74C-$F74D, $F74E Unknown
$F74F Flag that disables Knuckles' wall grab when set to a negative value.
$F750-$F75F Unused
$F760-$F761 Sonic's and Knuckles' top speed
$F762-$F763 Sonic's and Knuckles' acceleration
$F764-$F765 Sonic's and Knuckles' deceleration
$F766 Sonic's and Knuckles' current mapping frame number.
$F767 Unused
$F768 Angle value at Sonic's left sensor
$F769 Unused
$F76A Angle value at Sonic's right sensor
$F76B Unused
$F76C-$F76D Routine counter for object spawning.
$F76E-$F76F Camera X position rounded down to last multiple of $80. Used in the object spawning routine.
$F770-$F771 Camera Y position rounded down to last multiple of $80. Used in the object spawning routine.
$F772-$F775 Long pointer to level object list address of next object to spawn when moving right.
$F776-$F779 Long pointer to level object list of next object to spawn when moving left.
$F77A-$F77B Pointer into the object respawn table in RAM. Points to the entry associated with the next object to spawn when moving left.
$F77C-$F77D Pointer into the object respawn table in RAM. Points to the entry associated with the next object to spawn when moving right.
$F77E-$F793 Unused
$F794-$F795 Some type of timer used in palette fade routines.
$F796-$F799 Pointer to the currently used collision layer for players. Is always the same as either $F7B4 or $F7B8.
$F79A-$F7A9 Unused
$F7AA Boss flag. Set when a boss is active, and cleared after defeat or end of sequence.
$F7AB-$F7AF Unused
$F7B0-$F7B3 Unknown, used by some objects for storing player-specific state.
$F7B4-$F7B7 Pointer to collision layer 1 of this level.
$F7B8-$F7BB Pointer to collision layer 2 of this level.
$F7BC-$F7BF Unused
$F7C0 MHZ pollen and leaves counter. This count how many pollen or leaves are active, and will stop spawning more if 10 or more pollen/leaves are active.
$F7C1 Unknown flag used in MHZ.
$F7C2 Unknown
$F7C3 Unknown
$F7C4-$F7C5 Unknown
$F7C6 Reverse gravity flag. Only in Sonic & Knuckles.
$F7C7 Unknown
$F7C8 Wind tunnel flag. Set if player 1 is in a wind tunnel.
$F7C9 Wind tunnel flag. Set if player 2 is in a wind tunnel.
$F7CA Controller lock for controller 1.
$F7CB Controller lock for controller 2.
$F7CC-$F7CF Unused
$F7D0-$F7D1 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 Time bonus counter at the end of level result screen.
$F7D4-$F7D5 Ring bonus counter at the end of level result screen.
$F7D6-$F7D9 Unused
$F7DA-$F7DB 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.
$F7DC-$F7DD Unused, referenced in dead code.
$F7DE Tails' current mapping frame number.
$F7DF Tails' tails current mapping frame number.
$F7E0-$F7EF Level trigger array. This has different meanings in most levels, but generally it is used to determine if a switch has been pressed, and platforms or other objects may react to these button presses using this array.
$F7F0-$F7FF Level animation counter. Each word is a different counter, and these are used to process animated level art.
$F800-$FA7F Sprite table buffer. This is a temporary buffer used to store VDP sprite data, and it is DMA'd to VRAM each frame.
$FA80-$FA81 Unused, but cleared.
$FA82-$FA83, $FA84-$FA85, $FA86-$FA87, $FA88 Unknown
$FA89 Flag that if set, will tell Mecha Sonic's head to get deleted.
$FA8A-$FA8B Unknown
$FA8C-$FA8D Unused, but written to once.
$FA8E-$FA8F, $FA90-$FA91, $FA92-$FA93, $FA94-$FA95, $FA96-$FA97, $FA98-$FA99, $FA9A-$FAA1, $FAA2, $FAA3, $FAA4-$FAA5 Unknown
$FAA6-$FAA7 Pointer to a signpost object. Hidden Monitors use this to easily find the currently active signpost used for bouncing.
$FAA8 End-of-level flag. Set when a mid-boss or end boss is defeated, set back to zero when the results screen goes away.
$FAA9 Unknown flag which is something to do with control lock
$FAAA Flag which is set when a title card goes away, or when an Act 1 results screen goes away.
$FAAB Unknown flag which is only used by the LBZ1 boss.
$FAAC, $FAAD, $FAAE-$FAAF, $FAB0-$FAB1, $FAB2-$FAB3, $FAB4-$FAB5, $FAB6-$FAB7, $FAB8, $FAB9, $FABA-$FABB, $FABC-$FABD Unknown
$FABE Unused, but written to once.
$FABF Flag that if set, palette rotation scripts will not be processed.
$FAC0, $FAC1, $FAC2-$FAC3 Unknown
$FAC4-$FAC7 Unused
$FAC8-$FACB, $FACC, $FACD, $FACE-$FACF Unknown
$FAD0-$FAD9 Unused
$FADA-$FADD Unknown
$FADE-$FAED Data used by palette rotation scripts.
$FAEE-$FAEF Unused, however should not be written to; Needs to be 0 for palette rotation script routine.
$FAF0-$FAF1 Unknown
$FAF2-$FAF3 Unused
$FAF4-$FAF5 Unknown
$FAF6-$FAF7 Unused
$FAF8-$FAF9, $FAFA-$FAFB, $FAFC-$FAFD Unknown
$FAFE-$FAFF Unused
$FB00-$FBFB VDP command buffer. Stores up to 18 sets of queued up VDP commands to be issued later.
$FBFC-$FBFF VDP command buffer free slot. Stores the address of the first available empty place in the VDP command buffer.
$FC00-$FC7F Normal dry palette.
$FC80-$FCFF Target dry palette. Used to fade the underwater palette slowly.
$FD00-$FDFF 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.
$FE00-$FE01 Unused
$FE02-$FE03 Level restart flag.
$FE04-$FE05 Level frame timer.
$FE06 Object currently selected in debug mode.
$FE08 Object placement mode routine counter.
$FE09 Object placement mode flag (0 - normal, 1 - object placement, 2 - frame cycling)
$FE0A Delay countdown until camera movement starts in object placement mode.
$FE0B Current camera movement speed in object placement mode.
$FE0C-$FE0F Counts the number of times V-int has run.
$FE10 The current Zone. This is the value assigned to the Zone, not its position in the level list.
$FE11 Act number
$FE12 Life Count
$FE13-$FE17 Unused
$FE18 Number of continues.
$FE19 Super/Hyper Sonic flag. 1 means Super and -1 ($FF) means Hyper. Setting this will load the Super/Hyper 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 Flag which is set when the player has a time over.
$FE1B This bitfield tells the game if the player has collected extra lives from rings. Seems to work differently in S3k than in S2.
$FE1C Flag determines if the lives counter needs to be updated.
$FE1D Flag determines if the rings counter needs to be updated.
$FE1E Flag determines if the timer needs to be updated.
$FE1F Flag determines if the score counter needs to be updated.
$FE20-$FE21 Number of rings collected.
$FE22-$FE23 Minutes counter for the level timer.
$FE24 Seconds counter for the level timer.
$FE25 Frame counter for the level timer.
$FE26-$FE29 Score (divided by 10)
$FE2A ID of the last starpole the player has hit.
$FE2B-$FE47 Starpole variables. When you hit a starpole, these variables are stored from the current actual values. When you die, the values are loaded from here.
  • $FE2B - ID of the last starpole the player has hit.
  • $FE2C - Current zone.
  • $FE2D - Current act.
  • $FE2E-$FE2F - X-position of the starpole.
  • $FE30-$FE31 - Y-position of the starpole.
  • $FE32-$FE33 - Number of rings collected.
  • $FE34-$FE35 - Minutes counter for the level timer.
  • $FE36 - Seconds counter for the level timer.
  • $FE37 - Frames counter for the level timer.
  • $FE38-$FE39 - VDP pattern index for player 1.
  • $FE3A-$FE3B - Top and LRB collision bit for player 1.
  • $FE3C-$FE3D - Plane A X-position.
  • $FE3E-$FE3F - Plane A Y-position.
  • $FE40-$FE41 - Water Y-position.
  • $FE42 - Water fullscreen flag.
  • $FE43 - Extra lives from rings bits.
  • $FE44-$FE45 - Level's bottom boundary.
  • $FE46 - Screen resize routine counter.
  • $FE47 - Player 1's shield state.
$FE48 Flag that determines which of the two sets of variables to restore. 0 is for starpole, anything else is for the special stage one.
$FE49-$FE65 Special stage variables. When you enter a special stage, these variables are stored from the current actual values. When you return, the values are loaded from here.
  • $FE49 - ID of the last starpole the player has hit.
  • $FE4A - Current zone.
  • $FE4B - Current act.
  • $FE4C-$FE4D - X-position of the starpole.
  • $FE4E-$FE4F - Y-position of the starpole.
  • $FE50-$FE51 - Number of rings collected.
  • $FE52-$FE53 - Minutes counter for the level timer.
  • $FE54 - Seconds counter for the level timer.
  • $FE55 - Frames counter for the level timer.
  • $FE56-$FE57 - VDP pattern index for player 1.
  • $FE58-$FE59 - Top and LRB collision bit for player 1.
  • $FE5A-$FE5B - Plane A X-position.
  • $FE5C-$FE5D - Plane A Y-position.
  • $FE5E-$FE5F - Water Y-position.
  • $FE60 - Water fullscreen flag.
  • $FE61 - Extra lives from rings bits.
  • $FE62-$FE63 - Level's bottom boundary.
  • $FE64 - Screen resize routine counter.
  • $FE65 - Player 1's shield state.
$FE65 Routine counter for LRZ special rocks.
$FE66-$FE69 Unknown
$FE6A-$FE6D Unknown
$FE6E-$FEAF Oscillating numbers data.
$FEB0 Unknown
$FEB1 Unknown
$FEB2 Rings animation counter.
$FEB3 Rings animation frame.
$FEB4 Unknown
$FEB5 Unknown
$FEB6 Lost rings animation counter.
$FEB7 Lost rings animation frame.
$FEB8-$FEB9 Lost rings animation accumulator(?)
$FEBA-$FEBB Unknown
$FEBC-$FEBD Unused
$FEBE Unused, but referenced in some code.
$FEBF Extra lives bits from rings for player 2.
$FEC0-$FEC1 Tails' max speed
$FEC2-$FEC3 Tails' acceleration
$FEC4-$FEC5 Tails' deceleration
$FEC6 Tails' lives in 2P mode. Unused in S3K, but referenced in code.
$FEC7 Unknown
$FEC8-$FEC9 Rings collected since level load. Resets if you enter Special/Bonus stage. Starts recounting from 0 when level is reentered. Not sure what this is used for.
$FECA-$FECB Same as $FEC8, but for player 2.
$FECC-$FECD Strange counter, that is incremented when a monitor or a ring gives you an extra life, and also when a robotnik monitor has been destroyed.
$FECE-$FECF Strange counter, that is incremented when a robotnik monitor has been destroyed by player 2. Oddly, this counter does not get incremented for extra lives; Instead, $FECC is despite being player 2.
$FED0-$FED1 Number of rings counter for player 2. It is unclear if this is ever used for anything.
$FED2-$FED5 Unknown, seems to be unused.
$FED6-$FED9 Unknown, seems to be level timer for player 2, unknown if this is used in any way.
$FEDA Unknown
$FEDB Unused
$FEDC-$FEDD Unknown
$FEDE-$FEDF Unused, but cleared once.
$FEE0-$FF01 Unused
$FF02-$FF03 Unused, but cleared once.
$FF04-$FF05 Total rings remaining to be collected in a level. No perfect bonus is actually given for collecting all the rings, making this variable virtually useless.
$FF06-$FF07 Unused, but cleared once.
$FF08-$FF09 Player mode (00 = Sonic & Tails, 01 = Sonic, 02 = Tails, 03 = Knuckles)
$FF0A-$FF0B Character selected in level select (00 = Sonic & Tails, 01 = Sonic, 02 = Tails, 03 = Knuckles, 04 = Blue Knuckles)
$FF0C-$FF0D Unused, but cleared once.
$FF0E-$FF0F Number of kosinski compressed data pieces on the kosinski decompression queue ($FF40-$FF5F) waiting to be decompressed to RAM. The most significant bit of this being set signifies a decompression is in progress
$FF10-$FF37 Kosinski queue processing routine register backup. Registers d0-d6 and a0-a2 are backed up here in case the Kosinski queue processing routine is interrupted by V-Int. They're restored the next time the processing routine is called
$FF38-$FF39 Kosinski queue processing routine status register backup. In case the processing routine is interrupted by V-Int, the SR is stored here and restored the next time the routine is called
$FF3A-$FF3D Kosinski queue processing routine program counter backup. In the instance of the processing routine being interrupted by V-Int, when V-Int is ready to return, the processing does not resume. Instead, by means of the subroutine at $1BF0, program resumption is forced to occur at $1D0C, and the actual overwritten program counter value gets stored here. Next time the processing routine is called, the routine at $1CFC kicks in, pushing this value and the stored SR onto the stack and executing an RTE, causing both to get restored and the processing to resume.
$FF3E-$FF3F The Kosinski queue processing routine uses this to store words byte-swapped. It's used by the processing routine the same way the stack is used by the normal Kosinski decompression routine
$FF40-$FF5F The Kosinski decompression queue. Each entry consists of two longwords:
  • $00 - the source Kosinski data location
  • $04 - the destination RAM address to decompress to

Since this is 32 bytes long, only 4 pieces can be stored on it at one time.

$FF60-$FF61 Number of modules left to decompress in the current Kosinski Moduled archive. Bit 7 indicates that the current module has finished decompressing and can be DMA'd to VRAM.
$FF62-$FF63 The decompressed size of the last module of the KosinskiM data divided by 2. All other modules have a fixed decompressed size of $1000.
$FF64-$FF7B The KosinskiM decompression and DMA queue. Each entry consists of a longword followed by a word:
  • $00 - the source Kosinski module location
  • $04 - the destination VRAM address to DMA the decompressed module to

Like the decompression queue, this can also only store 4 pieces at a time.

$FF7C-$FF7D Unknown
$FF7E-$FF7F Unknown
$FF80-$FF81 Unknown, used in the level select.
$FF82-$FF83 Selected item in level select.
$FF84-$FF85 Selected sound in sound test.
$FF86 Option number in title screen.
$FF87-$FF89 Unused
$FF8A Unknown
$FF8B Competition mode type (0 = grand prix, 1 = match race, -1 = time attack).
$FF8C-$FF8D Unused
$FF8E-$FF8F Total amount of bonus added this frame.
$FF90-$FF91 Used to store what music to resume after other music like the drowning music.
$FF92-$FF95 Special Stage entry rings entered for this level. Each bit is a single entry ring, when that bit is set, the entry ring will not appear again.
$FF96 State of the main character's secondary status bitfield when the last special stage was entered, used to restore any shield the character had when he entered the special stage and cleared once the shield is restored.
$FF97 If set, the sprite and ring loaders will not clear the respawn table when the level loads. Used for returning from special and bonus stages.
$FF98-$FF99 Unused
$FF9A Apparent Zone in which the last starpole was hit (See $EE4E)
$FF9B Apparent Act in which the last starpole was hit (See $EE4B)
$FF9C Apparent Zone in which special stage or bonus stage was entered (See $EE4E)
$FF9D Apparent Act in which special stage or bonus stage was entered (See $EE4B)
$FF9E Unused
$FF9F Blue Spheres challenge uses this to determine whether the header was "SEGA MEGA DRIVE" (1) or "SEGA GENESIS" (0)
$FFA0 Unknown, something to do with lock-on header.
$FFA1 Unknown, something to do with blue spheres challenge.
$FFA2-$FFA5 Map section IDs in Blue Sphere
$FFA6-$FFA9 Level number in Blue Sphere
$FFAA, $FFAB, $FFAC, $FFAD Unknown
$FFAE-$FFAF 0 if locked on to Sonic 3; nonzero otherwise.
$FFB0 Number of chaos emeralds
$FFB1 Number of super emeralds
$FFB2-$FFB8 Array of finished special stages. Each byte represents one stage:
  • 0 - special stage not completed
  • 1 - chaos emerald collected
  • 2 - super emerald present but grayed
  • 3 - super emerald present and activated
$FFB9 Unused
$FFBA Flag that when set, prevents Sonic and Knuckles from transforming into super or hyper.
$FFBB If this is set to 0, Sonic 3 special stages will run. If it's 1, Sonic & Knuckles special stages will run.
$FFBC Title screen animation flag. Sonic 3 title screen uses the fullscreen Sonic animation to transition from SEGA to title screen. It uses 2 Plane A and Plane B nametables and switches between them after they have been updated. This flag keeps track of which one to transition to next.
$FFBD Delay timer before the next animation transition.
$FFBE-$FFBF Animation frame number for the title animation.
$FFC0-$FFC3 Amount of score required for the next extra life.
$FFC4-$FFC7 Amount of score required for the next extra life for player 2.
$FFC8-$FFC9 Unused
$FFCA-$FFCD Player 1's mappings address is stored here while in debug mode.
$FFCE-$FFCF Player 1's VDP pattern index is stored here while in debug mode.
$FFD0-$FFD1 Demo mode flag. Set when demo mode is active.
$FFD2-$FFD3 Demo number.
$FFD4 Blue Sphere flag. This is 1 in the standalone Blue Spheres game, and 0 in regular special stages.
$FFD5 Unused
$FFD6-$FFD7 Number of cycles between two V-ints. The purpose of this flag is not known, as the hardware always has specific processor speeds in 50hz and 60hz versions, so you could use the hardware version register to get the region.
$FFD8 Hardware register value, specifically the region bits (bit 6 and 7).
  • Bit 7 - If clear, it is a domestic model (Japan/Asia), else it is an overseas model.
  • Bit 6 - If clear, it is a NTSC (60hz) system, else it is a PAL (50hz) system.
$FFD9 Unused
$FFDA-$FFDB Debug mode flag.
$FFDC-$FFDF Unused
$FFE0 Level select cheat flag.
$FFE1 Slow motion cheat flag.
$FFE2-$FFE3 Debug mode cheat flag. If this flag is set, holding A while entering level enables debug mode.
$FFE4-$FFE5 Unused, but cleared and referenced in dead code.
$FFE6-$FFE7 Unused, but cleared and referenced in dead code.
$FFE8-$FFE9 2P versus mode flag.
$FFEA 2p mode player 1's character.
$FFEB 2p mode player 2's character.
$FFEC-$FFEF Unused
$FFF0-$FFF1 Must be $4EF9 (68k opcode for long jump) as this address is the vertical interrupt vector.
$FFF2-$FFF5 Pointer to the current vertical interrupt routine.
$FFF6-$FFF7 Must be $4EF9 (68k opcode for long jump) as this address is the horizontal interrupt vector.
$FFF8-$FFFB Pointer to the current horizontal interrupt routine.
$FFFC-$FFFF Contains the ASCII string "SM&K" to indicate that the checksum is correct.

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. Each object is allocated a block of $4A bytes. 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 Description
$00-$03 Pointer to object code. Note that this pointer does not necessarily remain constant for a single object.
$04 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.
  • Bit 2 is the coordinate system flag. If clear, the object will be positioned by absolute screen coordinates. This is used for things like the HUD and menu options. If set, the object will be positioned by the playfield coordinates, i.e. where it is in a level.
  • Bits 3 and 4 are either unused, or their purpose is unknown.
  • 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:
    • Word $16 of the status table indicates the number of child sprites.
    • Following this word is the actual data for each 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.
$05 Routine number. This is always an even value (i.e. it goes in units of 2)
$06 Height of the object, in pixels.
$07 Width of the object, in pixels.
$08-$09 Sprite priority, in units of $80 (00 = front).
$0A-$0B 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.
$0C-$0F Object's mappings offset.
$10-$11 If the object is Sonic, Tails or Knuckles, 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.
$12-$13 If the object is Sonic, Tails or Knuckles, this is the X subpixel playfield coordinate. Otherwise, it's unused.
$14-$15 If the object is Sonic, Tails or Knuckles, 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 the Y screen coordinate.
$16-$17 If the object is Sonic, Tails or Knuckles, this is the Y subpixel playfield coordinate. Otherwise, it's unused.
$18-$19 X speed.
$1A-$1B Y speed.
$1C-$1D Potential speed (inertia).
$1E Height/2
$1F Width/2
$20 Animation number.
$21 Restart animation flag (when $21 is not equal to $20, animation restarts)
$22 Current animation frame to display.
$23 Current frame in animation script.
$24 Animation frame duration (time until next frame).
$25 Animation counter.
$26 Angle. $00 represents flat ground. $80 is the ceiling, $40 is a wall to the left of the object, $C0 is a wall to the right of the object. $20 is a 45 degree slope going down to the right, $E0 is a 45 degree slope going up to the right, and so on.
$27 Second angle (different axis).
$28 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 increments the routine counter, 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.
$29 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.
$2A 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 RSS flag, set if the object should remember that it is destroyed. See offsets $3B and $3C below.
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).
$2B Object shield reaction bitfield.
Bit Hex Description
3 $08 Bounces off shield.
4 $10 Negated by fire shield.
5 $20 Negated by lightning shield.
6 $40 Negated by bubble shield.
$2C Object subtype. For example, the current monitor selected. Has a different meaning for Sonic, Tails and Knuckles.
$2E-2F Used as a timer/counter, upon completion the routine will jump to a pointer in $34.
$34-$37 Stores a code pointer branched to from various routines upon meeting certain conditions.
$3B If the RSS flag is set, this is the bit (0-7) to be cleared when the object is destroyed. See bit 2 of offset $2A above.
$3C-$3D If the RSS flag is set, this is the RAM address to be modified when the object is destroyed. See bit 2 of offset $2A above.
$46-$47 Used by child objects to point to their parent.
$48-$49 RAM location of the object's entry in the object respawn table.
Variables specific to Sonic, Tails and/or Knuckles
Offset Description
$25
  • If Sonic, it's unused.
  • If Tails, it's the number of flying frames remaining / 2.
  • If Knuckles, it's something gliding related.
$2A Status bitfield. Counting from the least significant bit:
Bit Hex Description
0 $01 Orientation. Clear is right and set is left.
1 $02 Set if in the air (jump counts).
2 $04 Set if jumping or rolling.
3 $08 Set if the character 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.

$2B Secondary status 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 Fire shield flag.
5 $20 Lightning shield flag.
6 $40 Bubble shield flag.
7 $80 Sets infinite inertia. While the character 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 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.
$2D Invert flipping flag.
$2E Object control flag. If bit 7 is not set, the character is under control of another object but can jump out (e.g. being carried by Tails), and if it is, the character is under control of another object and cannot jump out (e.g. LBZ tubes).
$2F Double jump flag. For Sonic:
  • 0 - on ground.
  • 1 - performing an instashield, fire dash, bubble bounce or lightning jump, or has performed the latter three.
  • 2 - has performed an instashield.

For Tails:

  • 0 - on ground.
  • 1 - gravity-affected flying.
  • Above 1 - gravity-less flying.

For Knuckles:

  • 0 - on ground.
  • 1 - gliding.
  • 2 - falling after a glide.
  • 3 - sliding across ground.
  • 4 - wall-climbing.
  • 5 - climbing over a wall and onto the ground.
$30 Number of flip revolutions remaining.
$31 Number of flip revolutions per frame divided by 256.
$32-$33 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.
$34 Remaining invulnerability time. Starts at $78 after Sonic is hit, and is decremented every frame until it reaches $00.
$35 Remaining time of invincibility. Decremented once every eight frames.
$36 Remaining time of Speed Shoes. Decremented once every eight frames.
$37 Some sort of bitfield. If bit 7 of this is set, whenever the player is hit, even if he does not have a shield the game will act like he does and he will just recoil instead of losing rings. If he actually has a shield, however, he will lose it, as the shield check takes precedence over this bit check. Used, for example, by the spinning tops in MGZ.
$38 Character ID:
  • 0 - Sonic
  • 1 - Tails
  • 2 - Knuckles
$39 Character looking up/ducking counter. Starts off at 0 and is incremented each frame the character is looking up/ducking. When this reaches $78, the camera starts to scroll. Reset to 0 upon release of the up/down button.
$3A Angle on ground in front of sprite.
$3B Angle on ground under sprite.
$3C Stick to convex surfaces flag.
$3D Set if charging a Spin Dash.
$3E-$3F 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.
$40 Set if jumping.
$42-43 RAM address of the last object Sonic stood on.
$44 Default height.
$45 Default width.
$46 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).
$47 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).
Variables specific to dynamically reloaded sprites, excluding Sonic, Tails and Knuckles
$34 Previous frame.
$38-$3B Pointer to uncompressed art.
$3C-$3F Pointer to dPLCs.
$40-$41 Address of art in VRAM (the same as starting art block * $20)


Sonic Community Hacking Guide
General
Sonic Music Hacking Guide | SonED2 Manual
Game-Specific
Sonic the Hedgehog (16-bit) | Sonic the Hedgehog (8-bit) | Sonic Eraser | Sonic CD (prototype 510) | Sonic CD | Sonic CD (PC) | Sonic CD (2011) | Sonic 2 (Nick Arcade prototype) | Sonic 2 (Simon Wai prototype) | Sonic 2 (16-bit) | Sonic 2 (8-bit) | Sonic 2 & Knuckles | Dr. Robotnik's Mean Bean Machine | Sonic Triple Trouble | Sonic 3 | Sonic & Knuckles | Sonic the Hedgehog 3 & Knuckles | Sonic & Knuckles Collection | Sonic Crackers | Sonic 3D: Flickies' Island | Chaotix | Sonic R PC | Sonic Jam 6 | Sonic Advance | Sonic Advance 2 | Sonic Advance 3 | Sonic Battle | Sonic Adventure | Sonic Adventure DX: Director's Cut | Sonic Adventure DX: PC | Sonic Adventure (2010) | Sonic Adventure 2 | Sonic Adventure 2: Battle | Sonic Adventure 2 (PC) | Sonic Heroes | Shadow the Hedgehog | Sonic Riders | Sonic the Hedgehog (2006) | Sonic & Sega All-Stars Racing | Sonic Unleashed (Xbox 360/PS3) | Sonic Colours | Sonic Generations | Sonic Lost World | Sonic Forces
Legacy Guides
The Nemesis Hacking Guides The Esrael Hacking Guides
ROM: Sonic 1 | Sonic 2 | Sonic 2 Beta | Sonic 3

Savestate: Sonic 1 | Sonic 2 Beta/Final | Sonic 3

Sonic 1 (English / Portuguese) | Sonic 2 Beta (English / Portuguese) | Sonic 2 and Knuckles (English / Portuguese)
Move to Sega Retro
Number Systems (or scrap) | Assembly Hacking Guide | Subroutine Equivalency List | 68000 Instruction Set | 68000 ASM-to-Hex Code Reference | VDP Documentation | Official Sega 32X Documentation | Official Mega-CD Documentation | Official Sega Mega Drive Documentation