SCHG:Sonic the Hedgehog (16-bit)

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ROM Hacking

Art Editing

There are several different tools that can be used to edit art besides the hex editor. SonED is probably the best tool to use for editing level art, and can also be used on palettes. HivePal is also a great tool for editing palettes. Sonik Sprite is useful for editing uncompressed art; it gets its name from its ability to edit Sonic's sprites. LOst Library is most likely the best choice for editing compressed art in the Nemesis format.

If, however, you still want to do it yourself, your best bet is to download the Sonic 1 Split disassembly. Decompress the archive into a new folder, and place your S1 ROM, in binary format and named "S1.bin", in that folder. Run the batch file "split.bat". This will split up all the art into its own binary files, which you can then decompress and edit. When you're done, run "combine.bat".

Uncompressed Art Locations

Most of this information was taken from Nemesis's guide. Please excuse any mistakes or misunderstandings, as that guide wasn't exactly well-written. A description is written in parentheses after the original name if I deem it necessary; if I don't know what it is, "Unknown" appears in that place. Please correct this if you know. It doesn't list the number of blocks taken up, so if you know, put it in. Otherwise, I'll find out eventually.

Uncompressed Art Locations

Offset	Description	# of blocks
Zone Independent
$1CADA	Numbers used on counters in game	?
$21AFE	Sonic	?
$6A324	Giant Ring	?
Green Hill Zone
$66AD6	Waterfall tiles	?
$66CD6	Flower with pointy petals	?
$670D6	Flower with curved petals	?
Marble Zone
$6755A	Lava surface	?
$67836	Lava	?
$67E56	Flame torch against stone	?
Scrap Brain Zone
$68156	Steam in background	?

Compressed Art Locations - Nemesis

See SCHG:Sonic the Hedgehog/Nemesis Compressed Art.

Compressed Art Locations - Kosinski format

• $3DCF2 - GHZ main level patterns
• $414D4 - LZ main level patterns
• $46016 - MZ main level patterns
• $4A7FE - SLZ main level patterns
• $510F0 - SYZ main level patterns
• $57A66 - SBZ main level patterns

Palette Locations

Usually, it's not really necessary to edit a palette in hex. Palette editors give you instant feedback for each RGB value, and the palette can be easily saved as a separate binary and reimported into the ROM. However, it is sometimes desireable or necessary to do it in hex, and it can't hurt to know how it's done.

These are the ROM offsets of the palettes in Sonic 1, as listed by HivePal:

Name	Offset
Sega Logo (Background)	$2208
Sega Logo (SEGA)	$20C0
Title Screen	$2288
Title Screen - Water Cycle	$1B66
Level Select	$2308
Sonic	$2388
Green Hill	$23A8
Green Hill - Water Cycle	$1B86
Labyrinth	$2408
Labyrinth - Sonic Underwater	$2828
Labyrinth - Sonic Underwater (Alt)	$2468
Labyrinth - Underwater	$2488
Labyrinth - Water Cycle	$1BA6
Labyrinth - Conveyor Cycle	$1BC6
Labyrinth - Conveyor Cycle Underwater	$1BD8
Marble	$24E8
Star Light	$2548
Star Light lights	$1C52
Spring Yard	$25A8
Spring Yard - Cycle 1	$1C76
Spring Yard - Cycle 2	$1C96
Scrap Brain Act 1	$2608
Scrap Brain Act 2/Final	$2668
Scrap Brain Act 3	$2748
Scrap Brain Act 3 - Sonic Underwater	$2848
Scrap Brain Act 3 - Sonic Underwater (Alt)	$27A8
Scrap Brain Act 3 - Underwater	$27C8
Scrap Brain Act 1/Act 2 - Cycle 1	$1D0A
Scrap Brain Act 1/Act 2 - Cycle 2	$1D1A
Scrap Brain Act 1/Act 2 - Cycle 3	$1D2A
Scrap Brain Act 1/Act 2 - Cycle 4	$1D3A
Scrap Brain Act 1/Act 2 - Cycle 5	$1D46
Scrap Brain Act 1/Act 2 - Cycle 6	$1D56
Scrap Brain Act 1/Act 2 - Cycle 7	$1D66
Scrap Brain Act 1/Act 2 - Cycle 8	$1D86
Scrap Brain Act 2 - Cycle 1	$1D90
Scrap Brain Act 2 - Cycle 2	$1DA0
Scrap Brain Act 3 - Water Cycle	$1BEA
Special Stage - Sonic	$26C8
Special Stage No. 1	$26E8
Special Stage No. 2	$2708
Special Stage No. 3	$2728
Special Stage Title Card	$2868
Special Stage Cycle 1	$4ACA
Special Stage Cycle 2	$4B12
Special Stage Cycle 3	$4B92
Continue - Sonic	$28E8
Continue	$2908
Ending - Sonic	$2928
Ending	$2948

Object Editing

Object Pointer List

ID #	Description	Code	Mappings	Subparameters
01	Sonic	$12BD8	??
02	????	$D5B2	??
03	????	$D5B2	??
04	????	$D5B2	??
05	????	$D5B2	??
06	????	$D5B2	??
07	????	$D5B2	??
08	LZ water splash	$142F0	??
09	Sonic in Special Stage	$1B984	??
0A	Drowning countdown numbers	$13C98	$14152
0B	LZ vertical pole	$11206	$11326 $11331	$00 - Unbreakable $01 - Breaks in 1 Seconds $02 - Breaks in 2 Seconds $03 - Breaks in 3 Seconds $04 - Breaks in 4 Seconds $05 - Breaks in 5 Seconds $06 - Breaks in 6 Seconds
0C	LZ doors that open and close	$11346	??	$02
0D	End of level signpost	$EB28	??
0E	????	$A61C	??
0F	????	$A69C	??
10	????	$1C022	??
11	GHZ Bridge	$7328	??	$06 - 6 logs $07 - 7 logs $08 - 8 logs $09 - 9 logs $0A - 10 logs $0B - 11 logs $0C - 12 logs $0D - 13 logs $0E - 14 logs $0F - 15 logs

RAM Hacking

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	Metablock table
$F600	Screen Mode $00 - Sega Screen $04 - Title Screen $08 - Demo Mode $0C - Normal Level $10 - Special Stage $14 - Continue Screen $18 - Ending Sequence $1C - Credits
$F616-$F617	Camera Y Position for previous frame
$F618-$F619	Value of $F70C for previous frame
$F61A-$F61B	Camera X Position for previous frame
$F61C-$F61D	Value of $F708 for previous frame
$F61E-$F61F	Value of $F71C for previous frame
$F620-$F621	Value of $F718 for previous frame
$F680	Address queue for Pattern Load Cues
$F700-$F701	Camera X Position
$F704-$F705	Camera Y Position
$F744	Scroll Hold Flag (set to stop all scrolling dead)
$F754-$F755 $F756-$F757 $F758-$F759 $F75A-$F75B	Bitfields used by the scrolling engine
$F760-$F761	Sonic's Top Speed
$F762-$F763	Sonic's Acceleration
$F764-$F765	Sonic's Deceleration
$F7AA	Screen Lock Flag (Set to lock screen)
$F7C8	Control Lock Flag (Set to lock controls)
$FA00-$FA80	Underwater Palette Storage
$FE02	Restart Level Flag (Set to restart level)
$FE04	Level Timer
$FE10-$FE11	Zone/Act
$FE12-$FE13	Rings
$FE14	Remaining Air (When underwater)
$FE16	Last Special Stage Entered
$FE18	Continues
$FE1C	Lives Counter (Set to update lives total on screen)
$FE1D	Ring Counter (Set to update rings total on screen)
$FE1E	Time Counter (Set to update current time on screen)
$FE1F	Score Counter (Set to update score total on screen)
$FE26-$FE29	Score
$FE2C	Shield Flag (Set to take a single hit without losing rings)
$FE2D	Invincibility Flag (Set to make Sonic invincible)
$FE2E	Speed Shoes Flag (Set to activate speed shoe physics)
$FE30	Lamppost Counter
$FE57	Emeralds
$FFF4	Credits Index Number

Sprite Status Table

The Sprite Status Table is located at RAM address $D000. Each entry is $40 bytes long. Here is a list of all the values for one entry in the SST:

Offset	Size	Description
$00	byte	Object type
$01	byte	Action 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. Sonic uses the playfield positioning system. Bits 3, 4, and 5 are either unused, or their purpose is unknown. Bit 6 is Sonic's "Ride B" flag Bit 7 is the draw object flag. It will be set if the object was onscreen when it came time to draw things. Otherwise, it is clear. There should be no reason to edit this flag, but it's good to know what it does.
$02	word	Starting art block. First nybble: Palette line the sprite will use. Latter 3 nybbles: Starting art block in VRAM for which the object reads from. Multiply by $20 to get VRAM address; divide VRAM address by $20 to get this value.
$04	long	Mappings offset
$08	word	If in playfield positioning mode, it is the X playfield coordinate. If in screen positioning mode, it is the X screen coordinate.
$0A	word	If the object is in playfield positioning mode, this is the X subpixel coordinate. If in screen positioning mode, it's the Y screen coordinate.
$0C	word	If in playfield positioning mode, it is the Y playfield coordinate. If in screen positioning mode, it is unused.
$0E	word	If the object is in playfield positioning mode, this is the Y subpixel coordinate. If in screen positioning mode, it is unused.
$10	word	Horizontal (X) velocity
$12	word	Vertical (Y) velocity
$14	byte	Ground velocity (inertia).
$16	byte	Height/2
$17	byte	Width/2
$18	byte	Sprite priority (00 = front).
$19	byte	Width of the object, in pixels
$1A	byte	Current animation frame to display. i.e, the frame currently being displayed on-screen, according to the animation script (currently parsed mappings frame, in other words).
$1B	byte	Current frame in animation script. i.e, the frame entry IN the animation script being currently processed.
$1C	byte	Animation number. When an animation ID is moved here, it's processed and displayed.
$1D	byte	Restart animation flag (when $1D is not equal to $1C, animation restarts)
$1E	byte	Animation frame duration (time until next frame).
$20	byte	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.
$21	byte	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	byte	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 Unknown or unused. 5 $20 Set if Sonic is pushing on this object. 6 $40 Unknown or unused. 7 $80 Unknown or unused. Note that these bits have different meanings for Sonic (see below).
$23	byte	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	byte	Routine counter.
$25	byte	Second routine counter. This is used for some of the more complicated objects.
$26	word	Angle.
$28	byte	Object subtype. For example, the current monitor selected. See the Object List above for values. Has a different meaning for Sonic.
$29-$3F		Object's scratch RAM
Object-specific variables
Offset	Size	Description
$22	byte	Sonic: Special bitfield. Counting from the least significant bit: Bit Hex Description 0 $01 Orientation. Clear is left and set is right. 1 $02 Set if Sonic is in the air (jump counts). 2 $04 Set if jumping or rolling. 3 $08 Set if Sonic 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 the first 3 bits (0-2) are used in the character object as a second routine counter.
$28	byte	Sonic: 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.
$2B	byte	Sonic: Unused
$30-$31	word	Sonic: Remaining invulnerability time. Starts at $0078 after Sonic is hit, and seems to decrement every frame until it reaches $0000.
$32-$33	word	Sonic: Remaining time of invincibility.
$34-$35	word	Sonic: Remaining time of Speed Shoes.
$36	byte	Sonic: Angle of ground at Sonic's front collision hot spot ($03 is "edge of ground")
$37	byte	Sonic: Angle of ground at Sonic's rear collision hot spot
$39	byte	Sonic: Unused.
$3A-$3B	word	Sonic: Unused.
$3C	byte	Sonic: Set if jumping.
$3D	byte	Sonic: SST index of object currently being stood on. (multiply by $40 and add $D000 to get the object's address).
Boss Variables
Offset	Size	Description
$21	byte	Hit counter. Number of hits it takes to defeat a boss.
$30	word	X position
$38	word	Y position
$3E	byte	Number of times to flash when hit