Game Boy format

This document describes the format of data in Prince of Persia 1 for the Game Boy (GB) and the Game Boy Color (GBC).

General

Byte order: Little-endian (Intel) byte order is used, unless noted otherwise.

Numbering of bits: The least significant bit of a byte is bit 0, the most significant bit of a byte is bit 7.

Addresses: The Game Boy (Color) uses banked ROM.

• Offsets 0x0000..0x3FFF always refer to the first 16 kB of the ROM.
• Offsets 0x4000..0x7FFF refer to the currenly paged 16 kB bank.
  • Linear Address = Bank * 0x4000 + (Offset - 0x4000) = (Bank << 14) | (Offset & 0x3FFF)

Versions:

• Game Boy Color, Europe
• Game Boy, Europe
• Game Boy, Japan
• Game Boy, USA

Levels

The level table

Offset:

• GBC: 0x1DC2C..0x1DC51, 19 levels
• GB (EU/JP/US): 0x1E189..0x1E1A8, 16 levels

For each level, there is a 2-byte offset, to be understood in the same Bank where the table is (Bank 7).

The levels are numbered as:

• Level 0: Various. (Palace in the #Level settings, i.e. used for princess room.)
  • Room 1: menu (select new game, continue, or training)
  • Room 2: password (linked from room 1)
  • Room 5: princess room (intro and cutscenes) (the starting position points here)
  • Room 6: language select (EU only) (also exists in the JP version, but not used)
  • Room 8 (GBC): left of princess room (linked from room 5)
• Levels 1-14 match the DOS version.
• Level 15 (GBC): Princess room. (ending)
• Level 16 (GBC) / Level 15 (GB): Same offset as level 0. (But it's dungeon in the #Level settings, i.e. used for the other rooms of that level.)
• Level 17 (GBC): Training part 1.
• Level 18 (GBC): Training part 2.

Compression

• 1 byte: Number of replacement pairs.
• For each replacement pair:
  • 1 byte: "left"
  • 1 byte: "right"
• 2 byte: Length after decompression.
• Compressed data follows:

repeat while you don't have enough output bytes:
	read 1 byte from input;
	if the byte appears in "left":
		count := 1;
		repeat:
			read 4 bits from input through a 8-bit queue into value;
			That is:
				first time, you read a byte from input and use bits 7..4;
				second time, you use bits 3..0 of the already read byte and discard the byte.
			count := count + value;
		while value = 0xF;
		output the byte, repeated count times;
	else if the byte appears in "right":
		output the corresponding "left" byte;
	else:
		output the byte as is;
	end if;
end repeat;

Level format

Tiles:

• For each 24 rooms:
  • For each 30 tiles:
    • 1 byte: Tile. The bottom 5 bits are the tile type (0x00..0x1F); the top 3 bits are the modifier (0..7). See #Tile types.
  • Or: A single 0xFF byte, meaning that all tiles are 0x00. (This is a second layer of compression.)

Room links:

• For each 24 rooms:
  • For each direction in left, right, above, below:
  • 1 byte: The room adjacent in that direction.
    • Bottom 7 bits: room number. (1..24, or 0 for no room.)
    • Top 1 bit (GBC): if 1, the next level will start when the prince exits the room in that direction. (Used on levels 6, 12, 14, 17.)

Starting place:

• 1 byte: Starting room. (1..24)
• 1 byte: Starting tilepos. (0..29)
• 1 byte: Starting direction. (0x00=right, 0xFF=left)

Guards:

• For each 24 rooms:
  • 1 byte: Guard info. The bottom 7 bits are the tilepos. (0..29, or 30 if there is no guard) The top 1 bit is the direction. (0=right, 1=left)

Door links:

• For each door link:
  • 1 byte: button room (1..24)
  • 1 byte: button tilepos (0..29)
  • 1 byte: effect: 0 = close, 1 = open
  • 1 byte: target room (1..24)
  • 1 byte: target tilepos (0..29)
• 1 byte: 0xFF, marks the end of door links and level data.

Tile types

These mostly match the DOS version.

Modifiers were usually copied from (the bottom 3 bits of) the modifiers the DOS levels, even for tiles where this makes no difference. For example, many empty tiles have 7 as modifier where the DOS level had 0xFF.

tile id	tile type	modifiers and notes
0x00	empty	0 = nothing, 1 or 2 = wall pattern (in dungeon), 3 = window
0x01	floor	0 = nothing, 1 = wall pattern (in dungeon)
0x02	spikes
0x03	column
0x04	gate	1 = open, 2 = closed, others = open (not used)
0x05	mirror after jump	Palace only. Not used in level data: 0x0D becomes this after the prince jumps through it. Same as 0x0D, except: No reflection. No black rectangle. The prince won't lose HP if he jumps through it.
0x06	close button	The modifier is ignored, door links are stored differently from the DOS version.
0x07	gate top with floor	0 = with arch, 1 = black, 2 = with pattern
0x08	big column bottom
0x09	big column top
0x0A	potion	0 = used in password room (+1 hp), 1 = heal (+1 hp), 2 = life, 3 = float, 4 = appears on level 9 where the DOS version has the flip potions (+1 hp), 5 = hurt (-1 hp), 6 or 7 = (not used) (+1 hp)
0x0B	loose floor
0x0C	gate top without floor	0 = with arch, 1 = black, 2 = with pattern
0x0D	mirror	Palace only. Not used in level data: Placed on level 4 when the exit door opens. Different from DOS: it occupies the right edge of the tile, and the rest is covered by a black rectangle to cover the reflection. Reflection appears only on level 4 room 4.
0x0E	broken floor
0x0F	open button	The modifier is ignored, door links are stored differently from the DOS version.
0x10	level door left	0 = open (language/menu rooms), 2 = closed (regular levels), others = open (not used)
0x11	level door right
0x12	chomper
0x13	torch
0x14	wall
0x15	skeleton
0x16	sword	Dungeon only.
0x17	mirror left	Palace only. Not used in level data. Placed on left side of mirror to cover the mirror image, and there it appears as a black rectangle.
0x18	balcony	Appears as a regular floor. Used on level 6 and 14 where the DOS version has the right half of balconies.
0x19	arch column
0x1A	arch down	Palace only.
0x1B	small arch	Palace only.
0x1C	big arch left	Palace only.
0x1D	big arch right	Palace only.
0x1E	torch with broken floor	Not used in level data: a regular torch becomes this when a loose floor lands on it.
0x1F	shadow floor	Appears only when you step on it. Used on level 12.

Level settings

GB:

• 0x000CE..0x000DC: guard HPs, indexed by level
• 0x000DD..0x000EB: guard move(?) probability, indexed by level
• 0x000EC..0x000FA: guard move(?) delay, indexed by level
• 0x1E1A9..0x1E1B8: Level types: 0 = dungeon, 1 = palace
• 0x1E1B9..0x1E1C8: type of level entry?
  • 0x05 = short run (level 1)
  • 0x08 = long run (level 13)
  • 0x2C = fall (level 7)
  • 0x67 = standing (most levels)
  • 0x7B = princess (level 0)

GBC:

• 0x00041..0x00047: guard colors, indexed by HP
• 0x000BA..0x000CC: guard HPs, indexed by level
• 0x000CD..0x000DF: guard move(?) probability, indexed by level
• 0x000E0..0x000F2: guard move(?) delay, indexed by level
• 0x1DC52..0x1DC64: Level types: 0 = dungeon, 1 = palace, 2 = dungeon (training), 3 = palace (princess room)
• 0x1DC65..0x1DC8A: level palette selection (2-byte offsets, to be understood in Bank 2)
  • 0x47D0 = (dungeon) blue (level 1, 12, 13, 16)
  • 0x5BB4 = (palace) orange (level 4)
  • 0x6EE0 = (dungeon) red (level 17, 18)
  • 0x6F20 = (palace) pink (level 0, 14, 15)
  • 0x6F60 = (dungeon) green (level 7)
  • 0x6FA0 = (dungeon) brown (level 2)
  • 0x6FE0 = (dungeon) purple (level 3)
  • 0x7020 = (dungeon) teal (level 8)
  • 0x7060 = (dungeon) maroon (level 9)
  • 0x70A0 = (palace) green (level 6)
  • 0x70E0 = (palace) blue (level 5)
  • 0x7120 = (palace) red (level 10)
  • 0x7160 = (palace) yellow (level 11)
• 0x1DC8B..0x1DCB0: sprite palette selection (2-byte offsets, to be understood in Bank 2)
  • 0x71A0 = (most levels)
  • 0x71E0 = (level 6, 7)
  • 0x7220 = (level 5)
  • 0x7260 = (level 10)
  • 0x72A0 = (level 11)
  • 0x72E0 = (level 14)
• 0x1DCB1..0x1DCC3: Type of level entry:
  • 0x05 = short run (level 1, 15, 18)
  • 0x08 = long run (level 13)
  • 0x2E = fall (level 7)
  • 0x6A = standing (most levels)
  • 0xA4 = princess (level 0)

Palettes (GBC)

A palette is 64 bytes long, and contains 32 colors, grouped into 8 sets of 4 colors each.

Each color is stored on 16 bits (2 bytes):

• Bits 0..4: Red Intensity. (0x00..0x1F)
• Bits 5..9: Green Intensity. (0x00..0x1F)
• Bits 10..14: Blue Intensity. (0x00..0x1F)
• Bit 15: Unused.

Offsets:

• 0x087D0..0x0880F: level background palette: 1 set of 32 colors, referenced from #Level settings
• 0x09BB4..0x09BF3: level background palette: 1 set of 32 colors, referenced from #Level settings
• 0x0AEE0..0x0B19F: level background palettes: 11 sets of 32 colors, referenced from #Level settings
• 0x0B1A0..0x0B31F: level sprite palettes: 6 sets of 32 colors, referenced from #Level settings
• 0x1137F..0x113AE: title screen background palette
• 0x12B96..0x12BC5: story frame+text background palette
• 0x2925C..0x2929B: copyrights screen background palette (Red Orb)

Texts

version	story texts table offset	copyrights text offset	credits texts offsets	story text languages
GBC	0x12FEE	see #Other graphics (GBC)	0x13016, 0x13033, 0x1304B, 0x13070, 0x1308F	German, French, Spanish, English, Italian
GB EU	0x13087	0x130AF	0x131DE, 0x131F9, 0x1321D, 0x1323C, 0x1325D	German, English, Spanish, French, Italian
GB JP	0x13087	0x130AF	0x13205, 0x1322A, 0x1324E, 0x1326D, 0x1328E	(ununsed), Japanese, (unused), (unused), (unused)

The story texts table contains 20 offsets (2 bytes each) for each 4 occasions (intro 1, intro 2, bad ending, good ending) and for each 5 languages.

Fonts are stored in #Tilesets.

European

The decoding of European texts:

• Repeat until you meet the end of text marker:
  • Read a byte.
  • Subtract 0x20 and truncate the result to a byte.
  • The lower 6 bits tell the index of the character within the font.
  • The upper 2 bits tell what is after the character:
    • 00 = nothing
    • 01 = new line
    • 10 = space
    • 11 = end of text

The character set:

 !"Ñ$Ç&'®®©+,-./
0123456789:Ù¡=¿?
ÄABCDEFGHIJKLMNO
PQRSTUVWXYZÖÜÀÈÌ

• This mostly corresponds to range 0x20..0x5F from ASCII, but most symbols were replaced with accented letters or other symbols.
• The zero is used for Ø in BRØDERBUND's name.
• The two instances of ® are the top and bottom halves.

Japanese

This is only for story texts, the others are encoded as European.

The decoding of Japanese texts:

• Repeat until you meet the end of text marker:
  • Read a byte.
  • It can have the following values:
    • 0x00..0x7F = The index of the character within the font.
    • 0xFE = new line
    • 0xFF = end of text

The character set:

　んわらやまはなたさかあゃぁりみ
ひにちしきいぃるゆむふぬつすくう
ゅっれめへねてせけえぇをろよもほ
のとそこおょぉンワラヤマハナタサ
カアャァリミヒニチシキイィルユム
フヌツスクウュッレメヘネテセケエ
ェヲロヨモホノトソコオョォ？！゛
゜」「…、。ゥー６０

• This is different from all encodings that I've seen so far.
• There is some logic if you compare it with the usual syllable tables:
  • Elsewhere, the syllables are ordered first by consonant (-,K,S,T,N,H,M,Y,R,W), and then by vowel (A,I,U,E,O).
  • Here, the syllables are ordered first by vowel (A,I,U,E,O), and then by consonant, but in reverse order (W,R,Y,M,H,N,T,S,K,-).

Sprites (GBC)

start address	size of each item	contents
0x28000	2 bytes	map offset (b/w)
0x28168	2 bytes	map offset (color)
0x282D0	2 bytes	tiles offset (b/w)
0x28438	2 bytes	tiles offset (color)
0x285A0	1 byte	bank for map and tiles (b/w)
0x28654	1 byte	bank for map and tiles (color)
0x28708	1 byte	X offset in tiles (+ = backwards)
0x287BC	1 byte	X hit test?
0x28870	1 byte	Y offset in tiles (+ = up)
0x28924	1 byte	Y hit test?
0x289D8	2 bytes	offset of associated sound effect (in bank 0x0F), see #Sound effects (GBC)
0x28B40	1 byte	?
0x28BF4	1 byte	?
0x28CA8	1 byte	flags bit 0: unknown bit 1: unknown bit 2: Does the char press the floor? Used with loose floors and buttons. bit 3: unknown

• Every table has 0xB4 = 180 items.
• It seems that the Color version can run in b/w mode as well, with different graphics. Change the byte at offset 0x143 to 0x00 for this.
• Offsets and banks can be all zero, in this case there are no sprites in this group.

At the map offset there is the following data:

• 1 byte: number of images in sprite group
• 1 byte: width of each image
• 1 byte: height of each image
• for each image:
  • for each row:
    • for each column:
      • 1 byte: 1-based index of tile, or 0 for none

At the tile offset there is the following data:

• 1 byte: compression marker
• 1 byte: number of tiles
• for each tile:
  • 4 bits: compressed size of tile in bytes (first read bits 7..4, then read bits 3..0)
  • Possible values are 9..15, and 0 which means 16.
• (pad to whole byte using 0 bits, if necessary)
• for each tile:
  • for each pixel row: (0..7)
    • Read 1 byte.
    • If it's equal to the compression marker, repeat the last two bytes.
    • Otherwise, output the byte, read another byte, and output it as well.

Tiles

The Game Boy (Color) uses 2-bit planar tiles.

Tiles are in this format: (after decompression)

for B=0..7:
	byte B of plane 0
	byte B of plane 1

To get the color index of a pixel, from X and Y coordinates:

color = 0
for P=0..1:
	read bit 7-X of byte Y of plane P of the tile, and write it into bit P of color

This color index can be further modified by colormaps. See #Maps.

Other graphics (GBC)

Tilesets

They use the same compression as sprite tiles.

• 0x08810: color dungeon
• 0x09BF4: color palace
• 0x0AA57: status bar
• 0x101B8: b/w intro+font
• 0x113BF: color intro+font
• 0x1240E: b/w font+frame
• 0x12BD6: color font+frame
• 0x20004: b/w spikes
• 0x20023: b/w spikes?
• 0x20045: b/w spikes?
• 0x20066: color spikes
• 0x20087: color spikes?
• 0x200AE: color spikes?
• 0x200D7: ??? dungeon button
• 0x20143: ??? palace button
• 0x201B4: ??? dungeon button
• 0x2021D: ??? palace button
• 0x22306: b/w dungeon
• 0x231D2: b/w palace
• 0x2929C: Red Orb credits

Maps

• Tilesets are from the list above.
• Maps are not compressed.
• Colormaps: the lower 3 bits of each byte contain which 4-color group of the palette (0..7) to use for each tile.
  • I.e. bits 4..2 of the color index come from the colormap, while bits 1..0 come from the tile itself.

tileset offset	map offset	colormap offset	width	height	contents
0x08810	0x08000	0x083E8	2	5*100	color dungeon tiles
0x09BF4	0x093E4	0x097CC	2	5*100	color palace tiles
0x101B8	0x10050	-	20	18	b/w title
0x113BF	0x1105F	0x11217	20	18	color title
0x1240E	0x122A6	-	20	18	b/w story frame
0x12BD6	0x12876	0x12A2E	20	18	color story frame
0x22306	0x21F1E	-	2	5*100	b/w dungeon tiles
0x231D2	0x22DEA	-	2	5*100	b/w palace tiles
0x2929C	0x28D5C	0x28FDC	20	32	Red Orb credits

Other

There is an unused sprite group with map offset = 0x3B444, tiles offset = 0x3B523. It seems to show a pile of bones becoming a guard!?

Offsets 0xA9DF..0xAA56 contain various bits that can appear in the status bar. To be used with the tileset at 0x0AA57.

At offset 0xB320 there is some data compressed using the same method as the levels. If forms a nice 32*32 array, and it seems to be used in room drawing.

Sound effects (GBC)

Sound effects are stored at offsets 0x3C000..0x3C0B3.

Format:

• Read 1 byte:
  • 0x01 = fill sound registers 0xFF10..0xFF14 from the next 5 bytes (sound channel 1)
  • 0x02 = fill sound registers 0xFF16..0xFF19 from the next 4 bytes (sound channel 2)
  • 0x04 = fill sound registers 0xFF20..0xFF23 from the next 4 bytes (sound channel 4)
  • otherwise (usually 0x00) = end

The meaning of each register can be found in various Game Boy hardware specifications.

Various hacks (GBC)

meaning	offset	size	default value	new value
Starting minutes	0x0191	1 byte	0x3C = 60
Starting HP (for both new game and training)	0x080D	1 byte	0x03 = 3
Training level number - 1	0x0664	1 byte	0x10 = 16 = level 17
Skip most of the intro and start the training level directly.	0x02E3	3 bytes	0xCD 0x5F 0x20	0xC3 0x63 0x06
Skip Red Orb screen.	0x023E	2 bytes	0x38 0xF7	0x18 0x19

TODO

• (Music?)