SEGA Master System format

This document describes the format of data in Prince of Persia 1 for the Sega Master System.

(A similar but slightly different version was released for the Sega Game Gear.)

General

Byte order

Little-endian (Intel) byte order is used, unless noted otherwise. This is the native endianness of the Z80 CPU in the Sega Master System.

Addresses

There are two kinds of addresses (pointers) in the ROM. Both are stored on 2 bytes.

1. Linear addresses. These are simply an address into the ROM. Linear pointers can address only the first 64 kiB of the ROM, but they can point to any byte within that area.

2. Banked addresses. These can be converted to linear addresses with the following code:

int BankedToLinear(int address) {
	int bank = address & 0x000F;
	int offset = address & 0xFFF0;
	// assert(0x8000 <= offset && offset <= 0xBFFF);
	return (bank << 14) + (offset - 0x8000);
}

Banked pointers can address the whole 256 kiB of the ROM, but only in increments of 16 bytes.

Levels

The level table

The level table starts at offset 0x6A7C. (TODO: In the Game Gear version it starts at 0x719C.)

There are 14 levels. The table stores 20 bytes about each level:

Size	Contents
2 bytes	Always 0x60C9.
2 bytes	Banked address of graphics tiles: 0x8003 (0x0C000) for dungeon levels, 0x94C3 (0x0D4C0) for palace levels.
2 bytes	Linear address of level tiles (2x2 blocks of graphics tiles): 0xA5B2 for dungeon levels, 0xA8D2 for palace levels.
2 bytes	Banked address of level's #Graphics map.
1 byte	Level type: 0x05=dungeon, 0x85=palace.
1 byte	Starting direction: 0x00=left, 0x20=right.
1 byte	Starting X coordinate.
1 byte	Starting Y coordinate.
1 byte	Starting room. (0..23)
1 byte	Starting animation.
4 bytes	Unknown. Their values are frequently similar to the previous 4 bytes.
2 bytes	Linear address of the level's #Room links and objects table.

Graphics map

The first 64 bytes contain the list of level tiles used in the map. Unused entries are filled with 0xFF.

After that comes the map itself. Each level is 128 tiles wide and 36 tiles tall. (Levels 13 and 14 are shorter, they are only 24 and 12 tiles tall, respectively.)

Each tile index is stored on 6 bits, so the level is 128*6/8 = 96 bytes wide.

The bits are read starting from the least significant bit of each byte.

The map consists of 24 rooms arranged in 3 rows and 8 columns. (Level 13 and 14 contain only 2 and 1 rows of rooms, respectively.) Each room is 36/3=12 tiles tall and 128/8=16 tiles wide.

(TODO: Which tiles are walls or floors?)

Room links and objects table

This table is preceded by a 2-byte number which tells the length of the following chunk of data. All offsets stored within this table are interpreted as offsets within this chunk.

The data within the chunk is arranged as follows:

Size	Contents
24*2 bytes	The offset of the #Objects' data for each room. Zero if the room doesn't exist.
24*4 bytes	Room links for each room. Unlike in most other versions of PoP, their order is above,right,below,left. The rooms are numbered from 0 to 23 (0x00 to 0x17). 0xFF means no room. 0x80 means a special exit (used on level 6 and 12).
the rest	#Objects' data.

Level 14 is special: Only the first 8 rooms exist. The rest of the rooms have zero offsets. The room links are included only for the first 5 rooms.

You can detect the number of rooms from the first offset: (offset-0x30)/4 gives how many rooms have room links.

Objects' data

Each object is stored as a byte telling what kind of object it is, followed by argument bytes whose number and meaning depends on the type of the object.

(TODO: figure out the unknown argument bytes)

value	object	argument bytes	notes
0x27	level door	xx yy ?? 07 ?? ?? ??	x*=8,y*=8; If fourth byte is not 07 then the door opens by itself.
0x29	mirror? (level 4)	xx yy
0x2B	spike	xx yy
0x2C	sword	xx yy
0x2D	red (hurt) potion	xx yy
0x2E	blue (heal) potion	xx yy
0x2F	green (life) potion	xx yy
0x30	pink (slow fall) potion	xx yy
0x31	chomper	xx yy
0x32	gate	xx yy cl ?? op ?? ??	op: 0-5
0x3E	skeleton wake up (level 3)	xx yy	x*=32,y*=64;
0x3F	skeleton continue (level 3)	xx yy	x*=32,y*=64;
0x40	skeleton (level 3)	xx yy	Used after the other two skeleton objects, but why?
0x41	loose floor	xx yy	x*=8,y*=8;
0x42	falling loose floor (level 13)	xx yy	x*=8,y*=8;
0x61	close button	xx yy 00 ln ln	x*=8,y*=8; ln: address of triggered object within the level data chunk. For some reason, exit doors are always triggered by close buttons.
0x62	open button	xx yy 00 ln ln	x*=8,y*=8; ln: address of triggered object within the level data chunk.
0x64	guard type	tp tp	(TODO: what does the argument mean?)
0x66	shadow steps (level 6)	xx yy
0x69	shadow steals (level 5)	xx yy
0x6F	princess (level 14)	xx yy
0x70	mouse (level 8)	xx yy
0x74	shadow fights (level 12)	xx yy
0xB5	guard	xx yy
0xDE	shadow from mirror? (level 4)	xx yy
0xFF	end	-	Marks the end of object data for this room.

TODO

• Tiles
• Sprites
• Texts
• (Music???)