Castlevania II: Belmont's Revenge/RAM map

The following article is a RAM map for Castlevania II: Belmont's Revenge.

Please add more.

Legend: [u] is unsigned, [s] is signed, [d] is binary-coded decimal. [2] is a 2 byte word, [3] and so on likewise. [p] is a 2-byte pointer. [b] is big-endian; otherwise, values are assumed to be little-endian.

During entity update routines, register d stores the high byte of the entity data. Belmont's data begins at c000, so d is always c0 during belmont's update routine. Most of Belmont's entity data, such as the velocity data, repeats every 0x100 bytes for subsequent entities.

0x7FFF [u] index of currently-loaded swappable bank.
0xC001 Belmont state (0: standing. 1: walking. 2: crouching. 3: jumping.)
0xC002 Belmont's substate (0: none. 1: attacking, including both whip and subweapon. 2: knockback.)
0xC008 flags set when Belmont is hurt? Reset bits 0 and 1 to induce iframes; set bit 7 to cause knockback.
0xC009 Belmont's facing (CHR code). Bit 5 is Belmont's facing (20: left. 0: right.); bit 6 is Belmont's vertical flip, etc.
0xC00A Belmont's image. (see "Images" in ROM map.)
0xC00B Belmont's animation frame minus animation base (?)
0xC00C Belmont's animation timer (when walking, repeatedly counts down from C to 0)
0xC00F [s2] Belmont's Y velocity. Negative is upward
0xC011 [u] Belmont's Y subpixel
0xC012 [u] Belmont's Y pixel
0xC014 [s2] Belmont's X velocity. Negative is leftward.
0xC016 [u] Belmont's X subpixel
0xC017 [u] Belmont's X pixel
0xC018 [u] hitstun
0xC300 [u] subweapon projectile id. (0 if no subweapon being thrown currently; 1 if cross/axe; 2 if holy water.)
0xC301 [u] subweapon mode. (0: belmont is still winding up to toss. 1: in the air. 2: become flame/return [cross])
0xC880 game mode (0: konami logo. 1: title screen. 2: title fade-in. 3: stage select and title screen selected. 4: stage entry. 5: normal gameplay. 6: death. 7: game over. 9: Credits. D: password entry. E: intro reel.)
0xC882 global 1-byte game timer
0xC886 current input (1: right. 2: left. 4: up. 8: down. 10: A. 20: B. 40: select. 80: start)
0xC887 input pressed (like 0xC886, but only what was just pressed this frame.)
0xC8C0 current stage (0: plant (glitched). 1: plant. 2: crystal. 3: cloud. 4: rock. 5: Drac 1. 6: Drac 2. 7: Drac 3.)
0xC8C1 current substage (initially 0, increments every time belmont passes through a door.)
0xC8C2 [d3] points/score
0xC8C5 [d] lives ("rest")
0xC980... array of values to copy to vram during the next vblank. Format is:
  - [2 bytes] address to update
  - [1 byte] bits 0-6: stride (e.g. 1 to edit consecutive values). bit 7: unknown.
  - [...] any data other than $FF
  - [1 byte] $FF terminator. Can be followed by more such packets.
0xCA82 [u2] screen scroll speed (horizontal)
0xCA86 [u] Screen x. Every screen that Belmont moves right, this increments, and vice versa.
0xCA8B [u2] screen scroll speed (vertical)
0xCA8D [u] Screen y. Every screen that Belmont moves downward, this increments, and vice versa.
0xCA90 [p] pointer to base of 4x4 tile-chunk map. Each tile-chunk is 16 bytes, each byte representing 1 tile in the chunk. This generally depends on the level.
0xCA92 [p] pointer to bank 6 base of 4x4 tile chunk data for this sublevel. Every 20 bytes is a screen of 4x4 tile chunks.
0xCa95 low bit is 1 if sublevel scrolls vertically, otherwise horizontal.
0xCA97 [u] low nibble is current screen in tile chunk data. Upper nibble is screen scrolling constraint (see $DD00). This is set by looking up the screen (x,y) coords in the $DD00 screen array.
0xCBC3 [u] stores screen dimension (0xa0 if horizontal, 0x80 if vertical) for various operations.
0xCBE0... array of what lanterns have been smashed. (e.g. if Belmont returns to this area, then the lantern will remain gone.)
0xC8D0 subweapon (0: none. 1: axe (us) / cross (jp). 2: holy water)
0xC8D1 whip upgrade (0: leather. 1: chain. 2: fireball)
0xCC80 [d2] time remaining
0xCC86 [d] hearts
0xCC89 [u] Belmont's hitpoints
0xC88C [u] next free index of $c980 array plus $80.
0xD000 - 0xD800: copy of vram background tiles? Presumably for access outside of vblank/hblank.
0xDD00 - 0xDDFF: Sublevel area layout. A grossly inefficient use of space. A 16x16 array of screens. The low byte in the array indicates which screen of 4x4 tile chunk data to use (i.e. added to the pointer at $CA92). High byte as follows: (9-begin. 8-middle. A-end. B-single screen.). This array is indexed by the x and y screen coordinates at $CA86 and $CA8D.
0xDEA0 [u] scratch? entity loading: x position. Also commonly used as an iterator.
0xDEA1 [u] scratch? entity loading: y position. Also commonly used as an iterator.
0xDEA4 [u] scratch? entity loading: category. (0=misc, 1=enemies, 2=items)
0xFF80-0xFFFE stack (127 bytes)

Entities

Each entity has 20 bytes of data, located at **00 (where ** ranges from C0-D7).

• • 00: entity ID (see the ROM map for a listing)
  • 01: state?
  • 05: entity load index (see $DEA4)
  • 09: sprite flags (flip, palette, etc.)
  • 0A: image (see "Images" in ROM map)
  • 0B-0D: animation data (TODO)
  • 0F: [s2] Y velocity (subpixel, pixel)
  • 11: [bu2] Y position (pixel, subpixel)
  • 14: [s2] X velocity (subpixel, pixel)
  • 16: [bu2] X position (pixel, subpixel)
  • 18: timer