Castlevania II: Belmont's Revenge/ROM map

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

Format for PRG-ROM is Bank:RAM address.

(r:symbol) marks the start of a callable subroutine. (RSTxy:symbol) marks a callable subroutine which can be called with the special quick-access RST commands. (t:symbol) marks the start of a data table.

X:7FFF all swappable banks store list their bank number as the last byte of the bank.
0:0000 (RST00:jumptable_entity_state) jumptable (indirect jump by entry in table following call to RST00 according to current entity's state variable)
0:0003 (r:jumptable) jumptable by A.
0:0008 (RST08:ld_from_table) hl <- (hl + 2a)
0:000C (r:ld_hl_hl) hl <- (hl)
0:0010 (RST10:entity_set_image) sets entity's image (see "Images" section below)
0:0018 (RST18:entity_set_timer) sets entity property $08 to A. This seems to be the entity's timer, such as how long until fire despawns or belmont's hitstun.
0:0028 (RST28:add_hl_a) hl += a, then a <- l.
0:0030 (RST30:entity_inc_state) increments the state variable (D:01) of the current entity.
0:0038 (RST38:entity_get_y) get Y position of current entity.
0:01D9 (r:longcall_2_438D) stores current bank (read from $7FFF) on stack, calls routine 2:438D, then returns to caller bank.
0:0D23 (r:entity_set_state_and_substate) entity state <- b, substate (attacking) <- c
0:297B (r:leftshift_bc_4) leftshifts bc by 4.
0:2986 (r:lda_00) a <- $00
0:2989 (r:lda_06) a <- $06
0:298C (r:lda_7F) a <- $7F
0:298F (r:lda_06) a <- $80
0:2AC7 (r:wait_for_blank) Seems to wait to the end of the current blanking period (if applicable) and then to the start of the next.
0:35A9 (r:mbc_bankswap_1) loads swappable bank 1.
0:35AA (r:mbc_bankswap) loads swappable bank from cpu register a.
0:35AF (r:mbc_bankswap_2) loads swappable bank 2.
0:35B5 (r:mbc_bankswap_6) loads swappable bank 6.
0:35BB (r:mbc_bankswap_7) loads swappable bank 7.
0:35C1 (r:mbc_bankswap_3) loads swappable bank 3.
0:38E0 (r:entity_set_animation) Set animation (prop 0C,0B,0A) to (bc):0:(bc+1) (bc):0:(bc+1)
0:3DAC (r:entity_set_x_velocity_0) Entity x velocity <- 00.
0:3DAF (r:entity_set_x_velocity) Entity x velocity <- cb.
0:3DB4 (r:entity_set_y_velocity_0) Entity y velocity <- 00.
0:3DB7 (r:entity_set_y_velocity) Entity y velocity <- cb.
0:3DBA (r:write_word) (hl) <- cb
0:3DBE (r:entity_get_x_velocity) cb <- Entity x velocity.
0:3DC5 (r:entity_get_y_velocity) cb <- Entity x velocity.
0:3DC8 (r:read_word) cb <- (hl)
3:5242 (t:stage_table_unkA) (index via load_substage_data): ??
3:58AC (t:stage_table_unkB) (index via load_substage_data): ??
3:5D25 (t:stage_table_lantern) (index via load_substage_data): lantern data
3:2868 (r:load_substage_data) hl <- ((hl + stage) + substage).
6:421D (r:entity_update) Belmont frame update routine. Called from 0:05FA.
6:4235-4241 Belmont update jumptable
6:427F Belmont state 0 (standing) routine
6:4289 Belmont state 2 (crouching) routine
6:42E9 Belmont state 1 (walking) routine
6:4293 Belmont state 3 (jumping) routine
6:42A1 Belmont state 4 (??) routine
6:44A6 Belmont state 5 (??) routine
6:44D2 Belmont state 6 (??) routine
6:4510 Belmont state 7 (??) routine
6:461B (r:input_A_pressed) A gets zero or 10 depending on if the A button was pressed this frame. Status flags set
6:4621 (r:input_up_down_held) A and status flags
6:4627 (r:input_left_right_held) A and status flags
6:462D (r:input_B_pressed) A and status flags
6:4633 (r:input_B_held) A and status flags
6:4639 (r:input_down_held) A and status flags
6:464B (r:input_up_held) A and status flags
6:4651 (r:input_any_held) A and status flags
6:4801 (r:belmont_set_walk) Read left/right input and set Belmont to be walking left or right accordingly.
6:4817 (r:entity_move_face_right) Entity moves and faces right at velocity  0x90
6:4817 (r:entity_move_face_left)  Entity moves and faces left at velocity -0x90

Bank swap routines:

- All are in bank 0, and all write to $2180 to change the bank. For some reason, bank 5 is always swapped inline rather than by function call.

Images

- Entities' images are stored in property 0A. Editing this value will change the entity's image -- for example, the axe might appear as a torch, at least until the axe's animation restores the image to the next frame of axe animation. Below is a partially-complete table of images (Please contribute!).

0: Torch (frame 0)
1: Torch (frame 1)
2: Coin (frame 0)
3: Coin (frame 1)
4: Score Orb
5: Small heart
6: Large Heart
7: Wall meat
08: fire (frame 0)
09: fire (frame 1)
0A: 1-up
0B: holy water (icon)
0C: holy water (projectile)
0D-10: Axe/Cross (frames 0-3)
11-23: Belmont poses
24-29: whip

and so on.

Entity indices (stored in RAM addresses XY00, XY >= $C6)

- 00: (no lantern) - 01: Lantern/Item: Axe/Cross - 02: Lantern/Item: Holy Water - 03: Lantern/Item: Coin - 04: Lantern/Item: Whip Upgrade Orb - 05: Lantern/Item: Small Heart - 06: Big Heart - 07: (debris) - 08: (debris with big heart?) - 09: Rat? - 0A: ? - 0B: breakable block? - 0C: Punaguchi - 0D: Punaguchi - 0E: Rat? - 0F: ? (explodes when struck) - 10-13: ? - 14: vertically moving flame? - 15-16: ? - 17-1B: ? (palette cycles, and turns to flame when struck.) - 1C: ? (ascends) - 1D: ? (gravity) - 1E: ? (descends) - 1F: bat? - 20: bat? - 21: ? (sessile enemy) - 22: Lantern/Item: orb that crashes the game - 23-24: ? - 25: eyeball spawner (right) - 26: eyeball spawner (left) - 27-29: ? - 2A: (immediately explodes) - 2B: ? (deals contact damage, but cannot be destroyed) - 2C: ? (like 2B but larger and does more damage) - 2D: ? (like 2D) - 2E: ? - 2F: ? - 30: