Contra (NES)/RAM map: Difference between revisions

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Chip tiny.png The following article is a RAM map for Contra (NES).

Address Size    Description
------- ----    -----------
     18    1    Game Routine Index - which game routine to execute.
                Index in game_routine_pointer_table (bank 7 CPU address $c24d)
     19    1    Game End Routine Index/Game Routine Init Flag - after beating
                the game, used to index into game_end_routine_tbl to sequence
                the screen fade, helicopter animation, credits, restart level
                1, among other things.
                Also used during setup of a level to ensure routines have been
                completed.
     1a    1    Frame Counter - loops from 0x00 to 0xff increments once per
                frame.
                Also known as the global timer
     1b    1    NMI Check - set to 0x01 at start of nmi and 0x00 at end. Used
                to track if nmi occurred before game loop finished
     1c    1    Demo Mode - 0x00 not in demo mode, 0x01 in demo mode
     1d    1    Player Mode - 0x01 for 1 player, 0x07 for 2 player.  Not sure
                why developer just didn't use 0x22 (Player Mode) instead
     1f    1    Demo Level End Flag - whether or not demo for the level has
                been completed and the new demo level should start
     20    1    PPU Ready - 0x00 when at least 5 executions of nmi_start have
                happened indicating the PPU is ready
     21    1    Graphics Buffer Offset - current write offset into
                CPU_GRAPHICS_BUFFER (RAM address $700, which contains pattern
                table tiles that are written to PPU.
     22    1    Player Mode - 0x00 = single player, 0x01 = 2 player
     23    1    Graphics Buffer Mode - defines format of the
                CPU_GRAPHICS_BUFFER. 0xff is for super-tile data, 0x00 is for
                text strings and palette data
     24    1    Konami Code Status - 0x00 not entered, 0x01 entered
     25    1    Pause State - 0x00 when not paused 0x01 when paused
     27    1    Demo Level - the current level when in demo mode. Only ever
                0x00, 0x01 or 0x02 as those are the only levels demoed
     28    1    Intro Theme Delay - timer to prevent starting a level until the
                intro theme is complete (including explosion sound).
     29    1    Game Over Delay Timer - timer after dying before showing score.
                Goes from 0x60 to 0x00
     2a    2    Delay Time - the 2-byte value of the current delay
     2c    1    Level Routine Index - which level routine to execute. Index
                into level_routine_ptr_tbl (bank 7 CPU address $ce35)
     2d    1    End Level Routine Index - index into either
                end_level_sequence_ptr_tbl (bank 3 CPU address $be09)
                or end_game_sequence_ptr_tbl (bank 4 CPU address $b949)
     2e    1    Demo Fire Delay Timer - the number of frames to delay before
                player starts firing when demoing
     2f    1    Player Weapon Strength - the damage strength of the player 1's
                current weapon. Based on bits 0-2 of P1 Current Weapon.
                Default = 0x00, M = 0x02, F = 0x01, S = 0x03, L = 0x02.
                Player 2's weapon doesn't affect this field.
     30    1    Current Level - 0x00 to 0x07 represent levels 1 through 8.
                0x9 is interpreted as game over sequence
     31    1    Game Completion Count - the number of times the game has been
                completed (final boss defeated)
     32    1    P1 Number Lives - 0x00 is last life, on game over stays 0x00
                and P1 Game Over Status becomes 0x01
     33    1    P1 Number Lives - 0x00 is last life, on game over stays 0x00
                and P2 Game Over Status becomes 0x01
     34    1    Random Number - random number (randomized between interrupts)
     36    1    Number Palettes To Load - the number of palettes to load into
                CPU memory
     37    1    Indoor Screen Cleared - whether indoor screen has had all cores
                destroyed (0 = not cleared, 1 = cleared, 0x80 = cleared and
                electric fence removed)
     38    1    P1 Game Over Status - 0x00 not game over, 0x01 game over
     39    1    P2 Game Over Status - 0x00 not game over, 0x01 game over or
                player 2 not playing (1 player game)
     3a    1    Number Continues - the number of continues remaining
     3b    1    Boss Defeated Flag - whether or not the level boss has been
                defeated (0x00 = no, 0x01 = yes).  After set to 0x01, the end
                level sequence logic uses this value as well using values
                0x81 and 0x02.
     3c    2    P1 Extra Life Score - the 2-byte value of the score required
                for the next extra life
     3e    2    P2 Extra Life Score Low (collides with Konami Code Number
                Correct)
     3f    1    Konami Code Number Correct - the number of successful inputs of
                the Konami code sequence 0x0a for all correct.
     3f    1    Extra Life Score High (P2)
     40    1    Level Location Type  - 0x00 = outdoor, 0x01 = indoor (base)
                0x80 on indoor/base boss screen and indoor/base levels when
                players advancing to next screen
     41    1    Level Scrolling Type - 0x00 = horizontal (and indoor/base)
                0x01 = vertical
     42    2    Level Screen Supertiles Pointer - 2-byte address to bank 2
                containing which super-tiles to use for each screen of the
                level (level_x_supertiles_screen_ptr_table)
     44    2    Level Supertile Data Pointer - 2-byte pointer to super-tile
                data, which defines pattern table tiles of the super-tiles that
                are used to make level blocks
     46    2    Level Supertile Palette Data - 2-byte pointer address to the
                palettes used for each super-tile. Each byte describes the 4
                palettes for a single super-tile
     48    1    Level Alternate Graphics Position - how far into level (in
                number of screens) before loading alternate graphic data
     49    1    Collision Code 1 Tile Index - pattern table tiles below this
                index (but not 0x00) are considered Collision Code 1 (floor)
     4a    1    Collision Code 0 Tile Index - pattern table tiles >= 0x49 and
                less than this tile index are Collision Code 0 (empty)
     4b    1    Collision Code 2 Tile Index - pattern table tiles >= $4a and
                less than this tile index are Collision Code 2 (water)
     4c    4    Level Palette Cycle Indexes - palette indexes into
                game_palettes (bank 7 CPU address $d227) to cycle through for
                the level for the 4th nametable palette index
     50    8    Level Palette Index - the level's initial background palettes
                [$50 to $54) and sprite palettes [$54 to $58).
                Offsets into game_palettes (bank 7 CPU address $d227).
     58    1    Level Stop Scroll - the screen of the level to stop scrolling.
                Set to 0xff when boss auto scroll starts
     59    1    Level Solid Background Collision Check - used to determine
                whether to check for bullet and weapon item solid bg collisions
                When non-zero, specifies weapon item should check for solid bg
                collisions.  When negative, used to let bullet (player and
                enemy) collision detection code to know to look for
                bullet-solid background collisions.
     5a    1    P1 Demo Input Number of Frames - how many even-numbered frames
                to continue pressing the button specified in Demo Input Value
                ($5c) for demo
     5b    1    P2 Demo Input Number of Frames
     5c    1    P1 Demo Input Value - the current controller input pressed
                during demo
     5d    1    P2 Demo Input Value
     5e    1    P1 Demo Input Table Index - when in demo, stores the offset
                into specific demo_input_tbl_lX_pX (bank 5)
     5f    1    P2 Demo Input Table Index
     60    1    PPU Write Tile Offset - the current write offset of the
                super-tile data, number of tiles outside the current view.
                Horizontal levels loops from 0x00 to 0x1f. Vertical starts with
                0x1d goes down to 0x00 before looping.
     61    1    Level Transition Timer - used in vertical levels to time
                animation between sections for every 'up' input. Also used in
                indoor levels between screens to animate moving forward.
     62    2    PPU Write Address- 2-byte PPU write address to
                CPU Graphics Buffer ($700)
     64    1    Level Screen Number - the screen number of the current level,
                i.e. how many screens into the level
     65    1    Level Screen Scroll Offset - the number of pixels into Level
                Screen Number the level has scrolled. Goes from 0x00-0xff for
                each screen (256 pixels)
     66    2    Attribute Table Write Address - the 2-byte attribute table
                write address
     68    1    Frame Scroll - how much to scroll the screen this frame based
                on player velocity (usually 0x00 or 0x01). For vertical levels,
                up to 0x04
     69    1    Supertile Nametable Offset - base nametable offset into memory
                address into CPU graphics buffer starting at Level Screen
                Supertiles ($0600). Always either 0x00 (nametable 0) or 0x40
                (nametable 1), points to area that contains the super-tile
                indexes for screen
     6a    1    Sprite Load Type - which sprites to load
                0x00 = normal sprites, 0x01 = Heads Up Display (HUD) sprites
     6b    1    Continue End Selection - 0x00 = "CONTINUE" is selected
                0x01 = "END" is selected. Used in game over screen
     71    1    Alternate Graphic Data Loading Flag
                0x00 = alternate graphics data should not be loaded
                0x01 = alternate graphics data should be loaded
                0x02 = alternate graphics data are currently being loaded
     72    1    Level Palette Cycle - the current iteration of the palette
                animation loop. 0x00 up to entry for level in
                lvl_palette_animation_count (bank 7 CPU address $d181)
     73    1    Indoor Scroll - scrolling on indoor level changes
                0x00 = not scrolling; 0x01 = scrolling, 0x02 = finished
     74    1    Background Palette Adjust Timer - timer used for adjusting
                background palette colors (not sprite palettes). Used for
                fade-in effect of dragon and boss UFO as well as indoor
                transitions
     75    1    Auto Scroll Timer 0 - used when completing scroll to show a
                boss, e.g. vertical level dragon screen
     76    1    Auto Scroll Timer 1 - used when completing scroll to show a
                boss, e.g. alien guardian
     77    1    Tank Auto Scroll - amount to scroll every frame for snow field
                tanks (dogras), regardless of Auto Scroll Timer 0 and 1
     78    1    Pause Palette Cycle - 0x00 = nametable palettes
                0x03 and 0x04 will cycle through colors like normal.  Non-zero
                values will pause palette color cycling.
     79    1    Soldier Generation Routine - which routine is currently in use
                for generating soldiers. Index into soldier_generation_ptr_tbl
                (bank 2 CPU address $b537)
     7a    1    Soldier Generation Timer - a timer between soldier generation.
                0x00 = no generation.
     7b    1    Soldier Generation X Position - the initial x position of the
                generated soldier
     7c    1    Soldier Generation Y Position - the initial y position of the
                generated soldier
     7d    1    Falcon Flash Timer - the number of frames to flash the screen
                for falcon weapon item
     7f    1    Tank Ice Join Scroll Flag - whether or not to have the ice
                joint enemy move left while player walks right to simulate
                being on the background. (snow field level)
     80    2    Enemy Level Routines - 2-byte address to the correct
                enemy_routine_level_XX (bank 7) for the current level, used to
                retrieve enemy routines for the level-specific enemies
     82    1    Enemy Screen Read Offset - read offset into
                level_xx_enemy_screen_xx (bank 2) table, which specifies the
                enemies on each screen of a level
     83    1    Enemy Current Slot - specifies the current enemy slot that is
                being executed
     84    1    Boss Auto Scroll Complete - set when boss reveal auto-scrolling
                has completed
     85    1    Boss Screen Enemies Destroyed - used on level 3 and level 7
                boss screens to keep track of how many dragon arm orbs or
                mortar launchers have been destroyed respectively
     86    1    Wall Core Remaining - remaining wall cores/wall platings to
                destroy until can advance to next screen. For level 4 boss,
                used to count remaining boss gemini
     87    1    Wall Plating Destroyed Count - used in indoor/base boss levels
                to keep track of how many wall platings (ENEMY_TYPE 0x0a) have
                been destroyed
     88    1    Indoor Enemy Attack Count - used in indoor/base levels to
                specify how many 'rounds' of attack have happened per screen,
                max 0x07 before certain enemies no longer generate. Indoor
                soldiers, jumping soldiers, indoor rollers, and wall core check
                this value
     89    1    Indoor Red Soldier Created - used in indoor/base levels to
                indicate if a red jumping soldier has been created, to prevent
                creation of another
     8a    1    Grenade Launcher Flag - used in indoor/base levels to indicate
                that a grenade launcher enemy (ENEMY_TYPE 0x17) is on the
                screen. Prevents other indoor enemies from being generated
     8b    1    Alien Fetus Aim Timer Index - used to keep track of the index
                into alien_fetus_aim_timer_tbl (bank 0 CPU address $b7e8) to
                set the delay between re-aiming towards the player
     8e    1    Enemy Attack Flag - whether or not enemies will fire at player,
                also whether or not random enemies are generated, bosses ignore
                this value
     90    1    P1 Player State - 0x00 falling into level, 0x01 normal state,
                0x02 when dead, 0x03 can't move
     91    1    P2 Player State - same as P1 Player State.  If p2 not playing,
                set to 0x00
     92    1    P1 Indoor Transition X Accumulator - used to help calculate
                fractional x velocity when moving between screens on
                indoor/base levels
     93    1    P2 Indoor Transition X Accumulator
     94    1    P1 Player Jump Coefficient - used to keep track of fractional y
                velocity on vertical levels for overflowing fractional
                velocity. Also used to help calculate fractional y velocity
                when moving between screens on indoor/base levels.
     95    1    P2 Player Jump Coefficient
     96    1    P1 Indoor Transition X Fractional Velocity - indoor animation
                transition when walking into screen x fractional velocity
     97    1    P2 Indoor Transition X Fractional Velocity
     98    1    P1 Player X Velocity - the player's x velocity (0x00, 0x01, or
                0xff)
     99    1    P2 Player X Velocity
     9a    1    P1 Indoor Transition Y Fractional Velocity - indoor animation
                transition when walking into screen y fractional velocity
     9b    1    P2 Indoor Transition Y Fractional Velocity
     9c    1    P1 Indoor Transition Y Fast Velocity - indoor animation
                transition when walking into screen y fast velocity
     9d    1    P2 Indoor Transition Y Fast Velocity
     9e    1    P1 Player Animation Frame Timer - value that is incremented
                every frame when player is walking. Used to wait 0x08 frames
                before incrementing Player Animation Frame Index ($a6) for
                animating player walking
     9f    1    P2 Player Animation Frame Timer
     a0    1    P1 Player Jump Status - the status of the player jump. Similar
                to Edge Fall Code ($a4)
                  * high nibble is for facing direction
                  * bit 7 - set when jumping left
                  * low nibble is 0x01 when jumping, 0x00 when not
     a1    1    P2 Player Jump Status
     a2    1    P1 Player Frame Scroll - how much player is causing the frame
                to scroll by, see Frame Scroll ($68)
     a3    1    P2 Player Frame Scroll
     a4    1    P1 Edge Fall Code - similar to Player Jump Status ($a0). Used
                to initiate gravity pulling player down
                  * if bit 7 set, then falling through platform
                  * if bit 6 is set, then walking left off edge
                  * if bit 5 is set, then walking right off ledge
     a5    1    P2 Edge Fall Code
     a6    1    P1 Player Animation Frame Index - which frame of the player
                animation. Depends on player state. For example, if player is
                running, this cycles from 0x00 to 0x05.
     a7    1    P2 Player Animation Frame Index
     a8    1    P1 Player Indoor Animation Y - the y position the player was at
                when they started walking into screen after clearing an indoor
                level. I believe it's always 0xa8 since y position is
                hard-coded for indoor levels
     a9    1    P2 Player Indoor Animation Y
     aa    1    P1 Current Weapon - low nibble is what weapon P1 has, high
                nibble 1 is rapid fire flag, commonly abbreviated MFSL
                0x00 - Regular, 0x01 - Machine Gun, 0x02 - Flame Thrower
                0x03 - Spray, 0x04 - Laser, bit 4 set for rapid fire
     ab    1    P2 Current Weapon
     ac    1    P1 Player M Weapon Fire Time - used when holding down the B
                button with the m weapon.  High nibble is number of bullets
                generated (up to 0x06), low nibble is counter before next
                bullet is generated (up to 0x07)
     ad    1    P2 Player M Weapon Fire Time
     ae    1    P1 New Life Invincibility Timer - timer for invincibility after
                dying
     af    1    P2 New Life Invincibility Timer
     b0    1    P1 Invincibility Timer - timer for player invincibility (b
                weapon). Decreases every 8 frames., usually set to 0x80 except
                level 7 when set to 0x90.
     b1    1    P2 Invincibility Timer
     b2    1    P1 Player Water State
                  * bit 1 - horizontal sprite flip flag
                  * bit 2 - set when player in water, or exiting water
                  * bit 3 - player is walking out of water
                  * bit 4 - finished initialization for entering water
                  * bit 7 - player is walking out of water
     b3    1    P2 Player Water State
     b4    1    P1 Player Death Flag - bit 0 specifies whether player has died,
                bit 1 specifies player was facing left when hit, used so player
                dies lying in appropriate direction
     b5    1    P2 Player Death Flag
     b6    1    P1 Player On Enemy - whether or not the player is on top of
                another enemy (0x14 - mining cart, 0x15 - stationary mining
                cart, 0x10 - floating rock platform)
     b7    1    P2 Player On Enemy
     b8    1    P1 Player Fall X Freeze - used to prevent changing X velocity
                shortly after walking off/falling through ledge, set to Y post
                of ledge + 0x14
     b9    1    P2 Player Fall X Freeze
     ba    1    P1 Player Hidden - 0x00 player visible, 0x01/0xff player
                invisible (any non-zero). I believe it is meant to track
                distance off screen the player is
     bb    1    P2 Player Hidden
     bc    1    P1 Player Sprite Sequence - which animation to show for the
                player
                  * outdoor - 0x00 standing (no animation), 0x01 gun pointing
                  up, 0x02 crouching, 0x03 walking or curled jump animation,
                  0x04 dead animation
                  * indoor - 0x00 standing facing back wall, 0x01 electrocuted,
                  0x02 crouching, 0x03 walking left/right animation, 0x05
                  walking into screen (advancing), 0x06 dead animation
     bd    1    P2 Player Sprite Sequence
     be    1    P1 Player Indoor Animation X - the x position the player was at
                when they started walking into screen after clearing an indoor
                level
     bf    1    P2 Player Indoor Animation X
     c0    1    P1 Player Aim Previous Frame - backup of Player Aim Direction
                ($c2)
     c1    1    P2 Player Aim Previous Frame - backup of Player Aim Direction
                ($c3)
     c2    1    P1 Player Aim Direction - which direction the player is aiming
                [0x00-0x0a] depends on level and jump status (00 up facing
                right, 1 up-right, 2 right, 3 right-down, 4 crouching facing
                right, 5 crouching facing left, etc).  There are 0x02 up and
                0x02 down values depending on facing direction.
     c3    1    P2 Player Aim Direction
     c4    1    P1 Player Y Fractional Velocity - the fractional portion of the
                player's y velocity
     c5    1    P2 Player Y Fractional Velocity
     c6    1    P1 Player Y Fast Velocity - the integer portion of the player's
                y velocity. Positive pulls down, negative pulls up
     c7    1    P2 Player Y Fast Velocity
     c8    1    P1 Electric Shock Timer - timer for player being shocked, used
                to freeze player and modify look after touching electricity
     c9    1    P2 Electric Shock Timer
     ca    1    P1 Indoor Player Jump Flag - used when entering new screen to
                tell the engine to cause the player to jump
     cb    1    P2 Indoor Player Jump Flag
     cc    1    P1 Player Water Timer - timer used for getting into and out of
                water
     cd    1    P2 Player Water Timer
     ce    1    P1 Player Recoil Timer - how many frames to be pushed back/down
                from recoil
     cf    1    P2 Player Recoil Timer
     d0    1    P1 Indoor Player Advance Flag - whether or not the player is
                walking into screen when advancing between screens on indoor
                levels, used for animating player
     d1    1    P2 Indoor Player Advance Flag
     d2    1    P1 Player Special Sprite Timer - used to track animation for
                player death animation.  For outdoor levels, it is a timer that
                increments once player hit, every 0x08 frames updates to next
                animation frame until 0x04.  Also used to track jumping curl
                animation (loops from 0x00-0x04)
     d3    1    P2 Player Special Sprite Timer
     d4    1    P1 Player Fast X Velocity Boost - the x fast velocity boost
                from landing on a non-dangerous enemy, e.g. moving cart or
                floating rock in vertical level
     d5    1    P2 Player Fast X Velocity Boost
     d6    1    P1 Player Sprite Code - sprite code of the player
     d7    1    P2 Player Sprite Code - sprite code of the player
     d8    1    P1 Player Sprite Flip - stores player sprite horizontal (bit 6)
                and vertical (bit 7) flip flags before saving into SPRITE_ATTR.
                Bit 3 specifies whether the Player Animation Frame Index ($a6)
                is even or odd
     d9    1    P2 Player Sprite Flip
     da    1    P1 Player Background Flag and Edge Detect
                  * bit 7 specifies the player's sprite attribute for
                    background priority. Allows player to walk behind opaque
                    background (OAM byte 2 bit 5).  0x00 = sprite in
                    foreground, 0x01 = sprite is background
                  * bit 0 allows the player to keep walking horizontally off a
                    ledge without falling
     db    1    P2 Player Background Flag and Edge Detect
     df    1    Game Over Bit Field - combination of both players game over
                status.
                  * 0x00 = p1 not game over, p2 game over (or not playing)
                  * 0x01 = p1 game over, p2 not game over
                  * 0x02 = p1 nor p2 are in game over
     ec    2    Sound Table Pointer - 2-byte address pointing of index into
                sound_table_00 (bank 1 CPU address $88e8)
     f1    1    P1 Controller State - stores the currently-pressed buttons
                  * bit 7 - A
                  * bit 6 - B
                  * bit 5 - select
                  * bit 4 - start
                  * bit 3 - up
                  * bit 2 - down
                  * bit 1 - left
                  * bit 0 - right
     f2    1    P2 Controller State
     f5    1    P1 Controller State Diff - stores the difference between the
                controller input between reads. Useful for events that should
                only trigger on first button press
     f6    1    P2 Controller State Diff
     f9    1    P1 Controller Known Good - used in input-reading code to know
                the last known valid read of controller input (similar to
                P1 Controller State ($f1)
     fa    1    P2 Controller Known Good
     fc    1    Vertical Scroll - the number of pixels to vertically scroll
                down.
                  * horizontal levels are always 0xe0 (224 pixels or
                  28 tiles down)
                  * indoor/base are always 0xe8 (232 or 29 tiles down)
                  * waterfall level (vertical level) starts at 0x00 and
                  decrements as players move up screen (wrapping)
     fd    1    Horizontal Scroll - the horizontal scroll component of the
                PPUSCROLL, [0x00 - 0xff]
     fe    1    PPU Mask Settings - used to store value of PPUMASK before
                writing to PPU
     ff    1    PPU Control Settings - used to set PPUCTRL value for next frame
    100    6    Sound Command Length - how many video frames the sound count
                should last for, i.e. the time to wait before reading next
                sound command.  One for each of the 0x06 sound slots.
    106    6    Sound Code - the sound code for each of the 0x06 sound slots
    10c    6    Sound Pulse Length - APU_PULSE_LENGTH for each of the 0x06
                sound slots
    112    6    Sound Command Adress Low Byte - low byte of address to current
                sound command.  0x06 slots, one for each sound slot
    118    6    Sound Command Address High Byte - high byte of address to
                current sound command. 0x06 slots, one for each sound slot
    11e    2    Sound Volume Envelope - pulse channel volume.  Either an
                offset into pulse_volume_ptr_tbl (bank 1 CPU address $8001)
                which specifies the volume for the frame or a specific volume
                to use. When bit 7 is set, then the volume will auto
                decrescendo.
    120    1    Sound Current Slot - the current sound slot 0x00-0x05
                inclusively.
    121    1    Percussion Index Backup - backup location for
                percussion_tbl (bank 1 CPU address $82cd) index to restore
                after call to play_sound (bank 7 CPU address $c16b)
    122    1    Initial Sound Code - the sound code to load. Sound codes
                greater than 0x5a are dmc sounds
    123    1    Sound Channel Register Offset - 0x00 for first pulse channel,
                0x04 for second, 0x08 for triangle, 0x0c for noise
    124    1    Sound Flags - sound channel flags
                  * bit 0 - 0 = sound effect, 1 = music
                  * bit 1 - 1 = decrescendo end pause complete, resume
                    decrescendo, 0 = keep volume constant
                  * bit 2 - 0 = use lvl_config_pulse (bank 1 CPU address $8154)
                    to set volume for frame, 1 = automatic decrescendo logic
                  * bit 3 - signifies that a shared (child) sound command is
                    executing. Used to know, after finishing parsing a sound
                    command, whether or not to done or should return to parent
                    sound command
                  * bit 4 - slightly flatten note
                  * bit 5 - 1 = decrescendo should be paused for a duration
                  * bit 6 - mute flag (1 = muted, 0 = not muted)
                  * bit 7 - sweep flag
    12a    1    Level Pulse Volume Index - index into level pulse volume table
    12a    1    Pulse Volume Duration - the number of video frames to decrement
                the volume for, before stopping decrescendo and keeping final
                volume
    12f    1    Pause State 1 - whether or not the game is paused, used for
                sound logic (see Pause State ($25))
    130    1    Pulse Channel 1 Decrescendo End Pause - number of video frames
                before end of sound command in which the decrescendo will
                resume
    131    1    Pulse Channel 2 Decrescendo End Pause
    132    4    Sound Pitch Adjust - the amount added to the sound byte low
                nibble before loading the correct note period value
    136    6    Sound Command Multiplier - amount to multiply to when
                calculating when to stop decrescendo
    13c    6    Sound Volume Adjust - used to adjust volume amount when setting
                volume
    142    1    Sound Slot 0 Config Low - the value to merge with the high
                nibble before storing in APU channel config register for pulse
                channel
    143    1    Sound Slot 1 Config Low
    144    1    Sound Triangle Config - in memory value for the triangle
                channel configuration.
    148    6    Sound Repeat Count - used for 0xfe sound commands to specify
                how many times to repeat a shared sound part
    14e    1    Pulse Channel 1 Sound Config High - the value to merge with the
                volume when saving the pulse config
    14f    1    Pulse Channel 2 Sound Config High
    152    1    Pulse Channel 1 Sound Config High - Sound Slot 0x04
    154    6    Sound Length Multiplier - value used when determining how many
                video frames to wait before reading next sound command.
    15a    6    Sound Period Rotate - when not 0x04, the number of times to
                shift the high byte of note period index into the low byte
    160    6    Pulse Volume - low nibble only, stores the volume for the pulse
                channels
    166    6    New Sound Code Low Address - sound command return location low
                byte once sound command specified executes
    16c    6    New Sound Code High Address - sound command return location
                high byte once sound command specified executes
    172    6    Sound Pulse Period - APU Pulse Period value
    178    1    Sound Slot 0 Vibrato Control - [0x00-0x03], 0x80 = no vibrato.
                Even values cause the note to stay the same, odd values cause
                vibrato 0x03 = pitch up, 0x01 = pitch down
    179    1    Sound Slot 1 Vibrato Control
    17a    1    Sound Slot 0 Volume Timer - sound command counter; increments
                up to Vibrato Delay ($17e), at which vibrato will be checked,
                only increments when Vibrato Control ($178) is non-negative,
                i.e. not 0x80
    17b    1    Sound Slot 1 Volume Timer
    17c    1    Sound Slot 0 Note - the pulse channel note that is sustained or
                has the vibrato applied to for pulse channels (in Contra only
                ever sustained no vibrato)
    17d    1    Sound Slot 1 Note
    17e    1    Sound Slot 0 Pulse Vibrato Delay - used to delay start of
                vibrato until Sound Volume Timer ($17a) has counted up to this
                value. If a note isn't as long as the delay, then vibrato
                won't be considered for a note
    17f    1    Sound Slot 1 Pulse Vibrato Delay
    180    1    Sound Slot 0 Vibrato Amount - the amount of vibrato to apply
    181    1    Sound Slot 1 Vibrato Amount - the amount of vibrato to apply
    190    1    Level End Delay Timer - a delay timer before beginning level
                end animation sequence
    191    1    Level End Sequence 1 Timer - a delay timer specifying the
                duration of end_level_sequence_01 (bank 3 CPU address $be3c).
                Decremented every other frame
    192    1    P1 Level End Level Routine State - used by level end routines
                for managing animation state. For example, indoor level end
                animations have 4 states: walk to elevator, initialize elevator
                sprite, ride elevator
    193    1    P2 Level End Level Routine State - used by level end routines
    194    1    Level End Players Alive - the number of players alive at the
                end of the level, used to know if should play level end music
    195    1    Soldier Generation Screen - the current screen that soldiers
                are being generated for
    196    1    Screen Generation Soldiers - the total number of soldiers that
                have been generated for the current screen
    200  100    OAM DMA CPU Buffer - OAMDMA (sprite) data, read once per frame
    300    a    Player Sprites - player sprites, p1 and p2 sprite, then player
                bullets
    30a   10    Enemy Sprites - enemy sprites to load on screen
    31a    a    Player Sprite Y Positions - y position on screen of each player
                sprite.
    324   10    Enemy Y Positions - y position on screen of each enemy sprite
    334   10    Player Sprite X Positions - x position of screen of each player
                sprite and player bullets
    33e   10    Enemy X Positions - x position on screen of each enemy sprite
    34e    a    Player Sprite Attributes - sprite attribute, specifies palette,
                vertical flip, horizontal flip, and whether to adjust y
                position
                  * bit 0 and 1 - sprite palette
                  * bit 2 - 0 to use default palette from sprite code
                  *       - 1 to use palette specified in bits 0 and 1
                  * bit 3 - whether to add 0x01 to sprite y position, used for
                    recoil effect firing weapon
                  * bit 5 - bg priority
                  * bit 6 - whether to flip the sprite horizontally
                  * bit 7 - whether to flip the sprite vertically
    358   10    Enemy Sprites Attributes - enemy sprite attribute. See
                specification above for Player Sprite Attributes
    368   10    Player Bullet Sprite Code - the sprite codes to load for the
                bullet
    378   10    Player Bullet Sprite Attribute - the sprite attributes for the
                bullet (see Player Sprite Attributes ($34e) for specification)
                Used for L bullets for flipping the angled sprites depending on
                direction
    388   10    Player Bullet Slot - 0x00 when no bullet, otherwise stores
                bullet type + 1, i.e. 0x01 basic, 0x02 M, 0x03 F bullet,
                0x04 S,0x05 L, can be negative sometimes
    398   10    Player Bullet Velocity Y Accumulator - an accumulator to keep
                track of Player Bullet Y Velocity Fractional ($3f8) being added
                to itself have elapsed before adding 1 to Player Bullet Y
                Position ($3b8)
    3a8   10    Player Bullet Velocity X Accumulator - an accumulator to keep
                track of Player Bullet X Velocity Fractional ($3e8) being added
                to itself have elapsed before adding 1 to Player Bullet X
                Position ($3c8)
    3b8   10    Player Bullet Y Position - the bullet's sprite y position
    3c8   10    Player Bullet X Position - the bullet's sprite x position.  For
                F bullets, Player Bullet FS X ($478) and this value together
                determine x position
    3d8   10    Player Bullet Y Velocity Fractional - percentage out of 0-255
                set number of frames until Y position is incremented by an
                additional 1 unit
    3e8   10    Player Bullet X Velocity Fractional - percentage out of 0-255
                set number of frames until X position is incremented by an
                additional 1 unit
    3f8   10    Player Bullet Y Velocity Fast - player bullet velocity y
                integer part
    408   10    Player Bullet X Velocity Fast - player bullet velocity x
                integer part
    418   10    Player Bullet Timer - 'timer' starts at 0x00. Used by F, S
                (indoor only) and L
                  * for indoor S, used to specify size of bullet
                  * For F, used to set x and y pos when traveling to create
                    swirl. Increments or decrements every frame depending on
                    firing direction (left decrement, right increment)
                  * For L used to spread out 4 lasers for one shot
    428   10    Player Bullet Aim Direction - the direction of the bullet
                0x00 for up facing right, incrementing clockwise up to #09 for
                up facing left
    438   10    Player Bullet Routine - 0x00, 0x01, or 0x03
    448   10    Player Bullet Owner - 0x00 player 1 bullet, 0x01 player 2
                bullet
    458   10    Player Bullet F Rapid - 0x01 for player indoor bullets for F
                weapon when rapid fire is enabled
    458   10    Player Bullet S Indoor Adjust - for indoor S bullets, specifies
                whether to adjust Player bullet X Position ($3c8) by an
                additional -1 (0xff) every frame
    468   10    Player Bullet Distance - represents how far a bullet has
                traveled
                  * for S outdoor bullets, used to determine the size (scale)
                    of the bullet
                  * for F on indoor levels, used to determine spiraling
                    position based on distance from player
    468   10    Player Bullet S Adjust Accumulator - for indoor S weapons,
                stores accumulated fractional velocity where overflow affects
                Player Bullet S Indoor Adjust ($458)
    478   10    Player Bullet FS X - used to offset from general x direction of
                bullet for swirl effect in F bullet and spread effect in S
                bullet (indoor). Specifies center x position on screen f bullet
                swirls around. Used when firing f bullet either left, right, or
                at an angle
    488   10    Player Bullet F Y - center y position on screen f bullet swirls
                around. Used when firing f bullet either up, down, or at an
                angle.
    488   10    Player Bullet S Rapid - for S weapon in indoor levels,
                specifies whether weapon is rapid fire or not
    498   10    Player Bullet Velocity FS X Accumulator - an accumulator to
                keep track of Player Bullet X Velocity Fractional ($3e8) being
                added to itself have elapsed before adding 1 to
                Player Bullet X Position ($3c8)
    4a8   10    Player Bullet Velocity F Y Accumulator - (for F weapon only) an
                accumulator to keep track of Player Bullet Y Velocity
                Fractional ($3d8) being added to itself have elapsed before
                adding 1 to Player Bullet Y Position ($3b8)
    4a8   10    Player Bullet S Bullet Number - for S weapon only, specifies
                the number the bullet in the current 'spray' for the shot. Per
                shot of S weapon, 0x05 bullets are generated. If no other
                bullets exist then $04a8 would have 0x00, $04a9 would have 0x01
                $04a9 would have 0x02, etc.
    4b8   10    Enemy Routine - enemy routine indexes. Subtract 1 to get real
                routine, since all offsets are off by 1
    4c8   10    Enemy Y Velocity Accumulator - an accumulator to keep track of
                Enemy Y Velocity Fractional ($4f8) being added to itself have
                elapsed before adding 1 to Enemy Y Position ($324)
    4d8   10    Enemy X Velocity Accumulator - an accumulator to keep track of
                Enemy X Velocity Fractional ($518) being added to itself have
                elapsed before adding 1 to Enemy X Position ($33e)
    4e8   10    Enemy Y Velocity Fast - the number of units to add to Enemy Y
                Position ($324) every frame
    4f8   10    Enemy Y Velocity Fractional - percentage out of 0-255 of a unit
                to add, e.g. if 0x80 (0x80/0xff = 50%), then every other frame
                will cause Y position to increment by 1
    508   10    Enemy X Velocity Fast - the number of units to add to
                Enemy X Position ($33e) every frame
    518   10    Enemy X Velocity Fractional - percentage out of 0-255 of a unit
                to add, e.g. if 0x80 (0x80/0xff = 50%), then every other frame
                will cause X position to increment by 1
    528   10    Enemy Type - enemy type, e.g. 0x03 = flying capsule
    538   10    Enemy Animation Delay - used for various delays by enemy logic
    548   10    Enemy Variable A - variable used for various purposes by some
                enemy types, e.g. the sound code to play when enemy hit by
                player bullet. Dragon arm orb uses it for adjusting enemy
                position, fire beam uses it for animation delay
    558   10    Enemy Attack Delay - the delay before an enemy attacks, for
                weapon items and grenades this is used for helping calculate
                falling arc trajectory instead of enemy delay
    558   10    Enemy Variable B - for weapon items and grenades this is used
                for helping calculate falling arc trajectory instead of enemy
                delay
    568   10    Enemy Frame - animation frame the enemy is in, typically
                indexes into an enemy type-specific table of sprite codes
    588   10    Enemy Score Collision - represents 3 things for an enemy
                  * SSSS CCCC - score code and collision type
                  * also explosion type
    578   10    Enemy HP - typically the HP of the enemy
    598   10    Enemy State Width - various properties
                  * bit 7 set to allow bullets to travel through enemy, e.g.
                    weapon item
                  * bit 6 specifies whether player can land on enemy (floating
                    rock and moving cart), bit 4 also has to be 0
                  * bit 4 and 5 specify the collision box type
                  * bit 3 determines the explosion type
                  * bit 2 for bullets specifies whether to play sound on
                    collision
                  * bit 1 specifies whether to play explosion noise; also
                    specifies width of enemy
                  * bit 0 - 0x00 test player-enemy collision, 0x01 means to
                  skip player-enemy collision test
    5a8   10    Enemy Attributes - enemy type-specific attributes that define
                how an enemy behaves and/or looks
    5b8   10    Enemy Variable 1 - a byte available to each enemy for whatever
                they want to use it for
    5c8   10    Enemy Variable 2 - a byte available to each enemy for whatever
                they want to use it for
    5d8   10    Enemy Variable 3 - a byte available to each enemy for whatever
                they want to use it for
    5e8   10    Enemy Variable 4 - a byte available to each enemy for whatever
                they want to use it for
    600   80    Level Screen Supertiles - CPU  memory address where super tiles
                indexes for the screens of the level are loaded. 2 screens are
                stored in the CPU buffer.  The second screen loaded at $0640.
    680   20    Background Collision Data - map of collision types for each of
                the super-tiles for both nametables, each 2 bits encode 1/4 of
                a super-tile's collision information. First 8 nibbles are a row
                of the top of super-tile, the next 8 are the middle middle.
                Not used on base (indoor) levels
    700   50    CPU Graphics Buffer - used to store data that will be then
                moved to the PPU. repeating structure
                  * byte 0 is multifaceted
                      * if 0x0, then done writing graphics buffer to PPU
                      * if greater than 0x0, then there is data to write, this
                        byte is the offset into vram_address_increment
                        * both 0x01, and 0x03 signify VRAM address increment to
                          0, meaning to add 0x1 every write to PPU (write
                          across)
                        * 0x02 signifies VRAM address increment is 1, meaning
                          add 0x20 (32 in decimal) every write to PPU (write
                          down)
                  * if Graphics Buffer Mode ($23) is 0xff then
                    * byte 1 is length of the tiles being written per group
                    * byte 2 is the number of $701-sized blocks to write to the
                      PPU
                    * for each block, the block prefixed with 2 bytes
                      specifying PPU address (high byte, then low byte)
                  * if Graphics Buffer Mode ($23) is 0x00
                    * if byte 0x00 is 0x00, then no drawing takes place for
                      frame
                    * blocks of text/palette data prefixed with 2 bytes
                      specifying PPU address (high byte, then low byte). the
                      block of text is ended with a 0xff, if the byte after
                      0xff is the vram_address_increment offset. then the the
                      process continues, i.e. read 0x02 PPU address bytes,
                      read next text
    7c0   20    Palette CPU Buffer - the CPU memory address of the palettes
                eventually loaded into the PPU $3f00 to $3f1f
    7e0    2    High Score - the 2-byte high score
    7e2    2    Player 1 Score - the 2-byte score for player 1
    7e4    2    Player 2 Score - the 2-byte score for player 2
    7ec    1    Previous ROM Bank - the previously-loaded PRG BANK
    7ed    1    Previous ROM Bank 1 - the previously-loaded PRG BANK, but used
                only when playing sounds, otherwise a duplicate use of
                Previous ROM Bank ($7ec)