river-raid: Memory map

Page	Byte	Address	Description
64	0	4000	Screen pixels.
88	0	5800	Screen attributes.
88	32	5820	Screen attributes row 1.
90	32	5A20	Screen attributes row 16 (boundary for visible sprite area).
90	64	5A40	Screen attributes row 17 (start of lower screen area).
91	0	5B00	Screen row address lookup table (64 entries × 2 bytes = 128 bytes).
91	128	5B80	Unused area.
92	120	5C78	Interrupt counter. Incremented by the interrupt handler.
92	121	5C79	Unused
92	210	5CD2	Game initialization and interrupt setup
93	6	5D06	Return to control selection dialog
93	16	5D10	Start gameplay or overview mode based on user selection
93	43	5D2B	Start overview mode
93	53	5D35	Start gameplay mode
93	63	5D3F	Array of possible starting bridge values.
93	67	5D43	Game status buffer entry at 5D43
93	68	5D44	Initialize game state for overview/demo mode.
93	159	5D9F	Decrease player 2 lives
93	166	5DA6	Initialize and start gameplay mode
94	238	5EEE	Terrain fragment render counter (0-7). Tracks which of the 8 terrain fragments to render next. Incremented after each fragment, wraps at 8.
94	239	5EEF	Frame tick (0-255). Incremented each game frame for animation timing. Bit 0 alternates every frame, bits 0-1 cycle every 4 frames, etc.
94	240	5EF0	Current bridge number (0-47).
94	241	5EF1	Raw input port value from last keyboard/joystick read. Format depends on input interface type.
94	242	5EF2	Road tank center flag ($00 = inactive, $01 = road tank is at center X=$80).
94	243	5EF3	Player missile Y coordinate in pixels (0-255). $00 when no missile active.
94	244	5EF4	Player missile X coordinate in pixels (0-255).
94	245	5EF5	Collision detection mode for current render pass. Determines which collision handler to invoke on pixel overlap.
94	246	5EF6	Y coordinate where collision was detected, in pixels.
94	247	5EF7	Pointer to current plane sprite data. Points into all_ff sprite bank, offset by speed for animation frame selection.
94	249	5EF9	Island rendering line counter. Tracks current scanline during island terrain rendering (0-23).
94	250	5EFA	Island terrain profile index (0-7). Selects which of 8 island shapes from data_terrain_profiles to render.
94	251	5EFB	Island definition byte 2. Second byte from island data at data_islands, controls island width/shape.
94	252	5EFC	Island definition byte 3. Third byte from island data at data_islands, controls island rendering parameters.
94	253	5EFD	Island starting line index. Screen line (0-23) where island rendering begins. Initialized to $10 (16).
94	254	5EFE	Unused
95	0	5F00	Viewport slots array (15 slots for active game objects).
95	46	5F2E	Explosion animation fragments array.
95	95	5F5F	Object activation interval bitmask
95	96	5F60	Current slot pointer. Iterator for traversing viewport_slots during object processing.
95	98	5F62	Pointer to a slot from exploding_fragments
95	100	5F64	Current scroll speed in pixels per frame.
95	101	5F65	Low fuel warning sound period (0-127). Used as delay loop iteration count for speaker ON/OFF phases. Lower values = higher pitch. Decremented each frame, creating a rising-then-resetting warble effect.
95	102	5F66	Fuel level (0-255). $FF=full tank, $00=empty.
95	103	5F67	Input interface type ($00=Keyboard, $01=Sinclair, $02=Kempston, $03=Cursor).
95	104	5F68	Current gameplay mode
95	105	5F69	Plane sprite bank offset. $00=centered, $04=banked left/right. Reset to $00 at the start of each frame, then set to $04 by restore_plane_state_after_render after the banked sprite is rendered. Read by add_fuel, but always $00 at that call site — the check is dead code.
95	106	5F6A	Player 1's current bridge number (0-47). Saved when switching players in 2-player mode.
95	107	5F6B	Player 2's current bridge number (0-47). Saved when switching players in 2-player mode.
95	108	5F6C	Bridge section indicator. $00=normal terrain, $02=bridge terrain section. Set when plane enters bridge area.
95	109	5F6D	Bridge destruction flag ($00 = intact, $01 = destroyed).
95	110	5F6E	Y-position of destroyed bridge in pixels. Updated during scroll to track bridge debris position on screen.
95	111	5F6F	Unused.
95	112	5F70	Vertical scroll offset (16-bit, little-endian). Accumulated distance traveled in pixels. Used to calculate level slot index and bridge position.
95	114	5F72	Player plane X coordinate in pixels (0-255). $78 (120) is horizontal center. Changes by 2 pixels per left/right input.
95	115	5F73	Pointer to helicopter missile coordinates in viewport_slots array. Updated when advanced helicopter fires.
95	117	5F75	Helicopter missile state. Bit 7 set when missile active. Lower bits track missile animation/position.
95	118	5F76	Current level terrain array index (1-255). Points to current element in level definition at level_terrains. Incremented as terrain scrolls.
95	119	5F77	Current terrain profile number (0-7). Index into terrain sprite table at data_terrain_profiles. Loaded from first byte of level element at level_terrains.
95	120	5F78	Cached terrain element data (2 bytes). Stores bytes 2-3 of current level element for object spawning.
95	122	5F7A	Terrain extras byte. Additional terrain rendering flags from level data.
95	123	5F7B	Current screen memory pointer. Points to pixel address being rendered during terrain drawing.
95	125	5F7D	Terrain sub-position (0-3). Index within current terrain element. Incremented every 4 scroll units, triggers new terrain load at 0.
95	126	5F7E	Pointer to the text to be displayed in the scroller.
95	128	5F80	Unused
95	129	5F81	Overview mode frame counter. Counts scroll iterations during attract mode. Game starts after 5 increments or key press.
95	130	5F82	Unused
95	131	5F83	Saved stack pointer. Captured at init, restored when starting new life to unwind any nested calls.
95	133	5F85	Saved HL register during collision detection. Preserved across collision handler calls.
95	135	5F87	Saved DE register during collision detection. Preserved across collision handler calls.
95	137	5F89	Saved BC register during collision detection. Preserved across collision handler calls.
95	139	5F8B	Collision coordinates (Y in high byte, X in low byte). Set by collision detection when overlap found.
95	141	5F8D	Saved object coordinates during rendering. Backup of object position for multi-pass rendering.
95	143	5F8F	Backup of plane missile coordinates. Saved before movement, used for collision detection and erasure.
95	145	5F91	Main gameplay loop
95	218	5FDA	Scan cursor keys
96	10	600A	Scan Kempston joystick
96	57	6039	Scan Sinclair joystick
96	104	6068	Scan keyboard
96	165	60A5	Render player plane and terrain fragments
97	36	6124	Calculate fuel gauge sprite offset
97	54	6136	Collision detection dispatcher
97	94	615E	Handle COLLISION_MODE_FIGHTER collision detection
97	187	61BB	Check collision against bridges and viewport objects
98	73	6249	Increment player 2's bridge counter
98	83	6253	Unused
98	86	6256	Handle COLLISION_MODE_FUEL_DEPOT (initiate refueling)
98	104	6268	Check collision with explosion fragments
98	206	62CE	End of fragment list - no collision found
98	212	62D4	Get Y offset for balloon collision
98	215	62D7	Get Y offset for fuel depot collision
98	218	62DA	Increase vertical coordinate of the object by the value of state_speed.
98	224	62E0	Decrease vertical coordinate of the object by the value of state_speed.
98	232	62E8	Check missile collision against viewport objects
99	252	63FC	Reset gameplay mode to normal and exit collision system
100	20	6414	Handle missile hit on regular helicopter
100	35	6423	Handle missile hit on ship
100	68	6444	Handle missile hit on advanced helicopter
100	83	6453	Handle missile hit on fighter
100	98	6462	Handle missile hit on balloon
100	120	6478	Handle collision with fuel depot
100	158	649E	Jump to collision finalization
100	161	64A1	Handle refueling from fuel depot
100	180	64B4	Unused
100	188	64BC	Print current bridge number on status line
100	229	64E5	Print bridge number for Player 2
100	241	64F1	Common bridge printing for Player 2
101	6	6506	Print a space character
101	10	650A	Handle player death
101	104	6568	Restart gameplay for current player
101	111	656F	Check if Player 2 has lives remaining when Player 1 is out
101	119	6577	Game Over
101	135	6587	Setup Player 2 status line during overview mode
101	171	65AB	Switch to Player 2 after Player 1 death
101	187	65BB	Switch to Player 2 when Player 1 dies in two-player mode
101	203	65CB	Handle Player 2 death and determine next game state
101	222	65DE	Switch to Player 1 after Player 2 death
101	243	65F3	Move player plane right by 2 pixels
102	48	6630	Restore plane state after rendering
102	66	6642	Move player plane left by 2 pixels
102	130	6682	Render player plane sprite
102	204	66CC	Load banked plane sprite address
102	208	66D0	Advance game scroll and update bridge position
102	238	66EE	Update bridge Y position during scroll
103	4	6704	Clear bridge when scrolled off screen
103	10	670A	Handle up/accelerate input
103	23	6717	Handle down/decelerate input
103	36	6724	Handle fire button input
103	60	673C	Missile animation pass selector. $01=first pass (erase at old position), $00=second pass (draw at new position). Two-pass rendering prevents flicker.
103	61	673D	Animate and render player missile
103	142	678E	Clear CONTROLS_BIT_FIRE_SOUND flag
103	148	6794	Finalize collision and erase missile sprite
104	49	6831	Add $0800 offset to screen pointer
104	54	6836	Add $1000 offset to screen pointer
104	59	683B	Scroll screen pixels vertically
104	161	68A1	Clear top screen rows after scrolling
104	183	68B7	Scroll screen attributes up by one row
104	197	68C5	Copy bottom attribute row to row 1 and refill bottom
104	233	68E9	Initialize bridge state for current player
105	39	6927	Render bridge attributes to bottom row
105	59	693B	Terrain edge rendering counter
105	60	693C	Initialize bridge approach state
105	71	6947	Clear bridge destroyed flag
105	77	694D	Advance to next bridge/level
105	99	6963	Wrap bridge index from 49 to 1
105	107	696B	Initialize island state from terrain data
105	144	6990	Render one line of island terrain
106	63	6A3F	Calculate mirrored right edge position
106	69	6A45	Calculate offset right edge position
106	74	6A4A	Get player 2's bridge progress
106	79	6A4F	Load next terrain fragment and initialize rendering state
106	163	6AA3	Render one pixel line of terrain
107	88	6B58	Calculate mirrored right edge (terrain extras mode 1)
107	94	6B5E	Calculate offset right edge (terrain extras mode 2)
107	99	6B63	Load canal sprite (river-adjacent side)
107	107	6B6B	Load canal sprite (road-adjacent side)
107	115	6B73	Load road/bridge sprite
107	123	6B7B	Render special terrain fragment (bridge/road area)
107	176	6BB0	Control state bitmask. Bit 0=FIRE, 1=SPEED_DECREASED, 2=SPEED_ALTERED, 3=LOW_FUEL, 4=BONUS_LIFE, 5=EXPLODING.
107	177	6BB1	Keep the game paused
107	191	6BBF	Handle the Enter key pressed
107	210	6BD2	Reset to control selection screen.
107	219	6BDB	Maskable interrupt handler (IM 2)
107	237	6BED	Process control state flags and trigger sound effects
108	36	6C24	Return from interrupt handler
108	43	6C2B	Unused
108	48	6C30	Bonus life sound progress counter (0-64). Incremented each interrupt during jingle. Sound completes when reaching $40 (64).
108	49	6C31	Play bonus life sound effect
108	82	6C52	Complete bonus life sound sequence
108	93	6C5D	Play normal speed engine sound
108	122	6C7A	Explosion sound tick counter. Counts down from $18 (24) to 0. Value also controls pitch - higher values = lower frequency.
108	123	6C7B	Play explosion sound effect
108	173	6CAD	Complete explosion sound sequence
108	184	6CB8	Play fast speed engine sound
108	214	6CD6	Play slow speed engine sound
108	244	6CF4	Play low fuel warning sound
109	23	6D17	Level overview screen
109	221	6DDD	Reset scrolling title text
109	235	6DEB	Initializes the starting bridge based on the value of state_game_mode using starting_bridges for the lookup.
109	255	6DFF	Consume fuel and update gauge display
110	64	6E40	Add fuel during refueling
110	134	6E86	Set low fuel warning flag
110	140	6E8C	Clear low fuel warning flag
110	146	6E92	Play tank full sound
110	156	6E9C	Create explosion fragment at coordinates
110	171	6EAB	Add object entry to a set
110	188	6EBC	Write object entry to set
110	200	6EC8	Process and render all active explosions
111	99	6F63	Load frame 1/5 explosion sprite
111	103	6F67	Load frame 2/4 explosion sprite
111	107	6F6B	Load frame 3 explosion sprite
111	111	6F6F	Load explosion erasure sprite
111	115	6F73	Reset explosions set pointer
111	122	6F7A	Remove completed explosion from set
111	128	6F80	Spawn objects from level data slot
111	187	6FBB	Render rock sprite
111	230	6FE6	Load pointer to right-facing enemy sprites
111	234	6FEA	Set up object screen position for rendering
111	246	6FF6	Spawn and render enemy on screen
112	56	7038	Load ship screen attributes
112	59	703B	Load fighter screen attributes
112	62	703E	Load tank screen attributes
112	70	7046	Set XOR blending mode for sprite rendering
112	81	7051	Render fuel station
112	108	706C	Render balloon
112	142	708E	Main viewport slot processing loop.
113	4	7104	Ship or helicopter operation routine
113	19	7113	Advance left-facing ship or helicopter
113	40	7128	Continue ship/helicopter rendering
113	85	7155	Reset left-moving fighter position
113	88	7158	Fighter operation routine
113	107	716B	Continue fighter operation
113	146	7192	Advance right-facing fighter
113	159	719F	Reset right-moving fighter position
113	162	71A2	Animate tank shell explosion
114	14	720E	Finish tank shell explosion animation
114	36	7224	Handle non-activated object
114	72	7248	Load right-facing helicopter rotor sprite
114	76	724C	Animate object (helicopter rotor)
114	89	7259	Animate helicopter rotor
114	139	728B	Advance tank right by 4 pixels
114	144	7290	Signal road tank at center
114	150	7296	Tank operation routine
114	230	72E6	Set XOR/XOR blending mode
114	239	72EF	Set OR/OR blending mode
114	248	72F8	Adjust tank position for left orientation
114	253	72FD	Adjust tank position for right orientation
115	2	7302	Operate tank on river bank
115	67	7343	Initialize tank shell state
115	88	7358	Cancel and remove tank shell
115	94	735E	Check shell initialization condition
115	128	7380	Invert coordinate for position calculation
115	131	7383	Tank shell state flags and speed
115	132	7384	Tank shell trajectory step (0-7)
115	133	7385	Tank shell position (BC format: C=X, B=Y)
115	135	7387	Invert shell coordinate delta
115	142	738E	Invert helicopter missile offset
115	147	7393	Operate helicopter missile
115	208	73D0	Remove helicopter missile
115	216	73D8	Add X offset for right-facing missile spawn
115	221	73DD	Render helicopter missile (spawn new)
116	21	7415	Handle helicopter missile collision
116	65	7441	Operate tank shell
116	160	74A0	Erase off-screen tank shell
116	198	74C6	Trigger tank shell explosion
116	228	74E4	Remove tank shell from game
116	238	74EE	Handle tank after bridge destruction
117	70	7546	Get bridge number for player 1
117	76	754C	Operate fuel station
117	138	758A	Clip fuel station height to viewport
117	162	75A2	Advance right-facing ship or helicopter
117	186	75BA	Load enemy sprite pointer
117	208	75D0	Reverse enemy direction at river bank
118	39	7627	Reset current_slot_ptr to the start of viewport_slots.
118	46	762E	Remove an object from the viewport array.
118	73	7649	Operate balloon movement and rendering.
118	172	76AC	A useless procedure that unconditionally jumps to operate_viewport_slots.
118	175	76AF	Right-facing balloon movement.
118	218	76DA	Handle balloon terrain collision.
119	39	7727	Unused
120	0	7800	Control type chosen from the dialog before the validation
120	1	7801	Overview mode flag ($00 - No, $01 - Yes)
120	2	7802	Stores the number of remaining iterations before the control choice dialog switches to overview mode
120	4	7804	Clear screen and enter setup menu.
120	16	7810	Temporary stack pointer used by the control choice dialog
120	18	7812	Keyboard configuration;
122	185	7AB9	Initial game setup
122	205	7ACD	Wait until the user chooses a valid control type or switch to the overview mode on timeout.
123	7	7B07	Wait until the user chooses a valid game mode.
123	87	7B57	Switch to overview/demo mode on timeout.
123	97	7B61	Unused
128	0	8000	Status line 1: fuel gauge and lives display.
128	49	8031	Status line 2: player scores header.
128	79	804F	Status line 3: bridge number position.
128	82	8052	Status line 3 text: "BRIDGE" label.
128	90	805A	Status line 4: "FUEL" label.
128	95	805F	End marker for status_line_4 length calculation
128	99	8063	River bank shape profiles (15 profiles × 16 bytes = 240 bytes).
129	83	8153	Game Over message.
129	130	8182	Credits message with copyright and Activision logo.
129	229	81E5	Unused
130	93	825D	User-defined graphics data (13 characters).
130	197	82C5	Solid fill pattern (48 bytes of $FF).
130	245	82F5	Sprite erasure pattern (60 bytes of $00).
131	49	8331	Terrain pixels for pre/post bridge sections (2×16 bytes).
131	81	8351	Road and bridge pixel patterns (2×16 bytes).
131	113	8371	Road and bridge color attributes (2×16 bytes).
131	145	8391	Unused alternate road attributes.
131	177	83B1	Player plane sprite (4 frames × 16 bytes).
131	241	83F1	Player plane banked sprite (4 frames × 16 bytes).
132	49	8431	Player missile sprite (4 frames × 8 bytes).
132	81	8451	Missile trail sprite (4 frames × 8 bytes).
132	113	8471	Explosion sprite frame 1 (2×1 tiles).
132	129	8481	Explosion sprite frame 2 (2×1 tiles).
132	145	8491	Explosion sprite frame 3 (2×1 tiles).
132	161	84A1	Array [4] of rock sprites (3×2 tiles, 48 bytes).
133	97	8561	Control selection menu text.
133	179	85B3	Array [5] arrays of enemy headed left sprites (each element is 3×1 tiles × 4 frames = 96 bytes).
135	147	8793	Array [5] arrays of enemy headed right sprites (each element is 3×1 tiles × 4 frames = 96 bytes).
137	114	8972	Array [4] of balloon sprites (2×2 tiles, 32 bytes).
137	242	89F2	Left terrain edge masks (4 widths: 10, 12, 14, 16 pixels).
137	250	89FA	Right terrain edge masks (4 widths: 16, 14, 12, 10 pixels).
138	2	8A02	Generate firing sound effect.
138	27	8A1B	Scroll the text crawl row left by 1 pixel.
138	51	8A33	Initialize UDG and screen attributes.
138	78	8A4E	Calculate screen address from pixel coordinates.
138	134	8A86	Fuel sprite
138	184	8AB8	Helicopter rotor sprite (left-facing, 4 frames × 4 bytes).
138	200	8AC8	Helicopter rotor sprite (right-facing, 4 frames × 4 bytes).
138	216	8AD8	Unused explosion animation sprite (6 frames × 8 bytes).
139	8	8B08	Pointer to collision handler routine at collision_dispatcher. Called when sprite rendering detects pixel overlap.
139	10	8B0A	Previous object coordinates (Y high, X low). Position before movement, used for sprite erasure.
139	12	8B0C	Current object coordinates (Y high, X low). Position after movement, used for sprite drawing.
139	14	8B0E	Pointer to current sprite frame data. Set before calling render routines.
139	16	8B10	Pointer to sprite data for erasure. Points to previous frame or erase pattern.
139	18	8B12	Screen memory address for drawing new sprite position. Calculated from object_coordinates.
139	20	8B14	Screen memory address for erasing old sprite position. Calculated from previous_object_coordinates.
139	22	8B16	Output sprite pointer after rendering. Advanced by frame size during render loop.
139	24	8B18	Unused
139	26	8B1A	Sprite width in tiles (1-3). Used by render loop to process correct number of bytes per row.
139	27	8B1B	Unused
139	30	8B1E	Render a sprite at position from previous_object_coordinates.
139	60	8B3C	Render an object with collision detection.
139	112	8B70	Process one row of sprite rendering.
139	148	8B94	Adjust screen address for third-of-screen crossing.
139	163	8BA3	Process old position screen address adjustment.
139	198	8BC6	Adjust old position for third-of-screen crossing.
140	11	8C0B	Render one row of sprite data to screen.
140	27	8C1B	Self-modifying blending operation (erasure).
140	60	8C3C	Self-modifying blending operation (drawing).
140	69	8C45	Jump to collision dispatcher
140	74	8C4A	Unused
143	252	8FFC	Tank shell explosion sprite (6 frames × 32 bytes).
144	188	90BC	Player 1 score ones and tens digits (2 ASCII chars)
144	190	90BE	Player 1 score hundreds and thousands digits
144	192	90C0	Player 1 score ten-thousands and hundred-thousands digits
144	194	90C2	Player 2 score ones and tens digits (2 ASCII chars)
144	196	90C4	Player 2 score hundreds and thousands digits
144	198	90C6	Player 2 score ten-thousands and hundred-thousands digits
144	200	90C8	High score storage for bridge 1 (6 ASCII digits).
144	206	90CE	High score storage for bridges 2-4 (18 ASCII digits, 6 per bridge).
144	224	90E0	Add score points for a hit target
145	9	9109	Add a life to the current player.
145	34	9122	Update and print score for current player.
145	59	913B	Increase a digit in the player 1's score.
145	75	914B	Print a digit from player 1's score.
145	105	9169	Increase a digit in the player 2's score.
145	121	9179	Print a digit from player 2's score.
145	145	9191	Handle carry for player 1's score digit.
145	169	91A9	Handle carry for player 2's score digit.
145	193	91C1	Print player 2's score on the status line.
145	232	91E8	Print player 2 score area or high score on status line.
146	58	923A	Game mode configuration byte
146	59	923B	Player 1 lives remaining (0-3). Initialized to LIVES_INITIAL (4) at new game, then immediately decremented to 3 at the end of the first scroll-in (play). Decremented again at the end of each subsequent scroll-in after a death. Game over is triggered when 0 at the time of the player's next death.
146	60	923C	Player 2 lives remaining (0-3). Initialized to LIVES_INITIAL (4) at new game, then immediately decremented to 3 at the end of the first scroll-in (play). Decremented again at the end of each subsequent scroll-in after a death. Game over is triggered when 0 at the time of the player's next death.
146	61	923D	Current active player ($01=PLAYER_1, $02=PLAYER_2).
146	62	923E	Print lives for current player.
146	79	924F	Continue printing lives after count has been loaded.
146	100	9264	Print six spaces to clear old lives display.
146	119	9277	Player 2 branch of print_lives.
146	131	9283	Pointer to state_controls at state_controls. Allows indirect access to control state bitmask.
146	133	9285	Saved BC register during attribute setting. Preserved across attribute routine calls.
146	135	9287	Saved DE register during attribute setting. Preserved across attribute routine calls.
146	137	9289	Saved HL register during attribute setting. Preserved across attribute routine calls.
146	139	928B	Sprite width in tiles for attribute routine. Determines how many attribute cells to update.
146	141	928D	Set screen attributes for sprite area.
147	93	935D	Return point when attribute color is zero.
147	103	9367	Early exit from old position attribute loop.
147	107	936B	Early exit from new position attribute loop.
147	111	936F	Handle old position attributes when sprite is at screen top (row 0).
147	136	9388	Handle new position attributes when sprite is at screen top (row 0).
147	161	93A1	Compare two 6-digit scores.
147	184	93B8	Return 1 (first score less than second).
147	187	93BB	Return $FF (first score greater than second).
147	190	93BE	Update high score table from current player score.
147	242	93F2	Check if player 2 score beats player 1 score.
148	10	940A	Clear the screen by setting all pixel bytes to $00 and all attributes to the value set in D.
148	35	9423	Load pointer to current player's lives counter.
148	48	9430	Unused
149	0	9500	Level terrain data (48 levels × 256 bytes = 12,288 bytes).
198	0	C600	Island shape definitions (35 islands × 3 bytes = 105 bytes).
198	105	C669	Unused
200	0	C800	Level object spawn data (48 levels × 256 bytes = 12,288 bytes total).