Game 1 Unit 16 of 64 1 hr learning time

Phase 1 Complete

Review Phase 1 and preview what comes next.

25% of Neon Nexus

Mark as complete Completed!

What You Built

A complete NES game. From nothing to playable in 16 units.

Phase 1 Complete

Press Start. Navigate the neon grid. Avoid enemies. Collect all items. Win.

See It In Action

Neon Nexus gameplay — navigate the grid and collect items while avoiding enemies

Phase 1 Summary

You learned the fundamentals of NES development:

Unit	Topic	What You Built
1	Hello NES	Coloured screen with a sprite
2	Moving the Player	D-pad controlled movement
3	Understanding What We Built	Deep dive into PPU, VBlank, OAM
4	The Background	Bordered arena with nametable
5	Custom Tiles	Designed your own tile graphics
6	Colour and Attributes	Multi-coloured arena
7	Enemies Appear	Multiple enemy sprites
8	Enemy Movement	Patrol patterns
9	Collision Detection	Bounding box collision
10	Lives and Death	Lives, death, respawn
11	Collectibles	Items to collect
12	Scoring	Points for collection
13	Sound Effects	APU pulse channel
14	Win Condition	Level completion
15	Game States	Title, playing, game over, win
16	Phase 1 Complete	Review and polish

Technical Skills Acquired

PPU (Picture Processing Unit):

Pattern tables for tile graphics
Nametables for background layout
Attribute tables for colour regions
OAM for sprite management
VBlank timing for safe updates

CPU (6502):

Memory-mapped I/O
Zero page for fast access
Indexed addressing modes
Branching and comparisons
Subroutine structure

APU (Audio Processing Unit):

Pulse channel basics
Frequency control
Sweep unit for effects

Game Logic:

State machine architecture
Collision detection
Input handling with edge detection
Score and lives tracking

The Complete Code

; =============================================================================
; NEON NEXUS - Unit 16: Phase 1 Complete
; =============================================================================
; The complete Phase 1 game. Title screen, gameplay, game over, and win.
; Navigate the neon grid. Avoid enemies. Collect items. Survive.
; =============================================================================

PPUCTRL   = $2000
PPUMASK   = $2001
PPUSTATUS = $2002
OAMADDR   = $2003
PPUSCROLL = $2005
PPUADDR   = $2006
PPUDATA   = $2007
OAMDMA    = $4014
APUSTATUS = $4015
JOYPAD1   = $4016

; APU Pulse 1 registers
APU_PULSE1_CTRL = $4000
APU_PULSE1_SWEEP = $4001
APU_PULSE1_LO = $4002
APU_PULSE1_HI = $4003

BTN_START  = %00010000
BTN_UP     = %00001000
BTN_DOWN   = %00000100
BTN_LEFT   = %00000010
BTN_RIGHT  = %00000001

; Game states
STATE_TITLE    = 0
STATE_PLAYING  = 1
STATE_GAMEOVER = 2
STATE_WIN      = 3

PLAYER_START_X  = 124
PLAYER_START_Y  = 116
PLAYER_SPEED    = 2
ENEMY_SPEED     = 1
NUM_ENEMIES     = 4
NUM_ITEMS       = 4
STARTING_LIVES  = 3
COLLISION_DIST  = 6
COLLECT_DIST    = 8
INVULN_TIME     = 90

TILE_BORDER    = 1
TILE_FLOOR     = 2
TILE_CORNER_TL = 3
TILE_CORNER_TR = 4
TILE_CORNER_BL = 5
TILE_CORNER_BR = 6
SPRITE_PLAYER  = 7
SPRITE_ENEMY   = 8
SPRITE_LIFE    = 9
SPRITE_ITEM    = 10

ARENA_LEFT   = 16
ARENA_RIGHT  = 232
ARENA_TOP    = 24
ARENA_BOTTOM = 208

DIR_RIGHT = 1
DIR_LEFT  = $FF
DIR_DOWN  = 1
DIR_UP    = $FF
BG_COLOUR = $0F

.segment "ZEROPAGE"
player_x:       .res 1
player_y:       .res 1
buttons:        .res 1
buttons_prev:   .res 1      ; Previous frame buttons (for edge detection)
temp:           .res 1
row_counter:    .res 1
frame_count:    .res 1
lives:          .res 1
invuln_timer:   .res 1
game_state:     .res 1      ; Current game state
items_collected: .res 1
score_lo:       .res 1
score_hi:       .res 1

enemy_x:        .res NUM_ENEMIES
enemy_y:        .res NUM_ENEMIES
enemy_dir_x:    .res NUM_ENEMIES
enemy_dir_y:    .res NUM_ENEMIES

item_x:         .res NUM_ITEMS
item_y:         .res NUM_ITEMS
item_active:    .res NUM_ITEMS

.segment "OAM"
oam_buffer:     .res 256

.segment "BSS"

.segment "HEADER"
    .byte "NES", $1A, 2, 1, $01, $00, 0,0,0,0,0,0,0,0

.segment "CODE"

reset:
    sei
    cld
    ldx #$40
    stx $4017
    ldx #$FF
    txs
    inx
    stx PPUCTRL
    stx PPUMASK
    stx $4010

@vblank1:
    bit PPUSTATUS
    bpl @vblank1

    lda #0
@clear_ram:
    sta $0000, x
    sta $0100, x
    sta $0200, x
    sta $0300, x
    sta $0400, x
    sta $0500, x
    sta $0600, x
    sta $0700, x
    inx
    bne @clear_ram

@vblank2:
    bit PPUSTATUS
    bpl @vblank2

    jsr load_palette
    jsr draw_arena
    jsr set_attributes

    ; Hide all sprites initially
    lda #$FF
    ldx #0
@hide_all:
    sta oam_buffer, x
    inx
    bne @hide_all

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL

    ; Enable APU channels
    lda #%00000001
    sta APUSTATUS

    ; Start in title state
    lda #STATE_TITLE
    sta game_state

    lda #%10000000
    sta PPUCTRL
    lda #%00011110
    sta PPUMASK

; =============================================================================
; Main Loop - State Machine
; =============================================================================
main_loop:
    jsr read_controller

    lda game_state
    cmp #STATE_TITLE
    beq @title_state
    cmp #STATE_PLAYING
    beq @playing_state
    cmp #STATE_GAMEOVER
    beq @gameover_state
    cmp #STATE_WIN
    beq @win_state
    jmp main_loop

@title_state:
    jsr handle_title
    jmp main_loop

@playing_state:
    jsr handle_playing
    jmp main_loop

@gameover_state:
    jsr handle_gameover
    jmp main_loop

@win_state:
    jsr handle_win
    jmp main_loop

; =============================================================================
; State Handlers
; =============================================================================

handle_title:
    ; Show title screen sprites
    jsr show_title_sprites

    ; Check for Start button press (new press only)
    lda buttons
    and #BTN_START
    beq @no_start
    lda buttons_prev
    and #BTN_START
    bne @no_start           ; Already pressed last frame

    ; Start pressed! Begin game
    jsr init_game
    lda #STATE_PLAYING
    sta game_state
    jsr play_collect_sound  ; Start game sound

@no_start:
    ; Store previous buttons
    lda buttons
    sta buttons_prev
    rts

handle_playing:
    jsr move_player
    jsr move_enemies
    jsr check_enemy_collisions
    jsr check_item_collisions
    jsr check_win_condition
    jsr update_all_sprites

    ; Store previous buttons
    lda buttons
    sta buttons_prev
    rts

handle_gameover:
    ; Show game over display
    jsr show_gameover_sprites

    ; Check for Start to restart
    lda buttons
    and #BTN_START
    beq @no_restart
    lda buttons_prev
    and #BTN_START
    bne @no_restart

    ; Restart game
    lda #STATE_TITLE
    sta game_state

@no_restart:
    lda buttons
    sta buttons_prev
    rts

handle_win:
    ; Show win display
    jsr show_win_sprites

    ; Check for Start to restart
    lda buttons
    and #BTN_START
    beq @no_restart
    lda buttons_prev
    and #BTN_START
    bne @no_restart

    ; Back to title
    lda #STATE_TITLE
    sta game_state

@no_restart:
    lda buttons
    sta buttons_prev
    rts

; =============================================================================
; Display Routines
; =============================================================================

show_title_sprites:
    ; Hide all sprites first
    lda #$FF
    ldx #0
@hide_loop:
    sta oam_buffer, x
    inx
    bne @hide_loop

    ; Show player sprite in center as "logo"
    lda #100                ; Y position
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0
    sta oam_buffer+2
    lda #124                ; X position
    sta oam_buffer+3

    ; Show some items as decoration
    lda #100
    sta oam_buffer+4
    lda #SPRITE_ITEM
    sta oam_buffer+5
    lda #%00000010
    sta oam_buffer+6
    lda #100
    sta oam_buffer+7

    lda #100
    sta oam_buffer+8
    lda #SPRITE_ITEM
    sta oam_buffer+9
    lda #%00000010
    sta oam_buffer+10
    lda #148
    sta oam_buffer+11
    rts

show_gameover_sprites:
    ; Hide all sprites
    lda #$FF
    ldx #0
@hide_loop:
    sta oam_buffer, x
    inx
    bne @hide_loop

    ; Show enemies as "defeat" indicator
    lda #100
    sta oam_buffer+0
    lda #SPRITE_ENEMY
    sta oam_buffer+1
    lda #%00000001
    sta oam_buffer+2
    lda #112
    sta oam_buffer+3

    lda #100
    sta oam_buffer+4
    lda #SPRITE_ENEMY
    sta oam_buffer+5
    lda #%00000001
    sta oam_buffer+6
    lda #128
    sta oam_buffer+7

    lda #100
    sta oam_buffer+8
    lda #SPRITE_ENEMY
    sta oam_buffer+9
    lda #%00000001
    sta oam_buffer+10
    lda #144
    sta oam_buffer+11
    rts

show_win_sprites:
    ; Hide all sprites
    lda #$FF
    ldx #0
@hide_loop:
    sta oam_buffer, x
    inx
    bne @hide_loop

    ; Show player and items as "victory" indicator
    lda #100
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0
    sta oam_buffer+2
    lda #124
    sta oam_buffer+3

    ; Items around player
    lda #92
    sta oam_buffer+4
    lda #SPRITE_ITEM
    sta oam_buffer+5
    lda #%00000010
    sta oam_buffer+6
    lda #116
    sta oam_buffer+7

    lda #92
    sta oam_buffer+8
    lda #SPRITE_ITEM
    sta oam_buffer+9
    lda #%00000010
    sta oam_buffer+10
    lda #132
    sta oam_buffer+11

    lda #108
    sta oam_buffer+12
    lda #SPRITE_ITEM
    sta oam_buffer+13
    lda #%00000010
    sta oam_buffer+14
    lda #116
    sta oam_buffer+15

    lda #108
    sta oam_buffer+16
    lda #SPRITE_ITEM
    sta oam_buffer+17
    lda #%00000010
    sta oam_buffer+18
    lda #132
    sta oam_buffer+19
    rts

; =============================================================================
; Game Initialisation
; =============================================================================

init_game:
    lda #STARTING_LIVES
    sta lives
    lda #0
    sta invuln_timer
    sta items_collected
    sta score_lo
    sta score_hi

    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    jsr init_enemies
    jsr init_items
    rts

init_enemies:
    lda #48
    sta enemy_x+0
    sta enemy_y+0
    lda #DIR_RIGHT
    sta enemy_dir_x+0
    lda #DIR_DOWN
    sta enemy_dir_y+0

    lda #200
    sta enemy_x+1
    lda #48
    sta enemy_y+1
    lda #DIR_LEFT
    sta enemy_dir_x+1
    lda #DIR_DOWN
    sta enemy_dir_y+1

    lda #48
    sta enemy_x+2
    lda #176
    sta enemy_y+2
    lda #DIR_RIGHT
    sta enemy_dir_x+2
    lda #DIR_UP
    sta enemy_dir_y+2

    lda #200
    sta enemy_x+3
    lda #176
    sta enemy_y+3
    lda #DIR_LEFT
    sta enemy_dir_x+3
    lda #DIR_UP
    sta enemy_dir_y+3
    rts

init_items:
    lda #80
    sta item_x+0
    lda #64
    sta item_y+0
    lda #1
    sta item_active+0

    lda #168
    sta item_x+1
    lda #64
    sta item_y+1
    lda #1
    sta item_active+1

    lda #80
    sta item_x+2
    lda #160
    sta item_y+2
    lda #1
    sta item_active+2

    lda #168
    sta item_x+3
    lda #160
    sta item_y+3
    lda #1
    sta item_active+3
    rts

; =============================================================================
; Collision Detection
; =============================================================================

check_enemy_collisions:
    lda invuln_timer
    beq @check
    dec invuln_timer
    rts

@check:
    ldx #0
@check_enemy:
    lda player_x
    sec
    sbc enemy_x, x
    bpl @check_x_pos
    eor #$FF
    clc
    adc #1
@check_x_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    lda player_y
    sec
    sbc enemy_y, x
    bpl @check_y_pos
    eor #$FF
    clc
    adc #1
@check_y_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    jsr player_hit
    rts

@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @check_enemy
    rts

check_item_collisions:
    ldx #0
@check_item:
    lda item_active, x
    beq @next_item

    lda player_x
    sec
    sbc item_x, x
    bpl @item_x_pos
    eor #$FF
    clc
    adc #1
@item_x_pos:
    cmp #COLLECT_DIST
    bcs @next_item

    lda player_y
    sec
    sbc item_y, x
    bpl @item_y_pos
    eor #$FF
    clc
    adc #1
@item_y_pos:
    cmp #COLLECT_DIST
    bcs @next_item

    ; Collected!
    lda #0
    sta item_active, x
    inc items_collected
    lda score_lo
    clc
    adc #100
    sta score_lo
    lda score_hi
    adc #0
    sta score_hi
    jsr play_collect_sound

@next_item:
    inx
    cpx #NUM_ITEMS
    bne @check_item
    rts

player_hit:
    jsr play_death_sound
    dec lives
    lda lives
    beq @game_over

    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    lda #INVULN_TIME
    sta invuln_timer
    rts

@game_over:
    lda #STATE_GAMEOVER
    sta game_state
    rts

; =============================================================================
; Win Condition
; =============================================================================

check_win_condition:
    lda items_collected
    cmp #NUM_ITEMS
    bne @not_yet
    lda game_state
    cmp #STATE_WIN
    beq @not_yet            ; Already won
    lda #STATE_WIN
    sta game_state
    jsr play_victory_sound
@not_yet:
    rts

; =============================================================================
; Sound Effects
; =============================================================================

play_collect_sound:
    lda #%10011111
    sta APU_PULSE1_CTRL
    lda #0
    sta APU_PULSE1_SWEEP
    lda #$C4
    sta APU_PULSE1_LO
    lda #%00001000
    sta APU_PULSE1_HI
    rts

play_death_sound:
    lda #%10011111
    sta APU_PULSE1_CTRL
    lda #%10001111
    sta APU_PULSE1_SWEEP
    lda #$00
    sta APU_PULSE1_LO
    lda #%00001011
    sta APU_PULSE1_HI
    rts

play_victory_sound:
    lda #%10011111
    sta APU_PULSE1_CTRL
    lda #%10000111
    sta APU_PULSE1_SWEEP
    lda #$FF
    sta APU_PULSE1_LO
    lda #%00000011
    sta APU_PULSE1_HI
    rts

; =============================================================================
; Sprite Updates
; =============================================================================

update_all_sprites:
    jsr update_player_sprite
    jsr update_enemy_sprites
    jsr update_item_sprites
    jsr update_lives_display
    rts

update_player_sprite:
    lda game_state
    cmp #STATE_PLAYING
    bne @hide

    lda invuln_timer
    beq @show
    and #%00000100
    beq @show

@hide:
    lda #$FF
    sta oam_buffer+0
    rts

@show:
    lda player_y
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0
    sta oam_buffer+2
    lda player_x
    sta oam_buffer+3
    rts

update_enemy_sprites:
    ldx #0
    ldy #4
@loop:
    lda enemy_y, x
    sta oam_buffer, y
    iny
    lda #SPRITE_ENEMY
    sta oam_buffer, y
    iny
    lda #%00000001
    sta oam_buffer, y
    iny
    lda enemy_x, x
    sta oam_buffer, y
    iny
    inx
    cpx #NUM_ENEMIES
    bne @loop
    rts

update_item_sprites:
    ldx #0
    ldy #20
@loop:
    lda item_active, x
    beq @hide_item

    lda item_y, x
    sta oam_buffer, y
    iny
    lda #SPRITE_ITEM
    sta oam_buffer, y
    iny
    lda #%00000010
    sta oam_buffer, y
    iny
    lda item_x, x
    sta oam_buffer, y
    iny
    jmp @next_item

@hide_item:
    lda #$FF
    sta oam_buffer, y
    iny
    iny
    iny
    iny

@next_item:
    inx
    cpx #NUM_ITEMS
    bne @loop
    rts

update_lives_display:
    ldy #36
    ldx lives
    beq @hide_all

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #16
    sta oam_buffer, y
    iny

    cpx #1
    beq @hide_rest

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #26
    sta oam_buffer, y
    iny

    cpx #2
    beq @hide_rest

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #36
    sta oam_buffer, y
    rts

@hide_rest:
@hide_all:
    rts

; =============================================================================
; Enemy Movement
; =============================================================================

move_enemies:
    ldx #0
@enemy_loop:
    lda enemy_x, x
    clc
    adc enemy_dir_x, x
    sta enemy_x, x
    cmp #ARENA_LEFT
    bcs @check_right
    lda #DIR_RIGHT
    sta enemy_dir_x, x
    lda #ARENA_LEFT
    sta enemy_x, x
    jmp @move_y
@check_right:
    cmp #ARENA_RIGHT
    bcc @move_y
    lda #DIR_LEFT
    sta enemy_dir_x, x
    lda #ARENA_RIGHT
    sec
    sbc #1
    sta enemy_x, x
@move_y:
    lda enemy_y, x
    clc
    adc enemy_dir_y, x
    sta enemy_y, x
    cmp #ARENA_TOP
    bcs @check_bottom
    lda #DIR_DOWN
    sta enemy_dir_y, x
    lda #ARENA_TOP
    sta enemy_y, x
    jmp @next_enemy
@check_bottom:
    cmp #ARENA_BOTTOM
    bcc @next_enemy
    lda #DIR_UP
    sta enemy_dir_y, x
    lda #ARENA_BOTTOM
    sec
    sbc #1
    sta enemy_y, x
@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @enemy_loop
    rts

; =============================================================================
; PPU Setup
; =============================================================================

load_palette:
    bit PPUSTATUS
    lda #$3F
    sta PPUADDR
    lda #$00
    sta PPUADDR
    ldx #0
@loop:
    lda palette_data, x
    sta PPUDATA
    inx
    cpx #32
    bne @loop
    rts

draw_arena:
    bit PPUSTATUS
    lda #$20
    sta PPUADDR
    lda #$00
    sta PPUADDR
    lda #0
    sta row_counter
@draw_row:
    lda row_counter
    cmp #0
    beq @top_row
    cmp #1
    beq @top_row
    cmp #28
    beq @bottom_row
    cmp #29
    beq @bottom_row
    jmp @middle_row
@top_row:
    lda row_counter
    cmp #0
    bne @top_row_inner
    lda #TILE_CORNER_TL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@top_fill:
    sta PPUDATA
    dex
    bne @top_fill
    lda #TILE_CORNER_TR
    sta PPUDATA
    jmp @next_row
@top_row_inner:
    lda #TILE_BORDER
    ldx #32
@top_inner_fill:
    sta PPUDATA
    dex
    bne @top_inner_fill
    jmp @next_row
@bottom_row:
    lda row_counter
    cmp #29
    bne @bottom_row_inner
    lda #TILE_CORNER_BL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@bottom_fill:
    sta PPUDATA
    dex
    bne @bottom_fill
    lda #TILE_CORNER_BR
    sta PPUDATA
    jmp @next_row
@bottom_row_inner:
    lda #TILE_BORDER
    ldx #32
@bottom_inner_fill:
    sta PPUDATA
    dex
    bne @bottom_inner_fill
    jmp @next_row
@middle_row:
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA
    lda #TILE_FLOOR
    ldx #28
@floor_fill:
    sta PPUDATA
    dex
    bne @floor_fill
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA
@next_row:
    inc row_counter
    lda row_counter
    cmp #30
    beq @done_drawing
    jmp @draw_row
@done_drawing:
    rts

set_attributes:
    bit PPUSTATUS
    lda #$23
    sta PPUADDR
    lda #$C0
    sta PPUADDR
    ldx #8
    lda #$00
@attr_top:
    sta PPUDATA
    dex
    bne @attr_top
    ldx #6
@attr_floor:
    lda #$00
    sta PPUDATA
    lda #%01010101
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    lda #$00
    sta PPUDATA
    dex
    bne @attr_floor
    ldx #8
    lda #$00
@attr_bottom:
    sta PPUDATA
    dex
    bne @attr_bottom
    rts

; =============================================================================
; Input
; =============================================================================

read_controller:
    lda #1
    sta JOYPAD1
    lda #0
    sta JOYPAD1
    ldx #8
@read_loop:
    lda JOYPAD1
    lsr a
    rol buttons
    dex
    bne @read_loop
    rts

move_player:
    lda buttons
    and #BTN_UP
    beq @check_down
    lda player_y
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_TOP
    bcc @check_down
    sta player_y
@check_down:
    lda buttons
    and #BTN_DOWN
    beq @check_left
    lda player_y
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_BOTTOM
    bcs @check_left
    sta player_y
@check_left:
    lda buttons
    and #BTN_LEFT
    beq @check_right
    lda player_x
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_LEFT
    bcc @check_right
    sta player_x
@check_right:
    lda buttons
    and #BTN_RIGHT
    beq @done
    lda player_x
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_RIGHT
    bcs @done
    sta player_x
@done:
    rts

; =============================================================================
; NMI Handler
; =============================================================================

nmi:
    pha
    txa
    pha
    tya
    pha
    lda #0
    sta OAMADDR
    lda #>oam_buffer
    sta OAMDMA
    inc frame_count
    lda #0
    sta PPUSCROLL
    sta PPUSCROLL
    pla
    tay
    pla
    tax
    pla
    rti

irq:
    rti

; =============================================================================
; Data
; =============================================================================

palette_data:
    .byte BG_COLOUR, $11, $21, $31
    .byte BG_COLOUR, $13, $23, $33
    .byte BG_COLOUR, $19, $29, $39
    .byte BG_COLOUR, $16, $26, $36
    .byte BG_COLOUR, $30, $27, $17    ; Player
    .byte BG_COLOUR, $16, $26, $36    ; Enemies
    .byte BG_COLOUR, $1A, $2A, $3A    ; Items (green)
    .byte BG_COLOUR, $30, $27, $17

.segment "VECTORS"
    .word nmi
    .word reset
    .word irq

.segment "CHARS"
; Tile 0: Empty
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
; Tile 1: Border
.byte %11111111,%10000001,%10000001,%11111111,%11111111,%00010001,%00010001,%11111111
.byte %00000000,%01111110,%01111110,%00000000,%00000000,%11101110,%11101110,%00000000
; Tile 2: Floor
.byte %00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%10000001
.byte %00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000
; Tile 3: Corner TL
.byte %11111111,%11000000,%10100000,%10010000,%10001000,%10000100,%10000010,%10000001
.byte %00000000,%00111111,%01011111,%01101111,%01110111,%01111011,%01111101,%01111110
; Tile 4: Corner TR
.byte %11111111,%00000011,%00000101,%00001001,%00010001,%00100001,%01000001,%10000001
.byte %00000000,%11111100,%11111010,%11110110,%11101110,%11011110,%10111110,%01111110
; Tile 5: Corner BL
.byte %10000001,%10000010,%10000100,%10001000,%10010000,%10100000,%11000000,%11111111
.byte %01111110,%01111101,%01111011,%01110111,%01101111,%01011111,%00111111,%00000000
; Tile 6: Corner BR
.byte %10000001,%01000001,%00100001,%00010001,%00001001,%00000101,%00000011,%11111111
.byte %01111110,%10111110,%11011110,%11101110,%11110110,%11111010,%11111100,%00000000
; Tile 7: Player (sprite)
.byte %00011000,%00011000,%00111100,%01111110,%11111111,%10111101,%00100100,%00100100
.byte %00000000,%00011000,%00011000,%00111100,%01000010,%01000010,%00011000,%00000000
; Tile 8: Enemy (sprite)
.byte %00011000,%00111100,%01111110,%11111111,%11111111,%01111110,%00111100,%00011000
.byte %00000000,%00011000,%00100100,%01000010,%01000010,%00100100,%00011000,%00000000
; Tile 9: Life icon (sprite)
.byte %00000000,%00100100,%01111110,%01111110,%00111100,%00011000,%00000000,%00000000
.byte %00000000,%00000000,%00000000,%00100100,%00011000,%00000000,%00000000,%00000000
; Tile 10: Item (data core - diamond)
.byte %00000000,%00011000,%00111100,%01111110,%01111110,%00111100,%00011000,%00000000
.byte %00000000,%00000000,%00011000,%00100100,%00100100,%00011000,%00000000,%00000000

.res 8192 - 176, $00

Build It

ca65 nexus.asm -o nexus.o
ld65 -C nes.cfg nexus.o -o nexus.nes

What’s Next: Phase 2

Phase 2 expands the game with:

Level Data Structure - Define levels as data, not code
Multiple Levels - Progress through different arenas
Player Animation - Frame-based sprite animation
Enemy Animation - Animated threats
Background Music - Multi-channel APU music
Power-Ups - Temporary abilities
Smarter Enemies - AI improvements
Title Screen Graphics - Proper title display
HUD Display - Score and lives on screen

Congratulations

You built a real NES game. It runs on actual hardware. It has a title screen, gameplay, win and lose conditions, sound effects, and complete game flow.

Phase 2 takes this foundation and builds something bigger. More levels. More features. More polish.

The neon grid awaits.

What Changed

Unit 15 → Unit 16

+3-2

1	1		`; =============================================================================`
2		-	`; NEON NEXUS - Unit 15: Game States`
	2	+	`; NEON NEXUS - Unit 16: Phase 1 Complete`
3	3		`; =============================================================================`
4		-	`; Add a state machine with title screen, playing, game over, and win states.`
	4	+	`; The complete Phase 1 game. Title screen, gameplay, game over, and win.`
	5	+	`; Navigate the neon grid. Avoid enemies. Collect items. Survive.`
5	6		`; =============================================================================`
6	7
7	8		`PPUCTRL = $2000`