Game 1 Unit 7 of 64 1 hr learning time

Enemies Appear

Add enemy sprites to the arena.

11% of Neon Nexus

Mark as complete Completed!

What You’re Building

Enemies in the arena. Four hostile sprites waiting for you.

Enemies Appear

The arena now feels dangerous.

Enemy Data

Enemies need positions. We store them in zero page for fast access:

NUM_ENEMIES = 4

.segment "ZEROPAGE"
enemy_x:     .res NUM_ENEMIES
enemy_y:     .res NUM_ENEMIES

Four bytes for X positions, four for Y. Simple arrays.

Initialising Enemies

Place enemies at the four corners of the play area:

init_enemies:
    ; Enemy 0: Top-left
    lda #48
    sta enemy_x+0
    lda #48
    sta enemy_y+0

    ; Enemy 1: Top-right
    lda #200
    sta enemy_x+1
    lda #48
    sta enemy_y+1

    ; Continue for enemies 2 and 3...
    rts

Multiple Sprites in OAM

The player uses OAM slots 0-3. Enemies use slots 4-19 (4 enemies × 4 bytes each):

update_enemy_sprites:
    ldx #0              ; Enemy index
    ldy #4              ; OAM offset (after player)

@loop:
    ; Y position
    lda enemy_y, x
    sta oam_buffer, y
    iny

    ; Tile index
    lda #SPRITE_ENEMY
    sta oam_buffer, y
    iny

    ; Attributes: palette 1
    lda #%00000001
    sta oam_buffer, y
    iny

    ; X position
    lda enemy_x, x
    sta oam_buffer, y
    iny

    inx
    cpx #NUM_ENEMIES
    bne @loop
    rts

Sprite Palettes

Enemies use a different palette from the player:

; Sprite palettes
.byte BG_COLOUR, $30, $27, $17  ; Palette 0: Player (white/orange)
.byte BG_COLOUR, $16, $26, $36  ; Palette 1: Enemy (red)

The attribute byte’s low 2 bits select the sprite palette.

The Enemy Tile

A hostile diamond shape:

; Tile 8: Enemy sprite
.byte %00011000
.byte %00111100
.byte %01111110
.byte %11111111
.byte %11111111
.byte %01111110
.byte %00111100
.byte %00011000

The Code

; =============================================================================
; NEON NEXUS - Unit 7: Enemies Appear
; =============================================================================
; Add enemy sprites to the arena.
; =============================================================================

; -----------------------------------------------------------------------------
; NES Hardware Addresses
; -----------------------------------------------------------------------------
PPUCTRL   = $2000
PPUMASK   = $2001
PPUSTATUS = $2002
OAMADDR   = $2003
PPUSCROLL = $2005
PPUADDR   = $2006
PPUDATA   = $2007
OAMDMA    = $4014

JOYPAD1   = $4016
JOYPAD2   = $4017

; Controller buttons
BTN_A      = %10000000
BTN_B      = %01000000
BTN_SELECT = %00100000
BTN_START  = %00010000
BTN_UP     = %00001000
BTN_DOWN   = %00000100
BTN_LEFT   = %00000010
BTN_RIGHT  = %00000001

; -----------------------------------------------------------------------------
; Game Constants
; -----------------------------------------------------------------------------
PLAYER_START_X = 124
PLAYER_START_Y = 116
PLAYER_SPEED   = 2

NUM_ENEMIES    = 4

; Tile indices (background)
TILE_EMPTY     = 0
TILE_BORDER    = 1
TILE_FLOOR     = 2
TILE_CORNER_TL = 3
TILE_CORNER_TR = 4
TILE_CORNER_BL = 5
TILE_CORNER_BR = 6

; Sprite tiles
SPRITE_PLAYER  = 7
SPRITE_ENEMY   = 8

; Arena boundaries
ARENA_LEFT   = 16
ARENA_RIGHT  = 232
ARENA_TOP    = 16
ARENA_BOTTOM = 208

BG_COLOUR = $0F

; -----------------------------------------------------------------------------
; Memory Layout
; -----------------------------------------------------------------------------
.segment "ZEROPAGE"
player_x:    .res 1
player_y:    .res 1
buttons:     .res 1
temp:        .res 1
row_counter: .res 1

; Enemy positions (4 enemies)
enemy_x:     .res NUM_ENEMIES
enemy_y:     .res NUM_ENEMIES

.segment "OAM"
oam_buffer:  .res 256

.segment "BSS"

; -----------------------------------------------------------------------------
; iNES Header
; -----------------------------------------------------------------------------
.segment "HEADER"
    .byte "NES", $1A
    .byte 2
    .byte 1
    .byte $01
    .byte $00
    .byte 0,0,0,0,0,0,0,0

; -----------------------------------------------------------------------------
; Code
; -----------------------------------------------------------------------------
.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
    jsr init_enemies

    ; Set up player
    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    ; Initialise player sprite (OAM slot 0)
    lda player_y
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0              ; Attributes: palette 0, no flip
    sta oam_buffer+2
    lda player_x
    sta oam_buffer+3

    ; Set up enemy sprites in OAM
    jsr update_enemy_sprites

    ; Hide remaining sprites (after player + 4 enemies = 5 sprites used)
    lda #$FF
    ldx #20             ; Start after 5 sprites (5*4=20)
@hide_sprites:
    sta oam_buffer, x
    inx
    bne @hide_sprites

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL

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

main_loop:
    jsr read_controller
    jsr move_player
    jmp main_loop

; -----------------------------------------------------------------------------
; Initialise Enemies - Place 4 enemies at corners of play area
; -----------------------------------------------------------------------------
init_enemies:
    ; Enemy 0: Top-left area
    lda #48
    sta enemy_x+0
    lda #48
    sta enemy_y+0

    ; Enemy 1: Top-right area
    lda #200
    sta enemy_x+1
    lda #48
    sta enemy_y+1

    ; Enemy 2: Bottom-left area
    lda #48
    sta enemy_x+2
    lda #176
    sta enemy_y+2

    ; Enemy 3: Bottom-right area
    lda #200
    sta enemy_x+3
    lda #176
    sta enemy_y+3

    rts

; -----------------------------------------------------------------------------
; Update Enemy Sprites in OAM
; -----------------------------------------------------------------------------
update_enemy_sprites:
    ldx #0              ; Enemy index
    ldy #4              ; OAM offset (after player sprite)

@loop:
    ; Y position
    lda enemy_y, x
    sta oam_buffer, y
    iny

    ; Tile
    lda #SPRITE_ENEMY
    sta oam_buffer, y
    iny

    ; Attributes: palette 1 (different colour from player)
    lda #%00000001
    sta oam_buffer, y
    iny

    ; X position
    lda enemy_x, x
    sta oam_buffer, y
    iny

    inx
    cpx #NUM_ENEMIES
    bne @loop

    rts

; -----------------------------------------------------------------------------
; Load Palette
; -----------------------------------------------------------------------------
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
; -----------------------------------------------------------------------------
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 Attribute Table
; -----------------------------------------------------------------------------
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_rows:
    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_rows

    ldx #8
    lda #$00
@attr_bottom:
    sta PPUDATA
    dex
    bne @attr_bottom

    rts

; -----------------------------------------------------------------------------
; Read Controller
; -----------------------------------------------------------------------------
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
; -----------------------------------------------------------------------------
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 ===
nmi:
    pha
    txa
    pha
    tya
    pha

    lda #0
    sta OAMADDR
    lda #>oam_buffer
    sta OAMDMA

    ; Update player sprite position
    lda player_y
    sta oam_buffer+0
    lda player_x
    sta oam_buffer+3

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL

    pla
    tay
    pla
    tax
    pla
    rti

irq:
    rti

; -----------------------------------------------------------------------------
; Data
; -----------------------------------------------------------------------------
palette_data:
    ; Background palettes
    .byte BG_COLOUR, $11, $21, $31  ; Palette 0: Blue
    .byte BG_COLOUR, $13, $23, $33  ; Palette 1: Purple
    .byte BG_COLOUR, $19, $29, $39  ; Palette 2: Green
    .byte BG_COLOUR, $16, $26, $36  ; Palette 3: Red
    ; Sprite palettes
    .byte BG_COLOUR, $30, $27, $17  ; Palette 0: Player (white/orange)
    .byte BG_COLOUR, $16, $26, $36  ; Palette 1: Enemy (red)
    .byte BG_COLOUR, $30, $27, $17
    .byte BG_COLOUR, $30, $27, $17

; -----------------------------------------------------------------------------
; Vectors
; -----------------------------------------------------------------------------
.segment "VECTORS"
    .word nmi
    .word reset
    .word irq

; -----------------------------------------------------------------------------
; CHR-ROM
; -----------------------------------------------------------------------------
.segment "CHARS"

; Tile 0: Empty
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00

; Tile 1: Border (brick pattern)
.byte %11111111
.byte %10000001
.byte %10000001
.byte %11111111
.byte %11111111
.byte %00010001
.byte %00010001
.byte %11111111
.byte %00000000
.byte %01111110
.byte %01111110
.byte %00000000
.byte %00000000
.byte %11101110
.byte %11101110
.byte %00000000

; Tile 2: Floor (subtle grid)
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %10000001
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000
.byte %00000000

; Tile 3: Corner TL
.byte %11111111
.byte %11000000
.byte %10100000
.byte %10010000
.byte %10001000
.byte %10000100
.byte %10000010
.byte %10000001
.byte %00000000
.byte %00111111
.byte %01011111
.byte %01101111
.byte %01110111
.byte %01111011
.byte %01111101
.byte %01111110

; Tile 4: Corner TR
.byte %11111111
.byte %00000011
.byte %00000101
.byte %00001001
.byte %00010001
.byte %00100001
.byte %01000001
.byte %10000001
.byte %00000000
.byte %11111100
.byte %11111010
.byte %11110110
.byte %11101110
.byte %11011110
.byte %10111110
.byte %01111110

; Tile 5: Corner BL
.byte %10000001
.byte %10000010
.byte %10000100
.byte %10001000
.byte %10010000
.byte %10100000
.byte %11000000
.byte %11111111
.byte %01111110
.byte %01111101
.byte %01111011
.byte %01110111
.byte %01101111
.byte %01011111
.byte %00111111
.byte %00000000

; Tile 6: Corner BR
.byte %10000001
.byte %01000001
.byte %00100001
.byte %00010001
.byte %00001001
.byte %00000101
.byte %00000011
.byte %11111111
.byte %01111110
.byte %10111110
.byte %11011110
.byte %11101110
.byte %11110110
.byte %11111010
.byte %11111100
.byte %00000000

; Tile 7: Player sprite
.byte %00011000
.byte %00011000
.byte %00111100
.byte %01111110
.byte %11111111
.byte %10111101
.byte %00100100
.byte %00100100
.byte %00000000
.byte %00011000
.byte %00011000
.byte %00111100
.byte %01000010
.byte %01000010
.byte %00011000
.byte %00000000

; Tile 8: Enemy sprite (hostile diamond shape)
.byte %00011000
.byte %00111100
.byte %01111110
.byte %11111111
.byte %11111111
.byte %01111110
.byte %00111100
.byte %00011000
.byte %00000000
.byte %00011000
.byte %00100100
.byte %01000010
.byte %01000010
.byte %00100100
.byte %00011000
.byte %00000000

; Fill rest of CHR-ROM
.res 8192 - 144, $00

Build It

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

Four enemies now occupy the arena. They don’t move yet - that’s next.

Static enemies aren’t threatening. Unit 8 makes them patrol.

What Changed

Unit 6 → Unit 7

+115-39

1	1		`; =============================================================================`
2		-	`; NEON NEXUS - Unit 6: Colour and Attributes`
	2	+	`; NEON NEXUS - Unit 7: Enemies Appear`
3	3		`; =============================================================================`
4		-	`; Use the attribute table to add colour regions to the arena.`
	4	+	`; Add enemy sprites to the arena.`
5	5		`; =============================================================================`
6	6
7	7		`; -----------------------------------------------------------------------------`
			...
35	35		`PLAYER_START_X = 124`
36	36		`PLAYER_START_Y = 116`
37	37		`PLAYER_SPEED = 2`
	38	+
	39	+	`NUM_ENEMIES = 4`
38	40
39	41		`; Tile indices (background)`
40	42		`TILE_EMPTY = 0`
			...
47	49
48	50		`; Sprite tiles`
49	51		`SPRITE_PLAYER = 7`
	52	+	`SPRITE_ENEMY = 8`
50	53
51	54		`; Arena boundaries`
52	55		`ARENA_LEFT = 16`
			...
65	68		`buttons: .res 1`
66	69		`temp: .res 1`
67	70		`row_counter: .res 1`
	71	+
	72	+	`; Enemy positions (4 enemies)`
	73	+	`enemy_x: .res NUM_ENEMIES`
	74	+	`enemy_y: .res NUM_ENEMIES`
68	75
69	76		`.segment "OAM"`
70	77		`oam_buffer: .res 256`
			...
123	130		`jsr load_palette`
124	131		`jsr draw_arena`
125	132		`jsr set_attributes`
	133	+	`jsr init_enemies`
126	134
127	135		`; Set up player`
128	136		`lda #PLAYER_START_X`
			...
130	138		`lda #PLAYER_START_Y`
131	139		`sta player_y`
132	140
133		-	`; Initialise player sprite`
	141	+	`; Initialise player sprite (OAM slot 0)`
134	142		`lda player_y`
135	143		`sta oam_buffer+0`
136	144		`lda #SPRITE_PLAYER`
137	145		`sta oam_buffer+1`
138		-	`lda #0`
	146	+	`lda #0 ; Attributes: palette 0, no flip`
139	147		`sta oam_buffer+2`
140	148		`lda player_x`
141	149		`sta oam_buffer+3`
142	150
143		-	`; Hide other sprites`
	151	+	`; Set up enemy sprites in OAM`
	152	+	`jsr update_enemy_sprites`
	153	+
	154	+	`; Hide remaining sprites (after player + 4 enemies = 5 sprites used)`
144	155		`lda #$FF`
145		-	`ldx #4`
	156	+	`ldx #20 ; Start after 5 sprites (5*4=20)`
146	157		`@hide_sprites:`
147	158		`sta oam_buffer, x`
148	159		`inx`
			...
152	163		`sta PPUSCROLL`
153	164		`sta PPUSCROLL`
154	165
155		-	`; Enable rendering`
156	166		`lda #%10000000`
157	167		`sta PPUCTRL`
158	168		`lda #%00011110`
			...
164	174		`jmp main_loop`
165	175
166	176		`; -----------------------------------------------------------------------------`
167		-	`; Load Palette - Four distinct background palettes`
	177	+	`; Initialise Enemies - Place 4 enemies at corners of play area`
	178	+	`; -----------------------------------------------------------------------------`
	179	+	`init_enemies:`
	180	+	`; Enemy 0: Top-left area`
	181	+	`lda #48`
	182	+	`sta enemy_x+0`
	183	+	`lda #48`
	184	+	`sta enemy_y+0`
	185	+
	186	+	`; Enemy 1: Top-right area`
	187	+	`lda #200`
	188	+	`sta enemy_x+1`
	189	+	`lda #48`
	190	+	`sta enemy_y+1`
	191	+
	192	+	`; Enemy 2: Bottom-left area`
	193	+	`lda #48`
	194	+	`sta enemy_x+2`
	195	+	`lda #176`
	196	+	`sta enemy_y+2`
	197	+
	198	+	`; Enemy 3: Bottom-right area`
	199	+	`lda #200`
	200	+	`sta enemy_x+3`
	201	+	`lda #176`
	202	+	`sta enemy_y+3`
	203	+
	204	+	`rts`
	205	+
	206	+	`; -----------------------------------------------------------------------------`
	207	+	`; Update Enemy Sprites in OAM`
	208	+	`; -----------------------------------------------------------------------------`
	209	+	`update_enemy_sprites:`
	210	+	`ldx #0 ; Enemy index`
	211	+	`ldy #4 ; OAM offset (after player sprite)`
	212	+
	213	+	`@loop:`
	214	+	`; Y position`
	215	+	`lda enemy_y, x`
	216	+	`sta oam_buffer, y`
	217	+	`iny`
	218	+
	219	+	`; Tile`
	220	+	`lda #SPRITE_ENEMY`
	221	+	`sta oam_buffer, y`
	222	+	`iny`
	223	+
	224	+	`; Attributes: palette 1 (different colour from player)`
	225	+	`lda #%00000001`
	226	+	`sta oam_buffer, y`
	227	+	`iny`
	228	+
	229	+	`; X position`
	230	+	`lda enemy_x, x`
	231	+	`sta oam_buffer, y`
	232	+	`iny`
	233	+
	234	+	`inx`
	235	+	`cpx #NUM_ENEMIES`
	236	+	`bne @loop`
	237	+
	238	+	`rts`
	239	+
	240	+	`; -----------------------------------------------------------------------------`
	241	+	`; Load Palette`
168	242		`; -----------------------------------------------------------------------------`
169	243		`load_palette:`
170	244		`bit PPUSTATUS`
			...
183	257		`rts`
184	258
185	259		`; -----------------------------------------------------------------------------`
186		-	`; Draw Arena (same as Unit 5)`
	260	+	`; Draw Arena`
187	261		`; -----------------------------------------------------------------------------`
188	262		`draw_arena:`
189	263		`bit PPUSTATUS`
			...
289	363		`rts`
290	364
291	365		`; -----------------------------------------------------------------------------`
292		-	`; Set Attribute Table - Different palettes for different regions`
	366	+	`; Set Attribute Table`
293	367		`; -----------------------------------------------------------------------------`
294	368		`set_attributes:`
295	369		`bit PPUSTATUS`
			...
297	371		`sta PPUADDR`
298	372		`lda #$C0`
299	373		`sta PPUADDR`
300		-
301		-	`; Attribute table: 8 bytes per row, 8 rows = 64 bytes`
302		-	`; Each byte controls 4 16x16 pixel areas (32x32 total)`
303		-	`; Bits: 76=BR, 54=BL, 32=TR, 10=TL`
304	374
305		-	`; Row 0-1: All border (palette 0)`
306	375		`ldx #8`
307		-	`lda #$00 ; All palette 0`
	376	+	`lda #$00`
308	377		`@attr_top:`
309	378		`sta PPUDATA`
310	379		`dex`
311	380		`bne @attr_top`
312	381
313		-	`; Rows 2-5: Border edges (palette 0), floor varies`
314		-	`; Create a gradient effect: palette 1 in centre`
315		-	`ldx #6 ; 6 rows of attributes for floor area`
	382	+	`ldx #6`
316	383		`@attr_floor_rows:`
317		-	`; Byte 0: Left edge - palette 0`
318	384		`lda #$00`
319	385		`sta PPUDATA`
320		-
321		-	`; Bytes 1-6: Floor area with palette 1`
322		-	`lda #%01010101 ; All palette 1`
	386	+	`lda #%01010101`
323	387		`sta PPUDATA`
324	388		`sta PPUDATA`
325	389		`sta PPUDATA`
326	390		`sta PPUDATA`
327	391		`sta PPUDATA`
328	392		`sta PPUDATA`
329		-
330		-	`; Byte 7: Right edge - palette 0`
331	393		`lda #$00`
332	394		`sta PPUDATA`
333		-
334	395		`dex`
335	396		`bne @attr_floor_rows`
336	397
337		-	`; Row 7: Bottom border (palette 0)`
338	398		`ldx #8`
339	399		`lda #$00`
340	400		`@attr_bottom:`
			...
425	485		`lda #>oam_buffer`
426	486		`sta OAMDMA`
427	487
	488	+	`; Update player sprite position`
428	489		`lda player_y`
429	490		`sta oam_buffer+0`
430	491		`lda player_x`
			...
448	509		`; Data`
449	510		`; -----------------------------------------------------------------------------`
450	511		`palette_data:`
451		-	`; Background palette 0: Blue border`
452		-	`.byte BG_COLOUR, $11, $21, $31 ; Black, dark blue, light blue, cyan`
453		-	`; Background palette 1: Purple floor`
454		-	`.byte BG_COLOUR, $13, $23, $33 ; Black, dark purple, purple, light purple`
455		-	`; Background palette 2: Green (unused for now)`
456		-	`.byte BG_COLOUR, $19, $29, $39 ; Black, dark green, green, light green`
457		-	`; Background palette 3: Red (unused for now)`
458		-	`.byte BG_COLOUR, $16, $26, $36 ; Black, dark red, red, light red`
	512	+	`; Background palettes`
	513	+	`.byte BG_COLOUR, $11, $21, $31 ; Palette 0: Blue`
	514	+	`.byte BG_COLOUR, $13, $23, $33 ; Palette 1: Purple`
	515	+	`.byte BG_COLOUR, $19, $29, $39 ; Palette 2: Green`
	516	+	`.byte BG_COLOUR, $16, $26, $36 ; Palette 3: Red`
459	517		`; Sprite palettes`
460		-	`.byte BG_COLOUR, $30, $27, $17 ; White, orange, brown`
461		-	`.byte BG_COLOUR, $30, $27, $17`
	518	+	`.byte BG_COLOUR, $30, $27, $17 ; Palette 0: Player (white/orange)`
	519	+	`.byte BG_COLOUR, $16, $26, $36 ; Palette 1: Enemy (red)`
462	520		`.byte BG_COLOUR, $30, $27, $17`
463	521		`.byte BG_COLOUR, $30, $27, $17`
464	522
			...
471	529		`.word irq`
472	530
473	531		`; -----------------------------------------------------------------------------`
474		-	`; CHR-ROM - Same tiles as Unit 5`
	532	+	`; CHR-ROM`
475	533		`; -----------------------------------------------------------------------------`
476	534		`.segment "CHARS"`
477	535
			...
597	655		`.byte %00100100`
598	656		`.byte %00100100`
599	657		`.byte %00000000`
	658	+	`.byte %00011000`
	659	+	`.byte %00011000`
	660	+	`.byte %00111100`
	661	+	`.byte %01000010`
	662	+	`.byte %01000010`
600	663		`.byte %00011000`
	664	+	`.byte %00000000`
	665	+
	666	+	`; Tile 8: Enemy sprite (hostile diamond shape)`
601	667		`.byte %00011000`
	668	+	`.byte %00111100`
	669	+	`.byte %01111110`
	670	+	`.byte %11111111`
	671	+	`.byte %11111111`
	672	+	`.byte %01111110`
602	673		`.byte %00111100`
	674	+	`.byte %00011000`
	675	+	`.byte %00000000`
	676	+	`.byte %00011000`
	677	+	`.byte %00100100`
603	678		`.byte %01000010`
604	679		`.byte %01000010`
	680	+	`.byte %00100100`
605	681		`.byte %00011000`
606	682		`.byte %00000000`
607	683
608	684		`; Fill rest of CHR-ROM`
609		-	`.res 8192 - 128, $00`
	685	+	`.res 8192 - 144, $00`
610	686