Game 1 Unit 4 of 64 1 hr learning time

Custom Graphics

Design custom characters for notes, tracks, and hit zones. The game looks professional.

6% of SID Symphony

Mark as complete Completed!

The game works. Now make it look like a real game.

This unit replaces the placeholder ASCII characters with custom graphics. You’ll learn how the C64’s character system works by designing your own characters - notes that look like arrows, tracks that look like clean lines, hit zones that stand out.

Run It

Assemble and run:

acme -f cbm -o symphony.prg symphony.asm

Unit 4 Screenshot

Compare this to the previous units. The tracks are now clean horizontal lines. The hit zone is a distinctive yellow double bar. Notes are chevrons pointing left - arrows showing the direction of travel. The game looks professional.

Custom graphics — chevron notes, clean tracks, double-bar hit zone

The C64 Character System

The C64 displays characters from an 8×8 pixel grid. There are 256 characters, each defined by 8 bytes (one byte per row). The default characters live in ROM at $D000, but ROM is read-only.

To create custom characters:

Copy the ROM characters to RAM
Modify the RAM copy
Point the VIC-II chip to the RAM location

Copying the Character ROM

The character ROM shares address space with I/O chips. To read it, we temporarily remap memory:

; Copy Character ROM to RAM
; The C64's character ROM is read-only. To modify characters, we copy
; the ROM to RAM and point the VIC-II to our RAM copy.

CHARSET     = $3000             ; Our custom charset location

copy_charset:
            ; Disable interrupts - ROM switching must be atomic
            sei

            ; The C64's processor port at $01 controls memory mapping
            ; Bit 2 (CHAREN) = 0 makes character ROM visible at $D000
            lda $01
            pha                 ; Save current state
            and #$FB            ; Clear bit 2
            sta $01             ; Character ROM now at $D000-$DFFF

            ; Copy all 256 characters (256 * 8 = 2048 bytes)
            ldx #0
copy_loop:
            lda $D000,x         ; Copy 256 bytes at a time
            sta CHARSET,x       ; To our RAM location
            lda $D100,x
            sta CHARSET+$100,x
            ; ... (continues for all 8 pages)
            inx
            bne copy_loop

            ; Restore processor port
            pla
            sta $01

            ; Re-enable interrupts
            cli
            rts

The processor port at $01 controls what appears at certain addresses. When we clear bit 2, the character ROM becomes visible at $D000-$DFFF. We copy all 2KB to our RAM location at $3000.

Designing Characters

Each character is 8 bytes. Each bit in a byte is one pixel:

; Character Design - 8x8 Pixel Grids
; Each character is 8 bytes, one byte per row.
; Each bit is one pixel (1=foreground, 0=background).

; Character 128: Note (chevron pointing left)
; Design:
;   ......XX  = $06
;   ....XXXX  = $1E
;   ..XXXXXX  = $7E
;   XXXXXXXX  = $FE
;   XXXXXXXX  = $FE
;   ..XXXXXX  = $7E
;   ....XXXX  = $1E
;   ......XX  = $06

CHAR_NOTE   = 128

            lda #%00000110      ; Row 0: tip of arrow
            sta CHARSET + (CHAR_NOTE * 8) + 0
            lda #%00011110      ; Row 1: wider
            sta CHARSET + (CHAR_NOTE * 8) + 1
            lda #%01111110      ; Row 2: wider still
            sta CHARSET + (CHAR_NOTE * 8) + 2
            lda #%11111110      ; Row 3: full width (minus 1 pixel)
            sta CHARSET + (CHAR_NOTE * 8) + 3
            lda #%11111110      ; Row 4: same
            sta CHARSET + (CHAR_NOTE * 8) + 4
            lda #%01111110      ; Row 5: narrowing
            sta CHARSET + (CHAR_NOTE * 8) + 5
            lda #%00011110      ; Row 6: narrower
            sta CHARSET + (CHAR_NOTE * 8) + 6
            lda #%00000110      ; Row 7: tip
            sta CHARSET + (CHAR_NOTE * 8) + 7

The note character is a chevron pointing left - an arrow showing “this note is moving toward the hit zone.” The design uses binary literals so you can see the pixel pattern directly in the code.

Try This: Design Your Own Note

; Filled circle note:
;   ..XXXX..  = %00111100 = $3C
;   .XXXXXX.  = %01111110 = $7E
;   XXXXXXXX  = %11111111 = $FF
;   XXXXXXXX  = %11111111 = $FF
;   XXXXXXXX  = %11111111 = $FF
;   XXXXXXXX  = %11111111 = $FF
;   .XXXXXX.  = %01111110 = $7E
;   ..XXXX..  = %00111100 = $3C

            lda #$3C
            sta CHARSET + (CHAR_NOTE * 8) + 0
            lda #$7E
            sta CHARSET + (CHAR_NOTE * 8) + 1
            ; ... etc

Try This: Diamond Note

; Diamond shape:
;   ...XX...  = %00011000 = $18
;   ..XXXX..  = %00111100 = $3C
;   .XXXXXX.  = %01111110 = $7E
;   XXXXXXXX  = %11111111 = $FF
;   XXXXXXXX  = %11111111 = $FF
;   .XXXXXX.  = %01111110 = $7E
;   ..XXXX..  = %00111100 = $3C
;   ...XX...  = %00011000 = $18

Pointing VIC-II to Custom Characters

The VIC-II chip needs to know where to find character data:

; VIC-II Character Memory Pointer ($D018)
;
; The VIC-II chip uses $D018 to find both screen memory and character data.
;
; Bits 4-7: Screen memory location (within VIC bank)
; Bits 1-3: Character memory location (within VIC bank)
; Bit 0:    Not used for memory selection
;
; Character memory calculation:
;   Location = (bits 1-3) * $0800
;
;   %000 = $0000  (not usable - zero page)
;   %001 = $0800
;   %010 = $1000  (default: character ROM mapped here)
;   %011 = $1800
;   %100 = $2000
;   %101 = $2800
;   %110 = $3000  <- We use this
;   %111 = $3800
;
; For charset at $3000 with screen at $0400:
;   Screen: $0400 / $0400 = 1, bits 4-7 = %0001 = $10
;   Charset: $3000 / $0800 = 6, bits 1-3 = %110 = $0C
;   Combined: $10 | $0C = $1C

CHARPTR     = $D018

            lda #$1C            ; Screen at $0400, charset at $3000
            sta CHARPTR         ; VIC now uses our custom characters

The $D018 register controls both screen memory and character memory locations. We set it to $1C to use our charset at $3000 while keeping the screen at the default $0400.

Character Codes

We use character codes 128-130 for our custom graphics:

Code	Character	Purpose
128	Chevron	Note graphic
129	Horizontal line	Track line
130	Vertical bars	Hit zone marker

These codes (128+) are in the “reverse video” range of the original character set. We overwrite them with our custom designs. The standard letters and numbers (codes 0-127) remain intact for text display.

The Complete Code

; ============================================================================
; SID SYMPHONY - Unit 4: Custom Graphics
; ============================================================================
; Design custom characters for a polished look. Notes are arrows, tracks are
; clean lines, hit zones have distinctive markers. The game looks professional.
;
; Controls: Z = Track 1 (high), X = Track 2 (mid), C = Track 3 (low)
; ============================================================================

; ============================================================================
; CUSTOMISATION SECTION
; ============================================================================

; SID Voice Settings
VOICE1_WAVE = $21               ; Sawtooth
VOICE2_WAVE = $41               ; Pulse
VOICE3_WAVE = $11               ; Triangle

VOICE1_FREQ = $1C               ; High pitch
VOICE2_FREQ = $0E               ; Mid pitch
VOICE3_FREQ = $07               ; Low pitch

VOICE_AD    = $09               ; Attack=0, Decay=9
VOICE_SR    = $00               ; Sustain=0, Release=0
PULSE_WIDTH = $08               ; 50% duty cycle

; Visual Settings
BORDER_COL  = 0                 ; Black border
BG_COL      = 0                 ; Black background

TRACK1_NOTE_COL = 10            ; Light red
TRACK2_NOTE_COL = 13            ; Light green
TRACK3_NOTE_COL = 14            ; Light blue

TRACK_LINE_COL = 11             ; Dark grey
HIT_ZONE_COL = 7                ; Yellow

FLASH1_COL  = 2                 ; Red
FLASH2_COL  = 5                 ; Green
FLASH3_COL  = 6                 ; Blue

; ============================================================================
; MEMORY MAP
; ============================================================================

SCREEN      = $0400             ; Screen memory
COLRAM      = $D800             ; Colour RAM
BORDER      = $D020             ; Border colour
BGCOL       = $D021             ; Background colour
CHARPTR     = $D018             ; Character memory pointer

CHARSET     = $3000             ; Custom character set location

; SID registers
SID         = $D400
SID_V1_FREQ_LO = $D400
SID_V1_FREQ_HI = $D401
SID_V1_PWHI = $D403
SID_V1_CTRL = $D404
SID_V1_AD   = $D405
SID_V1_SR   = $D406

SID_V2_FREQ_LO = $D407
SID_V2_FREQ_HI = $D408
SID_V2_PWHI = $D40A
SID_V2_CTRL = $D40B
SID_V2_AD   = $D40C
SID_V2_SR   = $D40D

SID_V3_FREQ_LO = $D40E
SID_V3_FREQ_HI = $D40F
SID_V3_PWHI = $D411
SID_V3_CTRL = $D412
SID_V3_AD   = $D413
SID_V3_SR   = $D414

SID_VOLUME  = $D418

; CIA keyboard
CIA1_PRA    = $DC00
CIA1_PRB    = $DC01

; Track positions
TRACK1_ROW  = 8
TRACK2_ROW  = 12
TRACK3_ROW  = 16

; Hit zone
HIT_ZONE_COLUMN = 3

; Custom character codes (we'll define these)
CHAR_NOTE   = 128               ; Filled arrow/circle for notes
CHAR_TRACK  = 129               ; Thin horizontal line for tracks
CHAR_HITZONE = 130              ; Vertical bar for hit zone
CHAR_SPACE  = 32                ; Space

; Note settings
MAX_NOTES   = 8
NOTE_SPAWN_COL = 37

; Timing
FRAMES_PER_BEAT = 25

; Zero page
ZP_PTR      = $FB
ZP_PTR_HI   = $FC

; Variables
frame_count = $02
beat_count  = $03
song_pos    = $04
song_pos_hi = $05
temp_track  = $06

; ----------------------------------------------------------------------------
; BASIC Stub
; ----------------------------------------------------------------------------

            * = $0801

            !byte $0C, $08
            !byte $0A, $00
            !byte $9E
            !text "2064"
            !byte $00
            !byte $00, $00

; ----------------------------------------------------------------------------
; Main Program
; ----------------------------------------------------------------------------

            * = $0810

start:
            jsr copy_charset    ; Copy ROM charset and add custom chars
            jsr init_screen
            jsr init_sid
            jsr init_notes

            lda #<song_data
            sta song_pos
            lda #>song_data
            sta song_pos_hi

            lda #0
            sta frame_count
            sta beat_count

main_loop:
            lda #$FF
wait_raster:
            cmp $D012
            bne wait_raster

            inc frame_count
            lda frame_count
            cmp #FRAMES_PER_BEAT
            bcc no_new_beat

            lda #0
            sta frame_count
            jsr check_spawn_note
            inc beat_count

no_new_beat:
            jsr update_notes
            jsr reset_track_colours
            jsr check_keys

            jmp main_loop

; ----------------------------------------------------------------------------
; Copy Character Set from ROM to RAM
; ----------------------------------------------------------------------------
; Copies the standard character ROM to $3000, then adds custom characters

copy_charset:
            ; Disable interrupts during ROM access
            sei

            ; Make character ROM visible at $D000
            lda $01
            pha                 ; Save processor port
            and #$FB            ; Clear bit 2 (CHAREN)
            sta $01             ; Character ROM now at $D000

            ; Copy 2KB (256 characters * 8 bytes)
            ldx #0
copy_loop:
            lda $D000,x
            sta CHARSET,x
            lda $D100,x
            sta CHARSET+$100,x
            lda $D200,x
            sta CHARSET+$200,x
            lda $D300,x
            sta CHARSET+$300,x
            lda $D400,x
            sta CHARSET+$400,x
            lda $D500,x
            sta CHARSET+$500,x
            lda $D600,x
            sta CHARSET+$600,x
            lda $D700,x
            sta CHARSET+$700,x
            inx
            bne copy_loop

            ; Restore processor port
            pla
            sta $01

            ; Re-enable interrupts
            cli

            ; Define our custom characters
            jsr define_custom_chars

            ; Point VIC-II to our charset at $3000
            ; Screen at $0400 = %0001 in upper nibble
            ; Charset at $3000 = %110 in bits 1-3 = $0C
            lda #$1C
            sta CHARPTR

            rts

; ----------------------------------------------------------------------------
; Define Custom Characters
; ----------------------------------------------------------------------------
; Creates note, track, and hit zone graphics

define_custom_chars:
            ; Character 128: Note (filled chevron pointing left)
            lda #%00000110      ; Row 0
            sta CHARSET + (CHAR_NOTE * 8) + 0
            lda #%00011110      ; Row 1
            sta CHARSET + (CHAR_NOTE * 8) + 1
            lda #%01111110      ; Row 2
            sta CHARSET + (CHAR_NOTE * 8) + 2
            lda #%11111110      ; Row 3
            sta CHARSET + (CHAR_NOTE * 8) + 3
            lda #%11111110      ; Row 4
            sta CHARSET + (CHAR_NOTE * 8) + 4
            lda #%01111110      ; Row 5
            sta CHARSET + (CHAR_NOTE * 8) + 5
            lda #%00011110      ; Row 6
            sta CHARSET + (CHAR_NOTE * 8) + 6
            lda #%00000110      ; Row 7
            sta CHARSET + (CHAR_NOTE * 8) + 7

            ; Character 129: Track line (centered horizontal line)
            lda #%00000000      ; Row 0
            sta CHARSET + (CHAR_TRACK * 8) + 0
            lda #%00000000      ; Row 1
            sta CHARSET + (CHAR_TRACK * 8) + 1
            lda #%00000000      ; Row 2
            sta CHARSET + (CHAR_TRACK * 8) + 2
            lda #%11111111      ; Row 3 - the line
            sta CHARSET + (CHAR_TRACK * 8) + 3
            lda #%11111111      ; Row 4 - the line
            sta CHARSET + (CHAR_TRACK * 8) + 4
            lda #%00000000      ; Row 5
            sta CHARSET + (CHAR_TRACK * 8) + 5
            lda #%00000000      ; Row 6
            sta CHARSET + (CHAR_TRACK * 8) + 6
            lda #%00000000      ; Row 7
            sta CHARSET + (CHAR_TRACK * 8) + 7

            ; Character 130: Hit zone (vertical bars)
            lda #%01100110      ; Row 0
            sta CHARSET + (CHAR_HITZONE * 8) + 0
            lda #%01100110      ; Row 1
            sta CHARSET + (CHAR_HITZONE * 8) + 1
            lda #%01100110      ; Row 2
            sta CHARSET + (CHAR_HITZONE * 8) + 2
            lda #%01100110      ; Row 3
            sta CHARSET + (CHAR_HITZONE * 8) + 3
            lda #%01100110      ; Row 4
            sta CHARSET + (CHAR_HITZONE * 8) + 4
            lda #%01100110      ; Row 5
            sta CHARSET + (CHAR_HITZONE * 8) + 5
            lda #%01100110      ; Row 6
            sta CHARSET + (CHAR_HITZONE * 8) + 6
            lda #%01100110      ; Row 7
            sta CHARSET + (CHAR_HITZONE * 8) + 7

            rts

; ----------------------------------------------------------------------------
; Initialize Notes
; ----------------------------------------------------------------------------

init_notes:
            ldx #MAX_NOTES-1
            lda #0
init_notes_loop:
            sta note_track,x
            sta note_col,x
            dex
            bpl init_notes_loop
            rts

; ----------------------------------------------------------------------------
; Check Spawn Note
; ----------------------------------------------------------------------------

check_spawn_note:
            ldy #0

spawn_check_loop:
            lda (song_pos),y
            cmp #$FF
            beq spawn_restart_song

            cmp beat_count
            beq spawn_match
            bcs spawn_done

            jmp spawn_advance

spawn_match:
            iny
            lda (song_pos),y
            jsr spawn_note
            dey

spawn_advance:
            lda song_pos
            clc
            adc #2
            sta song_pos
            lda song_pos_hi
            adc #0
            sta song_pos_hi
            jmp spawn_check_loop

spawn_done:
            rts

spawn_restart_song:
            lda #<song_data
            sta song_pos
            lda #>song_data
            sta song_pos_hi
            lda #0
            sta beat_count
            rts

; ----------------------------------------------------------------------------
; Spawn Note
; ----------------------------------------------------------------------------

spawn_note:
            sta temp_track

            ldx #0
spawn_find_slot:
            lda note_track,x
            beq spawn_found_slot
            inx
            cpx #MAX_NOTES
            bne spawn_find_slot
            rts

spawn_found_slot:
            lda temp_track
            sta note_track,x
            lda #NOTE_SPAWN_COL
            sta note_col,x
            jsr draw_note
            rts

; ----------------------------------------------------------------------------
; Update Notes
; ----------------------------------------------------------------------------

update_notes:
            ldx #0

update_loop:
            lda note_track,x
            beq update_next

            jsr erase_note

            dec note_col,x
            lda note_col,x
            cmp #1
            bcc update_deactivate

            jsr draw_note
            jmp update_next

update_deactivate:
            lda #0
            sta note_track,x

update_next:
            inx
            cpx #MAX_NOTES
            bne update_loop
            rts

; ----------------------------------------------------------------------------
; Draw Note - Uses custom note character
; ----------------------------------------------------------------------------

draw_note:
            lda note_track,x
            cmp #1
            beq draw_note_t1
            cmp #2
            beq draw_note_t2
            cmp #3
            beq draw_note_t3
            rts

draw_note_t1:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_NOTE      ; Custom note character
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK1_NOTE_COL
            sta (ZP_PTR),y
            rts

draw_note_t2:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_NOTE
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK2_NOTE_COL
            sta (ZP_PTR),y
            rts

draw_note_t3:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_NOTE
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK3_NOTE_COL
            sta (ZP_PTR),y
            rts

; ----------------------------------------------------------------------------
; Erase Note - Restores track line character
; ----------------------------------------------------------------------------

erase_note:
            lda note_track,x
            cmp #1
            beq erase_note_t1
            cmp #2
            beq erase_note_t2
            cmp #3
            beq erase_note_t3
            rts

erase_note_t1:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_TRACK     ; Custom track character
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK1_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK1_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

erase_note_t2:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_TRACK
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK2_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK2_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

erase_note_t3:
            lda note_col,x
            clc
            adc #<(SCREEN + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(SCREEN + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI

            ldy #0
            lda #CHAR_TRACK
            sta (ZP_PTR),y

            lda note_col,x
            clc
            adc #<(COLRAM + TRACK3_ROW * 40)
            sta ZP_PTR
            lda #>(COLRAM + TRACK3_ROW * 40)
            adc #0
            sta ZP_PTR_HI
            lda #TRACK_LINE_COL
            sta (ZP_PTR),y
            rts

; ----------------------------------------------------------------------------
; Initialize Screen
; ----------------------------------------------------------------------------

init_screen:
            lda #BORDER_COL
            sta BORDER
            lda #BG_COL
            sta BGCOL

            ; Clear screen with spaces
            ldx #0
            lda #CHAR_SPACE
clr_screen:
            sta SCREEN,x
            sta SCREEN+$100,x
            sta SCREEN+$200,x
            sta SCREEN+$2E8,x
            inx
            bne clr_screen

            ; Set all colours to track line colour
            ldx #0
            lda #TRACK_LINE_COL
clr_colour:
            sta COLRAM,x
            sta COLRAM+$100,x
            sta COLRAM+$200,x
            sta COLRAM+$2E8,x
            inx
            bne clr_colour

            jsr draw_tracks
            jsr draw_hit_zones
            jsr draw_labels

            rts

; ----------------------------------------------------------------------------
; Draw Tracks - Uses custom track character
; ----------------------------------------------------------------------------

draw_tracks:
            ; Track 1
            lda #CHAR_TRACK
            ldx #0
draw_t1:
            sta SCREEN + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne draw_t1

            ; Track 2
            lda #CHAR_TRACK
            ldx #0
draw_t2:
            sta SCREEN + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne draw_t2

            ; Track 3
            lda #CHAR_TRACK
            ldx #0
draw_t3:
            sta SCREEN + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne draw_t3

            rts

; ----------------------------------------------------------------------------
; Draw Hit Zones - Uses custom hit zone character
; ----------------------------------------------------------------------------

draw_hit_zones:
            lda #CHAR_HITZONE   ; Custom hit zone character

            ; Draw hit zone bars spanning all three tracks
            sta SCREEN + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta SCREEN + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta SCREEN + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN
            sta SCREEN + ((TRACK3_ROW+2) * 40) + HIT_ZONE_COLUMN

            ; Colour the hit zones
            lda #HIT_ZONE_COL
            sta COLRAM + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta COLRAM + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN

            sta COLRAM + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN
            sta COLRAM + ((TRACK3_ROW+2) * 40) + HIT_ZONE_COLUMN

            rts

; ----------------------------------------------------------------------------
; Draw Labels
; ----------------------------------------------------------------------------

draw_labels:
            ldx #0
draw_title:
            lda title_text,x
            beq draw_title_done
            sta SCREEN + 13,x
            lda #1              ; White
            sta COLRAM + 13,x
            inx
            bne draw_title
draw_title_done:

            ; Track labels - use standard characters for letters
            lda #$1A            ; Z (screen code)
            sta SCREEN + (TRACK1_ROW * 40)
            lda #TRACK1_NOTE_COL
            sta COLRAM + (TRACK1_ROW * 40)

            lda #$18            ; X
            sta SCREEN + (TRACK2_ROW * 40)
            lda #TRACK2_NOTE_COL
            sta COLRAM + (TRACK2_ROW * 40)

            lda #$03            ; C
            sta SCREEN + (TRACK3_ROW * 40)
            lda #TRACK3_NOTE_COL
            sta COLRAM + (TRACK3_ROW * 40)

            ldx #0
draw_instr:
            lda instr_text,x
            beq draw_instr_done
            sta SCREEN + (23 * 40) + 6,x
            lda #TRACK_LINE_COL
            sta COLRAM + (23 * 40) + 6,x
            inx
            bne draw_instr
draw_instr_done:

            rts

title_text:
            !scr "sid symphony"
            !byte 0

instr_text:
            !scr "custom graphics active"
            !byte 0

; ----------------------------------------------------------------------------
; Initialize SID
; ----------------------------------------------------------------------------

init_sid:
            ldx #$18
            lda #0
clear_sid:
            sta SID,x
            dex
            bpl clear_sid

            lda #$0F
            sta SID_VOLUME

            lda #$00
            sta SID_V1_FREQ_LO
            lda #VOICE1_FREQ
            sta SID_V1_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V1_PWHI
            lda #VOICE_AD
            sta SID_V1_AD
            lda #VOICE_SR
            sta SID_V1_SR

            lda #$00
            sta SID_V2_FREQ_LO
            lda #VOICE2_FREQ
            sta SID_V2_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V2_PWHI
            lda #VOICE_AD
            sta SID_V2_AD
            lda #VOICE_SR
            sta SID_V2_SR

            lda #$00
            sta SID_V3_FREQ_LO
            lda #VOICE3_FREQ
            sta SID_V3_FREQ_HI
            lda #PULSE_WIDTH
            sta SID_V3_PWHI
            lda #VOICE_AD
            sta SID_V3_AD
            lda #VOICE_SR
            sta SID_V3_SR

            rts

; ----------------------------------------------------------------------------
; Reset Track Colours
; ----------------------------------------------------------------------------

reset_track_colours:
            ldx #0
            lda #TRACK_LINE_COL
reset_t1:
            sta COLRAM + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne reset_t1

            ldx #0
reset_t2:
            sta COLRAM + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne reset_t2

            ldx #0
reset_t3:
            sta COLRAM + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne reset_t3

            ; Restore key labels
            lda #TRACK1_NOTE_COL
            sta COLRAM + (TRACK1_ROW * 40)
            lda #TRACK2_NOTE_COL
            sta COLRAM + (TRACK2_ROW * 40)
            lda #TRACK3_NOTE_COL
            sta COLRAM + (TRACK3_ROW * 40)

            ; Restore hit zone colours
            lda #HIT_ZONE_COL
            sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN
            sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN

            jsr redraw_all_notes

            rts

; ----------------------------------------------------------------------------
; Redraw All Notes
; ----------------------------------------------------------------------------

redraw_all_notes:
            ldx #0
redraw_loop:
            lda note_track,x
            beq redraw_next
            jsr draw_note
redraw_next:
            inx
            cpx #MAX_NOTES
            bne redraw_loop
            rts

; ----------------------------------------------------------------------------
; Check Keys
; ----------------------------------------------------------------------------

check_keys:
            lda #$FD
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_x_key
            jsr play_voice1
            jsr flash_track1

check_x_key:
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$80
            bne check_c_key
            jsr play_voice2
            jsr flash_track2

check_c_key:
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_keys_done
            jsr play_voice3
            jsr flash_track3

check_keys_done:
            lda #$FF
            sta CIA1_PRA
            rts

; ----------------------------------------------------------------------------
; Play Voices
; ----------------------------------------------------------------------------

play_voice1:
            lda #VOICE1_WAVE
            ora #$01
            sta SID_V1_CTRL
            rts

play_voice2:
            lda #VOICE2_WAVE
            ora #$01
            sta SID_V2_CTRL
            rts

play_voice3:
            lda #VOICE3_WAVE
            ora #$01
            sta SID_V3_CTRL
            rts

; ----------------------------------------------------------------------------
; Flash Tracks
; ----------------------------------------------------------------------------

flash_track1:
            ldx #0
            lda #FLASH1_COL
flash_t1_loop:
            sta COLRAM + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne flash_t1_loop
            lda #1
            sta COLRAM + (TRACK1_ROW * 40)
            rts

flash_track2:
            ldx #0
            lda #FLASH2_COL
flash_t2_loop:
            sta COLRAM + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne flash_t2_loop
            lda #1
            sta COLRAM + (TRACK2_ROW * 40)
            rts

flash_track3:
            ldx #0
            lda #FLASH3_COL
flash_t3_loop:
            sta COLRAM + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne flash_t3_loop
            lda #1
            sta COLRAM + (TRACK3_ROW * 40)
            rts

; ----------------------------------------------------------------------------
; Song Data
; ----------------------------------------------------------------------------

song_data:
            !byte 0, 1
            !byte 2, 2
            !byte 4, 3
            !byte 6, 1

            !byte 8, 2
            !byte 10, 3
            !byte 12, 1
            !byte 14, 2

            !byte 16, 3
            !byte 18, 1
            !byte 20, 2
            !byte 22, 3

            !byte 24, 1
            !byte 25, 2
            !byte 26, 3
            !byte 28, 1
            !byte 29, 2
            !byte 30, 3

            !byte $FF

; ----------------------------------------------------------------------------
; Note Arrays
; ----------------------------------------------------------------------------

note_track:
            !fill MAX_NOTES, 0

note_col:
            !fill MAX_NOTES, 0

Try This: Thicker Track Lines

; Three-pixel thick track:
            lda #%00000000      ; Row 0
            sta CHARSET + (CHAR_TRACK * 8) + 0
            lda #%00000000      ; Row 1
            sta CHARSET + (CHAR_TRACK * 8) + 1
            lda #%11111111      ; Row 2 - top of line
            sta CHARSET + (CHAR_TRACK * 8) + 2
            lda #%11111111      ; Row 3 - middle
            sta CHARSET + (CHAR_TRACK * 8) + 3
            lda #%11111111      ; Row 4 - bottom
            sta CHARSET + (CHAR_TRACK * 8) + 4
            lda #%00000000      ; Row 5
            sta CHARSET + (CHAR_TRACK * 8) + 5

Try This: Dotted Track Lines

; Dotted track (alternating pixels):
            lda #%00000000
            sta CHARSET + (CHAR_TRACK * 8) + 0
            sta CHARSET + (CHAR_TRACK * 8) + 1
            sta CHARSET + (CHAR_TRACK * 8) + 2
            lda #%10101010      ; Alternating pattern
            sta CHARSET + (CHAR_TRACK * 8) + 3
            lda #%01010101      ; Offset pattern
            sta CHARSET + (CHAR_TRACK * 8) + 4
            lda #%00000000
            sta CHARSET + (CHAR_TRACK * 8) + 5

What You’ve Learnt

Character ROM - Default characters at $D000, read-only
Memory remapping - Processor port $01 controls what’s visible at certain addresses
Character definitions - 8 bytes per character, 1 bit per pixel
VIC-II pointer - $D018 tells the VIC where to find screen and character memory
Binary pixel design - Use %xxxxxxxx notation to visualise character shapes

What’s Next

In Unit 5, we’ll detect when keypresses actually match notes in the hit zone. Right now, pressing keys plays sounds regardless of timing - we’ll add real hit detection.

What Changed

Unit 3 → Unit 4

+198-83

1	1		`; ============================================================================`
2		-	`; SID SYMPHONY - Unit 3: Making It Your Own`
	2	+	`; SID SYMPHONY - Unit 4: Custom Graphics`
3	3		`; ============================================================================`
4		-	`; Customise the game to make it yours. Change the SID voices, pick your own`
5		-	`; colours, experiment with waveforms and ADSR. Learn the internals by`
6		-	`; modifying them and hearing/seeing the results.`
	4	+	`; Design custom characters for a polished look. Notes are arrows, tracks are`
	5	+	`; clean lines, hit zones have distinctive markers. The game looks professional.`
7	6		`;`
8	7		`; Controls: Z = Track 1 (high), X = Track 2 (mid), C = Track 3 (low)`
9	8		`; ============================================================================`
10	9
11	10		`; ============================================================================`
12		-	`; CUSTOMISATION SECTION - Change these values and reassemble!`
	11	+	`; CUSTOMISATION SECTION`
13	12		`; ============================================================================`
14		-
15		-	`; --- SID Voice Settings ---`
16		-	`; Waveforms: $11=triangle, $21=sawtooth, $41=pulse, $81=noise`
17		-	`VOICE1_WAVE = $21 ; Sawtooth - bright, buzzy`
18		-	`VOICE2_WAVE = $41 ; Pulse - hollow, reedy`
19		-	`VOICE3_WAVE = $11 ; Triangle - soft, mellow`
20		-
21		-	`; Frequencies (higher = higher pitch)`
22		-	`; Common notes: $07=C3, $0E=C4, $1C=C5, $38=C6`
23		-	`VOICE1_FREQ = $1C ; High pitch (C5)`
24		-	`VOICE2_FREQ = $0E ; Mid pitch (C4)`
25		-	`VOICE3_FREQ = $07 ; Low pitch (C3)`
26	13
27		-	`; ADSR - Attack/Decay/Sustain/Release`
28		-	`; Attack: 0-15 (0=2ms, 15=8s) Decay: 0-15 (0=6ms, 15=24s)`
29		-	`; Sustain: 0-15 (volume level) Release: 0-15 (0=6ms, 15=24s)`
30		-	`VOICE_AD = $09 ; Attack=0 (instant), Decay=9 (medium)`
31		-	`VOICE_SR = $00 ; Sustain=0 (none), Release=0 (instant)`
	14	+	`; SID Voice Settings`
	15	+	`VOICE1_WAVE = $21 ; Sawtooth`
	16	+	`VOICE2_WAVE = $41 ; Pulse`
	17	+	`VOICE3_WAVE = $11 ; Triangle`
32	18
33		-	`; Pulse width (only affects pulse wave, $41)`
34		-	`PULSE_WIDTH = $08 ; $08 = 50% duty cycle (square wave)`
	19	+	`VOICE1_FREQ = $1C ; High pitch`
	20	+	`VOICE2_FREQ = $0E ; Mid pitch`
	21	+	`VOICE3_FREQ = $07 ; Low pitch`
35	22
36		-	`; --- Visual Settings ---`
37		-	`; Colours: 0=black, 1=white, 2=red, 3=cyan, 4=purple, 5=green`
38		-	`; 6=blue, 7=yellow, 8=orange, 9=brown, 10=light red`
39		-	`; 11=dark grey, 12=grey, 13=light green, 14=light blue, 15=light grey`
	23	+	`VOICE_AD = $09 ; Attack=0, Decay=9`
	24	+	`VOICE_SR = $00 ; Sustain=0, Release=0`
	25	+	`PULSE_WIDTH = $08 ; 50% duty cycle`
40	26
41		-	`BORDER_COL = 6 ; Blue border`
	27	+	`; Visual Settings`
	28	+	`BORDER_COL = 0 ; Black border`
42	29		`BG_COL = 0 ; Black background`
43	30
44		-	`TRACK1_NOTE_COL = 10 ; Light red notes on track 1`
45		-	`TRACK2_NOTE_COL = 13 ; Light green notes on track 2`
46		-	`TRACK3_NOTE_COL = 14 ; Light blue notes on track 3`
	31	+	`TRACK1_NOTE_COL = 10 ; Light red`
	32	+	`TRACK2_NOTE_COL = 13 ; Light green`
	33	+	`TRACK3_NOTE_COL = 14 ; Light blue`
47	34
48		-	`TRACK_LINE_COL = 11 ; Dark grey track lines`
49		-	`HIT_ZONE_COL = 7 ; Yellow hit zone`
	35	+	`TRACK_LINE_COL = 11 ; Dark grey`
	36	+	`HIT_ZONE_COL = 7 ; Yellow`
50	37
51		-	`; Track flash colours (when key pressed)`
52		-	`FLASH1_COL = 2 ; Red flash for track 1`
53		-	`FLASH2_COL = 5 ; Green flash for track 2`
54		-	`FLASH3_COL = 6 ; Blue flash for track 3`
	38	+	`FLASH1_COL = 2 ; Red`
	39	+	`FLASH2_COL = 5 ; Green`
	40	+	`FLASH3_COL = 6 ; Blue`
55	41
56	42		`; ============================================================================`
57		-	`; END OF CUSTOMISATION - Code below uses the settings above`
	43	+	`; MEMORY MAP`
58	44		`; ============================================================================`
59	45
60		-	`; ----------------------------------------------------------------------------`
61		-	`; Memory Addresses`
62		-	`; ----------------------------------------------------------------------------`
	46	+	`SCREEN = $0400 ; Screen memory`
	47	+	`COLRAM = $D800 ; Colour RAM`
	48	+	`BORDER = $D020 ; Border colour`
	49	+	`BGCOL = $D021 ; Background colour`
	50	+	`CHARPTR = $D018 ; Character memory pointer`
63	51
64		-	`SCREEN = $0400`
65		-	`COLRAM = $D800`
66		-	`BORDER = $D020`
67		-	`BGCOL = $D021`
	52	+	`CHARSET = $3000 ; Custom character set location`
68	53
69	54		`; SID registers`
70	55		`SID = $D400`
71	56		`SID_V1_FREQ_LO = $D400`
72	57		`SID_V1_FREQ_HI = $D401`
73		-	`SID_V1_PWLO = $D402`
74	58		`SID_V1_PWHI = $D403`
75	59		`SID_V1_CTRL = $D404`
76	60		`SID_V1_AD = $D405`
			...
78	62
79	63		`SID_V2_FREQ_LO = $D407`
80	64		`SID_V2_FREQ_HI = $D408`
81		-	`SID_V2_PWLO = $D409`
82	65		`SID_V2_PWHI = $D40A`
83	66		`SID_V2_CTRL = $D40B`
84	67		`SID_V2_AD = $D40C`
			...
86	69
87	70		`SID_V3_FREQ_LO = $D40E`
88	71		`SID_V3_FREQ_HI = $D40F`
89		-	`SID_V3_PWLO = $D410`
90	72		`SID_V3_PWHI = $D411`
91	73		`SID_V3_CTRL = $D412`
92	74		`SID_V3_AD = $D413`
			...
103	85		`TRACK2_ROW = 12`
104	86		`TRACK3_ROW = 16`
105	87
106		-	`; Hit zone column`
	88	+	`; Hit zone`
107	89		`HIT_ZONE_COLUMN = 3`
	90	+
	91	+	`; Custom character codes (we'll define these)`
	92	+	`CHAR_NOTE = 128 ; Filled arrow/circle for notes`
	93	+	`CHAR_TRACK = 129 ; Thin horizontal line for tracks`
	94	+	`CHAR_HITZONE = 130 ; Vertical bar for hit zone`
	95	+	`CHAR_SPACE = 32 ; Space`
108	96
109	97		`; Note settings`
110		-	`NOTE_CHAR = $57 ; Filled dot character`
111		-	`TRACK_CHAR = $2D ; Minus character`
112	98		`MAX_NOTES = 8`
113	99		`NOTE_SPAWN_COL = 37`
114	100
			...
146	132		`* = $0810`
147	133
148	134		`start:`
	135	+	`jsr copy_charset ; Copy ROM charset and add custom chars`
149	136		`jsr init_screen`
150	137		`jsr init_sid`
151	138		`jsr init_notes`
			...
181	168		`jsr check_keys`
182	169
183	170		`jmp main_loop`
	171	+
	172	+	`; ----------------------------------------------------------------------------`
	173	+	`; Copy Character Set from ROM to RAM`
	174	+	`; ----------------------------------------------------------------------------`
	175	+	`; Copies the standard character ROM to $3000, then adds custom characters`
	176	+
	177	+	`copy_charset:`
	178	+	`; Disable interrupts during ROM access`
	179	+	`sei`
	180	+
	181	+	`; Make character ROM visible at $D000`
	182	+	`lda $01`
	183	+	`pha ; Save processor port`
	184	+	`and #$FB ; Clear bit 2 (CHAREN)`
	185	+	`sta $01 ; Character ROM now at $D000`
	186	+
	187	+	`; Copy 2KB (256 characters * 8 bytes)`
	188	+	`ldx #0`
	189	+	`copy_loop:`
	190	+	`lda $D000,x`
	191	+	`sta CHARSET,x`
	192	+	`lda $D100,x`
	193	+	`sta CHARSET+$100,x`
	194	+	`lda $D200,x`
	195	+	`sta CHARSET+$200,x`
	196	+	`lda $D300,x`
	197	+	`sta CHARSET+$300,x`
	198	+	`lda $D400,x`
	199	+	`sta CHARSET+$400,x`
	200	+	`lda $D500,x`
	201	+	`sta CHARSET+$500,x`
	202	+	`lda $D600,x`
	203	+	`sta CHARSET+$600,x`
	204	+	`lda $D700,x`
	205	+	`sta CHARSET+$700,x`
	206	+	`inx`
	207	+	`bne copy_loop`
	208	+
	209	+	`; Restore processor port`
	210	+	`pla`
	211	+	`sta $01`
	212	+
	213	+	`; Re-enable interrupts`
	214	+	`cli`
	215	+
	216	+	`; Define our custom characters`
	217	+	`jsr define_custom_chars`
	218	+
	219	+	`; Point VIC-II to our charset at $3000`
	220	+	`; Screen at $0400 = %0001 in upper nibble`
	221	+	`; Charset at $3000 = %110 in bits 1-3 = $0C`
	222	+	`lda #$1C`
	223	+	`sta CHARPTR`
	224	+
	225	+	`rts`
	226	+
	227	+	`; ----------------------------------------------------------------------------`
	228	+	`; Define Custom Characters`
	229	+	`; ----------------------------------------------------------------------------`
	230	+	`; Creates note, track, and hit zone graphics`
	231	+
	232	+	`define_custom_chars:`
	233	+	`; Character 128: Note (filled chevron pointing left)`
	234	+	`lda #%00000110 ; Row 0`
	235	+	`sta CHARSET + (CHAR_NOTE * 8) + 0`
	236	+	`lda #%00011110 ; Row 1`
	237	+	`sta CHARSET + (CHAR_NOTE * 8) + 1`
	238	+	`lda #%01111110 ; Row 2`
	239	+	`sta CHARSET + (CHAR_NOTE * 8) + 2`
	240	+	`lda #%11111110 ; Row 3`
	241	+	`sta CHARSET + (CHAR_NOTE * 8) + 3`
	242	+	`lda #%11111110 ; Row 4`
	243	+	`sta CHARSET + (CHAR_NOTE * 8) + 4`
	244	+	`lda #%01111110 ; Row 5`
	245	+	`sta CHARSET + (CHAR_NOTE * 8) + 5`
	246	+	`lda #%00011110 ; Row 6`
	247	+	`sta CHARSET + (CHAR_NOTE * 8) + 6`
	248	+	`lda #%00000110 ; Row 7`
	249	+	`sta CHARSET + (CHAR_NOTE * 8) + 7`
	250	+
	251	+	`; Character 129: Track line (centered horizontal line)`
	252	+	`lda #%00000000 ; Row 0`
	253	+	`sta CHARSET + (CHAR_TRACK * 8) + 0`
	254	+	`lda #%00000000 ; Row 1`
	255	+	`sta CHARSET + (CHAR_TRACK * 8) + 1`
	256	+	`lda #%00000000 ; Row 2`
	257	+	`sta CHARSET + (CHAR_TRACK * 8) + 2`
	258	+	`lda #%11111111 ; Row 3 - the line`
	259	+	`sta CHARSET + (CHAR_TRACK * 8) + 3`
	260	+	`lda #%11111111 ; Row 4 - the line`
	261	+	`sta CHARSET + (CHAR_TRACK * 8) + 4`
	262	+	`lda #%00000000 ; Row 5`
	263	+	`sta CHARSET + (CHAR_TRACK * 8) + 5`
	264	+	`lda #%00000000 ; Row 6`
	265	+	`sta CHARSET + (CHAR_TRACK * 8) + 6`
	266	+	`lda #%00000000 ; Row 7`
	267	+	`sta CHARSET + (CHAR_TRACK * 8) + 7`
	268	+
	269	+	`; Character 130: Hit zone (vertical bars)`
	270	+	`lda #%01100110 ; Row 0`
	271	+	`sta CHARSET + (CHAR_HITZONE * 8) + 0`
	272	+	`lda #%01100110 ; Row 1`
	273	+	`sta CHARSET + (CHAR_HITZONE * 8) + 1`
	274	+	`lda #%01100110 ; Row 2`
	275	+	`sta CHARSET + (CHAR_HITZONE * 8) + 2`
	276	+	`lda #%01100110 ; Row 3`
	277	+	`sta CHARSET + (CHAR_HITZONE * 8) + 3`
	278	+	`lda #%01100110 ; Row 4`
	279	+	`sta CHARSET + (CHAR_HITZONE * 8) + 4`
	280	+	`lda #%01100110 ; Row 5`
	281	+	`sta CHARSET + (CHAR_HITZONE * 8) + 5`
	282	+	`lda #%01100110 ; Row 6`
	283	+	`sta CHARSET + (CHAR_HITZONE * 8) + 6`
	284	+	`lda #%01100110 ; Row 7`
	285	+	`sta CHARSET + (CHAR_HITZONE * 8) + 7`
	286	+
	287	+	`rts`
184	288
185	289		`; ----------------------------------------------------------------------------`
186	290		`; Initialize Notes`
			...
298	402		`rts`
299	403
300	404		`; ----------------------------------------------------------------------------`
301		-	`; Draw Note`
	405	+	`; Draw Note - Uses custom note character`
302	406		`; ----------------------------------------------------------------------------`
303	407
304	408		`draw_note:`
			...
321	425		`sta ZP_PTR_HI`
322	426
323	427		`ldy #0`
324		-	`lda #NOTE_CHAR`
	428	+	`lda #CHAR_NOTE ; Custom note character`
325	429		`sta (ZP_PTR),y`
326	430
327	431		`lda note_col,x`
			...
345	449		`sta ZP_PTR_HI`
346	450
347	451		`ldy #0`
348		-	`lda #NOTE_CHAR`
	452	+	`lda #CHAR_NOTE`
349	453		`sta (ZP_PTR),y`
350	454
351	455		`lda note_col,x`
			...
369	473		`sta ZP_PTR_HI`
370	474
371	475		`ldy #0`
372		-	`lda #NOTE_CHAR`
	476	+	`lda #CHAR_NOTE`
373	477		`sta (ZP_PTR),y`
374	478
375	479		`lda note_col,x`
			...
384	488		`rts`
385	489
386	490		`; ----------------------------------------------------------------------------`
387		-	`; Erase Note`
	491	+	`; Erase Note - Restores track line character`
388	492		`; ----------------------------------------------------------------------------`
389	493
390	494		`erase_note:`
			...
407	511		`sta ZP_PTR_HI`
408	512
409	513		`ldy #0`
410		-	`lda #TRACK_CHAR`
	514	+	`lda #CHAR_TRACK ; Custom track character`
411	515		`sta (ZP_PTR),y`
412	516
413	517		`lda note_col,x`
			...
431	535		`sta ZP_PTR_HI`
432	536
433	537		`ldy #0`
434		-	`lda #TRACK_CHAR`
	538	+	`lda #CHAR_TRACK`
435	539		`sta (ZP_PTR),y`
436	540
437	541		`lda note_col,x`
			...
455	559		`sta ZP_PTR_HI`
456	560
457	561		`ldy #0`
458		-	`lda #TRACK_CHAR`
	562	+	`lda #CHAR_TRACK`
459	563		`sta (ZP_PTR),y`
460	564
461	565		`lda note_col,x`
			...
479	583		`lda #BG_COL`
480	584		`sta BGCOL`
481	585
	586	+	`; Clear screen with spaces`
482	587		`ldx #0`
483		-	`lda #$20`
	588	+	`lda #CHAR_SPACE`
484	589		`clr_screen:`
485	590		`sta SCREEN,x`
486	591		`sta SCREEN+$100,x`
			...
489	594		`inx`
490	595		`bne clr_screen`
491	596
	597	+	`; Set all colours to track line colour`
492	598		`ldx #0`
493	599		`lda #TRACK_LINE_COL`
494	600		`clr_colour:`
			...
506	612		`rts`
507	613
508	614		`; ----------------------------------------------------------------------------`
509		-	`; Draw Tracks`
	615	+	`; Draw Tracks - Uses custom track character`
510	616		`; ----------------------------------------------------------------------------`
511	617
512	618		`draw_tracks:`
	619	+	`; Track 1`
	620	+	`lda #CHAR_TRACK`
513	621		`ldx #0`
514		-	`lda #TRACK_CHAR`
515	622		`draw_t1:`
516	623		`sta SCREEN + (TRACK1_ROW * 40),x`
517	624		`inx`
518	625		`cpx #38`
519	626		`bne draw_t1`
520	627
	628	+	`; Track 2`
	629	+	`lda #CHAR_TRACK`
521	630		`ldx #0`
522	631		`draw_t2:`
523	632		`sta SCREEN + (TRACK2_ROW * 40),x`
			...
525	634		`cpx #38`
526	635		`bne draw_t2`
527	636
	637	+	`; Track 3`
	638	+	`lda #CHAR_TRACK`
528	639		`ldx #0`
529	640		`draw_t3:`
530	641		`sta SCREEN + (TRACK3_ROW * 40),x`
			...
535	646		`rts`
536	647
537	648		`; ----------------------------------------------------------------------------`
538		-	`; Draw Hit Zones`
	649	+	`; Draw Hit Zones - Uses custom hit zone character`
539	650		`; ----------------------------------------------------------------------------`
540	651
541	652		`draw_hit_zones:`
542		-	`lda #$7D`
	653	+	`lda #CHAR_HITZONE ; Custom hit zone character`
543	654
544		-	`sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
	655	+	`; Draw hit zone bars spanning all three tracks`
	656	+	`sta SCREEN + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN`
545	657		`sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
	658	+	`sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
546	659		`sta SCREEN + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN`
547	660
548		-	`sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
549	661		`sta SCREEN + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN`
	662	+	`sta SCREEN + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
550	663		`sta SCREEN + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN`
551	664
552		-	`sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
553	665		`sta SCREEN + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN`
	666	+	`sta SCREEN + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
554	667		`sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN`
	668	+	`sta SCREEN + ((TRACK3_ROW+2) * 40) + HIT_ZONE_COLUMN`
555	669
	670	+	`; Colour the hit zones`
556	671		`lda #HIT_ZONE_COL`
557		-	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
	672	+	`sta COLRAM + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN`
558	673		`sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
	674	+	`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
559	675		`sta COLRAM + ((TRACK1_ROW+1) * 40) + HIT_ZONE_COLUMN`
560	676
561		-	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
562	677		`sta COLRAM + ((TRACK2_ROW-1) * 40) + HIT_ZONE_COLUMN`
	678	+	`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
563	679		`sta COLRAM + ((TRACK2_ROW+1) * 40) + HIT_ZONE_COLUMN`
564	680
565		-	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
566	681		`sta COLRAM + ((TRACK3_ROW-1) * 40) + HIT_ZONE_COLUMN`
	682	+	`sta COLRAM + (TRACK3_ROW * 40) + HIT_ZONE_COLUMN`
567	683		`sta COLRAM + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN`
	684	+	`sta COLRAM + ((TRACK3_ROW+2) * 40) + HIT_ZONE_COLUMN`
568	685
569	686		`rts`
570	687
			...
584	701		`bne draw_title`
585	702		`draw_title_done:`
586	703
587		-	`lda #$1A ; Z`
	704	+	`; Track labels - use standard characters for letters`
	705	+	`lda #$1A ; Z (screen code)`
588	706		`sta SCREEN + (TRACK1_ROW * 40)`
589	707		`lda #TRACK1_NOTE_COL`
590	708		`sta COLRAM + (TRACK1_ROW * 40)`
			...
603	721		`draw_instr:`
604	722		`lda instr_text,x`
605	723		`beq draw_instr_done`
606		-	`sta SCREEN + (23 * 40) + 8,x`
	724	+	`sta SCREEN + (23 * 40) + 6,x`
607	725		`lda #TRACK_LINE_COL`
608		-	`sta COLRAM + (23 * 40) + 8,x`
	726	+	`sta COLRAM + (23 * 40) + 6,x`
609	727		`inx`
610	728		`bne draw_instr`
611	729		`draw_instr_done:`
			...
617	735		`!byte 0`
618	736
619	737		`instr_text:`
620		-	`!scr "customise me!"`
	738	+	`!scr "custom graphics active"`
621	739		`!byte 0`
622	740
623	741		`; ----------------------------------------------------------------------------`
624		-	`; Initialize SID - Uses customisation constants`
	742	+	`; Initialize SID`
625	743		`; ----------------------------------------------------------------------------`
626	744
627	745		`init_sid:`
			...
635	753		`lda #$0F`
636	754		`sta SID_VOLUME`
637	755
638		-	`; Voice 1 - uses VOICE1_* constants`
639	756		`lda #$00`
640	757		`sta SID_V1_FREQ_LO`
641	758		`lda #VOICE1_FREQ`
			...
647	764		`lda #VOICE_SR`
648	765		`sta SID_V1_SR`
649	766
650		-	`; Voice 2 - uses VOICE2_* constants`
651	767		`lda #$00`
652	768		`sta SID_V2_FREQ_LO`
653	769		`lda #VOICE2_FREQ`
			...
659	775		`lda #VOICE_SR`
660	776		`sta SID_V2_SR`
661	777
662		-	`; Voice 3 - uses VOICE3_* constants`
663	778		`lda #$00`
664	779		`sta SID_V3_FREQ_LO`
665	780		`lda #VOICE3_FREQ`
			...
771	886		`rts`
772	887
773	888		`; ----------------------------------------------------------------------------`
774		-	`; Play Voices - Uses customisation waveforms`
	889	+	`; Play Voices`
775	890		`; ----------------------------------------------------------------------------`
776	891
777	892		`play_voice1:`
778	893		`lda #VOICE1_WAVE`
779		-	`ora #$01 ; Add gate bit`
	894	+	`ora #$01`
780	895		`sta SID_V1_CTRL`
781	896		`rts`
782	897
			...
793	908		`rts`
794	909
795	910		`; ----------------------------------------------------------------------------`
796		-	`; Flash Tracks - Uses customisation colours`
	911	+	`; Flash Tracks`
797	912		`; ----------------------------------------------------------------------------`
798	913
799	914		`flash_track1:`
			...
804	919		`inx`
805	920		`cpx #38`
806	921		`bne flash_t1_loop`
807		-	`lda #1 ; White label`
	922	+	`lda #1`
808	923		`sta COLRAM + (TRACK1_ROW * 40)`
809	924		`rts`
810	925