Game 1 Unit 5 of 64 1 hr learning time

Hit Detection

Detect when keypresses match notes in the hit zone. The core rhythm game mechanic.

8% of SID Symphony

Mark as complete Completed!

Now it’s a real game. Press the right key when a note reaches the hit zone.

Previously, pressing Z/X/C always played sounds regardless of timing. This unit adds the core rhythm game mechanic: hit detection. Press the key when a note is in the hit zone - you hear the sound and the note disappears. Miss the timing - nothing happens.

Run It

Assemble and run:

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

Unit 5 Screenshot

Watch notes scroll toward the hit zone. Press Z when a note on track Z reaches the yellow bar. If timed correctly, the note vanishes and the SID plays. Press too early or late - nothing.

Hit detection — notes must be in the hit zone when you press the key

The Hit Zone

Notes must be within a range of columns to count as “hittable”:

; Hit zone boundaries (column positions)
HIT_ZONE_MIN = 2                ; Left edge of hit zone
HIT_ZONE_MAX = 5                ; Right edge of hit zone

The hit zone spans columns 2-5. A note at column 2 is about to leave the zone. A note at column 5 is just entering. This gives the player a window of 4 columns to hit each note.

How Hit Detection Works

When a key is pressed, the game searches through all active notes looking for one that:

Is on the correct track (Z key = track 1, X = track 2, C = track 3)
Has an X position within the hit zone

; ----------------------------------------------------------------------------
; Check Hit - Find a note in the hit zone for the pressed track
; ----------------------------------------------------------------------------
; Input: key_pressed = track number (1-3)
; Output: Carry set if hit found, X = note index
;         Carry clear if no hit
; Side effect: Removes hit note from play

check_hit:
            ldx #0

check_hit_loop:
            ; Check if this note slot is active
            lda note_track,x
            beq check_hit_next  ; Empty slot - skip

            ; Check if note is on the pressed track
            cmp key_pressed
            bne check_hit_next  ; Wrong track - skip

            ; Check if note is in the hit zone
            lda note_col,x
            cmp #HIT_ZONE_MIN
            bcc check_hit_next  ; Too far left - skip
            cmp #HIT_ZONE_MAX+1
            bcs check_hit_next  ; Too far right - skip

            ; HIT! Note is in zone on correct track
            ; Erase the note from screen
            jsr erase_note

            ; Deactivate the note
            lda #0
            sta note_track,x

            ; Return with carry set (hit found)
            sec
            rts

check_hit_next:
            inx
            cpx #MAX_NOTES
            bne check_hit_loop

            ; No hit found - return with carry clear
            clc
            rts

The routine uses the carry flag to signal success or failure:

Carry set (SEC) - Hit found, note removed
Carry clear (CLC) - No hit, nothing changed

This is a common 6502 pattern. The branch instructions BCS (branch if carry set) and BCC (branch if carry clear) let the caller respond to the result.

Updating Key Handling

The key checking code now calls check_hit and only plays sound on success:

; ----------------------------------------------------------------------------
; Check Keys - Now with hit detection
; ----------------------------------------------------------------------------
; Checks if a key is pressed and if there's a matching note in the hit zone.
; Only plays sound and removes note on a successful hit.

check_keys:
            ; Check Z key (track 1)
            lda #$FD
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_x_key

            ; Z pressed - check for hit on track 1
            lda #1
            sta key_pressed
            jsr check_hit
            bcc check_x_key     ; No hit - don't play sound
            jsr play_voice1
            jsr flash_track1_hit

check_x_key:
            ; Check X key (track 2)
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$80
            bne check_c_key

            ; X pressed - check for hit on track 2
            lda #2
            sta key_pressed
            jsr check_hit
            bcc check_c_key     ; No hit - don't play sound
            jsr play_voice2
            jsr flash_track2_hit

check_c_key:
            ; Check C key (track 3)
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_keys_done

            ; C pressed - check for hit on track 3
            lda #3
            sta key_pressed
            jsr check_hit
            bcc check_keys_done ; No hit - don't play sound
            jsr play_voice3
            jsr flash_track3_hit

check_keys_done:
            lda #$FF
            sta CIA1_PRA
            rts

Compare this to Unit 4 where every keypress triggered a sound. Now BCC skips the sound if no hit was found.

The Complete Code

; ============================================================================
; SID SYMPHONY - Unit 5: Hit Detection
; ============================================================================
; Detect when keypresses match notes in the hit zone. Press the right key at
; the right time to hit notes and hear the SID play. Wrong timing does nothing.
;
; 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

HIT_COL     = 1                 ; White - flash on successful hit

; ============================================================================
; HIT DETECTION SETTINGS
; ============================================================================

; Hit zone boundaries (column positions)
HIT_ZONE_MIN = 2                ; Left edge of hit zone
HIT_ZONE_MAX = 5                ; Right edge of hit zone
HIT_ZONE_CENTRE = 3             ; Perfect hit position

; ============================================================================
; 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
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
key_pressed = $07               ; Which track key was pressed (0=none)

; ----------------------------------------------------------------------------
; 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
; ----------------------------------------------------------------------------

copy_charset:
            sei

            lda $01
            pha
            and #$FB
            sta $01

            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

            pla
            sta $01

            cli

            jsr define_custom_chars

            lda #$1C
            sta CHARPTR

            rts

; ----------------------------------------------------------------------------
; Define Custom Characters
; ----------------------------------------------------------------------------

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

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

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

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
            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
            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

            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

            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
; ----------------------------------------------------------------------------

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

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

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

            rts

; ----------------------------------------------------------------------------
; Draw Hit Zones
; ----------------------------------------------------------------------------

draw_hit_zones:
            lda #CHAR_HITZONE

            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

            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
            sta COLRAM + 13,x
            inx
            bne draw_title
draw_title_done:

            lda #$1A            ; Z
            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 "hit detection 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

            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)

            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 - Now with hit detection
; ----------------------------------------------------------------------------
; Checks if a key is pressed and if there's a matching note in the hit zone.
; Only plays sound and removes note on a successful hit.

check_keys:
            ; Check Z key (track 1)
            lda #$FD
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_x_key

            ; Z pressed - check for hit on track 1
            lda #1
            sta key_pressed
            jsr check_hit
            bcc check_x_key     ; No hit - don't play sound
            jsr play_voice1
            jsr flash_track1_hit

check_x_key:
            ; Check X key (track 2)
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$80
            bne check_c_key

            ; X pressed - check for hit on track 2
            lda #2
            sta key_pressed
            jsr check_hit
            bcc check_c_key     ; No hit - don't play sound
            jsr play_voice2
            jsr flash_track2_hit

check_c_key:
            ; Check C key (track 3)
            lda #$FB
            sta CIA1_PRA
            lda CIA1_PRB
            and #$10
            bne check_keys_done

            ; C pressed - check for hit on track 3
            lda #3
            sta key_pressed
            jsr check_hit
            bcc check_keys_done ; No hit - don't play sound
            jsr play_voice3
            jsr flash_track3_hit

check_keys_done:
            lda #$FF
            sta CIA1_PRA
            rts

; ----------------------------------------------------------------------------
; Check Hit - Find a note in the hit zone for the pressed track
; ----------------------------------------------------------------------------
; Input: key_pressed = track number (1-3)
; Output: Carry set if hit found, X = note index
;         Carry clear if no hit
; Side effect: Removes hit note from play

check_hit:
            ldx #0

check_hit_loop:
            ; Check if this note slot is active
            lda note_track,x
            beq check_hit_next  ; Empty slot - skip

            ; Check if note is on the pressed track
            cmp key_pressed
            bne check_hit_next  ; Wrong track - skip

            ; Check if note is in the hit zone
            lda note_col,x
            cmp #HIT_ZONE_MIN
            bcc check_hit_next  ; Too far left - skip
            cmp #HIT_ZONE_MAX+1
            bcs check_hit_next  ; Too far right - skip

            ; HIT! Note is in zone on correct track
            ; Erase the note from screen
            jsr erase_note

            ; Deactivate the note
            lda #0
            sta note_track,x

            ; Return with carry set (hit found)
            sec
            rts

check_hit_next:
            inx
            cpx #MAX_NOTES
            bne check_hit_loop

            ; No hit found - return with carry clear
            clc
            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 on Hit - White flash for successful hits
; ----------------------------------------------------------------------------

flash_track1_hit:
            ldx #0
            lda #HIT_COL        ; White for hits
flash_t1h_loop:
            sta COLRAM + (TRACK1_ROW * 40),x
            inx
            cpx #38
            bne flash_t1h_loop
            lda #1
            sta COLRAM + (TRACK1_ROW * 40)
            rts

flash_track2_hit:
            ldx #0
            lda #HIT_COL
flash_t2h_loop:
            sta COLRAM + (TRACK2_ROW * 40),x
            inx
            cpx #38
            bne flash_t2h_loop
            lda #1
            sta COLRAM + (TRACK2_ROW * 40)
            rts

flash_track3_hit:
            ldx #0
            lda #HIT_COL
flash_t3h_loop:
            sta COLRAM + (TRACK3_ROW * 40),x
            inx
            cpx #38
            bne flash_t3h_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: Narrower Hit Zone

Make timing more challenging:

HIT_ZONE_MIN = 3                ; Tighter window
HIT_ZONE_MAX = 4                ; Only 2 columns wide

The game becomes much harder - you need precise timing.

Try This: Wider Hit Zone

Make it more forgiving:

HIT_ZONE_MIN = 1                ; Very wide window
HIT_ZONE_MAX = 6                ; 6 columns to hit

Good for practice or accessibility.

What You’ve Learnt

Position-based collision - Check if a value falls within a range
Carry flag signalling - Use SEC/CLC and BCS/BCC for function results
Note consumption - One keypress removes one note
Conditional sound - Only play audio on successful game actions

What’s Next

In Unit 6, we’ll add scoring and visual feedback. Perfect hits will award more points than late hits. The screen will flash to celebrate success.

What Changed

Unit 4 → Unit 5

+140-78

1	1		`; ============================================================================`
2		-	`; SID SYMPHONY - Unit 4: Custom Graphics`
	2	+	`; SID SYMPHONY - Unit 5: Hit Detection`
3	3		`; ============================================================================`
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.`
	4	+	`; Detect when keypresses match notes in the hit zone. Press the right key at`
	5	+	`; the right time to hit notes and hear the SID play. Wrong timing does nothing.`
6	6		`;`
7	7		`; Controls: Z = Track 1 (high), X = Track 2 (mid), C = Track 3 (low)`
8	8		`; ============================================================================`
			...
38	38		`FLASH1_COL = 2 ; Red`
39	39		`FLASH2_COL = 5 ; Green`
40	40		`FLASH3_COL = 6 ; Blue`
	41	+
	42	+	`HIT_COL = 1 ; White - flash on successful hit`
	43	+
	44	+	`; ============================================================================`
	45	+	`; HIT DETECTION SETTINGS`
	46	+	`; ============================================================================`
	47	+
	48	+	`; Hit zone boundaries (column positions)`
	49	+	`HIT_ZONE_MIN = 2 ; Left edge of hit zone`
	50	+	`HIT_ZONE_MAX = 5 ; Right edge of hit zone`
	51	+	`HIT_ZONE_CENTRE = 3 ; Perfect hit position`
41	52
42	53		`; ============================================================================`
43	54		`; MEMORY MAP`
			...
88	99		`; Hit zone`
89	100		`HIT_ZONE_COLUMN = 3`
90	101
91		-	`; Custom character codes (we'll define these)`
	102	+	`; Custom character codes`
92	103		`CHAR_NOTE = 128 ; Filled arrow/circle for notes`
93	104		`CHAR_TRACK = 129 ; Thin horizontal line for tracks`
94	105		`CHAR_HITZONE = 130 ; Vertical bar for hit zone`
			...
111	122		`song_pos = $04`
112	123		`song_pos_hi = $05`
113	124		`temp_track = $06`
	125	+	`key_pressed = $07 ; Which track key was pressed (0=none)`
114	126
115	127		`; ----------------------------------------------------------------------------`
116	128		`; BASIC Stub`
			...
172	184		`; ----------------------------------------------------------------------------`
173	185		`; Copy Character Set from ROM to RAM`
174	186		`; ----------------------------------------------------------------------------`
175		-	`; Copies the standard character ROM to $3000, then adds custom characters`
176	187
177	188		`copy_charset:`
178		-	`; Disable interrupts during ROM access`
179	189		`sei`
180	190
181		-	`; Make character ROM visible at $D000`
182	191		`lda $01`
183		-	`pha ; Save processor port`
184		-	`and #$FB ; Clear bit 2 (CHAREN)`
185		-	`sta $01 ; Character ROM now at $D000`
	192	+	`pha`
	193	+	`and #$FB`
	194	+	`sta $01`
186	195
187		-	`; Copy 2KB (256 characters * 8 bytes)`
188	196		`ldx #0`
189	197		`copy_loop:`
190	198		`lda $D000,x`
			...
206	214		`inx`
207	215		`bne copy_loop`
208	216
209		-	`; Restore processor port`
210	217		`pla`
211	218		`sta $01`
212	219
213		-	`; Re-enable interrupts`
214	220		`cli`
215	221
216		-	`; Define our custom characters`
217	222		`jsr define_custom_chars`
218	223
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	224		`lda #$1C`
223	225		`sta CHARPTR`
224	226
			...
227	229		`; ----------------------------------------------------------------------------`
228	230		`; Define Custom Characters`
229	231		`; ----------------------------------------------------------------------------`
230		-	`; Creates note, track, and hit zone graphics`
231	232
232	233		`define_custom_chars:`
233	234		`; Character 128: Note (filled chevron pointing left)`
234		-	`lda #%00000110 ; Row 0`
	235	+	`lda #%00000110`
235	236		`sta CHARSET + (CHAR_NOTE * 8) + 0`
236		-	`lda #%00011110 ; Row 1`
	237	+	`lda #%00011110`
237	238		`sta CHARSET + (CHAR_NOTE * 8) + 1`
238		-	`lda #%01111110 ; Row 2`
	239	+	`lda #%01111110`
239	240		`sta CHARSET + (CHAR_NOTE * 8) + 2`
240		-	`lda #%11111110 ; Row 3`
	241	+	`lda #%11111110`
241	242		`sta CHARSET + (CHAR_NOTE * 8) + 3`
242		-	`lda #%11111110 ; Row 4`
	243	+	`lda #%11111110`
243	244		`sta CHARSET + (CHAR_NOTE * 8) + 4`
244		-	`lda #%01111110 ; Row 5`
	245	+	`lda #%01111110`
245	246		`sta CHARSET + (CHAR_NOTE * 8) + 5`
246		-	`lda #%00011110 ; Row 6`
	247	+	`lda #%00011110`
247	248		`sta CHARSET + (CHAR_NOTE * 8) + 6`
248		-	`lda #%00000110 ; Row 7`
	249	+	`lda #%00000110`
249	250		`sta CHARSET + (CHAR_NOTE * 8) + 7`
250	251
251	252		`; Character 129: Track line (centered horizontal line)`
252		-	`lda #%00000000 ; Row 0`
	253	+	`lda #%00000000`
253	254		`sta CHARSET + (CHAR_TRACK * 8) + 0`
254		-	`lda #%00000000 ; Row 1`
	255	+	`lda #%00000000`
255	256		`sta CHARSET + (CHAR_TRACK * 8) + 1`
256		-	`lda #%00000000 ; Row 2`
	257	+	`lda #%00000000`
257	258		`sta CHARSET + (CHAR_TRACK * 8) + 2`
258		-	`lda #%11111111 ; Row 3 - the line`
	259	+	`lda #%11111111`
259	260		`sta CHARSET + (CHAR_TRACK * 8) + 3`
260		-	`lda #%11111111 ; Row 4 - the line`
	261	+	`lda #%11111111`
261	262		`sta CHARSET + (CHAR_TRACK * 8) + 4`
262		-	`lda #%00000000 ; Row 5`
	263	+	`lda #%00000000`
263	264		`sta CHARSET + (CHAR_TRACK * 8) + 5`
264		-	`lda #%00000000 ; Row 6`
	265	+	`lda #%00000000`
265	266		`sta CHARSET + (CHAR_TRACK * 8) + 6`
266		-	`lda #%00000000 ; Row 7`
	267	+	`lda #%00000000`
267	268		`sta CHARSET + (CHAR_TRACK * 8) + 7`
268	269
269	270		`; Character 130: Hit zone (vertical bars)`
270		-	`lda #%01100110 ; Row 0`
	271	+	`lda #%01100110`
271	272		`sta CHARSET + (CHAR_HITZONE * 8) + 0`
272		-	`lda #%01100110 ; Row 1`
	273	+	`lda #%01100110`
273	274		`sta CHARSET + (CHAR_HITZONE * 8) + 1`
274		-	`lda #%01100110 ; Row 2`
	275	+	`lda #%01100110`
275	276		`sta CHARSET + (CHAR_HITZONE * 8) + 2`
276		-	`lda #%01100110 ; Row 3`
	277	+	`lda #%01100110`
277	278		`sta CHARSET + (CHAR_HITZONE * 8) + 3`
278		-	`lda #%01100110 ; Row 4`
	279	+	`lda #%01100110`
279	280		`sta CHARSET + (CHAR_HITZONE * 8) + 4`
280		-	`lda #%01100110 ; Row 5`
	281	+	`lda #%01100110`
281	282		`sta CHARSET + (CHAR_HITZONE * 8) + 5`
282		-	`lda #%01100110 ; Row 6`
	283	+	`lda #%01100110`
283	284		`sta CHARSET + (CHAR_HITZONE * 8) + 6`
284		-	`lda #%01100110 ; Row 7`
	285	+	`lda #%01100110`
285	286		`sta CHARSET + (CHAR_HITZONE * 8) + 7`
286	287
287	288		`rts`
			...
402	403		`rts`
403	404
404	405		`; ----------------------------------------------------------------------------`
405		-	`; Draw Note - Uses custom note character`
	406	+	`; Draw Note`
406	407		`; ----------------------------------------------------------------------------`
407	408
408	409		`draw_note:`
			...
425	426		`sta ZP_PTR_HI`
426	427
427	428		`ldy #0`
428		-	`lda #CHAR_NOTE ; Custom note character`
	429	+	`lda #CHAR_NOTE`
429	430		`sta (ZP_PTR),y`
430	431
431	432		`lda note_col,x`
			...
511	512		`sta ZP_PTR_HI`
512	513
513	514		`ldy #0`
514		-	`lda #CHAR_TRACK ; Custom track character`
	515	+	`lda #CHAR_TRACK`
515	516		`sta (ZP_PTR),y`
516	517
517	518		`lda note_col,x`
			...
583	584		`lda #BG_COL`
584	585		`sta BGCOL`
585	586
586		-	`; Clear screen with spaces`
587	587		`ldx #0`
588	588		`lda #CHAR_SPACE`
589	589		`clr_screen:`
			...
594	594		`inx`
595	595		`bne clr_screen`
596	596
597		-	`; Set all colours to track line colour`
598	597		`ldx #0`
599	598		`lda #TRACK_LINE_COL`
600	599		`clr_colour:`
			...
612	611		`rts`
613	612
614	613		`; ----------------------------------------------------------------------------`
615		-	`; Draw Tracks - Uses custom track character`
	614	+	`; Draw Tracks`
616	615		`; ----------------------------------------------------------------------------`
617	616
618	617		`draw_tracks:`
619		-	`; Track 1`
620	618		`lda #CHAR_TRACK`
621	619		`ldx #0`
622	620		`draw_t1:`
			...
625	623		`cpx #38`
626	624		`bne draw_t1`
627	625
628		-	`; Track 2`
629	626		`lda #CHAR_TRACK`
630	627		`ldx #0`
631	628		`draw_t2:`
			...
634	631		`cpx #38`
635	632		`bne draw_t2`
636	633
637		-	`; Track 3`
638	634		`lda #CHAR_TRACK`
639	635		`ldx #0`
640	636		`draw_t3:`
			...
646	642		`rts`
647	643
648	644		`; ----------------------------------------------------------------------------`
649		-	`; Draw Hit Zones - Uses custom hit zone character`
	645	+	`; Draw Hit Zones`
650	646		`; ----------------------------------------------------------------------------`
651	647
652	648		`draw_hit_zones:`
653		-	`lda #CHAR_HITZONE ; Custom hit zone character`
	649	+	`lda #CHAR_HITZONE`
654	650
655		-	`; Draw hit zone bars spanning all three tracks`
656	651		`sta SCREEN + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN`
657	652		`sta SCREEN + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
658	653		`sta SCREEN + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
			...
667	662		`sta SCREEN + ((TRACK3_ROW+1) * 40) + HIT_ZONE_COLUMN`
668	663		`sta SCREEN + ((TRACK3_ROW+2) * 40) + HIT_ZONE_COLUMN`
669	664
670		-	`; Colour the hit zones`
671	665		`lda #HIT_ZONE_COL`
672	666		`sta COLRAM + ((TRACK1_ROW-2) * 40) + HIT_ZONE_COLUMN`
673	667		`sta COLRAM + ((TRACK1_ROW-1) * 40) + HIT_ZONE_COLUMN`
			...
695	689		`lda title_text,x`
696	690		`beq draw_title_done`
697	691		`sta SCREEN + 13,x`
698		-	`lda #1 ; White`
	692	+	`lda #1`
699	693		`sta COLRAM + 13,x`
700	694		`inx`
701	695		`bne draw_title`
702	696		`draw_title_done:`
703	697
704		-	`; Track labels - use standard characters for letters`
705		-	`lda #$1A ; Z (screen code)`
	698	+	`lda #$1A ; Z`
706	699		`sta SCREEN + (TRACK1_ROW * 40)`
707	700		`lda #TRACK1_NOTE_COL`
708	701		`sta COLRAM + (TRACK1_ROW * 40)`
			...
735	728		`!byte 0`
736	729
737	730		`instr_text:`
738		-	`!scr "custom graphics active"`
	731	+	`!scr "hit detection active"`
739	732		`!byte 0`
740	733
741	734		`; ----------------------------------------------------------------------------`
			...
815	808		`cpx #38`
816	809		`bne reset_t3`
817	810
818		-	`; Restore key labels`
819	811		`lda #TRACK1_NOTE_COL`
820	812		`sta COLRAM + (TRACK1_ROW * 40)`
821	813		`lda #TRACK2_NOTE_COL`
			...
823	815		`lda #TRACK3_NOTE_COL`
824	816		`sta COLRAM + (TRACK3_ROW * 40)`
825	817
826		-	`; Restore hit zone colours`
827	818		`lda #HIT_ZONE_COL`
828	819		`sta COLRAM + (TRACK1_ROW * 40) + HIT_ZONE_COLUMN`
829	820		`sta COLRAM + (TRACK2_ROW * 40) + HIT_ZONE_COLUMN`
			...
850	841		`rts`
851	842
852	843		`; ----------------------------------------------------------------------------`
853		-	`; Check Keys`
	844	+	`; Check Keys - Now with hit detection`
854	845		`; ----------------------------------------------------------------------------`
	846	+	`; Checks if a key is pressed and if there's a matching note in the hit zone.`
	847	+	`; Only plays sound and removes note on a successful hit.`
855	848
856	849		`check_keys:`
	850	+	`; Check Z key (track 1)`
857	851		`lda #$FD`
858	852		`sta CIA1_PRA`
859	853		`lda CIA1_PRB`
860	854		`and #$10`
861	855		`bne check_x_key`
	856	+
	857	+	`; Z pressed - check for hit on track 1`
	858	+	`lda #1`
	859	+	`sta key_pressed`
	860	+	`jsr check_hit`
	861	+	`bcc check_x_key ; No hit - don't play sound`
862	862		`jsr play_voice1`
863		-	`jsr flash_track1`
	863	+	`jsr flash_track1_hit`
864	864
865	865		`check_x_key:`
	866	+	`; Check X key (track 2)`
866	867		`lda #$FB`
867	868		`sta CIA1_PRA`
868	869		`lda CIA1_PRB`
869	870		`and #$80`
870	871		`bne check_c_key`
	872	+
	873	+	`; X pressed - check for hit on track 2`
	874	+	`lda #2`
	875	+	`sta key_pressed`
	876	+	`jsr check_hit`
	877	+	`bcc check_c_key ; No hit - don't play sound`
871	878		`jsr play_voice2`
872		-	`jsr flash_track2`
	879	+	`jsr flash_track2_hit`
873	880
874	881		`check_c_key:`
	882	+	`; Check C key (track 3)`
875	883		`lda #$FB`
876	884		`sta CIA1_PRA`
877	885		`lda CIA1_PRB`
878	886		`and #$10`
879	887		`bne check_keys_done`
	888	+
	889	+	`; C pressed - check for hit on track 3`
	890	+	`lda #3`
	891	+	`sta key_pressed`
	892	+	`jsr check_hit`
	893	+	`bcc check_keys_done ; No hit - don't play sound`
880	894		`jsr play_voice3`
881		-	`jsr flash_track3`
	895	+	`jsr flash_track3_hit`
882	896
883	897		`check_keys_done:`
884	898		`lda #$FF`
885	899		`sta CIA1_PRA`
	900	+	`rts`
	901	+
	902	+	`; ----------------------------------------------------------------------------`
	903	+	`; Check Hit - Find a note in the hit zone for the pressed track`
	904	+	`; ----------------------------------------------------------------------------`
	905	+	`; Input: key_pressed = track number (1-3)`
	906	+	`; Output: Carry set if hit found, X = note index`
	907	+	`; Carry clear if no hit`
	908	+	`; Side effect: Removes hit note from play`
	909	+
	910	+	`check_hit:`
	911	+	`ldx #0`
	912	+
	913	+	`check_hit_loop:`
	914	+	`; Check if this note slot is active`
	915	+	`lda note_track,x`
	916	+	`beq check_hit_next ; Empty slot - skip`
	917	+
	918	+	`; Check if note is on the pressed track`
	919	+	`cmp key_pressed`
	920	+	`bne check_hit_next ; Wrong track - skip`
	921	+
	922	+	`; Check if note is in the hit zone`
	923	+	`lda note_col,x`
	924	+	`cmp #HIT_ZONE_MIN`
	925	+	`bcc check_hit_next ; Too far left - skip`
	926	+	`cmp #HIT_ZONE_MAX+1`
	927	+	`bcs check_hit_next ; Too far right - skip`
	928	+
	929	+	`; HIT! Note is in zone on correct track`
	930	+	`; Erase the note from screen`
	931	+	`jsr erase_note`
	932	+
	933	+	`; Deactivate the note`
	934	+	`lda #0`
	935	+	`sta note_track,x`
	936	+
	937	+	`; Return with carry set (hit found)`
	938	+	`sec`
	939	+	`rts`
	940	+
	941	+	`check_hit_next:`
	942	+	`inx`
	943	+	`cpx #MAX_NOTES`
	944	+	`bne check_hit_loop`
	945	+
	946	+	`; No hit found - return with carry clear`
	947	+	`clc`
886	948		`rts`
887	949
888	950		`; ----------------------------------------------------------------------------`
			...
908	970		`rts`
909	971
910	972		`; ----------------------------------------------------------------------------`
911		-	`; Flash Tracks`
	973	+	`; Flash Tracks on Hit - White flash for successful hits`
912	974		`; ----------------------------------------------------------------------------`
913	975
914		-	`flash_track1:`
	976	+	`flash_track1_hit:`
915	977		`ldx #0`
916		-	`lda #FLASH1_COL`
917		-	`flash_t1_loop:`
	978	+	`lda #HIT_COL ; White for hits`
	979	+	`flash_t1h_loop:`
918	980		`sta COLRAM + (TRACK1_ROW * 40),x`
919	981		`inx`
920	982		`cpx #38`
921		-	`bne flash_t1_loop`
	983	+	`bne flash_t1h_loop`
922	984		`lda #1`
923	985		`sta COLRAM + (TRACK1_ROW * 40)`
924	986		`rts`
925	987
926		-	`flash_track2:`
	988	+	`flash_track2_hit:`
927	989		`ldx #0`
928		-	`lda #FLASH2_COL`
929		-	`flash_t2_loop:`
	990	+	`lda #HIT_COL`
	991	+	`flash_t2h_loop:`
930	992		`sta COLRAM + (TRACK2_ROW * 40),x`
931	993		`inx`
932	994		`cpx #38`
933		-	`bne flash_t2_loop`
	995	+	`bne flash_t2h_loop`
934	996		`lda #1`
935	997		`sta COLRAM + (TRACK2_ROW * 40)`
936	998		`rts`
937	999
938		-	`flash_track3:`
	1000	+	`flash_track3_hit:`
939	1001		`ldx #0`
940		-	`lda #FLASH3_COL`
941		-	`flash_t3_loop:`
	1002	+	`lda #HIT_COL`
	1003	+	`flash_t3h_loop:`
942	1004		`sta COLRAM + (TRACK3_ROW * 40),x`
943	1005		`inx`
944	1006		`cpx #38`
945		-	`bne flash_t3_loop`
	1007	+	`bne flash_t3h_loop`
946	1008		`lda #1`
947	1009		`sta COLRAM + (TRACK3_ROW * 40)`
948	1010		`rts`