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.ROMBANKMAP
BANKSTOTAL 2
BANKSIZE $4000
BANKS 1
BANKSIZE $2000
BANKS 1
.ENDRO
.MEMORYMAP
DEFAULTSLOT 0
SLOTSIZE $4000
SLOT 0 $C000
SLOTSIZE $2000
SLOT 1 $0000
.ENDME
.ENUM $00
sleeping DB
color DB
frame_count DB
.ENDE
.bank 0 slot 0
.org $0000
RESET:
SEI
CLD
LDX #$FF
TXS
INX
STX $2000.w
STX $2001.w
STX $4010.w
LDX #$40
STX $4017.w
vblankwait1:
BIT $2002
BPL vblankwait1
clrmem:
LDA #$00
STA $0000, x
STA $0100, x
STA $0300, x
STA $0400, x
STA $0500, x
STA $0600, x
STA $0700, x
LDA #$FE
STA $0200, x
INX
BNE clrmem
LDA #%10000001
STA color
vblankwait2:
BIT $2002
BPL vblankwait2
LDA #%10000000
STA $2000
loop:
INC sleeping
wait_for_vblank_end:
LDA sleeping
BNE wait_for_vblank_end
; controller 1 latch
LDA #$01
STA $4016
LDA #$00
STA $4016
; controller 1 clock, reading the state of the A button
LDA $4016
AND #%00000001
BNE change_color
JMP loop_end
; reading the rest of the buttons is unnecessary, so we don't do it
change_color:
LDA #$00
STA frame_count
LDX color
CPX #%10000001
BEQ turn_green
CPX #%01000001
BEQ turn_red
turn_blue:
LDA #%10000001
STA color
JMP loop_end
turn_green:
LDA #%01000001
STA color
JMP loop_end
turn_red:
LDA #%00100001
STA color
loop_end:
JMP loop
NMI:
PHA
TXA
PHA
TYA
PHA
LDA color
STA $2001
LDA #$00
STA sleeping
PLA
TAY
PLA
TAX
PLA
RTI
.orga $FFFA
.dw NMI
.dw RESET
.dw 0
.bank 1 slot 1
.org $0000
.incbin "sprites.chr"
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