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n65/examples/my_background.asm

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; Create an iNES header
.ines {"prog": 1, "char": 1, "mapper": 0, "mirror": 1}
; Main code segment
.org $C000
start:
SEI ; disable IRQs
CLD ; disable decimal mode
LDX #$40
STX $4017 ; disable APU frame IRQ
LDX #$FF
TXS ; Set up stack
INX ; now X = 0
STX $2000 ; disable NMI
STX $2001 ; disable rendering
STX $4010 ; disable DMC IRQs
vblankwait1: ; First wait for vblank to make sure PPU is ready
BIT $2002
BPL vblankwait1
clrmem:
LDA #$00
STA $0000, X
STA $0100, X
STA $0200, X
STA $0400, X
STA $0500, X
STA $0600, X
STA $0700, X
LDA #$FE
STA $0300, X
INX
BNE clrmem
vblankwait2: ; Second wait for vblank, PPU is ready after this
BIT $2002
BPL vblankwait2
LDA #$60 ;intensify blues
STA $2001
forever:
JMP forever ;jump back to Forever, infinite loop
nmi:
RTI
.org $FFFA ;first of the three vectors starts here
.dw nmi ;when an NMI happens (once per frame if enabled) the processor will jump to the label NMI:
.dw start ;when the processor first turns on or is reset, it will jump to the label RESET:
.dw $0 ;external interrupt IRQ is not used in this tutorial