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8bitworkshop/presets/nes/ex0.asm

47 lines
877 B
NASM

include "nesdefs.asm"
;;;;; VARIABLES
seg.u RAM
org $0
;;;;; NES CARTRIDGE HEADER
NES_HEADER 0,2,1,0 ; mapper 0, 2 PRGs, 1 CHR, vertical
;;;;; START OF CODE
Start:
NES_INIT ; set up stack pointer, turn off PPU
jsr WaitSync ; wait for VSYNC
jsr ClearRAM ; clear RAM
jsr WaitSync ; wait for VSYNC (and PPU warmup)
lda #$3f ; $3F -> A register
ldy #$00 ; $00 -> Y register
sta PPU_ADDR ; write high byte first
sty PPU_ADDR ; $3F00 -> PPU address
lda #$1c ; $1C = light blue color
sta PPU_DATA ; $1C -> PPU data
lda #CTRL_NMI
sta PPU_CTRL ; enable NMI
lda #MASK_COLOR
sta PPU_MASK ; enable rendering
.endless
jmp .endless ; endless loop
;;;;; COMMON SUBROUTINES
include "nesppu.asm"
;;;;; INTERRUPT HANDLERS
NMIHandler:
rti
;;;;; CPU VECTORS
NES_VECTORS