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processor 6502
option output-file,"nes.nes"
option output-format,nes
option nes-vector,reset,start
option nes-vector,nmi,nmi
option nes-vector,brk,nmi
option nes-mirror,horizontal
vsync: macro
.wait
lda $2002
bpl wait
endm
start: org $c000
; Clear decimal and setup stack
;
cld
ldx #$ff
txs
; Wait for the PPU. Recommended practice is clear the flag, and
; wait for 2 VBL signals
;
bit $2002
vsync
vsync
; Setup PPU
;
lda #%00001000
sta $2000
lda #%00011110
sta $2001
; Setup the palette
;
loadpalette:
lda #$3f
sta $2006
lda #$00
sta $2006
ldx #0
.loop lda palette,x
sta $2007
inx
cpx #$20
bne loop
; Wait for a vysnc before loading the name table
;
vsync
; Load the name map
;
load_namemap:
lda #$20
sta $2006
lda #$40
sta $2006
ldx #0
.loop lda map,x
cmp #$ff
beq done
sta $2007
inx
jmp loop
.done
forever:
jmp forever
nmi:
rti
palette:
incbin "nes.pal"
incbin "nes.pal"
map:
db 'H'-'@'
db 'E'-'@'
db 'L'-'@'
db 'L'-'@'
db 'O'-'@'
db 0
db 'W'-'@'
db 'O'-'@'
db 'R'-'@'
db 'L'-'@'
db 'D'-'@'
db 255
;
; VROM
;
org 0
bank 1
incbin "tiles.chr"
|
