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processor 65c816
option output-file,snes.sfc
option output-format,snes
option snes-irq,vbl,handler
option snes-irq,irq,handler
; Initialise SNES
;
org $8000
sei
clc
xce
ldx #$1fff
txs
sep #$30 ; X,Y,A are 8 bit numbers
lda #$8F ; screen off, full brightness
sta $2100 ; brightness + screen enable register
stz $2101 ; Sprite register (size + address in VRAM)
stz $2102 ; Sprite registers (address of sprite memory [OAM])
stz $2103 ; "" ""
stz $2105 ; Mode 0, = Graphic mode register
stz $2106 ; noplanes, no mosaic, = Mosaic register
stz $2107 ; Plane 0 map VRAM location
stz $2108 ; Plane 1 map VRAM location
stz $2109 ; Plane 2 map VRAM location
stz $210A ; Plane 3 map VRAM location
stz $210B ; Plane 0+1 Tile data location
stz $210C ; Plane 2+3 Tile data location
stz $210D ; Plane 0 scroll x (first 8 bits)
stz $210D ; Plane 0 scroll x (last 3 bits) #$0 - #$07ff
lda #$FF ; The top pixel drawn on the screen isn't the top one in the tilemap, it's the one above that.
sta $210E ; Plane 0 scroll y (first 8 bits)
sta $2110 ; Plane 1 scroll y (first 8 bits)
sta $2112 ; Plane 2 scroll y (first 8 bits)
sta $2114 ; Plane 3 scroll y (first 8 bits)
lda #$07 ; Since this could get quite annoying, it's better to edit the scrolling registers to fix this.
sta $210E ; Plane 0 scroll y (last 3 bits) #$0 - #$07ff
sta $2110 ; Plane 1 scroll y (last 3 bits) #$0 - #$07ff
sta $2112 ; Plane 2 scroll y (last 3 bits) #$0 - #$07ff
sta $2114 ; Plane 3 scroll y (last 3 bits) #$0 - #$07ff
stz $210F ; Plane 1 scroll x (first 8 bits)
stz $210F ; Plane 1 scroll x (last 3 bits) #$0 - #$07ff
stz $2111 ; Plane 2 scroll x (first 8 bits)
stz $2111 ; Plane 2 scroll x (last 3 bits) #$0 - #$07ff
stz $2113 ; Plane 3 scroll x (first 8 bits)
stz $2113 ; Plane 3 scroll x (last 3 bits) #$0 - #$07ff
lda #$80 ; increase VRAM address after writing to $2119
sta $2115 ; VRAM address increment register
stz $2116 ; VRAM address low
stz $2117 ; VRAM address high
stz $211A ; Initial Mode 7 setting register
stz $211B ; Mode 7 matrix parameter A register (low)
lda #$01
sta $211B ; Mode 7 matrix parameter A register (high)
stz $211C ; Mode 7 matrix parameter B register (low)
stz $211C ; Mode 7 matrix parameter B register (high)
stz $211D ; Mode 7 matrix parameter C register (low)
stz $211D ; Mode 7 matrix parameter C register (high)
stz $211E ; Mode 7 matrix parameter D register (low)
sta $211E ; Mode 7 matrix parameter D register (high)
stz $211F ; Mode 7 center position X register (low)
stz $211F ; Mode 7 center position X register (high)
stz $2120 ; Mode 7 center position Y register (low)
stz $2120 ; Mode 7 center position Y register (high)
stz $2121 ; Color number register ($0-ff)
stz $2123 ; BG1 & BG2 Window mask setting register
stz $2124 ; BG3 & BG4 Window mask setting register
stz $2125 ; OBJ & Color Window mask setting register
stz $2126 ; Window 1 left position register
stz $2127 ; Window 2 left position register
stz $2128 ; Window 3 left position register
stz $2129 ; Window 4 left position register
stz $212A ; BG1, BG2, BG3, BG4 Window Logic register
stz $212B ; OBJ, Color Window Logic Register (or,and,xor,xnor)
sta $212C ; Main Screen designation (planes, sprites enable)
stz $212D ; Sub Screen designation
stz $212E ; Window mask for Main Screen
stz $212F ; Window mask for Sub Screen
lda #$30
sta $2130 ; Color addition & screen addition init setting
stz $2131 ; Add/Sub sub designation for screen, sprite, color
lda #$E0
sta $2132 ; color data for addition/subtraction
stz $2133 ; Screen setting (interlace x,y/enable SFX data)
stz $4200 ; Enable V-blank, interrupt, Joypad register
lda #$FF
sta $4201 ; Programmable I/O port
stz $4202 ; Multiplicand A
stz $4203 ; Multiplier B
stz $4204 ; Multiplier C
stz $4205 ; Multiplicand C
stz $4206 ; Divisor B
stz $4207 ; Horizontal Count Timer
stz $4208 ; Horizontal Count Timer MSB (most significant bit)
stz $4209 ; Vertical Count Timer
stz $420A ; Vertical Count Timer MSB
stz $420B ; General DMA enable (bits 0-7)
stz $420C ; Horizontal DMA (HDMA) enable (bits 0-7)
stz $420D ; Access cycle designation (slow/fast rom)
cli ; Enable interrupts
; Set the background color to green.
sep #$20 ; Set the A register to 8-bit.
lda #%10000000 ; Force VBlank by turning off the screen.
sta $2100
lda #%11100000 ; Load the low byte of the green color.
sta $2122
lda #%00000000 ; Load the high byte of the green color.
sta $2122
lda #%00001111 ; End VBlank, setting brightness to 15 (100%).
sta $2100
; Loop forever.
Forever:
jmp Forever
; IRQ vectors
;
handler:
rti
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