268 lines
6.2 KiB
Plaintext
268 lines
6.2 KiB
Plaintext
processor 6502
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include "vcs.h"
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include "macro.h"
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include "xmacro.h"
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seg.u Variables
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org $80
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PFPtr word ; pointer to playfield data
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PFIndex byte ; offset into playfield array
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PFCount byte ; lines left in this playfield segment
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Temp byte ; temporary
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YPos byte ; Y position of player sprite
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XPos byte ; X position of player sprite
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SpritePtr word ; pointer to sprite bitmap table
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ColorPtr word ; pointer to sprite color table
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; Temporary slots used during kernel
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Bit2p0 byte
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Colp0 byte
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YP0 byte
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; Height of sprite in scanlines
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SpriteHeight equ 9
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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seg Code
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org $f000
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Start
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CLEAN_START
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; Set up initial pointers and player position
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lda #<PlayfieldData
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sta PFPtr
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lda #>PlayfieldData
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sta PFPtr+1
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lda #<Frame0
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sta SpritePtr
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lda #>Frame0
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sta SpritePtr+1
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lda #<ColorFrame0
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sta ColorPtr
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lda #>ColorFrame0
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sta ColorPtr+1
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lda #242
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sta YPos
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lda #38
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sta XPos
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NextFrame
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VERTICAL_SYNC
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; Set up VBLANK timer
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TIMER_SETUP 37
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lda #$88
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sta COLUBK ; bg color
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lda #$5b
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sta COLUPF ; fg color
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lda #$68
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sta COLUP0 ; player color
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lda #1
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sta CTRLPF ; symmetry
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lda #0
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sta PFIndex ; reset playfield offset
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; Set temporary Y counter and set horizontal position
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lda YPos
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sta YP0 ; yp0 = temporary counter
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lda XPos
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ldx #0
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jsr SetHorizPos
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sta WSYNC
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sta HMOVE ; gotta apply HMOVE
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; Wait for end of VBLANK
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TIMER_WAIT
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sta WSYNC
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lda #0
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sta VBLANK
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; Set up timer (in case of bugs where we don't hit exactly)
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TIMER_SETUP 192
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SLEEP 10 ; to make timing analysis work out
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NewPFSegment
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; Load a new playfield segment.
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; Defined by length and then the 3 PF registers.
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; Length = 0 means stop
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ldy PFIndex ; load index into PF array
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lda (PFPtr),y ; load length of next segment
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beq NoMoreSegs ; == 0, we're done
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sta PFCount ; save for later
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; Preload the PF0/PF1/PF2 registers for after WSYNC
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iny
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lda (PFPtr),y ; load PF0
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tax ; PF0 -> X
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iny
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lda (PFPtr),y ; load PF1
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sta Temp ; PF1 -> Temp
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iny
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lda (PFPtr),y ; load PF2
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iny
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sty PFIndex
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tay ; PF2 -> Y
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; WSYNC, then store playfield registers
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; and also the player 0 bitmap for line 2
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sta WSYNC
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stx PF0 ; X -> PF0
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lda Temp
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sta PF1 ; Temp -> PF1
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lda Bit2p0 ; player bitmap
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sta GRP0 ; Bit2p0 -> GRP0
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sty PF2 ; Y -> PF2
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; Load playfield length, we'll keep this in X for the loop
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ldx PFCount
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KernelLoop
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; Does this scanline intersect our sprite?
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lda #SpriteHeight ; height in 2xlines
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isb YP0 ; INC yp0, then SBC yp0
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bcs .DoDraw ; inside bounds?
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lda #0 ; no, load the padding offset (0)
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.DoDraw
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; Load color value for both lines, store in temp var
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pha ; save original offset
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tay ; -> Y
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lda (ColorPtr),y ; color for both lines
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sta Colp0 ; -> colp0
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; Load bitmap value for each line, store in temp var
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pla
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asl ; offset * 2
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tay ; -> Y
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lda (SpritePtr),y ; bitmap for first line
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sta Bit2p0 ; -> bit2p0
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iny
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lda (SpritePtr),y ; bitmap for second line
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; WSYNC and store values for first line
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sta WSYNC
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sta GRP0 ; Bit1p0 -> GRP0
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lda Colp0
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sta COLUP0 ; Colp0 -> COLUP0
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dex
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beq NewPFSegment ; end of this playfield segment?
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; WSYNC and store values for second line
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sta WSYNC
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lda Bit2p0
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sta GRP0 ; Bit2p0 -> GRP0
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jmp KernelLoop
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NoMoreSegs
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; Change colors so we can see when our loop ends
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lda #0
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sta COLUBK
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; Wait for timer to finish
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TIMER_WAIT
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; Set up overscan timer
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TIMER_SETUP 30
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lda #2
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sta VBLANK
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jsr MoveJoystick
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TIMER_WAIT
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jmp NextFrame
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SetHorizPos
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sta WSYNC ; start a new line
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bit 0 ; waste 3 cycles
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sec ; set carry flag
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DivideLoop
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sbc #15 ; subtract 15
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bcs DivideLoop ; branch until negative
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eor #7 ; calculate fine offset
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asl
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asl
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asl
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asl
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sta RESP0,x ; fix coarse position
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sta HMP0,x ; set fine offset
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rts ; return to caller
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; Read joystick movement and apply to object 0
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MoveJoystick
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; Move vertically
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; (up and down are actually reversed since ypos starts at bottom)
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ldx YPos
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lda #%00100000 ;Up?
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bit SWCHA
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bne SkipMoveUp
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cpx #175
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bcc SkipMoveUp
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dex
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SkipMoveUp
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lda #%00010000 ;Down?
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bit SWCHA
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bne SkipMoveDown
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cpx #254
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bcs SkipMoveDown
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inx
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SkipMoveDown
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stx YPos
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; Move horizontally
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ldx XPos
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lda #%01000000 ;Left?
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bit SWCHA
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bne SkipMoveLeft
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cpx #1
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bcc SkipMoveLeft
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dex
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SkipMoveLeft
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lda #%10000000 ;Right?
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bit SWCHA
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bne SkipMoveRight
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cpx #153
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bcs SkipMoveRight
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inx
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SkipMoveRight
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stx XPos
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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align $100; make sure data doesn't cross page boundary
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PlayfieldData
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.byte 4,#%00000000,#%11111110,#%00110000
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.byte 8,#%11000000,#%00000001,#%01001000
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.byte 15,#%00100000,#%01111110,#%10000100
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.byte 20,#%00010000,#%10000000,#%00010000
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.byte 20,#%00010000,#%01100011,#%10011000
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.byte 15,#%00100000,#%00001100,#%01000100
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.byte 8,#%11000000,#%00110000,#%00110010
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.byte 4,#%00000000,#%11000000,#%00001100
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.byte 0
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; Bitmap data "standing" position
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Frame0
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.byte #0
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.byte #0
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.byte #%01101100;$F6
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.byte #%00101000;$86
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.byte #%00101000;$86
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.byte #%00111000;$86
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.byte #%10111010;$C2
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.byte #%10111010;$C2
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.byte #%01111100;$C2
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.byte #%00111000;$C2
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.byte #%00111000;$16
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.byte #%01000100;$16
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.byte #%01111100;$16
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.byte #%01111100;$18
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.byte #%01010100;$18
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.byte #%01111100;$18
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.byte #%11111110;$F2
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.byte #%00111000;$F4
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; Color data for each line of sprite
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ColorFrame0
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.byte #$FF;
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.byte #$86;
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.byte #$86;
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.byte #$C2;
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.byte #$C2;
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.byte #$16;
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.byte #$16;
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.byte #$18;
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.byte #$F4;
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; Epilogue
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org $fffc
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.word Start
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.word Start
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