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; "Vertical Auto Scroll" generator

; By Jimmy52905

; Fixed by yoshicookiezeus

; Uses first extra bit: YES

; If extra bit is set, the generator makes the screen scroll downwards instead of upwards

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STOP		dcb $10		; screen number the sprite should stop at when scrolling downwards



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	dcb "INIT"

	dcb "MAIN"                                    

	PHB                     

	PHK                     

	PLB                     

	JSR Main 

	PLB                     

	RTL      



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; Main sprite code

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Main:

	LDA $9D		;\ If sprites are locked...

	BNE Return	;/ Go to "Return".



	LDA $13		;\

	LSR A		; |

	BCC Return	;/ Only run code every other frame.



	STZ $1412	; Disable Vertical Scroll so that the code can run properly.



	LDA $18B9	;\ If the first extra bit is set...

	AND #$40	; |

	BNE Down	;/ Go to "Down".



	STZ $55		; Make sure that new tiles are uploaded from the top of the screen



	LDA $1464	;\

	ORA $1465	; |If the screen position is at the top of the level...

	BEQ Return	;/ Go to "Return".



	REP #$20	; 16-bit (accumulator).

	DEC $1464	; Make the screen scroll upwards automatically.

	SEP #$20	; 8-bit (accumulator).



Return:

	RTS		;Return from Subroutine.



Down:

	LDA #$02	;\ Make sure that new tiles are uploaded from the bottom of the screen

	STA $55		;/



	LDA $1465	;\ If the screen position is at screen 10 (last screen of a vertical layer 2 level)...

	CMP STOP	; |

	BEQ Return	;/ Go to "Return".



	REP #$20	; 16-bit (accumulator).

	INC $1464	; Make the screen scroll downwards automatically.

	SEP #$20	; 8-bit (accumulator).



	RTS		;Return from Subroutine.

#0 w200 t150

#0 @16 q7f v100 y10

o5

c4v95c+4v90d4v85d+4v80e4v75f4v70f+4v65g4v60g+4v55a4v50a+4v45b4

#1 @16 q7f v155 y10

o4

c4v150c+4v145d4v140d+4v135e4v130f4v125f+4v120g4v115g+4v110a4v105a+4v100b4

#2 @16 q7f v100 y10

o4

c4v105c+4v110d4v115d+4v120e4v125f4v130f+4v135g4v140g+4v145a4v150a+4v155b4

#3 @16 q7f v45 y10

o5

c4v50c+4v55d4v60d+4v65e4v70f4v75f+4v80g4v85g+4v90a4v95a+4v100b4