1  *TEST CASE FOR MODIFYING DLIST 8 WAY SCROLLING
                2  	ORG	$4000
                3  SCREEN	EQU	$5000
                4  NDLIST	EQU	$4900
4000 707070     5  DLIST	DB	$70,$70,$70,$47,$00,$50,$47,$80,$50
4009 470051     6  	DB	$47,$00,$51,$47,$80,$51,$47,$00,$52
4012 478052     7  	DB	$47,$80,$52,$47,$00,$53,$47,$80,$53
401B 470054     8  	DB	$47,$00,$54,$47,$80,$54,$47,$00,$48
4024 478048     9  	DB	$47,$80,$48,$41,$00,$49
               10  *VARIABLES
402A 00        11  XS	DS	1
402B 00        12  YS	DS	1
402C 00        13  SCLO	DS	1
402D 00        14  SCHI	DS	1
402E 00        15  TEMPH	DS	1
               16  *MAIN PROGRAM
402F A905      17  START	LDA	#$05		;TEST VALUES - INPUT YOUR OWN XS,YS
4031 8D2A40    18  	STA	XS
4034 A903      19  	LDA	#$03
4036 8D2B40    20  	STA	YS
               21  *MOVE DLIST
4039 A200      22  	LDX	#$00
403B BD0040    23  DLOOP	LDA	DLIST,X
403E 9D0049    24  	STA	NDLIST,X
4041 E8        25  	INX
4042 E02A      26  	CPX	#$2A		;44 ELEMENTS
4044 D0F5      27  	BNE	DLOOP
4046 204C40    28  	JSR	MODLIST		;MODIFY DISPLAY LIST
4049 4C4940    29  FOREVER	JMP	FOREVER		;ENDLESS LOOP
               30  *
               31  *SUBROUTINE TO MODIFY DISPLAY LIST FOR 8 WAY SCROLLING
               32  * - 128 (#$80) BYTES WIDE
               33  *INPUT ROUGH SCROLL COORDINATES XS,YS
404C A900      34  MODLIST	LDA	#>SCREEN
404E 8D2C40    35  	STA	SCLO
4051 A950      36  	LDA	#<SCREEN
4053 8D2D40    37  	STA	SCHI
4056 AD2B40    38  	LDA	YS
4059 4A        39  	LSR			;DIVIDE/2
405A 8D2E40    40  	STA 	TEMPH
405D 9005      41  	BCC	AA1		;SKIP IF EVEN
405F A980      42  	LDA	#$80		;ODD THEN LO BYTE ADDRESS BEGINS WITH #$80
4061 8D2C40    43  	STA	SCLO
4064 18        44  AA1	CLC
4065 AD2D40    45  	LDA	SCHI
4068 6D2E40    46  	ADC	TEMPH
406B 8D2D40    47  	STA	SCHI		;NEW HI BYTE
406E 8D0549    48  	STA	NDLIST+5
4071 18        49  	CLC
4072 AD2C40    50  	LDA	SCLO
4075 6D2A40    51  	ADC	XS
4078 8D2C40    52  	STA	SCLO		;NEW LO BYTE
407B 8D0449    53  	STA	NDLIST+4
407E A000      54  	LDY	#$00
4080 18        55  AA2	CLC
4081 AD2C40    56  	LDA	SCLO		;ADD #$80 TO EACH MODE LINE ADDRESS
4084 6980      57  	ADC	#$80		;STARTING WITH SECOND LINE
4086 8D2C40    58  	STA	SCLO
4089 990749    59  	STA	NDLIST+7,Y
408C AD2D40    60  	LDA	SCHI
408F 6900      61  	ADC	#$00
4091 8D2D40    62  	STA	SCHI
4094 990849    63  	STA	NDLIST+8,Y
4097 C8        64  	INY			;INCREMENT BY 3 TO REACH NEXT ADDRESS PAIR
4098 C8        65  	INY
4099 C8        66  	INY
409A C021      67  	CPY	#$21		;(12ROWS*3)-3
409C 90E2      68  	BL	AA2		;DONE?
409E 60        69  	RTS