6510 scroller

scroller.asm

BasicUpstart2(start)

* = $1000
start:	
	sei
	lda #$7f
	sta $dc0d
	sta $dd0d
	lda #$01
	sta $d01a
	lda $d011
	and #$7f
	sta $d011
	lda #$c0
	sta $d012
	lda #$00
	sta $d020
	sta $d021
	lda #<irq
	sta $0314                       
	lda #>irq
	sta $0315
	jsr clearscreen 
	cli
	jmp *

irq:
	jsr scroller

	dec $d019
	jmp $ea81

clearscreen:
	ldx #$00
	ldy #$01
clp:
	lda #$20
	sta $0400,x
	sta $0500,x
	sta $0600,x
	sta $0700,x
	tya
	sta $d800,x
	sta $d900,x
	sta $da00,x
	sta $db00,x
	tay
	inx
	bne clp
	rts

scroller:
	dec $d016
	lda $d016
	and #$07
	sta $d016
	cmp #$07
	beq newchar
	rts

newchar:
	ldx scrollpos
	lda scrolltext,x
	sta $0427	
	ldx #$00
ls:	
	lda $0401,x
	sta $0400,x
	inx
	cpx #$28
	bne ls
	inc scrollpos
	rts

scrollpos:
.byte $00

scrolltext:
.text " well this is just a scrolltext that has to be written. it was quite some time since last time if i remember correctly...  "