dos33fsprogs/demos/second/part00_boot/scroll.s
2023-10-06 00:21:16 -04:00

59 lines
725 B
ArmAsm

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scroll_screen:
ldx #8
stx INL
ldx #0
stx OUTL
scroll_yloop:
ldx INL
lda hposn_low,X
sta xloop_smc1+1
lda hposn_high,X
sta xloop_smc1+2
ldx OUTL
lda hposn_low,X
sta xloop_smc2+1
lda hposn_high,X
sta xloop_smc2+2
ldy #39
scroll_xloop:
xloop_smc1:
lda $2000,Y
xloop_smc2:
sta $2000,Y
dey
bpl scroll_xloop
inc INL
inc OUTL
lda INL
cmp #192
bne scroll_yloop
; blank bottom line
lda #$00
ldy #39
scroll_hline_xloop:
sta $23D0,Y
sta $27D0,Y
sta $2BD0,Y
sta $2FD0,Y
sta $33D0,Y
sta $37D0,Y
sta $3BD0,Y
sta $3FD0,Y
dey
bpl scroll_hline_xloop
rts