Posted By
Verona
on 2024-02-25
07:39:20
|  Re: Need help with raster interrupt
I use it this way:
(But I not use ROM at all, so you must modify it to your needs)
irq_start_point:
php
pha
txa
pha
tya
pha
lda $FF09
and #$02
bne raster_irq
jmp notraszter
raster_irq:
sta $FF09
lda $FF1C
and #1
beq not_hi_bit
jmp hi_bit_on
not_hi_bit:
lda $FF0A
and #255
ora #2
sta $FF0A
rrirq_start:
... Here comes what I do when raster IRQ happens.
An example:
lda $FF1D
rrirq_1:
cmp #22//22
bcc first_line_jobs
rrirq_2:
cmp #54
bcc second line jobs
...
jmp title_hi_bit_on
first_line_jobs:
...
second_line_jobs:
....
hi_bit_on:
lda $FF0A
and #255
ora #2
sta $FF0A
notraster:
pla
tay
pla
tax
pla
plp
rti
|
