[Coco] ASM Coders - Round two!
dave at ebonhost.com
Tue Aug 29 08:56:25 EDT 2006
Thanks to everyone who helped last time - here's round two!
The code as it stands can be found below
If you compile and run it as-is, it'll clear half the screen
but! when you simply uncomment the lines:
It clears half the screen, and draws some colored garbage 3/4 of the way
down the screen
I can't understand why it's doing this
am I trying to allocate memory that I'm not allowed to touch? Am I
swapping *out* some memory that's otherwise being used?
Im very lost and very confused!
Any help would be great!
-- code follows --
START lda #%01001100 Coco3, MMU on, DRAM constant, standard SCS 16K
internal 16K external ROM
lda #%10000000 graphics
lda #%00111110 200 lines of 320H by 16 colors
clr $FF9C clear vertical scroll
ldd #$C000 screen start divided by 8
std $FF9D vertical offset
clr $FF9F clear horizontal scroll
lda #$30 first block of graphics screen at $60000
sta $FFA1 mapped to $2000
CLRSCRN ldy #HSCLEN
CLRLOOP CLR ,X+
ENDLOOP JMP ENDLOOP
HRESSCRN EQU $2000
HSCLEN EQU $3E80
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