Re: LZ: Screen Reversing...
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Re: LZ: Screen Reversing...
On Wed, 2 Oct 1996, Frank wrote:
> I want to add screen reversing to my etch a sketch thing... i have the code
> from another program but it is uncommented can someone send me a commented
> version of screen reversing! (pixel on to pixel off and vice versa)
well.. (writing on-line, so prolly not 100% error-free)
; ------ clippityclippityclip ------------------
ld d, 4 ; big loop repeat counter
ld hl, $FC00 ; display mem address into hl
bigloop:
ld b, 0 ; counter for small loop repeat (256)
looppoop:
ld a, (hl) ; a <- byte in (hl)
neg ; a=0-a, so all 1->0 and 0->1
ld (hl), a ; store the byt back
inc hl ; increase the position in display mem
djnz looppoop ; decrease
dec d ; decrease big loop counter (big loop needed, so
; all the 1024 bytes of dispmem will be handled
jnz bigloop ; and if 0 not reached, then jump
; ------ clippityclippityclippyclippy ----------
That oughta do the trick... (not optimized, prolly could a bit, but I
won't bother...)
-P
References: