Posted By
Litwr
on 2022-02-11
13:03:58
|  Re: Is there such a thing as an interlaced picture for the +4?
Let me present a small program that shows the PAL color inversion effect. It shows also that this effect is quite easy to get.
*=$2000
lda #$28
sta $ff19
l1 lda $ff1d
cmp #$40
bne l1
inc $ff1d
l2 lda $ff1d
cmp #$50
bne l2
dec $ff1d
bne l1
BTW there is another utility to play with inverted colors - http://litwr2.atspace.eu/plus4.html?item=16
@mad Thanks for the link. I checked the Istavan's interrupt routine again. It seems that it does something that could turn PAL interlace on but it does this not the same way as it is documented on the PAL video timing specification site. The Istvan's routine does all $ff1e manipulation in line 1 and this is difficult to match with information on the site. Moreover the routine is the same for odd and even frames and it doesn't add/remove any delay. So I doubt very much about the routine ability to produce a true interlace picture. However IMHO it may be real to program the TED to generate the standard PAL interlace signal: for odd frames, we must push the TED to skip one short sync at 311, then set the line number to 1 and then again skip one short sync... IMHO there might be other variants to tern interlace on - we need more information.
It would be great if IstvanV could join our discussion. IMHO he is the best PAL signal expert among us. He can also completely clarify details about his great picture converter.
@Charles It would be very interesting to get something like this Amiga 500 screenshot. Nobody doubts that there are more than 400 raster lines.
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