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Old 14 October 2019, 11:40   #11
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Join Date: Sep 2018
Location: Germany
Posts: 33
Originally Posted by ross View Post
Hi dodke, just curious..
Why do you want to see a one more scanline?

(actually you can write to VHPOSW to increase/decrease lines, but so you also change video frequency )

[if I'm not wrong Dyna Blaster do this to fake a quasi-NTSC mode on PAL Amiga]
IIRC Dyna Blasters writes #$0000 for 50 Hz Pal to BeamCon0 ($DFF1DC) Register
and #$0020 for 60 Hz (NTSC) to BeamCon0 Register and you could change it by pressing space (or some other key?) in the menu (???).

AFAIK this is only possible for all ECS+ Agnus Amigas e.g. A600, A500+, A1200 and also on some A500 with Kickstart 1.3. (those Agnus where you can address 1 MB Chip Ram, even when it is located at $C00000 for CPU and therefore not usable for the OS).

Originally Posted by ross View Post
of course.

Has anyone ever tried to change the horizontal frequency?

EDIT: now that comes to mind, and if I remember correctly, there is a demo that does it to make an effect with the copper!
(only a little change to x value to shift initial copper position)
But to not lost sync every other line reset the position.
Yes, I've changed horizontal frequencies. If you change horizontal or vertical frequencies (other than vertical frequencies between 50 Hz to 60 Hz and horizontal 15,XX kHz) you need a multisync monitor (such as Amiga 1764, Amiga 1438, Mitsubishi EUM1491a, etc.). On other monitors it might be possible to slightly change the frequencies but not too much. I've tested this back in the days on my Phillips 88XX monitor. The monitor makes strange sounds if you change it too much

I've changed the frequencies in order to use all sprites on a resolution similar to productivty mode resolution (on AGA). The systems productivity mode is not appropriate for games with sprites at least if you want use all 8 sprites. Our first approach was to use a resolution with 640x512 Pixel x 64 Colors (or 640 x 256 x 64 Colors for non multisync monitors). We changed it later to 640x260 x 256 colors (so that we have to take no adjustments with 2 different resolutions) but we never finished the game and that's another story.

Last edited by Chrille; 14 October 2019 at 12:06.
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