256x256 pixel tweaked video mode

Hi,
my first post.

PC-engine hardware permits to switch color clock between 5Mhz and 7Mhz that means it can generate 256 or 320 pixels for each scanline.

I was wondering if something similar can be done on Amiga, in that way more stuff can be moved on the screen, with lower resolution off course.

I don't think ECS or AGA Amigas could change the color clock anyway they can tweak Vsynch and Hsynch timings.

How this can be used to obtain a 256x256 video mode on a regular TV? Maybe a multi-synch monitor is needed? Or is it just impossible?

Thanks,
Ovale

[TheDarkCoder]

Hi!

sei italiano?

You can simply use standard PAL sync but define a display window 256 pixel large. This require less BPL DMA fetches, hence more DMA slots are available for other stuff.

With a multi-sync monitor you can certainly play with non standard frequencies and find a tradeoff that best suits your needs.
Anyway to get 256 horizontal lines, i think you need frequencies similar to the standard PAL

TDC

Originally Posted by ovale

Hi,
my first post.

PC-engine hardware permits to switch color clock between 5Mhz and 7Mhz that means it can generate 256 or 320 pixels for each scanline.

I was wondering if something similar can be done on Amiga, in that way more stuff can be moved on the screen, with lower resolution off course.

I don't think ECS or AGA Amigas could change the color clock anyway they can tweak Vsynch and Hsynch timings.

How this can be used to obtain a 256x256 video mode on a regular TV? Maybe a multi-synch monitor is needed? Or is it just impossible?

Thanks,
Ovale

[Ratte]

HighGFX offers a 256x192 mode.
(LowRes DoubleScan)

Hi TheDarkCoder,
yes I'm Italian, Milan. Are you Italian?

About, your answer. I would like to have a full screen 256xNNN video mode.
I think that just cut the display window is not enough. I'm wrong?

Thanks

Ratte,
thanks for the hint. Just recently I re-started to have interest on Amiga (I stopped around 1994) so I'm out of synch.

I know that 22Khz (<31Khz) video modes are not viewable on modern multisynch monitors. It's still true?

Do you know if MonitorTVs (LCD TV with VGA/DVI port) support modes with <31Khz ?
At least in theory, they should go down up to 15Khz.

Thanks

[Cammy]

I'm guessing you want to be able to show a 256x256 image on a PAL screen, but have it completely fill the screen, as traditionally a 320x256 screen would? I would love to know if the Amiga has such a resolution, as the Sega Master System, Mega Drive and Super Nintendo all have a mode where they stretch a lower res image to fill the screen. That's why so many SNES games looked like they had larger sprites and no black borders, not because they had more pixels, but because the screen res was lower than the Amiga but it was stretched to fit the screen.

[Toni Wilen]

You can create 256x256 resolution but it won't be TV compatible (and most likely non-compatible with standard PC monitors too..)

Amiga's pixel clock is not programmable, only way to create custom resolutions is to change start and end position of hsync and vsync (which of course change refresh rates)

[TheDarkCoder]

Originally Posted by ovale

Hi TheDarkCoder,
yes I'm Italian, Milan. Are you Italian?

About, your answer. I would like to have a full screen 256xNNN video mode.
I think that just cut the display window is not enough. I'm wrong?

Thanks

ciao

sì, sono abruzzese!

I didn't understand you wanted a full-screen display. You are right, cutting the display window is not enough (although in this way you get more free DMA slots). Then the right answer to your question is the one given by Toni Wilen above. You are forced to a non-standard video frequecy.