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Post by Pyrofer on Aug 20, 2019 8:13:29 GMT
My issue with a full frame converter is it would be fixed at 1024 pixels wide.
Any screen mode that changes the total pixel width won't work. If it jiggles the width back and forth along the image and averages 1024 per line, you might still get a picture, but if its just 1 pixel off total, the image will not be in sync.
So I guess I still need a line doubler fallback mode to help deal with odd outputs on the VDC.
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Post by mirkosoft on Aug 20, 2019 8:23:30 GMT
My opinion is bit other. My converter works up to 1280x768 pixels. It has plus and minus too. 1280 is the best if you can reach in width. But 768 is not enough - reached VDC limit is 800H and 800V. Will be possible to extend it to 1280x800?
Miro
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Post by Pyrofer on Aug 20, 2019 9:38:52 GMT
"Standard" output from the VDC is 640 visible pixels, 800 active pixel area (borders included) and total 1024 pixels per line (sync/porch included).
My converter has to sample those pixels. So I match the VDC 16mhz dotclock and sample 1024 pixels per line. That gives me a perfect digical copy of the image.
In order to deal with modes where the width varies there are ONLY two options. 1) count the pixels and dynamically adjust the output width 2) sample only 1024 pixels no matter what is shown so you lose the perfect 1:1 capture
These are actually both complex things to do, option 1 requires some complex logic boyond the chips I currently use. Option 2 requires dropping the full frame decode and resyncing on every hsync pulse. Option 2 can be added into the full frame converter, so you should still be able to show most crazy modes but at the expense of clarity. option 1 will require a complete redesign and make the whole thing cost a lot more again, for a very very small use case.
My current thinking is that for the amount those odd modes are used there is no point making an even bigger adaptive circuit and I will try to squeeze option 2 in. That way you can see the picture but there will be some pixel shifting. It think most mode should fit inside the 1024 pixels I capture anyway, so it won't be the end of the world.
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Post by mirkosoft on Aug 20, 2019 9:51:29 GMT
If is possible to use crazy modes, then option 2 is the best.
Miro
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Post by tokra on Aug 20, 2019 15:33:19 GMT
Well, even the monitors of the past could not display all modes. For example most 1901s cannot display 400 vertcial lines (800 interlace) and cannot be adjusted for horizontal width, which means about 720 pixels is the visible maximum horizontally. The 1084 cannot display much more than 300 vertical lines (600 interlace) but can go wider horiztonally and display 800x600.
And then the crazy-modes of VGA-mode-mania only work on 31.5kHz-monitors.
So it will be near-impossible to build a device that can display every theoretical mode.
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Post by mirkosoft on Aug 20, 2019 15:39:03 GMT
Yes, Torsten. But experiments are welcome - even you - in my eyes best VDC graphician - did lot of work with crazy modes... In old thread about VDC overload were tests of 128x25 text mode - it can be nice to get it work with scandoubler... :)
Miro
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