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Posted By

TLC
on 2006-09-14
14:43:53
 Re: +4 biggest screen resolution

Bionic: I don't feel like in need of defending myself (what I wrote was not aimed at you primarily in the first place; it was rather triggered by something that I read in your post. For not making this clear, I'm sorry; for what I really meant with that post, I'm not.)

degauss: true interlace is a mode all TVs normally operate in. TVs, actually, show a screen of 625 rows at a rate of 25Hz. They don't simply draw 625 rows one after the other, the refresh is done in two turns, which helps to avoid flashing. To simplify things, two frames of "312.5" rows are drawn, one after the other, each shifted by one screen row from each other in the vertical direction.

The Plus/4 generates 312 rows at 50Hz; to be able to show this on a TV-display, the TED would keep on showing a frame of always the same polarity. (This is a kind of "semi-standard" way of generating the screen; Commodore and the other manufacturers at the time would all do this ). What you can see on the Plus/4's screen is effectively half the vertical resolution a TV can do. Instead, you have twice the framerate you have in the TVs regular operation mode, which results in a more useable screen for the computer, since the screen doesn't flash at the sharp edges of the screen content like it would do in interlace mode.

Whilst most other computers are stuck in 312 rows at 50Hz (or 212 rows at 60Hz for ntsc) mode, on the Plus/4 it might be possible to overcome this by some kind of ff1e magic (as frame polarity is determined by the vertical retrace part of the screen.)

As Bionic said before, it's unclear as of now whether it's possible to do real, full-featured interlace mode on the Plus/4 (problems arise around the PAL color encoding), but he managed to do it in monochrome, even together with the horizontal resolution increasement trick.



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