The weird thing then is that the article claims the effect can be triggered by border changes in the invisible part of the screen. Though I guess the screen he had probably just had a large amount of the tube hidden from the eye. The idea that border colour changes can somehow insert an extra 64us delay and an hsync does seem basically ridiculous but I thought it better to ask.
At least per the spec, TVs don't have any logic for alternate frames. Whether the next is even or odd depends on whether the long sync ends in the middle of a scan line or at the end. So computers like the Sam, with a rigid sync schedule, explicitly output a non-interlaced display only. However, modern TVs - even some late model CRTs with digital sync generators - often emulate that incorrectly, and emulator authors tend to be quite parochial and superstitious about this stuff for some reason, hence e.g. the mostly invented black scan lines a lot of them like to insert. On 2 Feb 2012, at 10:24, Geoff Winkless <[email protected]> wrote: > On 1 February 2012 20:42, Simon Owen <[email protected]> wrote: >> On 01/02/2012 20:07, Thomas Harte wrote: >>> I notice that whatever effect it thinks it is relying on doesn't work >>> in Sim Coupe. >> >> It's certainly nothing that's implemented at the moment, but if it's >> shown to be a real effect (like border pixels), it should go in. Though >> it does feel like it could be specific to CRTs, and more likely those >> that suffer from distortion due to intensity differences? > > I know the TV I first used would exhibit something similar. I wouldn't > have thought you could ever rely on it though. Certainly the 8833 I > ended up with wouldn't do it. > >> I remember there being some sample interlaced SAM pictures, which may >> have relied on the effect to give the necessary vertical shift to help >> with colour blending. > > I thought that was just about the fact that the TV would display > alternate lines each 50Hz - so you could switch screens between two > and effectively double your Y resolution, the problem being that you > could never tell which would be the "top" and which would be the > "bottom". > > If you're thinking of playing with stuff like that in SimCoupé, how > about adding in a screen start address OUT mod? I'd love to see what > could have been done with just a small change to the ASIC design :) > > Geoff
