[Coco] 384 or 450 scanlines ?

[Nick Marentes]

Arthur Flexser <flexser at ...> writes:

> 
> I guess what's puzzling me is this:  as I now understand it, every
> frame is ordinarily repeated twice in succession identically, with the
> second repetition landing smack on top of the first, with a frame
> occurring every 60th of a second and using only every other scan line.
>  Wouldn't it have looked better if the second repetition was one scan
> line offset from the first instead of on top of it?  Would the 6947Y
> VDG accomplish that?


Yes. That has me confused.

If it is the same frame being repeated directly over the last as in
progressive video mode and if the monitor is still interlacing the fields,
the displayed image should have no black intermediate scanlines, in other
words, it's scandoubling to create a standard 525 lines display from the 262.

This is clearly not the case so the shift in vertical offset between the 2
interlaced fields must be dependant on the video signal coming in and it can
switch between interlaced and progressive mode.

Nick