Re: IIgs Double HIRES

[Daniel Kruszyna <dan@krue.net>]

Geoff Body <gbody4@bigpond.com> wrote:
> To me the patent US4786893 appears to relate to possible IIGS video
> conversion from NTSC bit stream to RGB output and may help.

Thanks, Geoff, this is it!

I'll have to study it more tomorrow, but the gist is that there is a 4 bit
sliding window with some extra circuitry to check when the 4 bit pattern
changes. The input to the sliding window is compared to the oldest output bit
-- this makes a total of 5 consecutive bits considered, which is consistent
with my observations.

When a change is detected, the current color value is frozen until the new
value in the sliding window stabilizes -- also consistent with my observations.

-- Daniel