Re: Mental challenge: the rainbow

[Linards Ticmanis <ticmanis@gmx.de>]

On 02/09/2012 11:00 PM, Marc S. Ressl wrote:

> Another question... on PAL Apple II's, full-screen text is displayed
> in white (as is the case for NTSC, because there is no color carrier).
> But is that also true in mixed mode? In NTSC it is, because the color
> carrier is turned on.

Unlike NTSC Apples, PAL machines use two separate quartz oscillators for
the dot clock and the color clock. This prevents the color fringing in
mixed mode since the letter elements aren't output at a multiple of the
color carrier frequency.

On the downside, the presence of two independent quartzes gets you a
"beat frequency" which changes with the exact tuning of the quartzes (so
it goes up and down with heat etc.), this causes ugly moving moir�
patterns in graphics mode.

-- 
Linards Ticmanis