Re: Questions about pal clocks

From: Hársfalvi Levente (
Date: 2001-11-22 16:17:25


Jozsef Laszlo wrote:
> Hi folks,
> I have two questions about the clock generation in the C64.
> 1. The source Quartz for the PAL system is 17.73442 Mhz. If I replace
> this
> quartz with an 18.000 MHz one, will it work?
> Theoretically it should but I'm not sure in it.

It probably will, but the video timing / color burst will be slightly
off, thus the picture on the display will look strange / black & white.

> 2. The VIC-II chip needs two input clocks: the color phase clock (this
> is the
> 17.7Mhz I mentioned above), and the DOT clock. The 8701 generates both
> of
> them, the color clock is the same as the source clock, and the dot clock
> is
> the source*2/4.5 rate, which is approx 7.88 Mhz. So more or less the
> color and the
> dot clocks are synchronized. My question is: do they absoultely need
> this sync?

They don't (Marko could probably tell you some interesting parameters
about the first VIC-II equipped devices, with their separate 8Mhz dot
clock source). But if they're not, the picture will look like 'grainy'.


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