RE: Aw: My ColourPET Project

From: Martin Hoffmann-Vetter <>
Date: Fri, 12 Apr 2013 20:04:12 +0200
Message-ID: <004001ce37a8$23b040f0$>
Hello Steve,

> I think most computer monitors have a tolerance to slightly varying
> frequencies so I'm not so concerned about getting exact timing.

That's true. But if you and the monitor use the tolerance in different
directions ... ;-)

> Of course I can make an edit rom with values for PAL timing but it
> would be nice to have them verified with real hardware.

At this time i'm to busy to test it.

> What if any other side effects would there be in changing the main
> crystal to 16.128?

The CPU is running less than 1 percent faster! All other timings based on
Phi2 (VIA timer) are changed, too.

> Would the pet run at 18 MHz (like the CBM-II machines)?

No, the CBM-II machines divied the clock by 9. The width of characters are 9
pixel! But the CPU runs with 2 MHz, so the charcter clock of the CRTC is 2
MHz (instead 1 MHz), too. So the horizontal frequency is 15,748 kHz, very
near to the real 15,750 kHz. So it's a normal 18 MHz crystal used.


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Received on 2013-04-12 19:00:03

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