Re: strange c64 board

From: Richard Atkinson (
Date: 2000-02-07 15:53:27

On Mon, 7 Feb 2000, Marko Mäkelä wrote:

> Also interesting is the place for a crystal oscillator next to the 6569
> labelled "XT".  Could that be for the dot clock (if one would like to
> replace the colourclock-based dot clock with an exact 8 MHz source, like
> the UltiMax does)?

Very interesting... I must admit I'd never noticed that on any of my
boards, but if I could go back home and check I would.

You can certainly get oscillator modules in a 14 pin DIL package spacing
(ie. 0.3inch by 0.6inch). That doesn't explain why a board would have
space for *both* a seperate oscillator module and the PLL circuit required
to generate 8MHz from 14.31818MHz or 17.73447MHz. One thing's for sure -
the composite display of a C64 with 8MHz dot clock and 14MHz or 17MHz
colour clock looks *terrible*. S-Video looks okay, and if you can find an
NTSC machine with one of these boards, a 6567R5 or 6567R56A and an 8 pin
DIN video connector it might make an interesting exercise to run a C64
permanently in the original designer-intended 8MHz/14MHz configuration.
Unfortunately this won't do anything for the demo compatibility problems
of 6567R56A VIC-II chips.


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