Re: Dating a C-64 board

From: Marko Mäkelä (
Date: 1999-04-18 16:23:34

On Sun, 18 Apr 1999, Nicolas Welte wrote:

> The early 6567 chips also had a different timing that looks like it was
> made for exactly 1MHz system clock.

Yes, and the VIC-10 a.k.a. UltiMax actually has two crystals: 8 MHz for
dotclock and 14318181 Hz for color clock.  All 8-bit Commodores I have
seen contain only the color clock crystal, and the dot clock and bus clock
are derived from this crystal.  The factors are as follows:

	VIC-20		C64/C128
PAL	17734472/16	17734472/18
NTSC	14318181/14	14318181/14

> This is also the clock frequency of the Ultimax computer which uses a
> 6566 VIC-II chip.

Oh, there you said it. :-)

> It's a pity that you don't have your original C64 anymore. There's
> always the search for early chips to explore funny bugs. I think Andreas
> Boose wanted to know once if the reset bit, that is disabled in all
> known VIC-II chips is perhaps active in very early versions. Perhaps you
> could try it on your machine?

Funny that you had the same thought as me.

Also, I forgot to suggest in my previous message that maybe someone who
has built an adapter for reading the contents of 82S100 PLAs could read
out the truth table from the early PLA.  I don't think that there will be
any differences; I'm only suggesting this just in case.


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