[time-nuts] World's most accurate PC clock!

Magnus Danielson cfmd at bredband.net
Sun Jul 3 09:21:33 EDT 2005

From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] World's most accurate PC clock! 
Date: Sun, 03 Jul 2005 10:02:25 +0200
Message-ID: <27043.1120377745 at phk.freebsd.dk>

> In message < at>, "W. D." writes
> :
> >Is there a 'HowTo' for this somewhere?  How many pins are=20
> >connected and to where?  Where do you mount the chip?  Any
> >batteries involved?
> This is a little bit beyond "HOWTO" stuff.
> You need to find a suitable PLL chip.  ICST is a major manufacturer
> of these.  Most of them have anti-DYI pin-spacing though.
> Then you need to locate the Xtal on your motherboard which drives
> the clocks.  Again, a good place to start is to look for a PLL
> chip from ICST.  Usually there is a 14.318MHz xtal right next
> to that, but some botherboards use different frequencies these
> days and generate the 14.318MHz by PLL instead.

Which should be an approximation to 14,31818 MHz I would assume, since that is
2 *5*715909 Hz, but an approximation to that would be quite acceptable
considering it is usually +/- 100 ppm (for real TV uses it should be
+/- 3 ppm). Ever measured what is actually there in PLLed cases? (curiosity)

> You can then either remove the existing xtal and feed your signal
> to the right of the two holes (experiment or read datasheet for
> the on-board PLL chip) or you can try override it while it remains
> on the motherboard by feeding your signal into it.  Overriding
> gives jitter and most modern motherboards don't like that.

One should figure out which pin is the input to the CMOS inverter usually used
in such oscillators. This is where the signal shall be fed in.


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