Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!rsbx
From: rsbx@cbmvax.commodore.com (Raymond S. Brand)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Phi-2 Frequency on the CIA-B Chip
Message-ID: <10714@cbmvax.commodore.com>
Date: 9 Apr 90 14:50:55 GMT
References: <10713@netcom.UUCP>
Organization: Commodore, West Chester, PA
Lines: 23

In article <10713@netcom.UUCP>, mcmahan@netcom.UUCP (Dave Mc Mahan) writes:
> I have written a short test program that measures the frequency of the Phi-2
> clock signal on the CIA-B chip.  With repeated measurements over varying
> periods of time, I keep finding the clock frequency is about 713 KHz.  Is this
> correct?  I would have guessed that it is either the system clock (7.14 MHz)
> or the colorburst frequency.  Are my math calculations wrong?  If it IS
> 713 KHz, where is this generated from?
> 
>   -dave

On an NTSC machine the Phi-2 clock (E-Clock) will be at 715909hz and on a PAL
machine it will be 709379hz. On 68000 based motherboards this signal comes
from the E pin of the 68000, which is the processor clock divided by 10. BTW,
the CIAs may be clocked at different rates on future machines.

						rsbx

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