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From: rsbx@cbmvax.commodore.com (Raymond S. Brand)
Newsgroups: comp.sys.amiga
Subject: Re: Fast clocks...
Keywords: .
Message-ID: <13438@cbmvax.commodore.com>
Date: 26 Jul 90 01:32:56 GMT
References: <4975@uafhp.uark.edu>
Organization: Commodore-Amiga Inc, West Chester, PA
Lines: 45

In article <4975@uafhp.uark.edu>, bbs00068@uafcseg.uucp (Joel Kolstad) writes:
> 
> I recently got a 16MHz 68000 and the did ever popular trick of taking the
> 28MHz system clock, dividing it by two using a flip flop to get 14MHz, and
> feeding it to the 68000.  Well, this works real well, except for the the fact
> the clock gains about 10 seconds every minute!  Note that I'm talking about the
> internal clock of the Amiga -- a setclock opt load restores everything to 
> normal... for awhile!
> 
> Does anybody know how to fix this slight problem?  It's more of an annoyance 
> than anything else, but I'd really like to have my clock read the correct
> time!

A1000s A500s and [AB]2000s use the processor to generate a signal called the
"E-clock". This clocks at 1/10 the cpu clock and is used as the phi(??) clock
to the 8520s. The 8520s use this to clock the countdown counters, and the
timer.device uses the countdown counters to keep track of time.

Normally, the E-clock doesn't change too much, there is a value for NTSC
systems and a different one for PAL system, and they're within 1% of each other.What you've done is changed the system E-clock frequency to twice what it 
should be and confused the timer.device.

Fixes:
	Undo your hack (uh, I didn't think so..... :-)

	Build a divide-by-10 circuit to generate the E-Clock from the OLD
	processor clock.

	Build a divide-by-2 circuit to generate the E-clock from the E pin
	of you speedy processor.

> 
> Thanks in advance...
> 
> 					Joel Kolstad
> 				kolstad@cae.wisc.edu...

						rsbx

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