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From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: Problems with the Real Time Clock on my Amiga 2000
Message-ID: <2699@cbmvax.UUCP>
Date: Sat, 7-Nov-87 02:30:56 EST
Article-I.D.: cbmvax.2699
Posted: Sat Nov  7 02:30:56 1987
Date-Received: Mon, 9-Nov-87 04:56:06 EST
References: <17259@amdahl.amdahl.com> <552@esunix.UUCP> <21572@ucbvax.BERKELEY.EDU>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 44

In article <21572@ucbvax.BERKELEY.EDU> bryce@hoser.berkeley.edu (Bryce Nesbitt) writes:
> In article <552@esunix.UUCP> blgardne@esunix.UUCP (Blaine Gardner) writes:
> >in article <17259@amdahl.amdahl.com>, kim@amdahl.amdahl.com (Kim DeVaughn) says:
> > 
> >< It's easy to fix though ... there is a small trimmer capacitor just about
> >< directly to the front of the 86-pin coprocessor slot, very near to the
> >< Oki clock/calendar chip, that you can adjust.  On my machine, it was a
> >< bright yellow color.
> >
> >There has GOT to be a better way! George, Dave, anybody, if I've got an
> >oscilloscope (and an A2000 of course :-) where do I look, and for what
> >signal?
> 
> Anybody here:
> 
> Pin 1 of the OKI MSM6242B can be used for calibration.  Hook a scope
> to it (better yet, a frequency counter).
> You will probably see something close to:
> 
> 1/64th second > 1 second > 1 minute > 1 hour > -or-
> something strange (in the neighborhood)
> 
> It will probably be near 1/64th.  Adjust until it is exact.  (Beware
> that temperature affects crystals).
> If it is *not* at 1/64th of a second, register $E needs to be set
> to zero.  This falls in the category of "magic" unless you have
> the docs for the chip or perhaphs the A500/A2000 tech. ref.

Unless you have access to an accurate frequency counter, this menthod isn't
going to be any better than the twiddle until it seems about right method.
Think about error percentages, scope resolution and seconds/day...

If you do have access to good test equipment, then set up test mode much
as Bryce describes, then use a frequency counter in "period" mode to get
that 64 Hz, or 1 Hz test signal just on.

Perhaps someone can come up with some clever trick, whereby you jumper the
test pin on the clock chip over to the parallel port, then via software
compare the battery clock frequency to the line frequency?

-- 
George Robbins - now working for,	uucp: {ihnp4|rutgers|allegra}!cbmvax!grr
but no way officially representing	arpa: out to lunch...
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)