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From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: The time (my watch has troubles) has come ...
Message-ID: <2572@cbmvax.UUCP>
Date: Wed, 21-Oct-87 19:06:44 EDT
Article-I.D.: cbmvax.2572
Posted: Wed Oct 21 19:06:44 1987
Date-Received: Sat, 24-Oct-87 13:30:21 EDT
References: <16516@amdahl.amdahl.com>
Organization: Commodore Technology, West Chester, PA
Lines: 54

in article <16516@amdahl.amdahl.com>, kim@amdahl.amdahl.com (Kim DeVaughn) says:
> Keywords: I hope there are knobs in there
> 
> [ There ain't no such thing as a free line. ]
> 
> I've been burning-in my B2000, and have noticed that accuracy of both the
> normal internal clock (timer, really) and the battery-backed-up RTC are
> unacceptable.
> 
> Can someone at CATS (Dave, George, Carolyn) please tell me if/where the
> trimmers are so I can get these clocks running right?  I'd prefer not to
> have to go thru the hassle of returning the machine to the dealer for just
> an adjustment.

OK, here goes.  The trimmer for the RTC is relatively easy to get at with just
the box top off.  You'll need a "tweaking tool", which usually looks like a
long piece of plastic with a thin metal tip (for those out there not familiar
with this sort of high-tech equipment....).  The trimmer is located just a 
hair to the south of the Coprocessor slot.  It should be possible to adjust
this to be about as accurate as a digital watch, as the clock chip uses a 
common watch battery.  They're supposed to be adjusted on the production line,
though it's certainly possible that some fall out in shipping and all.  There
will probably be a slight varience in the clock frequency depending on whether
or not the unit's powered on, I don't know how much this varience can amount
to.

As for the internal system clock, that is based on the 60Hz tick from your
line voltage.  Or SHOULD be.  Because in fact, the B2000 can be internally
jumpered to count time off the vertical sync line, just as the A500 does.
This is all controlled by J300, which is (you guessed it) hidden under
the power supply.  It's the jumper just a bit to the North of the Paula
chip, if you do happen to open your machine up and look inside.  These are
supposed to be shipped in the line Tick position, which means the shunt
plug is to the left.  If this is installed properly, the only other thing
that could affect your timing here is lousy line frequency regulation in
your area.

> Though it should not matter, I have a 68010 in the machine (you *don't* have
> any s/w timing loops in there, do you?)

I've got one too, and as far as I know, my clocks stay pretty accurate.

> Why aren't these locked to the line frequency, which has very good long-term
> accuracy, though may suffer from short-term stability?

The OS clock is, or should be, but that only works when the machine is on.  The
RTC can't be, or it would lose its time base if the power went out or you
moved the machine.

> /kim
-- 
Dave Haynie     Commodore-Amiga    Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh
   "The B2000 Guy"              PLINK : D-DAVE H             BIX   : hazy
    "Computers are what happen when you give up sleeping" - Iggy the Cat