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From: toddpw@tybalt.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: IIgs & IWII Power ?'s
Message-ID: <1990Apr7.230632.6213@laguna.ccsf.caltech.edu>
Date: 7 Apr 90 23:06:32 GMT
References: <9004070940.AA18920@apple.com>
Sender: news@laguna.ccsf.caltech.edu
Organization: California Institute of Technology
Lines: 24

skann@gnh-applesauce.cts.com (Steve Kann) writes:

>        I disagree.. A couple of years ago, your assumptions about using the ac
>line as a timer would have been correct, but today, almopst all time sources
>are based on a quartz crystal.

This is more due to the fact that most clocks are now digitally controlled and
can actually use the crystals. There are still quite a few of the older clocks
in use, but even after they are all gone the line frequency will be tightly
regulated because a stable frequency is much easier to 'tune out' of a noise
sensitive circuit -- Broadcast television all over the world uses a frame rate
very close to the local line frequency, to reduce crossover noise from the
power line.

>It is obvious that the GS would be for two
>reasons 1) when the power is off, the clock is run off the battery, not the AC
>line, and 2) Unless I'm wrong, the clock uses the same timer as the CPU.

The clock has its own internal 32768 hz crystal, and it runs independently
of the CPU. Any access of the clock chip must go though a bizarre serial
interface which is handled by a 6522 in Macs and by the VGC in the IIGS.

Todd Whitesel
toddpw @ tybalt.caltech.edu