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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro
Subject: 74S124 as xtal osc
Message-ID: <4023@utzoo.UUCP>
Date: Tue, 3-Jul-84 19:10:20 EDT
Article-I.D.: utzoo.4023
Posted: Tue Jul  3 19:10:20 1984
Date-Received: Tue, 3-Jul-84 19:10:20 EDT
Organization: U of Toronto Zoology
Lines: 25

Has anybody had reasonable success using the 74S124 as a crystal
oscillator?  The TI data book claims it can be done, and has a few
sentences on how to do it, but...  When I tried it, I found it quite
impossible to convince the thing to start up cleanly on power-up.
It persisted in starting up in a messy mode that confused my frequency
counter, but from other evidence must have been a very high frequency.

The crystal I was using was 6.5536 MHz.  I was using only one of the
oscillators in the S124, with the other disabled.  I complied with
the databook recommendations on frequency-control input etc.  I was
fairly lavish about decoupling, and my power supply was on voltage and
reasonably clean.

I could generally succeed in convincing the thing to run at 6.5536 by
fiddling with small capacitors and such *after* the thing was going,
but no combination of capacitance would make it start up cleanly.  I
don't think I got a single clean startup.

I fixed the problem by switching to the MC4024 (second choice because
it's a little harder to find hereabouts), which -- with the same crystal,
same power supply, and same load -- starts cleanly every time, with no
extra capacitors present.  As a minor bonus, it eats much less power.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry