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From: phil@amdcad.UUCP (Phil Ngai)
Newsgroups: net.micro.pc
Subject: Re: PC/AT fast xtal warning
Message-ID: <8533@amdcad.UUCP>
Date: Tue, 21-Jan-86 03:10:05 EST
Article-I.D.: amdcad.8533
Posted: Tue Jan 21 03:10:05 1986
Date-Received: Wed, 22-Jan-86 05:22:32 EST
References: <604@harvard.UUCP> <1101@ptsfa.UUCP> <996@terak.UUCP>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: AMD, Sunnyvale, California
Lines: 52
Summary: parts is parts?

In article <996@terak.UUCP> doug@terak.UUCP (Doug Pardee) writes:
>manufacturer's FAST (tm) logic: one part had much lower input loading
>than Fairchild's "standard" part, making the input lines susceptible to
>noise on a board where Fairchild's part worked fine.

Lower input loading sounds like an advantage to me. If it causes
problems, is it possible the device was not used correctly? Remember
most input loadings are specified as maximums and even the original
manufacturer may improve the part and reduce the loading.

>Sometimes there are undocumented differences.  I've seen a problem with
>a 10K ECL part obtained from a second source which didn't occur with the
>Motorola MECL part.  The second sourced part had problems during initial
>power-up, and wasn't reliable until each input changed state once.

Yes, parts are not parts. Some second sources are complete or partial
redesigns. Differences in behavior, especially in unspecified modes of
operation are not uncommon. Some second sources are true second
sources where masks are exchanged. There is much less room for
differences in the latter case, probably no more chance than there is
for a difference between lots from the same manufacturer.

>Sometimes it's simply an ability to produce a faster part; AMD is a
>second-source for the iAPX86 CPU's, but they seem to produce a given
>speed part a few months before Intel does.

Actually, we tend to be VERY conservative in our testing. But we have
some very hot processes too.

>And DRAMs!  I'm beginning to think that no two DRAM chips are inter-
>changeable, even from the same manufacturer   1/2 :-)    Aw, the spec
>sheets are nearly identical, but their behavior is something else.

I can't say I've had much trouble. What exactly are you referring to?
There are some things you have to get right, and a lot of parameters
you have to satisfy, but once you've done so DRAMs seem to work quite
reliably for me.

DRAMs are getting horribly complicated these days. Page mode, nibble
mode, static column addressing, read-modify-write cycles,
self-refreshing, and hardly anyone implements the same set of features
or in the same way. What a mess. But I have personally used DRAMs in a
half a dozen circuits with no trouble. In production, too.  All boards
were tested over extreme temperature ranges with varying manufacturers.

-- 
 (C) 1986 Joe Random is not a valid copyright.
 Copyright 1986 Joe Random is.

 Phil Ngai +1 408 749 5720
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