Path: utzoo!attcan!uunet!mcsun!ukc!inmos!brac!davidb
From: davidb@brac.inmos.co.uk (David Boreham)
Newsgroups: comp.arch
Subject: Re: Do chip timing specs mean anything?
Message-ID: <9806@ganymede.inmos.co.uk>
Date: 20 Aug 90 10:40:49 GMT
References: <1990Aug4.152038.1132@sbcs.sunysb.edu> <1080006@hpvcfs1.HP.COM> <26C9CE2F.3723@ics.uci.edu> <1990Aug16.144744.21058@phri.nyu.edu>
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In article <1990Aug16.144744.21058@phri.nyu.edu> roy@phri.nyu.edu (Roy Smith) writes:
>	Not only will all 4 gates be subject to the same inter-batch and
>inter-manufacturer variations, but they will have aged the same amount,
>have been subjected to the same history of abuse and/or proper care, and
>will see the same power supply and temperature conditions, not to mention
>EMF, radiation, POM, etc.

Exactly, in fact you can use this to your advantage.
Suppose that you need to keep some strobe signals
within some minimal skew of each other. If you
put them all through the same buffer or PAL, you
will achieve much better skew than putting them
through different gates in different packages.

This is because the datasheet min/max Tpd figures
are for the total spread over operating voltage
and temperature and over all chips ever produced.
If you take two gates on the same die and at the 
same voltage and temperature then the Tpd is going
to be very close.

Unfortunately very few datasheets give answers
about how well matched different gates in the same
device are, usually only line drivers and clock
buffer chips.

If you want to get really smart then you can do 
things like load each output with exactly the
same capacitance, even if the design would not
normally give the same loading. Also you can
sometimes blow the same number of fuses in PAL
product terms, since the number and position of
blown fuses makes a difference to the delay for
each output.

David Boreham, INMOS Limited | mail(uk): davidb@inmos.co.uk or ukc!inmos!davidb
Bristol,  England            |     (us): uunet!inmos.com!davidb
+44 454 616616 ex 547        | Internet: davidb@inmos.com