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From: Joseph Legris
X-Mailer: Mozilla 4.77 [en]C-SYMPA (Win95; U)
Subject: Re: Grounding advice
References: <3D9DFA4D.firstname.lastname@example.org> <3D9E1B5A.209DA53D@xympatico.ca> <3DA07B85.email@example.com>
Date: Sun, 06 Oct 2002 21:17:13 -0400
NNTP-Posting-Date: Sun, 06 Oct 2002 21:11:16 EDT
Organization: Bell Sympatico
Ryan Gammon wrote:
> > This sounds like a timing problem - the capacitance of the voltmeter is
> > slowing the output transition just enough for the data to be clocked
> > into wherever it is going. Where is it going anyway?
> On the rising edge of a load signal (sent from microcontroller to
> cpld-acting-as-a-shift-register on the perfboard), the cpld changes
> three of its outputs, all going to a single sram address lines with no
> other fanout. The sram is on the perfboard. Putting a voltmeter between
> one of these cpld outputs (aka address line inputs) and ground seems to
> suppress the extra clock pulses on the cpld input
> I can see timing problems corrupting sram data, but not causing extra
> clock pulses on the cpld.
Are you sure that what you are calling "extra clock pulses" is really
that? Maybe spurious write cycles to the SRAM, caused by a glitch on
your CPLD output (address lines), produces a result that is identical to
that caused by extra clock pulses.
Can you post the whole circuit (or a block diagram) somewhere?
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