[SI-LIST] Re: source-termination and daisy chain question
- From: "Mark Woods" <mark.woods@xxxxxxxxxx>
- Date: Wed, 4 Jul 2007 16:01:00 -0700
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From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
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Sent: Tuesday, July 03, 2007 12:06 PM
To: olaney@xxxxxxxx
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Subject: [SI-LIST] Re: source-termination and daisy chain question
All very true. Consider also that if the trace is short compared to the
risetime, you can live with no termination at all. That's how classic
TTL design was usually done, and still applies if the scale is right for
the speed. Of course, some logic families require a termination to
create proper logic levels.
Orin
On Tue, 03 Jul 2007 07:45:00 -0700 Terry Fox <tfox@xxxxxxxxx> writes:
> Han,
>
> The answer depends upon the type of signal..
>
> If you are distributing a daisy chain multi drop clock, you need
> load
> termination. Clocks must have a clean edge.
>
> If you are distributing address or data which simply needs to settle
> prior
> to the clock edge, source serial termination is fine.
>
> Data or address lines are only required to get to the appropriate
>
> voltage prior to the set up time.
>
> One corner case involves a "T" connection for SDRAM memory clock.
> If
> there are only two drops and the arms of the "T" are identical,
> you can often use source serial termination. It is not the best,
> but it
> works. I would HIGHLY recommend simulating this configuration
> prior to layout and again after layout.
>
> If I have some time later, I will do some simulations and send you
> the link.
>
> TFox
> tfox@xxxxxxxxx
> www.siemc.com
>
>
>
> At 11:25 PM 7/2/2007, Han Li wrote:
>
> >Hi everyone,
> > It seems a simple question,But I still have something i
> >cannot completly understand.
> > A daisy chain is often used in multidrop topology, which
> need an
> >end-termination. And, source-termination doesnot work properly in
> >daisy chain,because the device in the middle of the chain would get
> a
> >plateau;using source-termination, all load should be at the end of
> the
> >line.
> > So, in a design , i should figure out minimul distance
> between,
> >say two receivers. In other words, I should decide beyond what
> distance
> >between two
> >receivers , source-termination should not be used, and this
> topology
> >can be named a daisy chain?
> > Could anyone provide a deeper explanation? Thanks a lot!
> >---- ------ -------
> >Driver---------revceiver_1-----------------------receiver_2
> >---- ------- --------
> > |-------------distance---------|
> >
> >
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