FreeLists / si-list / [SI-LIST] Re: source-termination and daisy chain question

[Eric Goodill <ericg@xxxxxxxxxxx>]

Han,
While I can't offer any immediate insight into your question, it's not 
always true that a source-terminated driver can't drive a daisy chain. 
Whoa--too many negatives. Let's say it's sometimes possible for a 
source-terminated driver to drive a daisy chain. Better.

What has worked in the past is to use a smaller value than optimal for 
the source-termination resistor. This provides a larger incident wave 
which can cross the receivers' switching threshold with margin. However, 
the non-optimal resistor value does not properly terminate the reflected 
wave, so the T-line rings more than normal. As long as the reflections 
do not cross any thresholds, you're okay. It's just a matter of analysis 
and margins, and if you're comfortable with the result, it can work.

-Eric

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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