RE: [SI-LIST] : RC terminations on multidrop busses

Abe Riazi (ariazi@anigma.com)
Thu, 12 Nov 1998 18:55:48 -0800

>Roy Leventhal Wrote:
>
>Hello to All,
>
>I am seeking information about people's experience (both theoretical and
>actual) using RC termination on the stubs on a daisy-chain multidrop bus.
>Why they work and why they don't work.
>
>The specifics of the situation are: frequencies in the 2MHz to 20MHz range,
>stubs that are electrically significant, heavily to lightly loaded
>backplane probably using BTL+ Futurebus I/Os.
>
>Thanks,
>
>Roy Leventhal
>3Com
>Roy_Leventhal@mw.3com.com
>847-797-2152
>
>
Hi Roy:

I have not used RC termination in a design, but have studied the laws
and equations which govern this type of termination.

I could not see any violations using RC termination for your
application.

When utilizing RC termination, the following rules apply:

1. The value of the resistor is given by:
R=Zo'
where Zo' is the loaded characteristic trace impedance.

2. The capacitor value is determined via:
C ~ 3Co
where Co represents total capacitance of the trace.

3. All stub lengths (including connection between capacitor and
resistor) should be kept as short as possible.

Good Luck!

Abe Riazi
>Anigma, Inc.
>

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