RE: [SI-LIST] : Non-standard bus termination (2nd posting)

Kassem Abdallah (kabdalla@emc.com)
Wed, 22 Sep 1999 10:12:16 -0400 (EDT)

> Has anybody out of there any suggestion about the following problem? (I think it
> is quite a common one).
>
> I?ve got a board with a non-standard bus of 34 traces. The bus drives a group of
> memories.
> The lenght of the bus is necessarily higher than the critical lenght (lcr =
> tr/2tpd): a termination could be useful. The problem: there are so many traces
> that one has to use too many components (34 resistors and 34 capacitors for AC
> parallel termination).
>
> What shall I do?
> Are there any special components (array) to terminate this type of bus?
> Shall I terminate the bus or not? (In past experience not always a termination
> was mandatory)

I am not the expert on SI Issues, but there are several resistor_packs
for termination available from a variety of vendors. However, You have
to be very carefull, because these packs sometimes cause noise and make
things worst. It depends on how the resistors network is packaged for
current/GND leads.( I suggest to look carfully at the schematics and do
some noise analysis).


Also, I "think" a 34-bit bus is not that WIDE, and if it is critical
data path, you might be better off terminating with single loads( may
be you can stick them on the backside of your board ?? It is a
compromise).

********************
|Kassem M. Abdallah|
|Digital Designer |
|EMC Corp. |
|Hopkinton MA 01748|
********************

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