[SI-LIST] Re: Routing a 125MHz bus with 1 Bidir, 2 Rcvrs and an input vector

Kevin,

 There are 2 things to consider with this network.
  First, you want the resistor to have no impact on the network (Except as
a keeper). To do this, place the resistor between the driver and the
receivers. I would route from the driver to the resistor and then to the
receivers such that I eliminate/minimize any stubs.

The second issue has to do with the receivers. The configuration (Daisy
chain or Balanced) will really depend on your timing requirements. I might
do the following: Route from the driver to a "virtual pin" and then route
from the virtual pin to each receiver with equal lengths.

                                Length A
                              ---------- receiver1
                              |
    Driver -------x------------ (Virtual pin)
                              |
                              ---------- receiver2
                                Length A

 Place the pullup/pulldown resistor at x

Doug

Douglas Burns
Principal Consultant
Signal Integrity Software, Inc.
6 Clock Tower Place
Maynard, MA 01754
978-461-0449 x14
dburns@xxxxxxxxxx
>
> Hi,
>
> I am interested in determining the safest routing stratagy for
> routing a 125MHz address bus.  The bus has 1 bidirection driver and 2
> rcvrs, and a 10k pullup or pulldown.
>
> The bi-direction driver uses the 10k pullup or pulldown resistors for
> power up configuration only.  Hence each address line would have the
> driver, 2 rcvrs and a 10k pullup or pulldown.  The resistors are
> contained in a resistor pack.  Also, the rcvrs are the same part.
>
> case 1
>
> Bi-Dir ------> rcvr
>            |-> rcvr
>            |-> 10k pullup
>
> case 2
>
> Bi-Dir ------> rcvr
>            |-> rcvr
>            |-> 10k pulldown
>
> We have determined that the bidirectional driver has an edge rate
> between 0.5ns and 1.5ns.
>
> I am concerned that the wrong topology and placement will affect the
> signal quality for the bus.
>
> Thanks,
>
> kevin
>
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Douglas J Burns
Principal Consultant
Signal Integrity Software, Inc.
6 Clock Tower Place
Maynard, MA 01754
978-461-0449 x14
www.sisoft.com


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