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[SI-LIST] Re: PCI/PCIX minimum lenghts?

From: "Nitin Sood" <Nitin.Sood@xxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Date: Thu, 10 Nov 2005 14:38:19 -0800
Ed,
I thought transmission line effects are only important when rise times =
are
comparable or shorter than the round trip time delay
Adding the series resistor would effect the rise time and make them =
longer
when compared to the round trip delay.
How does this solve Anders problem ? Please advice.=20

Thanks,
Nitin


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On
Behalf Of Dr. Edward P. Sayre
Sent: Thursday, November 10, 2005 8:59 AM
To: af@xxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: PCI/PCIX minimum lenghts?

Anders:

Try 10 - 25 ohm series resistors on the traces if you find the short =
link
causes ringing.  It will slow everything down and make the bus appear =
longer
than it really is.

ed
=3D=3D
At 12:21 PM 11/10/2005 +0100, Anders Frederiksen wrote:
>Hi people =3D),
>
>I'm working on a board with a PCI-X (66Mhz) and a PCI (33Mhz) bus. Both =

>busses are point to point embedded busses. According to specs the=20
>minimum length of a PCI bus seems to be ~95mm. Given the number of=20
>signals and the fact that the optimal length is ~3cm I understand the=20
>PCB designers frustrations! Thus I'd like to relax the minimum length=20
>constraint...
>
>Has anyone looked into "short PCI busses"? I see two possible issues: =
1.=20
>Bus being
>too short for transmission line theory to apply. Possibly affecting=20
>signal levels.
>2. Timing for host reads: The data will arrive earlier than "expected"=20
>due to the shorter clock (out) and data (return) propagation.
>
>My googling provided no usable results. Perhaps you guys would have a=20
>hint or two?
>
>Cheers,
>Anders
>
>
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+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
|        NORTH EAST SYSTEMS ASSOCIATES, INC.        |
|       -------------------------------------       |
|      "High Performance Engineering & Design"      |
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
| Dr. Ed Sayre               e-mail: esayre@xxxxxxxx|
| NESA, Inc.                 http://www.nesa.com/   |
| 235 Littleton Road, Ste 2  Tel +1.978.392-8787    |
| Westford, MA  01886        Fax +1.978.392-8686    |
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[SI-LIST] Re: PCI/PCIX minimum lenghts?

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