[SI-LIST] Re: PCI Bus Ringing, Overshoot

Hi Julian,

I suggest you to use the active Thevenin termination (with Schottky or
normal clamping diode)near the receiver (Load.A). The common mode potential
(clamp voltage)due to this diode combination should be around 3.3 to 3.6V.
Note a point that the clamping diode should never be used in 5V signalling
environment (according to PCI 2.1 specification).

Best Regards
Subramanya C K
Wipro Technologies, Bangalore- India


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Simba Julian
Sent: Tuesday, July 31, 2001 1:59 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] PCI Bus Ringing, Overshoot



Hi All,

I have a Board that is currently being routed and I'm not sure how to handle
ringing on my PCI bus (50Mhz 3.3V).
        Here's the stats:
                1. Xmission lines are 50 Ohms
                2. Three devices on PCI bus

The current placement of the three components gives me  Manhattan distances
of 10" and 3.7"


                A =============================== B =========== C
                                 <------- 10" ------->                          
  <-- 3.7" -->


I don't have much flexibility regarding the component placement.  And when
component B is driving, my simulations show me that component A is seeing
excessive overshoot and ringback(~5.5V with almost No Noise Margin).

My understanding of PCI, is that I cannot use any terminations.

Is there anything that can be done?


Thanks in advance
Simba Julian

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