RE: [SI-LIST] : BLVDS Hot Swap

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From: Steve Ash (Steve@sedonanetworks.com)
Date: Tue Apr 11 2000 - 13:29:39 PDT


Hi Francis!

Thanks for the response.

That is essentially the answer I was looking for. Given that a pair of
BLVDS signals should be right next to each other on the connector it is
probably safe to assume that both lines would see the same effect as they
would mate at roughly the same time in which case any glitches would occur
on both lines and get filtered at the differential receiver. I was
concerned about a situation where the differential lines might not mate
simultaneously in which case one side of the pair would momentarily short
(generate a glitch) at a slightly different time than the other side. How
likely is this to happen?...probably not very.
Although if only one side of the pair did get shorted I think this should
propagate through the terminating resistor to the other side of the pair as
well in which case the receiver may see roughly the same effect on both
sides of the pair thus the signals should cancel out as they pass thru the
receiver. Does this sound reasonable?

I was also concerned about the magnitude of the glitch that might result.
It may be that the BLVDS drivers have enough oomph that the resulting glitch
is not that great.

Does National have any test test data (pictures)regarding this?

Thanks,
steve ash
    

-----Original Message-----
From: Francis Chiu [mailto:Francis.Chiu@nsc.com]
Sent: Tuesday, April 11, 2000 3:38 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : BLVDS Hot Swap

.

  Hi, Steve,

  I don't quite get what you mean by "pre-charging" the BLVDS. The data
I get from my previous measurements shows the "glitch" that occurs
  during a hot swap is only a few millivolts and this occurs in BOTH
differential lines which means they will cancel out each other.

  The hot swap simply does not affect any BLVDS drivers/receivers, at
least for National Semiconductors parts.

        
Francis Chiu
 
Interface
Applications
        
National Semiconductor Corporation

                                                                                  
 

Steve@sedonanetworks.com on 04/07/2000 03:39:00 PM
To: si-list@silab.eng.sun.com@Internet
cc: (bcc: Francis Chiu/Americas/NSC)

Subject: [SI-LIST] : BLVDS Hot Swap

Does anybody out there have any data on pre-charging BLVDS (multipoint
LVDS)
signal lines in a HOT SWAP application for the purpose of preventing the
glitch that could occur when the BLVDS lines are momentarily shorted by
the
card being hot-plugged. I'm thinking that this may be required but I
have
not seen any mention of it with respect to BLVDS. What is the
recommended
method of doing this?

Somebody out there must be hot plugging BLVDS devices.

Thanks,

Stephen Ash
Senior Hardware Designer
Sedona Networks
10A Hearst Way
Kanata, Ontario
K2L 2P4

Tel: (613) 599-1600 ext. 5062
Fax: (613) 599-3040
Mailto:steve@sedonanetworks.com

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