RE: [SI-LIST] : BLVDS Hot Swap

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From: Francis Chiu ([email protected])
Date: Tue Apr 11 2000 - 15:46:47 PDT


   The scenario you mentioned depends on the connectors you used. In our case, we are using the AMP 2mm HM connectors, the design of these connectors
   makes it quite impossible for these errors to occur.

   The tests were done on a 20 slots backplane with a pitch of 0.8 inch, the several milivolts glitches we observed was on the NEAREST neighbor; on the far end
   of the backplane, the glitch was only a fraction of a few millivolts.
   Besides that, the receivers have internal filter circuits which will further filter out any glitches, these are National internal data and were not released in the
   data sheet.
 
   The hot swap test was performed on the 20 slot multipoint backplane using a nine channel BLVDS, the data rate is 100 Mega Bits per second. We were
   using a Tektronix MB100 Bert Tester, the max data rate for that tester is 100 MBits/s. The actual max data transfer rate for the BLVDS can be higher.
   During the course of the continuous test in 3 days, numerous hot swap combinations were executed, the error rate is 0 on all nine channels.

   We do have pictures and reports for the BLVDS test, it was done almost a year ago. If time permits, I will try to locate the report and email you a copy.

   Regards.

                                                                                                Francis

 

[email protected] on 04/11/2000 01:42:00 PM
To: [email protected]@Internet
cc: (bcc: Francis Chiu/Americas/NSC)

Subject: RE: [SI-LIST] : BLVDS Hot Swap

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:[email protected]]
Sent: Tuesday, April 11, 2000 3:38 PM
To: [email protected]
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

                                                                                  
 

[email protected] on 04/07/2000 03:39:00 PM
To: [email protected]@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:[email protected]

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