[SI-LIST] multi-drop bidirectional bus -- questions about simulation results
- From: "Dixon, Adam" <ad185064@xxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 27 Oct 2008 17:14:07 -0400
I would appreciate comments regarding simulation results and termination
theory/options of a multi-drop bidirectional bus. The si-list archives
have threads from 2002 to 2007 which have been informative (daisy-chain
vs. star vs. rake topology, source series and end terminations). I am
simulating a three device bus using Hyperlynx LineSim v7.7 with recently
downloaded IBIS models. Two of the devices yield good waveshapes
(monotonic edges, acceptable slew rates). The third device (PC133
SDRAM) has grossly different results based on working with three
different suppliers' models. Two SDRAM models yield non-monotonic edges
at one receiver and a borderline falling edge knee at the other
receiver. I initially simulated w/a source series termination at the
SDRAM (10 to 47 ohms) and no SS terminations for the other two devices.
I am now looking at end termination options, though I'd prefer SS if the
simulation results & theory ultimately make sense.
Also, I started searching for multi-drop bidirectional termination
materials in a few SI texts (Chapter 6 in Johnson's High-Speed Digital
Design, Chapter 21 in Ritchey's Right the First Time (Vol. 1) and
Chapter 8 in Bogatin's Signal Integrity-Simplified) and one or two
online app. notes. End termination is most frequently cited with
explanations for relative component placement, output driver strength,
minimizing stub lengths, etc. I believe I see simulation results
corresponding to Johnson's note about driver current of CMOS/TTL logic
gates and have been looking at relative component placement and the
"terminator" stub effect of Figure 21.5 in Ritchey's text.
I'm concerned about the gross difference in SDRAM model behaviors and if
I am overlooking or misunderstanding the topology and simulation method.
I've contacted two of the SDRAM suppliers for feedback and would
appreciate further comment if you have time to discuss. Thanks very
much!
Cheers,
Adam Dixon, hardware engineer
NCR Corporation
2651 Satellite Blvd.
Duluth, GA 30096
* (770) 623-7093
* ad185064@xxxxxxx
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
