MINUTES SCSI signal modeling study group (SSM)

Dean Wallace d_wallace at qlc.com
Wed Aug 11 10:16:53 PDT 1999

* From the T10 Reflector (t10 at t10.org), posted by:
* Dean Wallace <d_wallace at qlc.com>

The second meeting of the SCSI signal modeling study group
was held in Manchester NH July 29. 


1. Introductions
2. Attendance
3. Agenda development
4. Presentations
  4.1 Host bus adapter model (Tariq Abou-Jeyab, Adaptec)
  4.2 References useful for modeling and simulation (Jonathan Fasig WD)
  4.3 Difference between simulated and measured TDR traces
      (Martin Obuokiri Molex)
  4.4 Transmission line coupling parameters (Larry Barnes LSI Logic)
5. Output of group
6. SFF backplance
7. Components to be modeled
  7.1 Cable assemblies
    7.1.1 Cable media (bulk cable)
    7.1.2 Connectors (on cable assemblies)
    7.1.3 Transition region
  7.2 PCB's
  7.3 Connectors for non cable applications
  7.4 Termination
  7.5 Transceivers
    7.5.1 Chip packages
    7.5.2 Access to actual measurement points
8. Simulation integration strategy
9. System configurations
10. Data patterns
11. Data rate
12. Verification/correlation
  12.1 Physical measurement points
13. Definitions
14. Tools
  14.1 Behavioral
  14.2 Circuit
15. Next meetings
16. Action items

1. Introduction

Paul Aloisi of Unitrode opened the meeting and counducted the 
introductions and reviewed the meeting purpose. Paul also thanked
Hitachi cable for hosting the meeting.

2. Attendance

The following people were in attendance:

Tariq Abou-Jeyab         Adaptec
Bill Ham                 Compaq
Nicholaos Limberapoulas  C&M
John Ellis               FCI/Berg
Jackie Sylvia            Hitachi Cable
Larry Barnes             LSI Logic
Jie Fan                  Madison Cable
Martin Ogbuokiri         Molex
Farbod Falakfarsa        Quantum
Andrew Bishop            Quantum
Ivan Chan                Quantum
Ken Plourde              Tempflex
Paul Aloisi              Unitrode
Johnathan Fasig          Western Digital

3. Agenda development

The agenda shown was used.

4.1 Host bus adapter model (Tariq Abou-Jeyab, Adaptec)

The following material was presented, internal connector, external
connector, ASIC chip, terminator, and board construction. A discussion
followed on the basic purpose of the simulation effort and the definition
of terms and concepts. 
     One area of consideration is the definition of the term "IBIS". IBIS
is a behavioral model that is used to specify IO buffers inputs and outputs
and can be used for termination also. Connector models are also being considered
for an IBIS model. IBIS models do not include transmission lines or PCB'S. For
behavioral specifications the SCSI modeling study group will use only IBIS 
specification methodology for chip input, output, and terminator. For circuit type
specifications no specific position was taken but it was generally agreed that 
something like "spice" will be used.
     Tariq suggested that the microstrip and stripline constructions be considered
as the basic options within the PCB. The details of these models are a primary part
of the simulation requirements.

4.2 References useful for modeling and simulation (Jonathan Fasig, Western Digital)

Jonathan prodcued three useful lists of references, signal integrity publications,
online bookstores and publishers, and other related online services. Jonathan took 
an action item to send the lists electronically to Bill Ham for posting.

4.3 Difference between simulated and measured TDR traces (Martin Ogbuokiri, Molex)

Martin presented real data from a connector and an attempt to simulate the same 
measurement using a discrete lumped circuit model. There was approximately a 3x
difference between the measured and calculated results in terms of the time extent 
of the connector. The amplitude features however agreed within 4% (peak to peak only).
     The recommendations are, use only peak to peak results to validate the simulated
results. Ignore the timing features of the results. Do not use the average impedance
(over time) values. Better agreement could be obtained if the multiple reflection due
to the discontinuities in the test fixture and the connector were included in the 
model. Presently it requires special expertise to use the spice tool for simulating
multiple reflections due to the need to input many details of the physical test
     Martin has an action item to supply a block diagram of the simulation process 
used to do the simulation.

4.4 Transmission line coupling parameters (Larry Barnes, LSI Logic)

Larry presented the results of a comprehensive simulation relating to the intensity
of backwards crosstalk as a function of distance from a conductor. This models was a
first cut at understanding the issue. Two items that need to be added to this approach
are using differential signals and including ground lines were they exist in SCSI.
     One major result of this work was a very rapidly decreasing coupling with spacing.
Another possible result was an extended residual inductive coupling. This is probably
due to the way the ground returns were specified in the model. If the extended residual
inductive coupling is truly significant it could indicate more crosstalk but that 
conclusion needs to be validated.

5. Output of the group

     The effort will prodcue three types of output: (1) reports to the SCSI working
group, (2) a document containing the technical details, exact type of document TBD
and, (3) a web based repository for specific models.
     Larry Barnes volunteered to be the editor for the document.

6. SFF backplane

     Bill Ham noted this activity is still planned but not yet started.

7. Components to be modeled

7.1 Cable assemblies

     The cable assembly consists of: media, connectors, and transition region between
pure media and connector termination.

7.1.1 Cable media (bulk cable)

     Discussed at June meeting.

7.1.2 Connectors (on cable assemblies)

    A model similar to that used for cable media was suggested. A more general version
is required for an actual SCSI connector having many contacts. This model would have the
same general form as the model for the cable media. The discussion focused on the circuit
model approach. A behavioral model may also be attractive but no direction was taken at
this meeting. The integration of connector, chip, media, into a single simulation is a
major point of interest for this group.

7.1.3 Transition region

     The transition region is that part of the cable assembly that is between the
connector itself and the undisturbed cable media. This region has not been modeled
previously and no models or approaches are currently available. It was agreed that 
people who do the cable assembly design and manufacturing should be the source of the
simulation parameters for this part of the interconnect.

7.2 PCB's

     Dean Wallace to provide a target board model. Suggested that the following items
be added: vias, discontinuities, signals over discontinuities.

7.3 Connectors for non-cable applications

     At this point there is no difference between these connectors and connectors used
for cable applications. Molex will supply RGL transmission line matrix for VHDCI, SCA-2,
and HD68 connectors.

7.4 Termination

     Addressed in the June meeting.

7.5 Transceivers

     Due to the proprietary nature of transceiver design only behavioral models will be

7.5.1 chip packages

     Not discussed at this meeting.

7.5.2 Access to actual measurement points

     Not discussed at this meeting.

8 Simulation integration strategy

     Significant discussion on how to integrate the simulations from the different 
interconnect and chip elements since different simulation specification types are used
for the different elements. The common approach seems to be a circuit specification approach.
This requires behavioral specifications to be converted into a circuit model.
     The simulation strategy currently is: IBIS models for the IO buffers and SCSI
terminators and a Spice model for the cable media, connectors, PCB, and cable assembly
transition regions. It is possible to create circuit models from some behavioral tools
and vice versa, this allows tailoring the specific simulations to the nature of the specific
     An important goal and output for this work is a set of building blocks tha everyone can
use. For example, transceiver cells, package leads and bond wires etc, connectors, cable 
media, terminators, PCB's and the like. The integration of these building blocks into a
simulation strategy for several parts of the SCSI bus is a second phase for the effort. The
third phase is to ensure commonality between simulation input needs and the parameters 
available from the component suppliers. The reverse is also important: going from simulated
performance needs to parameters controllable by the component supplier. The specific
action is to agree on a way to tranlate between needed parameters for simulation and the
parameters available from physical measurement methods and specifications.

9. System configurations

     Not discussed at this meeting.

10. Data Patterns

     Not discussed at this meeting.

11. Data rate

     Not discussed at this meeting.

12.1 Physical measurement points

     Not discussed at this meeting.

13. Definitions

     Not discussed at this meeting.

14. Tools

     Not discussed at this meeting.

14.1 Behavioral

     Not discussed at this meeting.

14.2 Circuit
     Not discussed at this meeting.

The meeting schedule is:
Sept 01, 1999 Colorado Springs (Embassy Suites)
Sept 29, 1999 Chicago (Lisle) at Molex plant.


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