Minutes of SPI-2 LDV SCSI Working Group -- 1/8/96

Lohmeyer, John JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com
Mon Jan 22 07:35:00 PST 1996

* From the SCSI Reflector, posted by:
* <"Lohmeyer, John" <JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com>>

Minutes of SPI-2 LVDS Working Group Meeting 

Accredited Standards Committee*
X3, Information Technology
                                                   Doc. No.: X3T10/96-106r0
                                                       Date: January 22, 
                                                    Project: 1142-D
                                                  Ref. Doc.:
                                                   Reply to: John Lohmeyer

To:         Membership of X3T10

From:       Ralph Weber, Secretary X3T10
            John Lohmeyer, Chair X3T10
            Bill Ham, SPI-2 Technical Editor

Subject:    Minutes of X3T10 SPI-2 LVD SCSI Working Group Meeting
            Dallas, TX -- January 8, 1996


1. Opening Remarks

2. Approval of Agenda

3. Attendance and Membership

4. SPI-2 Document Review (X3T10/1142D) [Ham]

5. Releasing Bus from Active Negation [Uber]

6. Voltage Mode Drivers [Bridgewater]

7. Meeting Schedule

8. Adjournment

                              Results of Meeting

1.    Opening Remarks

John Lohmeyer, the X3T10 Chair, called the meeting to order at 9:03 a.m.,
Monday January 8, 1996.  He thanked Jim McGrath of Quantum for hosting the

As is customary, the people attending introduced themselves and a copy of 
attendance list was circulated.

2.    Approval of Agenda

Bill Ham noted that the draft agenda is very general and that details would 
needed.  But, he agreed to handle the details under the appropriate general
headings.  The draft agenda was approved without changes.

3.    Attendance and Membership

Attendance at working group meetings does not count toward minimum 
requirements for X3T10 membership.  Working group meetings are open to any
person or organization directly and materially affected by X3T10's scope of
work.  The following people attended the meeting:

         Name          S        Organization         Electronic Mail Address
 ---------------------- -- ------------------------- 
Mr. Norm Harris        P  Adaptec, Inc.             nharris at eng.adaptec.com
Mr. Lawrence J. Lamers A# Adaptec, Inc.             ljlamers at aol.com
Mr. Wally Bridgewater  V  Adaptec, Inc.             wally at eng.adaptec.com
Mr. Richard Moore      V  Adaptec, Inc. 
            richard_moore at corp.adapte
Mr. Richard B. Rauch   V  APCON, Inc.               rbr at apcon.com
Mr. Dennis R. Haynes   O  Burr-Brown Corp.          haynes_dennis at bbrown.com
Mr. Justin McEldowney  V  Burr-Brown Corp. 
         mceldowney_justin at bbrown.
Mr. Jaff Lin           A  BusLogic                  jaffl at buslogic.com
Mr. Lyle Conn          V  Conner Peripherals        lyle.conn at conner.com
Mr. Louis Grantham     P  Dallas Semiconductor      grantham at dalsemi.com
Dr. William Ham        A# Digital Equipment Corp.   ham at subsys.enet.dec.com
Mr. Ralph O. Weber     P  ENDL Associate            roweber at acm.org
Ms. Nancy Cheng        A# Hitachi Computer Products n_cheng at hitachi.com
Mr. George Penokie     P  IBM Corp.                 gop at rchvmp3.vnet.ibm.com
Mr. Dan Colegrove      A# IBM Corp.                 colegrove at vnet.ibm.com
Mr. Dean Wallace       P  Linfinity Micro 
          75671.3443 at compuserve.com
Mr. Frank Samela       A  Methode
Mr. Edward A. Gardner  V  Ophidian Designs          gardner at acm.org
Dr. Akira James Miura  A  Panasonic Technologies, 
  miura at tadw.research.panas
                          Inc                       onic.com
Mr. Skip Jones         P  QLogic Corp.              sk_jones at qlc.com
Mr. Ting Li Chan       A  QLogic Corp.              t_chan at qlc.com
Mr. Mark Evans         A  Quantum Corp.             mevans at qntm.com
Mr. Richard Uber       V  Quantum Corp.             duber at tdh.qntm.com
Mr. Gene Milligan      P  Seagate Technology 
       Gene_Milligan at notes.seaga
Mr. Gerald Houlder     A  Seagate Technology 
       Gerry_Houlder at notes.seaga
Mr. Dave Guss          A  Silicon Systems, Inc.     dave.guss at tus.ssi1.com
Mr. Daniel E. Moczarny V  Silicon Systems, Inc. 
    dan.moczarny at tus.ssi1.com
Mr. Robert N. Snively  P  Sun Microsystems Computer bob.snively at eng.sun.com
Mr. John Lohmeyer      P  Symbios Logic Inc. 
       john.lohmeyer at symbios.com
Mr. Frank Gasparik     V  Symbios Logic Inc. 
       frank.gasparik at symbios.co
Mr. Kevin Gingerich    V  Texas Instruments         4307725 at mcimail.com
Mr. John Wilson        V  Texas Instruments         jwilson at asic.sc.ti.com
Mr. Paul D. Aloisi     P  Unitrode Integrated       Aloisi at uicc.com
Mr. Matthew Thomas     A  Unitrode Integrated       thomasm at uicc.com
Mr. Tak Asami          A  Western Digital           asami at dt.wdc.com

35 People Present

Status Key:  P    -  Principal
             A,A# -  Alternate
             O    -  Observer
             L    -  Liaison
             V    -  Visitor

4.    SPI-2 Document Review (X3T10/1142D) [Ham]

Bill Ham expressed concern about signal glitches after releasing the bus 
a negation as noted in the last meeting.  John Lohmeyer said that his inputs
|from others have indicated that it will not be a problem as that was exactly
what the bus settle delay was intended for.  Dave Guss said that the 
would not be problems for targets but could represent problems for hosts,
because they are required to detect levels set by the targets.  John
(representing hosts) then became less certain about the degree of protection
offered in present implementations.

Bill Ham approached the day's work with the goal of writing improved wording
about required behavior after release from negation.  Almost every topic
discussed for the remainder of the day was cast in terms of its effect on
reducing the glitch problem.  In this regard, it was noted that glitches 
the bus is released normally are the most common problem, but glitches 
unexpected bus free may produce the most difficult to predict problems.

Kevin Gingerich presented a detailed model representing a differential bus 
both DC and AC terms.  He described all aspects of the model and suggested
that the group would benefit from adopting the model (or one like it) as a
development tool for examining bus properties.

Bill presented a new diagram for representing the capacitance loading
restrictions to be placed on device. This diagram was based on the values of
discrete capacitors between the signals and local ground.  After some
discussion it was decided that a measurement from - signal to local ground, 
measurement from + signal to ground, and a measurement between the two 
would be a better way to specify this requirement.  Maximum values for these
capacitances were agreed to be 20pF to ground and no more than 2pF 
between the signals.

Stub length (previously set at 0.2m) was discussed.  It was agreed to reduce
the total stub length to 0.1m and to split the 0.1m equally between inside 
outside the device.   Bill noted that the draft document will be changed but
that future discussions probably will revisit the stub length issue.

Limits on the differences between stub line lengths for several signals were
discussed.  Bill described the need for restricting differences in stub line
lengths as being skew management.  The need was generally agreed.  But,
several problems were raised regarding the details of the specification. 
strict limits on differences in stub lengths were discussed.  However, the
very strict limits were noted to prevent the usage of BGA chip technologies.
This lead to a realization that this specification would need to be 
written to distinguish between differences in length of the + and - parts of
the same signal, from data signal to data signal, from data signal to clock
signal and from data/clock signals to slow speed control signals.

Kevin Gingerich and Bill Ham led a discussion of test circuits.  Several
complexities were raised and reviewed.  Bill concluded that the group had
reached the point where the meeting discussion should end and people should
return to their offices to develop experimental circuits and collect test

One of the other concerns expressed at the last meeting involved the effects
of device leakage on the signals and on the bias from the terminators. 
some discussion it was determined that this leakage effect would not cause a
negative noise margin with the revised receiver sensitivity of 30 mV.

By the end of the meeting, the following list of agreed assumptions existed:

      A stub length of 0.1 m

      30 mV receivers

      110-135 Ohms cable impedance

      loaded cable impedance  85-135 ohms

      100-115 Ohms terminator resistance

      Requiring cable to have a capacitance/length of 15-50 pF/ft

      Capacative load 20 pF max +-0.5 pF each side of same signal
                                +- 2 pF data/parity signal to REQ/ACK

      Leakage +- 20 uA /pin/device

      Common mode impedance 100 to 500 ohms

      Ground offset max 0.5 V

We will use drivers that result in unequal assertions and negations to
eliminate the release glitch or will use symmetrical drivers if it is
determined that these glitches will be ignored by the protocol.

The SCSI general working group will be asked to determine how to guarantee
that release glitches would be ignored.

The next meeting will focus on finalizing the specifications on either a
symmetrical or asymmetrical driver.  It was noted by several silicon vendors
that they preferred the symmetrical scheme as this was significantly easier 
build and control.  Overall it appeared that there were at least two ways to
make LVD SCSI work and that one would be specified at the next meeting.

5.    Releasing Bus from Active Negation [Uber]

Richard Uber presented a circuit that he felt would be immune to glitches as
the target goes bus free.  Wally Bridgewater described an electrical problem
with the proposal, part of which was related to higher power consumption.
Richard noted that an asymmetrical assertion and negation signal may be 
to eliminate these glitches.

6.    Voltage Mode Drivers [Bridgewater]

Wally Bridgewater presented a revised proposal for voltage mode drivers.  He
stated that, after further consideration, the only difference between 
mode drivers and voltage mode drivers is where the resistors are located.
Also, the voltage mode dissipates less power on the chip, but more power

Bill's conclusion was that the goal of the standard should be to tell people
what the circuit should do and not how to build the circuits to do it.  The
standard will concentrate on the signal levels needed.

Wally also noted some single ended simulations of LVD SCSI signals that 
resonance points at different lengths and serious signal reductions.  This 
not pursued at this meeting because Bill Ham noted that he had seen similar
effects when changing the frequency when only the single ended signals were
examined.  In these cases, the differential signal remained constant.  This
left the issue unresolved but hopefully Wally's simulation results are not
indicative of a serious problem.

7.    Meeting Schedule

The next meeting of SPI-2 Working Group will be January 29-30, 1996 in 
CO at the Red Lion Inn (303-321-3333) hosted by Symbios Logic.  Another 
Working Group meeting is scheduled for Monday March 11, 1996, in San Diego, 
at the Hyatt Islandia (619) 22401234, hosted by Quantum Corp.

8.    Adjournment

The meeting was adjourned at 5:29 p.m. on Monday January 8, 1996.

John Lohmeyer             E-Mail:  john.lohmeyer at symbios.com
Symbios Logic Inc.         Voice:  719-573-3362
1635 Aeroplaza Dr.           Fax:  719-573-3037
Colo Spgs, CO 80916     SCSI BBS:  719-574-0424 300--14400 baud

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