Minutes of X3T10 Server SPI Study Group Meeting 4/11/95

Lohmeyer, John JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com
Wed Apr 19 15:00:00 PDT 1995


Accredited Standards Committee
X3, Information Technology
                                                Doc. No.: X3T10/95-196r0
                                                    Date: April 19, 1995
                                                 Project:
                                               Ref. Doc.:
                                                Reply to: John Lohmeyer

 To:            Membership of X3T10

From:           Larry Lamers Vice-Chair X3T10
                John Lohmeyer, Chair X3T10

Subject:        Minutes of X3T10 Server SPI Study Group Meeting
                Denver, CO -- April 11, 1995
     

     Agenda
1. Opening Remarks
2. Approval of Agenda
3. Attendance and Membership
4. Physical Topics
   4.1 Power Dissipation [Gingerich]]
   4.2 Summary of Tradeoffs [Ham]
   4.3 AC Termination
   4.4 Alternate Topologies
5. Other Topics
6. Meeting Schedule
7. Adjournment

     
Results of Meeting

1. Opening Remarks

John Lohmeyer, the X3T10 Chair, called the meeting to order at 9:00 a.m., 
Tuesday March 7, 1995.  He failed to thank the host (himself).

As is customary, the people attending introduced themselves and a copy of 
the attendance list was circulated.  Copies of the draft agenda and general 
information on X3T10 were made available to those attending.

2. Approval of Agenda

The draft agenda was approved.

3. Attendance and Membership

Attendance at working group meetings does not count toward minimum 
attendance 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:

John Lohmeyer     Symbios Logic
Larry Lamers      Adaptec
Bill Ham          Digital Equipment
Tak Asami         Western Digital
Paul Aloisi       Unitrode
Yousef Vazir      Adaptec
Mike Fitzpatrick  Seagate
John Ives         Symbios Logic
Mark Nossokoff    Symbios Logic
Dennis Haynes     Burr-Brown
Justin McEldowney Burr-Brown
Tracy Spitler     Symbios Logic
Frank Gasparik    Symbios Logic
Richard Mourn     Symbios Logic
Ting Chan         QLogic
Dean Wallace      Linfinity
Kevin Gingerick   Texas Instruments
David Steele      Symbios Logic
Wally Bridgewater Adaptec
Norm Harris       Adaptec

4. Physical Topics

4.1 Power Dissipation [Gingerich]]

Kevin Gingerich presented an analysis of the power dissipation using 
existing differential drivers.  He commented that the common mode voltage 
needs to be constrained to less than 7 v D.C.

Kevin+s model stated that the current supplied by the driver when turned on 
must be supplied for the time period that is needed to stabilize the bus 
(two round trip delays).  David Steele pointed out that up to four pulses 
can be on a 25 meter cable at one time.

Kevin stated that integrated drivers require you to get to 50 mW average 
dissipation per driver.   Reducing the Vcc to 3 volts significantly reduces 
the power dissipation (to around 40 mW) because it is a squared 
relationship.

John Lohmeyer stated that reducing the number of lines that are biased could 
reduce the power dissipation somewhat and balance the loads.  Candidates are 
the C/D, I/O, MSG, ATN, REQ, and ACK signals.  If SCAM is supported, then 
C/D, I/O, and MSG would need to be biased.

Wally Bridgewater stated that the goal should be 1/2 watt dissipation for a 
16-bit bus.  This allows the other SCSI circuitry to dissipate 1/2 watt for 
a total package dissipation of 1 watt.

The big load is the cable.

Lowering Vod also helps reduce power dissipation but eats into the noise 
margin.

Kevin stated that eliminating the backward compatibility requirement would 
allow us to consider us Low Voltage Differential Signaling (LVDS).  This 
method is used by SCI (IEEE 1596) and is being considered as a replacement 
for RS-422.  In a 3 volt process the dissipation is around 20 mW.

4.2 Summary of Tradeoffs [Ham]

Bill Ham constructed a chart listing the tradeoffs for various options.

An interface compatible with today+s SE and LVDS is the goal.  The price is 
adding 30 pins, a reference voltage,  and additional drivers.  This is not 
compatible with present differential implementations.

The standards work the needs to be done:
        LVDS differential sensing [Ham]
        LVDS pinout [Lohmeyer]
        LVDS signaling levels [Gingerich, Ham]
        LVDS termination [Aloisi]
        LVDS cable specifications [Ham]
        LVDS architectural document [McGrath]
The persons named in brackets is assigned an action item to complete the 
necessary wording for that section.

John Lohmeyer stated that as soon as Jim McGrath provided the scope and 
goals write-ups he would prepare the project proposal.

4.3 AC Termination

Paul pointed out that AC termination does reduce the system power even if it 
does not solve the driver problem.

4.4 Alternate Topologies

Bill Ham and Jim McGrath plan to co-author a technical report on alternate 
topologies.  This will include three sections: 1) real protocol length 
limits; 2) repeaters; and 3) bridges.

5. Other Topics

There was some informal discussion of the issues surrounding bridges and 
repeaters.  As mentioned above, Bill Ham and Jim McGrath plan to submit a 
document as a candidate for a technical report on this subject.

6. Meeting Schedule

The next meeting of X3T10 Server SPI Working Group will be May 9, 1995, in 
Harrisburg, PA at the Sheraton Inn Harrisburg (717-561-2800), hosted by AMP 
Incorporated.

7. Adjournment

The meeting was adjourned at 1:30 p.m. on Tuesday April 11, 1995.





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