May SSWG Minutes

R. S. Shergill rss at
Tue May 31 12:20:32 PDT 1994

Accredited Standards Committee         Operating under the procedures of
           The American National Standards Institute.
  X3 Secretariat, Computer and Business Equipment Manufacturers
                       Association (CBEMA)
    1250 Eye Street NW, Suite 200, Washington, DC 20005-3922
Telephone: 202-737-8888 (Press 1 twice) FAX: 202-638-4922 or 202-

               X3, Information Processing Systems

                                             Doc.  No.  X3T10/94-_____R0
                                             Date:     May 28,1994
                                             Ref. Doc.:
                                             Reply to: J. Lohmeyer
To:    Membership of X3T10

From:  Shergill/Lohmeyer

Subject:   Minutes of X3T9.2 FAST-20 SCSI Ad-hoc  May 5,1994


1.Opening Remarks                                          
2.Attendance and Membership, Introductions                 
3.Approval of Agenda                                       
4.Document Distribution                                    
5.Old Business                                             
     5.1  Testing Update (Ham)                             
     5.2  Review of Outstanding Issues                     
          a) System Level Issues                           
          b) Chip Level Issues                             
     5.3  Review of Project Proposal                       
     5.4  Review of Current FAST-20 Draft                  
6.Meeting Schedule                                         

                       Results of Meeting

1.Opening Remarks

John Lohmeyer convened the meeting at 9:30 AM.  John thanked Jim
McGrath of Quantum for hosting the meeting.

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

It  was stated that the meeting had been authorized by X3T10  and
would  be conducted under the X3 rules.  Ad hoc meetings take  no
final  actions, but prepare recommendations for approval  by  the
X3T10 task group.  The voting rules for the meeting are those  of
the  parent  committee, X3T10.  These rules are:   one  vote  per
company; and any participating company member may vote.

The  minutes of this meeting will be posted to the  SCSI  Reflector 
and will be included in the  next  committee mailing.

2.   Attendance and Membership, Introductions

Attendance at working group meetings does not count toward
minimum attendance requirements for X3T10 membership.  Working
group meetings are open to any person or company to attend and to
express their opinion on the subjects being discussed.

The following people attended the meeting.

             Name                       Organization
  ------------------------       --------------------------- 
  Mr. Wally Bridgewater          Adaptec, Inc.
  Mr. Mike Dreitlein             Adaptec, Inc.
  Mr. Norm Harris                Adaptec, Inc.
  Mr. Barry Litt                 Adaptec, Inc.
  Mr. Craig Stuber               Adaptec, Inc.
  Mr. Mark Knecht                Advanced Micro Devices
  Mr. Mark Jander                AT&T/ NCR Microelectronics
  Mr. John Lohmeyer              AT&T/ NCR Microelectronics
  Mr. Dale Smith                 Cirrus Logic
  Mr. Louis Grantham             Dallas Semiconductor
  Dr. William Ham                Digital Equipment Corp.
  Mr. Ron Roberts                Maxtor Corp.
  Mr. Robbie Shergill            National Semiconductor
  Mr. Ting Le Chan               QLogic Corp.
  Mr. Farbod Falakfarsa          Quantum Corp.
  Mr. James McGrath              Quantum Corp.
  Mr. Brian Davis                Seagate
  Mr. Stephen G. Finch           Silicon Systems, Inc.
  Mr. Vit Novak                  Sun Microsystems, Inc.
  Mr. Pete Tobias                Tandem Computers
  Mr. Paul D. Aloisi             Unitrode Integrated Circuits
  Mr. John Osterlund             Zadian
  22 People Present

3.   Approval of Agenda

The agenda was approved as proposed.


The minutes of the March 31, 1994, ad-hoc meeting were distributed by R. 



Bill Ham presented the results of further testing he had performed since 
the last meeting.

Bill suggested Fast-360 as a name in order to use same units as serial 
interfaces. John Lohmeyer suggested deferring this to the next plenary 
meeting - this was done.

Bill has taken additional data on fully loaded single-ended bus.
At worst-case positions along the bus the assertion and negation levels 
are badly degraded. 16 devices don't look feasible, 8 devices generally 

Wally Bridgewater asked if 3 meter cable with 16 devices would be 
actually better because of wider separation between devices. Bill 
thought that maybe possible.

Bill showed a 16-device scope picture where the waveform at the 4th 
position from the driver barely gets to 2 volts and doesn't get below 1 
volt. End-bus driving is worse than mid-bus driving. With 9 devices, 
only the 4.9" stub case is marginal at 20MT/s.

Bill stressed that the differential bus has no problems - he has tested 
30 MT/s operation at up to 21.5 meters.

Bill said that limiting the number of devices is best from backward 
compatibility standpoint. The other options are - limit node capacitance 
(will mean no switchable terminators), narrower thresholds, etc. Bill 
added that he had tried doubling up the transceivers. This showed only 
marginal improvement.

Bill concluded with the following suggestions - 
  - 1.5 meters
  - 8 devices
  - 4" max stubs
  - 25pf
  - cable impedance greater than 80 ohms
  - plus all others - active negation, slew rate control, narrower
    receiver threshold.

Norm Harris commented that all else is fine but Adaptec believes 3 
meters is possible - especially if cable impedance is increased to above 
100 ohms.

Vit Novak asked why the stub length can't be lower than 4"; because one 
of the applications for FAST-20 is going to be backplane bus.

John Lohmeyer asked if the TI driver's extra strength - due to its 
bipolar componentery - weakens this analysis? Bill Ham said the TI chip 
has a pure CMOS driver.

Brian Davis commented that Seagate silicon's pin capacitance is about 12 
pF. Paul Aloisi added that the termination chips' capacitance is about 3 
pF now - there are actually devices out there that have 15 pF total 



Norm Harris presented Adaptec's proposal:

 - Backing up to 1.5 meters will hurt SCSI in the market with respect to
   ATA-2. Therefore, we should stay with 3 meter cable length.

 - Specify impedance to be 100-ohm +/- 10

 - Specify maximum device capacitance to be 20pF

 - Specify maximum devices to be 7; although will go along with the
   agreement that exists currently on 8

 - Specify 3:1 load spacing to stub length ratio.

Dale Smith asked if the termination can be strengthened. This will mean 
stronger drivers - which will mean no backward compatibility. No one 
wanted to do this.

Vit Novak pointed out that instead of simple cable impedance, what's 
more important is the consistency of impedance all along the cable. 100 
ohms is not good because it can't be achieved on backplanes easily. So 
Vit suggested 90 +/-10. Adaptec argued for 95 +/-10 if 2:1 ratio is 
desired. Vit agreed to this because he can get upto 85 on the backplane. 
Bill Ham suggested 90 +/-6 for req/ack pair only and 90 +/-10 for all 
other signals. This sounded like a good way to go if the cable folks can 
do it. The group will expect the cable guys to provide input at 
Harrisburg. Norm will put this info on the Reflector and also call a 
couple of cable people.

On the issue of cable length, John Lohmeyer did not want to accept 3 
meters until Bill Ham has tested it. 

On capacitance, the group considered 20 pf as the target, broken down 
this way:
  12 for chip,
  3 for chip term,
  3 for trace
  2 for connector.

Jim McGrath came into the meeting at about this time and objected to 20 
pF limit. He hasn't seen a chip termination that specs worst-case 
capacitance of less than 5-6 pF. 20pf limit maybe required for a fully 
loaded bus, but what about the typical desktop application where you 
only need 3-4 devices maximum? Paul Aloisi commented that his latest 
termination chips have low capacitance - but McGrath raised the issue of 

Robbie Shergill suggested that total device capacitance for the system 
could be specified in addition to 25pF max limit per device. This way 
you could configure a fully loaded system by using lower-capacitances 
devices, or configure a lightly loaded system with 25pF devices. Adaptec 
argued that this will cause two classes of devices. After much 
discussion the group came back to one spec - 25pf - with an implementors 
note or annex that explains that a fully loaded system should minimize 
node capacitance. Vit Novak volunteered to write such a note.

Steve Finch raised the issue of how this capacitance is to be measured 
and how applicable that capacitance number would be to the application.

Bill Ham suggested that ground offset should be specified. He suggested 
50mv - no arguments. Bill Ham also pointed out that mixing 50 and 68-
wire cables (narrow/wide) would affect the signal delay skew and 
therefore should not be allowed. This was also agreed to. In addition, 
it was decided summarily that passive termination is not allowed with 



Adaptec, NCR, SSI, and National did not want the levels changed from the 
ones agreed upon in March meeting. It'll also cause problems for a 
receiver to meet older spec. Ham will test to see if using 8 devices 
will remove this problem anyway.

Slew rate:
Giles had commented on the reflector that 600mv/ns should be changed to 
540mv/ns to remain compliant with SPI. Adaptec agreed to this.

Test circuit for ac-specs other than slew-rate:
NCR and Q-Logic said that 200pF max is what the load spec their chip's 
AC parameters specs. No one had objections to using this as a test load.

Voh max:
Mark Knecht said that 5.25 v currently in SPI is too high for a 3.3v 
technology. He wanted some number in the 3.7 - 4.0 volt range. his 
concern is for DC levels higher than this - he understands that 
reflected transient voltages will get up higher than this. Mark will do 
a proposal. John Lohmeyer commented that it may not be too late to even 
change SPI in this respect.

5.3  Review of Project Proposal                       

John Lohmeyer reminded everyone about the ballots on Fast-20 proposal - 
ballots are due by May 13.

5.4  Review of Current FAST-20 Draft

No detailed review was done.


   May 18, 1994 -  in Harrisburg, PA
   June 2, 1994 -  in Milpitas, CA. (Will decide in Harrisburg if this
                                     meeting is still required).


The meeting was adjourned at 1:00 PM.

More information about the T10 mailing list