Minutes of Ultra-SCSI Ad-Hoc Meeting
R. S. Shergill
rss at berlioz.nsc.com
Fri Apr 8 14:59:49 PDT 1994
Doc No. __________
Minutes of the X3T10 Ultra SCSI Ad-Hoc Meeting
Held March 31, 1994, at Milpitas, California.
Chaired by: Jim McGrath, Quantum Corp (AM); and
John Lohmeyer, AT&T/NCR (PM).
Hosted by: Jim McGrath, Quantum Corp.
Minutes recorded by: Robbie Shergill, National Semiconductor Corp.
John Lohmeyer brought the meeting to order at 9:30 AM and asked each person in
attendance to introduce themselves. An attendance sheet was also circulated.
Name Company Phone e-mail
---- ------- ------ ------
Norm Harris Adaptec nharris at adaptec.com
Larry Lamers Adaptec 408-945-8600 ljlamers at aol.com
Mark Knecht AMD 408-235-8043 mark.knecht at amd.com
Joseph Chen Cirrus Logic 510-226-2101 chen at cirrus.com
Dave Weber Cirrus Logic 510-226-2367
Dale Smith Cirrus Logic 510-226-2151
Bill Gintz Conner 408-456-3648
Louis Grantham Dallas Semi. 214-450-8110 grantham at dalsemi.com
Michael Smith Dallas Semi. 214-450-0457 msmith at dalsemi.com
Bill Ham DEC 508-841-2629 ham at shwsys.enet.dec.com
Robert Liu Fujitsu 408-894-3790
George Rasko IBM 408-256-2427
Aaron Olbrich IBM 408-256-4049
Ron Roberts Maxtor 408-432-4322 ron_roberts at maxtor.com
John Goldie National Semi. 408-721-2075 cjfgsc at tevm2.nsc.com
Todd Nelson National Semi. 408-721-7846 ctwnsc at tevm2.nsc.com
Robbie Shergill National Semi. 408-721-7959 rss at berlioz.nsc.com
John Lohmeyer NCR/AT&T 719-573-3362 john.lohmeyer at ftcollinsco.ncr.com
Ting Chan Q-Logic 714-668-0487 t_chan at qlc.com
Jim McGrath Quantum 408-894-4504 jmcgrath at qntm.com
Chris Millsaps Quantum 408-894-4269
Farbod Falakfarsa Quantum 408-894-4066
Brian Davis Seagate 408-439-2137 brian_davis at notes.seagate.com
Mike Fitzpatrick Seagate 405-324-3478
Dean Wallace Silicon General 408-898-8121
Steve Finch Silicon Systems 714-573-6808 5723283 at mcimail.com
Vit Novak Sun vit.novak at sun.com
Pete Tobias Tandem 408-285-9913 tobias_pete at tandem.com
Kevin Gingerich TI 214-997-3378 4307725 at mcimail.com
Paul Aloisi Unitrode 603-429-8687 aloisi at uicc.com
Duncan Penman Zadian 408-293-0800
John briefly described the ANSI rules governing an ad-hoc meeting.
Jim McGrath next presented the proposed agenda for this meeting. The agenda was
discussed briefly and adopted as follows:
Introductions - McGrath
Date and Place of Next Meeting - McGrath
Purpose of this SSWG - McGrath
Cable Plant - Ham
Timing - Adaptec
Ad-Hoc Meeting: 5/5/94, at Milpitas; host: Quantum.
SCSI Working Group: 5/18/94, as part of Plenary Week in Harrisburg, PA.
Ad-Hoc Meeting: 6/2/94, at Milpitas; host: Quantum.
Larry Lamers was not sure about the need for the May 5th meeting. Jim McGrath
asserted, however, that a meeting before the next plenary week may be necessary
because if anyone has any objections then they have to be brought up as soon as
possible Since design work is already taking place, McGrath warned that significant
changes after the May 18th meeting will be very unpopular and better have very good
and well supported basis for them.
It was pointed out that the term "Ultra SCSI" is a trademark of Ultrastor, so we'll
have to come up with a different name. Turbo SCSI has been suggested. This issue
will be further discussed in the plenary. In this meeting John Lohmeyer suggested
FAST-20 and the group was basically in agreement - other than Bill Ham's comment
that FAST-40 may be better (i.e., assume wide applications).
Bill Ham presented the results of further work on his test setup.
The test setup has been improved since the last time. It now has real single ended
loads; shorter stub lengths; software for disabling active negation on data lines;
and 40mt/s diff xcvrs.
On this setup Bill Ham has demonstrated successful operation at 40mt/s over 20m.
However, Bill emphasis in the presentation was on the "ultra-SCSI 1" setup results.
Essentially, with a fully loaded system, Bill's system is showing about 39ns window
A critical parameter for such performance is the slew-rate. Steve Finch wants the
slew rate spec to be the same for Fast and Ultra operations because the same silicon
is going to accommodate both modes; but John Lohmeyer and Larry Lamers want to allow
faster slewrate if we can also accommodate "Ultra-2" operation (40MT/s) with it.
Larry wants minimum 350-400 mv/s and 800mv/s maximum; however, Bill Gintz sees
trouble before you get to 800mv/s due to worst case system conditions.
Bill's data shows very little jitter, but Paul Aloisi pointed out that this is with
the TI silicon that does not have compliant threshold levels as per the new spec.
Bill agreed that the jitter will get a lot worse with threshold movement, but still
not a problem in his opinion.
Bill agrees that he needs to do take more data with the receiver moved further down
the cable, but bottomline is that adding real SCSI loads doesn't degrade things
Bill Ham presented a set of recomendations based on his data. Each item was
There was agreement on 1.5 meter cable length. However, Paul Aloisi pointed out that
the SPI spec allows 32 devices on the bus. The group was in agreement that we don't
want to attempt more than 16 devices.
Bill had seen the timing window shift with longer stub lengths and as a result he
was suggesting moving the position of clock to favor setup time by 5ns. This was
deferred because the group needs to better understand this phenomenon. Finch
suspects that it may be caused by the TI chips' threshold levels.
Bill suggested minimum rise and fall time of 4ns and maximum 8ns (on a specified
test load). John Lohmeyer wanted the maximum time spec removed because the 2:1 ratio
is too restrictive for silicon. This was agreed to.
Dale Smith suggested using 600mv/s as the maximum slew-rate. Bill Gintz agreed as
long as this is on the test circuit which is very lightly loaded as compared to the
worst case system configuration. All agreed to this number.
Jim McGrath wanted to specify the worst-case capacitive loading. Bill Ham guessed
that worst-case capacitance is around 500pf. The group agreed that we should add a
worst case test load; the question is where should it go? McGrath wanted it added to
the spec itself, not just an annex, because it helps the silicon guys. Lohmeyer
wanted to survey the chip specs and make sure this worst case spec is as close to
that as possible. Group's feeling was that it has to be less than 500pf.
Bill's data showed limited signal swing that leaves no room for the hysteresis specs
agreed to at the last meeting. Bill wanted the hysteresis specs tightened up. This
was not well received since the hysteresis and threshold levels were carefully
chosen at the last meeting. Robbie Shergill asked why not tighten the environment
instead? For example, the cable length and the number of devices could be decreased.
Larry Lamers rather tighten up the environment also.
Kevin Gingrich wanted the system environment better defined before some of the
outstanding silicon issues can be resolved. Therefore, it was decided to come up
with the following lists of outstanding issues at the chip level and at the system
level. All participants are encouraged to focus on these issues.
List of Outstanding Issues:
A) Sysyem Level Issues:
1. Maximum number of devices.
2. Stub length and spacing.
3. Maximum load capacitance and the worst case test load circuit if different from
the current SPI circuit.
4. Termination options allowed
5. Allow mixed configurations of 8- and 16-bit devices?
B) Chip Level Issues:
1. Low-level voltage levels, i.e. hysteresis levels.
2. Maximum slew rate of 600 mv/s ?
3. Test circuits
4. Maximum Voh
5. Maximum Cl the chip drivers can handle
Bill Gintz next showed his data based on a Fast SCSI setup (3m). Bill showed that
actual logic trip levels vary with supply also, as well as the amount of hysteresis
varying with process and temp. Plus, he felt that some amount of glitch filtering
may need to be done. Bill showed the difference in signals depending upon the
termination used. He also mentioned the dependence on data pattern but he cant
define this very well. Bill Gintz's message is to limit the system envelope - "can't
be a smorgasbord at fast rates".
At the end, Bill Ham showed differential system data. Running at 40mt/s Bill's
system had 14ns of time window available.
There was no discussion concerning the timing numbers that have been agreed to at
the last two meetings.
The meeting was adjourned at 3:30 PM.
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