30mv Offset voltage

Bill Galloway BillG at breatech.com
Wed Nov 11 08:25:10 PST 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* "Bill Galloway" <BillG at breatech.com>
*
Paul,

The reason for bringing all of this up is a reflection that causes the
signal to briefly dip below 60mv.  If you go by the figures 44 and 45 then
the receiver may switch.  I know that most (if not all) real receivers will
not respond to this glitch because of their bandwidth.  There is nothing in
the spec that guarantees that a receiver will not see this glitch.  The only
guarantees are in the figures and in annex A.

I understand that Annex A is DC and that figure 45 is AC.... But if a
receiver is not allowed to switch at 30mv DC it will not even come close to
switching at 30mv AC.

What was the reason for the change late in SPI-2?? Everyone I have talked to
meets the 30mv offset easily (table A.5).

We need to give all of the margin that the receiver does not need back to
the system.

Bill Galloway
BREA Technologies Inc.
(281) 988-0358
BillG at breatech.com

-----Original Message-----
From: owner-t10 at Symbios.COM [mailto:owner-t10 at Symbios.COM]On Behalf Of
Aloisi, Paul
Sent: Tuesday, November 10, 1998 10:36 PM
To: 'SCSI Reflector'
Cc: 'Galloway, Bill'
Subject: FW: 30mv Offset voltage


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* "Aloisi, Paul" <aloisi at unitrode.com>
*
Bill,

We changed the threshold for the receivers late in the SPI-2 development, I
believe Annex A is wrong, it should be 60 mV there.

Annex A is DC and the figure 45 is AC

Paul

Paul D. Aloisi                             Phone: 603-429-8687
Unitrode MS 84                         Fax: 603-429-8963
7 Continental Blvd                     Email: aloisi at unitrode.com
Merrimack, NH 03054               Web Site: www.unitrode.com

> ----------
> From: 	Bill Galloway[SMTP:BillG at breatech.com]
> Sent: 	Tuesday, November 10, 1998 6:25 PM
> To: 	Aloisi, Paul
> Subject: 	30mv Offset voltage
>
> * From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
> * "Bill Galloway" <BillG at breatech.com>
> *
> Okay all you analog types.
>
> The way I read table A.5 (in SPI-3), a receiver can have up to +/-30mv of
> offset voltage.  Signal swings between 3.6V and 0.030V cannot cause the
> receiver to change.
>
> If this is true then I believe that Figures 44 and 45 are incorrect.
>
> All of the "May be detected" voltages should be 30mv not 60mv.
> The definition for Vtna and Vtan are correct but all other references to
> 60mv in the figure should be 30mv.
>
> Am I confused or are the figures wrong?????
>
> Bill Galloway
> BREA Technologies Inc.
> (281) 988-0358
> BillG at breatech.com
>
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