SPI-2/Fast-40 pins

Jim McGrath jmcgrath at qntm.com
Tue May 23 10:57:44 PDT 1995

        Reply to:   RE>>SPI-2/Fast-40 pins

Why over 3 meters?   Single ended SCSI is defined for 6 m.  Fast SCSI
was restricted to 3, and Fast-20 to 1.5 to 3, but this was only for
data transfer operations - since we never changed anything having
to do with non-DATA phase operations, the original 6 m should still
hold.  If we enhance REQ/ACK/DATA/PARITY to go > 6 m, then 6 m 
due to the other lines beomes the limiting factor.

Actually, the original 6 m single ended SCSI limit was probably a
REQ/ACK type limit as well, so maybe we can go longer.  Does anyone
remember (John?) and/or have done empirical tests?


Date: 5/22/95 1:02 PM
To: Jim McGrath
From: Walter Bridgewater x2371
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Date: Mon, 22 May 95 12:20:59 PDT
From: wally at eng.adaptec.com (Walter Bridgewater x2371)
Message-Id: <9505221920.AA19208 at eng.adaptec.com>
To: scsi at wichitaks.ncr.com
Subject: RE: SPI-2/Fast-40 pins

SCSI Reflector,

I agree that at least ack, req, data & parity have to be differential
for the reasons Tak suggest.

If the other 7 signals are single ended, 
Then their slew rates should be slowed down proportional to any
length increase beyond 3 meters.


Wally Bridgewater

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