SCSI - SPI-2 Issues for November Meeting

Paul D. Aloisi 603-429-8687 aloisi at
Mon Sep 19 10:47:23 PDT 1994

SPIT  (SPI-2) Issues

The first working group meeting for SCSI SPI - 2 (SPIT) will be 
in the next X3T10 meeting November, Tuesday morning in Palm Springs.

Several Key issues will be reviewed for the next generation of 
parallel SCSI. Smaller connectors, Smaller wire AWG (32), and 3.3 
Volt Termpwr issues.

There are new technology components available that will reduce 
the size of the cable and connector size to rival serial SCSI 
connector and cable size.

The new connectors will allow two SCSI connectors to be mounted 
on a standard module bulkhead, reducing the space requirements.

32 AWG wire reduces the insulation thickness to keep the same 
impedance. This will greatly reduce the cable size. 32 AWG wire 
is an issue for Termpwr. The single termpwr 28 AWG wire used in 
SCSI-2 has a DC resistance of  0.64 ohms for 3 meters and 1.28 
ohms for 6 meters. It supported 18 lines of termination. SCSI-3 
SPI used 4 - 30 AWG wires or 0.26 ohms for 3 meters, 0.54 ohms 
for 6 meters with 27 lines of termination. SPI-2 needs to use 
6 - 32 AWG wires or 0.28 for 3 meters, 0.56 ohms for 6 meters 
with 27 lines of termination.

New systems only have 3.3 volt power, 3.3 volt termpwr can be 
used, but these systems must interconnect with 5 volt termpwr. 
The new terminators need to operate over a range from 3.0 to 
5.25 Volts with regulation to keep the high performance now 
mater what the termpwr voltage is.

Diodes cann't be used for the termpwr line, there is not enough 
head room, unidirectional electronic circuit breakers can be 
used to develop termpwr with very little voltage drop. 

Lower capacitance devices need to be stressed as a goal, if not 
directly in the standard.

Fast-20, FAST-40, maybe even Fast-100 needs to be studied for 
the next generations of SPI. 

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