SCSI - SPI-2 Issues for November Meeting
Paul D. Aloisi 603-429-8687
aloisi at uicc.com
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.
More information about the T10