Proposal posted: SAS-3 addition of POWER DISABLE

Alvin Cox alvin.cox at
Thu Aug 16 09:32:49 PDT 2012

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This proposal changes the functions of P1, P2, and P3 from 3.3V. The signal
assignment of these pins have been changed by other standards that
intermate with SAS connectors. Please review this proposal. The proposal
may be downloaded at:
This proposal was introduced on the 8/16/12 SAS PHY call and will be the
first discussion item on the 8/23/12 SAS PHY call.
*Abstract *
This proposal documents the changes associated with the addition of POWER
DISABLE to SAS-3. This function provides a means for the SAS target device
with a SAS Drive plug connector or SAS MultiLink Drive plug connector to
remove D.C. power (+5V and +12V) from the drive circuitry when the power
disable signal is driven high by the system. The POWER DISABLE signal is
specified on P3. If POWER DISABLE is not supported, P3 shall be not
connected. P1 and P2 are shorted together to provide the same connection as
on SAS drives compliant with versions of the SAS standard previous to
SAS-3, and to be consistent with the recommended implementation specified
by SATA since P1 and P2 have been retired and P3 may implement DEVSLP. The
functional polarity of POWER DISABLE is consistent with DEVSLP if the
DEVSLP function is enabled.
 Extensive research was done prior to drafting this proposal with respect
to system implementation on P1, P2, and P3. No instances were found where
systems provided 3.3V power to these pins. Maintaining the connection of P1
to P2 provided the widest support of legacy implementations that used the
pins for functionality not specified by the SAS standard.
Alvin Cox
Seagate Technology, LLC
Cell 405-206-4809
Office 405-392-3738
E-Mail	alvin.cox at

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