Serial SCSI Bus

Small Computer Systems Interface

[Serial SCSI Description] [SAS Interface ICs]
[SAS Standard Organizations]

Serial Attached SCSI [SAS] Bus Description

The Serial Attached SCSI [SAS] Bus defines Physical layer, PHY Layer, Link Layer, Port layer, and Application Layer. SAS may also just be called Serial SCSI. The Physical Layer consists of two sets of differential lines, one receive set and one transmit set [4-wire total]. The PHY Layer connects the differential Transmitter and Receiver circuits [ICs] to the Physical Layer, which defines the cable, connector, and transceiver [Transmitter / Receiver] characteristics. The external connector will accept 4 physical links, while the cable may hold between 1 and 4 physical links. Internal connectors are also defined. Two data rates are defined: 1.5Gbps and 3.0Gbps over a 100 ohm [+ 15 ohm] differential impedance cable.
SAS uses the Serial ATA physical interface, including the connector receptacle and connector plugs.
SAS transmits data using 8B/10B at a maximum level of 1.2 volts [Tx voltage = 800-1600mV], [Rx voltage = 275-1600mV].
SAS uses big-endian, while SATA uses little-endian byte ordering. SAS uses a 32 bit CRC.
Like SATA, SAS uses LVDS switching.

Two types of ports are defined: A Narrow Port which communicates over a narrow link and contains only one transmit/receive pair, and Wide Port which communicates over a Wide link and contains more than one transmit/receive pair. The Port reside in the PHY layer, and the Link resides in the Physical layer

The Serial Attached SCSI - 2 (SAS-2) draft standard is the second generation of SAS, which adds an option for a 6 Gb/sec link speed. It is based upon SAS-1.1. It continues to document both a physical Layer that is compatible with Serial ATA and protocols for transporting SCSI commands to SAS devices and for transporting ATA commands to SATA devices. Refer to this page link for the Parallel SCSI bus description [older interface].

SAS Physical Link Connector PinOut
Signal 1 Physical 2 Physical 3 Physical 4 Physical
name Link Links Links Links
Rx 0+ S1 S1 S1 S1
Rx 0- S2 S2 S2 S2
Rx 1+ N/A S3 S3 S3
Rx 1- N/A S4 S4 S4
Rx 2+ N/A N/A S5 S5
Rx 2- N/A N/A S6 S6
Rx 3+ N/A N/A N/A S7
Rx 3- N/A N/A N/A S8
Tx 3- N/A N/A N/A S9
Tx 3+ N/A N/A N/A S10
Tx 2- N/A N/A S11 S11
Tx 2+ N/A N/A S12 S12
Tx 1- N/A S13 S13 S13
Tx 1+ N/A S14 S14 S14
Tx 0- S15 S15 S15 S15
Tx 0+ S16 S16 S16 S16
Signal Ground G1 - G9 G1 - G9 G1 - G9 G1 - G9
Chassis Ground Housing Housing Housing Housing

Serial Attached SCSI [SAS] uses three transport protocols:
... 1; Serial SCSI Protocol [SSP] which maps in SCSI, supporting multiple initiators and targets
... 2; Serial ATA Tunneled Protocol [STP] mapping Serial ATA, supporting multiple initiators and targets
... 3; Serial Management Protocol [SMP] a management protocol.

Serial SCSI is used as the physical interface for computer Hard Disk Drives [HDD].

{Serial SCSI Bus Index}

Serial SCSI Standard Organizations

SCSI Standards List {ANSI}

T10 SCSI Documents, Specifications and Reference Info []

Serial Attached SCSI - {SAS), 07/2003, released date
Serial Attached SCSI - 1.1 {SAS-1.1), 09/2005, released date
Serial Attached SCSI - 2.0 {SAS-2.0), 11/2007, released date

SCSI Trade Association

{Back to SAS Bus Index}

Serial SCSI Bus Interface IC Vendors

SCSI components might cover the physical portion [phy], or the protocol portion of the standard.
The physical or really the electrical portion would also be identical to the SATA specification, because they share that portion.

LSI Corporation {SAS Interface IC}

Silicon Bridge {SATA/SAS PHY Interface IC}

Vitesse {Serial Attached SCSI Phy Interface IC}

Select the COMPONENTS icon below for additional types of Integrated Circuit manufacturers.

{Back to Serial SCSI Bus Index}

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Modified 6/13/15
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