Serial Attached SCSI [SAS] Bus

The Serial Attached SCSI [SAS] Bus defines the 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