SSA Bus Description, Serial Storage Architecture pinout

SSA Bus

Serial Storage Architecture

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Serial Storage Architecture [SSA] Bus Description

Serial Storage Architecture [SSA] Bus defines the Physical layer interface.
Additional documents describe other layers, SSA may be used with SCSI protocols [SCSI-2 and/or SCSI-3].

Data transmission is 20MBps at up to 40 meters, with full duplex operation up to 40MB/s [20MBps in each direction].
A maximum distance of 2.5 kilometers is possible, but only at a rate of 5MBps.
SSA uses standard [5 volt] TTL switching levels [The differential voltage is 200mV].
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 1 to 2 physical links.

A character is defined as 10 bits. The Bit Encoding used is: Non Return to Zero (NRZ) encoding for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance. Lines are terminated to 3.3 volts [2.97 minimum / 3.63 maximum] via a 75 ohm resistor.
The differential cable impedance is 150 ohms. The internal connector pin-out is shown below, other connector pinouts are also defined. In addition a Power connector is defined.

I have the impression this bus is OBSOLETE, being defined at TTL levels. How ever, it may still reside on a few IBM main-frames. The pinout for a six pin internal port is shown below.

**Internal Port PinOut**
Pin	Signal Name
1	LineOut+
2	LineOut-
3	Chassis/Power GND
4	Logic GND
5	LineIn+
6	LineIn+

{SSA Bus Index}

SSA Standard Organizations

SSA Standards List {ANSI}

SSA Documents, Specifications and Reference Info {T10}

{SSA Interface Index}

SSA Standard

Serial Storage Architecture - Physical Layer 1 (SSA-PH1) Rev 9c 1996
Serial Storage Architecture - Physical Layer 2 (SSA-PH2) Rev 5b 1997
Serial Storage Architecture - SCSI-3 Protocol (SSA-S3P) Rev 5b 1997
Serial Storage Architecture - Transport Layer 2 (SSA-TL2) Rev 5b 1997

It appears that this specification has not been re-affirmed yet. So the release dates listed above for the standards appear to be current.

{Back to SSA Bus Index}

Engineering Design Key words: SSA Standard, SAS, Serial Storage Architecture Hard Drive Bus, Small Computer System Interface, SCSI Specification, SSA Spec, Ultra SCSI Personal Computer Interface, IC, SCSI III Physical Interface, Description, Pinout, Pin-Out, Signal Names, Mainframes, LAN servers, Direct Attached Storage [DAS], Networked Attached Storage [NAS], Storage Area Network [SAN], legacy Interface, Out-dated.


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