Serial Storage Architecture
[SSA Bus Description]
[SSA Standard Organizations] [SSA
OnLine Specifications]
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| 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I have the impression this bus is OBSOLETE, being defined at TTL levels.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.
| Pin |
|
|---|---|
| 1 | LineOut+ |
| 2 | LineOut- |
| 3 | Chassis/Power GND |
| 4 | Logic GND |
| 5 | LineIn+ |
| 6 | LineIn+ |
SSA Standards List {ANSI}
SSA Documents, Specifications and Reference Info {T10}
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.
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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