eSerial ATA Bus

External Serial ATA (Advanced Technology Attachment)


[eSATA Description] [Interface ICs]
[eSATA Connector/Cable] [eSATA Pinout]
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eSerial ATA Description

External SATA [eSATA] brings the SATA Hard Drive bus outside the PC chassis and allows external devices to be mounted to a SATA connection. The data cable runs out to a maximum of 6 feet. A shielded cable length of 3 feet or 6 feet is common for eSATA. The eSATA cable is shielded, but otherwise the same cable as used with SATA inside the PC. The external eSATA connector does not have the 'L' shaped key like the internal connector. Internal SATA style connectors will not mate with external SATA style connectors. The Serial ATA bus [SATA] is the serial version of the IDE [ATA] spec. SATA uses a 4 conductor cable with two differential pairs [Tx/Rx], plus an additional three grounds pins and a separate power connector. Data runs at 150MBps [1.5GHz] using 8B/10B encoding and 250mV signal swings. Later SATA enhancements move the data transfer speed to; 300MBps [3.0Gbps], and then 600MBps [6.0Gbps]. The current speed for SATA is 300Mbps [3Gbps]. The newest revision is called xSATA and allows external connects to 8 meters.




eSATA Protocol
Nothing in the protocol changes between the internal and external version of SATA. The difference between SATA and eSATA is in the physical section; the cable and connector, not the protocol. The SATA Frame structure used between Host and Device is shown in the graphic below. The frame is made up of multi Dwords, which are in turn encapsulated by flow control and CRC information. The SATA frame begins with a Start-of-frame [SOF]. The SOF is followed by the Frame Information Structure [FIS] which holds the Dwords. Then the Cyclic Redundancy Code [CRC] is placed in the frame. The final block in the message is an End-of-Frame [EOF]. SATA uses a 32bit CRC [calculated over the contents of a (FIS) Frame Information Structure].

SATA Message Frame
Serial ATA [SATA] Bus Protocol Frame

eSATA Electrical
Serial ATA uses LVDS [EIA/TIA-644] with voltages of 250mV. Serial ATA is a point-to-point interface where each device is directly connected to the host via a dedicated link. Because Serial ATA uses a dedicated link, adding another drive to the computer has no impact on bandwidth. 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. The termination resistor is 100 Ohms [+/- 5 Ohms] differential.

SATA Physical
Serial ATA and eSATA [External SATA] uses only 4 signal pins, improving pin efficiency over the parallel ATA interface which used 26 signal pins going between devices [over an 80 conductor ribbon cable onto a 40 pin header connector].
Serial ATA also provides the opportunity for devices to be 'hot-plugged', devices may be inserted or removed while the system is powered on.
The pin-out tables for Serial ATA are listed on the SATA pin Out page. The pinout between eSATA & SATA are identical, only the connection differs.

The primary function of eSATA was to form an interface between an external Hard Disk Drive and the host [computer], which of course would than form an interface between the connector on the case of the unit to the Motherboard within the computer.


SATA Interface IC's




eSATA IC Vendors
All IC functions with be listed on the main SATA page. Most SATA functions are SATA controllers or SATA bridges to another interface.
A few functions are stand alone serial PHY devices, but not that many to maintain two lists.

Both SATA and eSATA use LVDS [EIA/TIA-644] signalling with voltages of 250mV.
The real was the physical layer; the cable, and the connector, so they couldn't be interconnected.


SATA Standard Information

Serial ATA: High Speed Serialized AT Attachment; Revision 1.0, 1/2003
Serial ATA: High Speed Serialized AT Attachment; Revision 1a, 8/2001
Serial ATA II: Electrical Specification; Revision 1.0, 5/2004
eSATAp or eSATA/USB combo port [combining power over the eSATA cable & USB capability] SATA PHY Interface Specification [SAPIS] [Intel]

T13 [www.t13.org] {Technical Committee T13; AT Attachment} ...... Serial ATA {Serial ATA Working Group}


Serial ATA Pin Out

The Serial ATA bus is defined over two separate connectors, one for the data lines and one for the power lines.
The pinout for SATA is listed on the SATA Pinout page.


SATA Connectors and Cable Manufacturers

The cable uses two shielded pairs to carry data. The wire is 26 AWG solid copper wire. The impedance is 100 ohms. Common internal SATA cable lengths are 12, 18, and 36 inches. The internal cables maybe straight both ends or 90 degree. Shielded external SATA [eSATA] data cable run 3 feet or 6 feet. A Cable may also contain both SATA Data and Power combined into an 18 inch cable. Illuminated cable is also available. For reference; the older IDE flat cable is five times wider then the new Serial ATA round cable. The smaller Serial ATA cable allows for better air flow within the Personal Computer chassis.





The main benefit of eSATA over USB is that no bridge is required between two different interfaces.
Most external drives are just SATA drives placed in a case, so using eSATA is just using a shielded cable between two SATA interfaces.
If the external drive uses the USB interface than the physical drive needs to bridge SATA to USB to communicate with the host.
So an external drive with eSATA uses a SATA interface from the HDD through the case and to the host computer, no SATA-USB bridge required.

eSATA Connector Vendors

BAFO Technologies {7Pin Female - 7Pin Female eSATA External Cable with Metal Shield in 0.5 & 1.0 meter or 1.5 and 3.0 feet}

Belkin Corporation {External Serial ATA Cable}

Circuit Assembly {eSATA connectors & eSATA cables}

Molex {Top/bottom surface mount with shell &: dip mount with shell eSATA connectors}

Tripp Lite {7 Pin Straight Male eSATA connector}

Tyco Electronics {Surface mount &' through-hole plug or receptacle eSATA connectors}


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Modified 3/17/12
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