SATA pinout: S1-S7 data and P1-P15 power

Hot plug: contact lengths and precharge

The SATA plug has three contact lengths. On a backplane (drive plugged in directly), P4 and P12 mate first, then the precharge pins (P3, P7, P13) and the other grounds, and finally the signals and the remaining power pins. Each voltage therefore has one pin that feeds the drive before the other two: that is precharge. The Seagate Barracuda 7200.11 manual describes exactly this sequence.

With a cable, the order still exists but the specification states that hot plugging is not supported with the cable receptacle. For a hot-swap drive bay we therefore design a backplane that takes the drive plug directly, not a cable.

P3 and the PWDIS trap (SATA 3.3)

Up to SATA 3.1, P1, P2 and P3 carried 3.3 V and had to be bused together in the drive. The 3.3 V rail saw very little use and SATA-IO retired those pins. SATA 3.3 (published 2 February 2016) gives P3 a new job, Power Disable (PWDIS): a high level between 2.1 and 3.6 V cuts power to the drive electronics, which lets an enclosure hard-reset a drive remotely.

The trap: an older power supply or backplane that puts 3.3 V on P3 holds a PWDIS drive in permanent reset, and it never spins up. Western Digital documents this for its Ultrastar SATA drives and reports no damage; the usual workaround is a Molex to SATA adapter, which supplies no 3.3 V. On a host board we therefore never tie P3 to 3.3 V: we leave it open, or drive it from a dedicated output when remote power-off is wanted.

The 3.3 V on P1 and P2 is usually unused: WD Ultrastar drives declare them not used, and an industrial 2.5-inch SSD such as the Innodisk 3MG2-P leaves P1 to P3 and P13 to P15 unconnected. Check the target drive datasheet before you drop a rail.

P11: staggered spin-up and activity LED

P11 changes direction during power-up. Before PHYRDY it is an input: the host uses it to disable staggered spin-up (DSS). After PHYRDY it is an output: the drive signals activity (DAS), mostly useful on a backplane to light one LED per bay. A host uses only one of the two functions.

Pin P11 of the power cable receptacle is always grounded. A drive that sees P11 grounded spins up as soon as power is applied, with no staggered spin-up. To stagger the spin-up of several drives, the host board must leave P11 open, and the drive must support the feature. Western Digital caps the high level on P11 at 3.3 V.

Pair routing and AC coupling

Pairs A and B are AC-coupled differential links: one series capacitor on each wire, placed where the controller or redriver reference design puts it. Diodes (Pericom) recommends low-ESR X7R 10 nF capacitors in 0402 for its SATA redrivers; the TI SN75LVCP601 redriver datasheet lists 12 nF in its recommended operating conditions.

Route each pair at 100 Ω differential (±20 % target per the Diodes application note), with under 5 mils of length mismatch between + and -, pair-to-pair spacing above three times the gap, and few, symmetric vias. A swapped polarity or a swapped pair is the costliest mistake: A is the drive input, B its output. The internal cable is limited to 1 m.

Drive-side plug dimensions

The drive plug is defined mechanically by SFF-8482, which describes the SAS plug; its primary contact set follows the SATA layout, and SFF-8223 puts the connector in the same place so a SAS backplane accepts a SATA drive. The housing is 42.73 mm long (reference dimension) and 4.00 mm high. The 22 contacts, 0.84 mm wide, sit at 1.27 mm pitch: P15 and S1 are 15.875 mm either side of the centerline of the 33.43 mm slot.

That gives a contact zone of 18.62 mm for power (14 pitches plus one contact width) and 8.46 mm for data, with 6.35 mm between the P1 and S7 centers, or 5.51 mm edge to edge. For sequencing, SFF-8482 offsets the forward and set-back plug contacts by 0.50 mm nominal, which produces the three contact levels described above.

eSATA, mSATA and slimline SATA

eSATA is the external, hot-pluggable version of the data link: shielded cable up to 2 m, no L-shaped key, insertion depth raised from 5 to 6.6 mm, over 5,000 mating cycles against 50 for the internal connector, and its own electrical levels (Gen1m, Gen2m).

mSATA reuses the Mini PCI Express card format and connector, with a SATA interface behind it. An mSATA card fits a mini PCIe slot but only works if that slot is wired to a SATA host controller. An M.2 SSD can carry SATA too: see our page on M.2 keys.

The slimline connector of thin optical drives keeps the 7-pin data segment with a reduced power segment. The public sources we found disagree on how that segment is numbered; we do not publish its pinout until we can check it against a manufacturer document.