Hardware Reference
In-Depth Information
SATA Cables and Connectors
The physical transmission scheme for SATA uses
differential NRZ
(Non Return to Zero).
This uses a balanced pair of wires, each carrying +0.25V (one-quarter volt). The signals
aresentdifferentially:Ifonewireinthepaircarries+0.25V,theotherwirecarries−0.25V,
where the differential voltage between the two wires is always 0.5V (one-half volt). So,
for a given voltage waveform, the opposite voltage waveform is sent along the adjacent
wire.Differentialtransmissionminimizeselectromagneticradiationandmakesthesignals
easier to read on the receiving end.
A 15-pin power cable and power connector is optional with SATA, providing 3.3V power
in addition to the 5V and 12V provided via the industry-standard 4-pin device power con-
nectors. Although it has 15 pins, this new power connector design is only 24mm (0.945
inches). With 3 pins designated for each of the 3.3V, 5V, and 12V power levels, enough
capacity exists for up to 4.5 amps of current at each voltage, which is plenty for even the
most power-hungry drives. For compatibility with existing power supplies, SATA drives
can be made with the original, standard 4-pin device power connector or the new 15-pin
SATApowerconnector(orboth).Ifthedrivedoesn'thavethetypeofconnectoryouneed,
adapters are available to convert from one type to the other.
Figure 7.9
shows what the SATA signal and power connectors look like, and
Figure 7.10
shows SATA and PATA host adapters on a typical motherboard.
Figure 7.9
SATA signal and power connectors on a typical SATA hard drive.
