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68 Constellation.2 SAS Product Manual, Rev. H
The Ready LED Out signal is designed to pull down the cathode of an LED. The anode is attached to the
proper +3.3 volt supply through an appropriate current limiting resistor. The LED and the current limiting resis-
tor are external to the drive. See Table 15 for the output characteristics of the LED drive signals.
12.5.2 Differential signals
The drive SAS differential signals comply with the intra-enclosure (internal connector) requirements of the SAS
standard.
Table 16 defines the general interface characteristics.
12.6 SAS-2 Specification Compliance
Seagate SAS-2 drives are entirely compatible with the latest SAS-2 Specification (T10/1760-D) Revision 16.
The most important characteristic of the SAS-2 drive at 6Gb/s is that the receiver is capable of adapting the
equalizer to optimize the receive margins. The SAS-2 drive has two types of equalizers:
1. A Decision Feedback Equalizer (DFE) which utilizes the standard SAS-2 training pattern transmitted dur-
ing the SNW-3 training gap. The DFE circuit can derive an optimal equalization characteristic to compen-
sate for many of the receive losses in the system.
2. A Feed Forward Equalizer (FFE) optimized to provide balanced receive margins over a range of channels
bounded by the best and worst case channels as defined by the relevant ANSI standard.
12.7 Additional information
Please contact your Seagate representative for SAS electrical details, if required.
For more information about the Phy, Link, Transport, and Applications layers of the SAS interface, refer to the
Seagate SAS Interface Manual, part number 100293071.
For more information about the SCSI commands used by Seagate SAS drives, refer to the Seagate SCSI
Commands Reference Manual, part number 100293068.
Table 15: LED drive signal
State Test condition Output voltage
LED off, high 0 V
≤ VOH ≤ 3.6 V -100 μA < I
OH
< 100 μA
LED on, low I
OL
= 15 mA 0 ≤ V
OL
≤ 0.225 V
Table 16: General interface characteristics
Characteristic Units 1.5Gb/s 3.0Gb/s 6.0Gb/s
Bit rate (nominal) Mbaud 1500 3000 6000
Unit interval (UI)(nominal) ps 666.6 333.3 166.6
Impedance (nominal, differential ) ohm 100 100 100
Transmitter transients, maximum V ± 1.2 ± 1.2 ± 1.2
Receiver transients, maximum V ± 1.2 ± 1.2 ± 1.2