Seagate ST91000640SS SAS-2 Specification Compliance, Additional information, LED drive signal

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.

Table 15:	LED drive signal
State		Test condition	Output voltage
LED off, high		0 V ≤ VOH ≤ 3.6 V	-100 μA < IOH < 100 μA
LED on, low		IOL = 15 mA	0 ≤ VOL ≤ 0.225 V

12.5.2Differential 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.

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

12.6SAS-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.

12.7Additional 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.

68 Constellation.2 SAS Product Manual, Rev. H