Seagate ST373207LW, ST3146855LC, ST3146855LW Cables for low voltage differential drivers/receivers

Single-ended I/O cable pin assignments for LW drives are shown in Table 18.

Single-ended I/O pin assignments for LC models are shown in Table 19. The LC model does not require an I/O cable. It is designed to connect directly to a back panel connector.

10.7.1.3Cables for low voltage differential drivers/receivers

The SPI-3 and SPI-4 specification for differential impedance for LVD cables is 122.5 + 12.5 ohms.

The maximum SCSI bus length between the terminators for a SCSI LVD point-to-point system (one initiator and one target) is 25 meters (82 feet).

The maximum SCSI bus length between the terminators for a SCSI LVD multidrop system (up to 16 total SCSI devices) is 12 meters (39.37 feet). However, implementation of this 12-meter total length is dependent on the configuration of the system and the choice of cable. See Tables 22 and 23 for examples of recommended SCSI LVD cable types and lengths.

It should be noted from the data in Tables 22 and 23 that shielded round twisted-pair cables can be used to implement a 12-meter system, while Twist-n-flat cables cannot be used to implement a 12-meter system due to higher levels of attenuation and crosstalk. In addition, twist-n-flat cables with shorter sections of twist allow greater crosstalk and their lengths must be reduced as shown in Table 23.

Table 22: Shielded round twisted-pair cables—into a multi-drive backplane

		Single-	Single-		Conductor
	Differential	ended	ended	Time	DC	Maximum shielded round
Cable	impedance	impedance,	capacitance,	delay,	resistance,	twisted-pair cable length
description	, nominal	nominal	maximum	nominal	nominal	for U160/U320
30 AWG	130 ohms	90 ohms	17 pF/ft	1.36 ns/ft	0.113 ohms/ft	12 meters minus the SCSI
solid						trace length of the backplane
28 AWG	123 ohms	80 ohms	19 pF/ft	1.54 ns/ft	0.067 ohms/ft	12 meters minus the SCSI
stranded						trace length of the backplane
28 AWG	132 ohms	85 ohms	20 pF/ft	1.50 ns/ft	0.065 ohms/ft	12 meters minus the SCSI
stranded						trace length of the backplane

Table 23: Twist-n-flat cables—into a multi-drive backplane

			Single-		Conductor	Maximum Twist-n-flat
	Differential	Single-ended	ended	Time	DC	cable length
	impedance	impedance,	capacitance,	delay,	resistance,
Cable description	, nominal	nominal	maximum	nominal	nominal	U320	U160
TPE, 22.25” twist,
1.75” flat, (24” flat	131 ohms	93 ohms	15.3 pF/ft	1.45 ns/ft	0.105 ohms/ft	3.05 meters	6.1 meters
to flat), 30 AWG						(10.0 ft)	(20.0 ft)
solid tinned copper
TPE, 8.1” twist,
1.75” flat, (9.85” flat	131 ohms	93 ohms	15.3 pF/ft	1.45 ns/ft	0.105 ohms/ft	2.45 meters	4.9 meters
to flat), 30 AWG						(8.33 ft)	(16.66 ft)
solid tinned copper
TPE, 4.25” twist,
1.75” flat, (6” flat to	131 ohms	93 ohms	15.3 pF/ft	1.45 ns/ft	0.105 ohms/ft	1.52 meters	3.04 meters
flat), 30 AWG solid						(5.0 ft)	(10.0 ft)
tinned copper

70 Cheetah 15K.5 SCSI Product Manual, Rev. J