Seagate ST3300655LW Product Manual page 78

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.
9.7.1.3 Cables 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
Differential
Cable impedance
description , nominal
30 AWG
130 ohms
solid
28 AWG
123 ohms
stranded
28 AWG
132 ohms
stranded
Table 23: Twist-n-flat cables—into a multi-drive backplane
Differential
impedance
Cable description , nominal
TPE, 22.25" twist,
1.75" flat, (24" flat
131 ohms
to flat), 30 AWG
solid tinned copper
TPE, 8.1" twist,
1.75" flat, (9.85" flat
131 ohms
to flat), 30 AWG
solid tinned copper
TPE, 4.25" twist,
1.75" flat, (6" flat to
131 ohms
flat), 30 AWG solid
tinned copper
72
Single- Single-
ended ended
impedance, capacitance,
nominal maximum
90 ohms 17 pF/ft
80 ohms 19 pF/ft
85 ohms 20 pF/ft
Single-
Single-ended ended
impedance, capacitance,
nominal maximum
93 ohms 15.3 pF/ft
93 ohms 15.3 pF/ft
93 ohms 15.3 pF/ft
Conductor
Time DC
delay, resistance,
nominal nominal
1.36 ns/ft 0.113 ohms/ft
1.54 ns/ft 0.067 ohms/ft
1.50 ns/ft 0.065 ohms/ft
Conductor
Time DC
delay, resistance,
nominal nominal
1.45 ns/ft 0.105 ohms/ft
1.45 ns/ft 0.105 ohms/ft
1.45 ns/ft 0.105 ohms/ft
Cheetah 15K.5 SCSI Product Manual, Rev. D
Maximum shielded round
twisted-pair cable length
for U160/U320
12 meters minus the SCSI
trace length of the backplane
12 meters minus the SCSI
trace length of the backplane
12 meters minus the SCSI
trace length of the backplane
Maximum Twist-n-flat
cable length
U320 U160
3.05 meters 6.1 meters
(10.0 ft) (20.0 ft)
2.45 meters 4.9 meters
(8.33 ft) (16.66 ft)
1.52 meters 3.04 meters
(5.0 ft) (10.0 ft)