Seagate CHEETAH 15K.5 SCSI ST3146855LC - Manual (Page 76)

70 Cheetah 15K.5 SCSI Product Manual, Rev. J
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.
10.7.1.3 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
Cable
description
Differential
impedance
, nominal
Single-
ended
impedance,
nominal
Single-
ended
capacitance,
maximum
Time
delay,
nominal
Conductor
DC
resistance,
nominal
Maximum shielded round
twisted-pair cable length
for U160/U320
30 AWG
solid
130 ohms 90 ohms 17 pF/ft 1.36 ns/ft 0.113 ohms/ft
12 meters minus the SCSI
trace length of the backplane
28 AWG
stranded
123 ohms 80 ohms 19 pF/ft 1.54 ns/ft 0.067 ohms/ft
12 meters minus the SCSI
trace length of the backplane
28 AWG
stranded
132 ohms 85 ohms 20 pF/ft 1.50 ns/ft 0.065 ohms/ft
12 meters minus the SCSI
trace length of the backplane
Table 23: Twist-n-flat cables—into a multi-drive backplane
Cable description
Differential
impedance
, nominal
Single-ended
impedance,
nominal
Single-
ended
capacitance,
maximum
Time
delay,
nominal
Conductor
DC
resistance,
nominal
Maximum Twist-n-flat
cable length
U320 U160
TPE, 22.25” twist,
1.75” flat, (24” flat
to flat), 30 AWG
solid tinned copper
131 ohms 93 ohms 15.3 pF/ft 1.45 ns/ft 0.105 ohms/ft
3.05 meters
(10.0 ft)
6.1 meters
(20.0 ft)
TPE, 8.1” twist,
1.75” flat, (9.85” flat
to flat), 30 AWG
solid tinned copper
131 ohms 93 ohms 15.3 pF/ft 1.45 ns/ft 0.105 ohms/ft
2.45 meters
(8.33 ft)
4.9 meters
(16.66 ft)
TPE, 4.25” twist,
1.75” flat, (6” flat to
flat), 30 AWG solid
tinned copper
131 ohms 93 ohms 15.3 pF/ft 1.45 ns/ft 0.105 ohms/ft
1.52 meters
(5.0 ft)
3.04 meters
(10.0 ft)