Terminator Requirements - Seagate ST373453LC - Cheetah 73.4 GB Hard Drive Product Manual

Cheetah 15K.3 SCSI Product Manual, Rev. G
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 20 and 21 for examples of recommended SCSI
LVD cable types and lengths.
It should be noted from the data in Tables 20 and 21 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 21.
Table 20: 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 21: Twist-n-flat cables—into a multi-drive backplane
Differential
Cable description impedance,
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
9.8

Terminator requirements

Caution: These drives do not have onboard internal terminators. The user, systems integrator or host equip-
ment manufacturer must provide a terminator arrangement external to the drive when termination is
required. For LW drives, terminator modules can be purchased that plug between the SCSI I/O
cable and the drive I/O connector or on the end of a short I/O cable stub extending past the last
cable connector. LC drives are designed to be plugged into a backpanel connector without cabling.
Single-ended Single-ended
impedance, capacitance,
nominal maximum
90 ohms 17 pF/ft
80 ohms 19 pF/ft
85 ohms 20 pF/ft
Single-ended Single-ended
impedance, capacitance,
nominal maximum
93 ohms 15.3 pF/ft
93 ohms 15.3 pF/ft
93 ohms 15.3 pF/ft
Time Conductor 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
Time Conductor 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
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)
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