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Cheetah 73LP Product Manual, Rev. E

Single-ended I/O pin assignments for LC models are shown in Table 14. The LC model does not require an I/O cable. It is designed to connect directly to a backpanel connector.

9.7.1.3Cables for low voltage differential drivers/receivers

The SPI-3 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 17 and 18 for examples of recommended SCSI LVD cable types and lengths.

It should be noted from the data in Tables 17 and 18 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 18.

Table 17:

Example shielded round twisted-pair cables—into a multi-drive backplane

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Differential

 

Single-ended

Single-ended

Time

 

Conductor 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 18:

Example twist-n-flat cables—into a multi-drive backplane

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Maximum

 

 

 

 

 

 

 

 

 

 

 

 

 

 

twist-n-flat

 

 

 

Differential

Single-ended

Single-ended

 

Time

 

Conductor DC

cable length

 

 

 

impedance,

impedance,

capacitance,

 

delay,

 

resistance,

for U160

Cable description

nominal

nominal

maximum

 

nominal

 

nominal

transfer rate

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TPE, 22.25" twist, 1.75"

131 ohms

93 ohms

15.3 pF/ft

 

1.45 ns/ft

 

0.105 ohms/ft

6.1 meters

flat, (24" flat to flat), 30

 

 

 

 

 

 

 

 

 

 

 

(20.0 feet)

AWG solid tinned copper

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TPE, 8.1" twist, 1.75" flat,

131 ohms

93 ohms

15.3 pF/ft

 

1.45 ns/ft

 

0.105 ohms/ft

4.9 meters

(9.85" flat to flat), 30 AWG

 

 

 

 

 

 

 

 

 

 

 

(16.66 feet)

solid tinned copper

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TPE, 4.25" twist, 1.75"

131 ohms

93 ohms

15.3 pF/ft

 

1.45 ns/ft

 

0.105 ohms/ft

3.04 meters

flat, (6" flat to flat), 30

 

 

 

 

 

 

 

 

 

 

 

(10.0 feet)

AWG solid tinned copper

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9.8Terminator 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/LWV drives, use terminator modules 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 connec- tor. LC/LCV drives are designed to be plugged into a backpanel connector without cabling.

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Seagate ST336605LW/LC/LCV manual Cables for low voltage differential drivers/receivers, Terminator requirements