Seagate ST373455LW ユーザーズマニュアル

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.

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.

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

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)