Seagate ST336807LW Cheetah 10K.7 SCSI Product Manual - Page 92
SCSI LVD cable types and lengths.
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Single-ended I/O cable pin assignments for LW drives are shown in Table 15. Single-ended I/O pin assignments for LC models are shown in Table 16. 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 19 and 20 for examples of recommended SCSI LVD cable types and lengths. It should be noted from the data in Tables 19 and 20 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 20. Table 19: Example shielded round twisted-pair cables - into a multi-drive backplane Cable description Differential impedance, nominal Singleended impedance, nominal Singleended 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 82 Cheetah 10K.7 SCSI Product Manual, Rev. D