Seagate ST3300655LC Cheetah 15K.5 SCSI Product Manual - Page 76

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 Differential Cable impedance description , 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 Table 23: Twist-n-flat cables-into a multi-drive backplane Cable description Differential impedance , nominal Single-ended impedance, nominal Singleended 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 3.04 meters (5.0 ft) (10.0 ft) 70 Cheetah 15K.5 SCSI Product Manual, Rev. J