Fujitsu MAB3091, MAC3045, MAB3045 manual Total cable length of Scsi cable, Scsi cable requirements

The maximum length of the SCSI cable is as follow. If more than one SCSI device is connected, the total cable length must not exceed the value given in Table 4.2. The cable length between single-ended type SCSI devices must be more than 30 cm (recommended: 50 cm or more). Each system should decide the cable length between SCSI devices so that the total cable length of the system satisfies the specification.

Table 4.4 Total cable length of SCSI cable

Type	16-bit SCSI
	Fast SCSI	Ultra SCSI
Single-ended	Up to 3 m	Up to 3.0 m
	[Up to 6 m is allowable for	[4 SCSI devices having
	5 MB/s or less]	capacitance of 25 pF]
		Up to 1.5 m
		[5 to 8 SCSI devices
		having capacitance of 25 pF]

For the SCSI cables, the use of 25- and 34-pair twisted pair cables satisfying the requirements in Table 4.5 is recommended.

Table 4.5	SCSI cable requirements
Requirements		16-bit SCSI (34-pair)
Conductor size		30 AWG or bigger
Characteristic impedance		90 to 132 Ω
Twist pair cable condition		Pins n and n + 33

To maintain the transmission characteristics and reduce signal reflection, cables having different a characteristic impedance must not be used on the same SCSI bus.

When an SCSI device is connected to the SCSI cable at a point other than either end of the cable, connection to the SCSI connector must be at a branch point of the cable. If an SCSI device is connected to last SCSI device except when the cable has a terminating resistor. (See Figure 4.27.)

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