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C141-E035-02EN4 - 26
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
16-bit SCSI
Fast SCSI Ultra SCSI
Single-ended Up to 3 m
[Up to 6 m is allowable for
5 MB/s or less]
Up to 3.0 m
[4 SCSI devices having
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.)
Type