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7.3 Physical Requirements
C156-E228-02EN 7-9
7.3.2 Interface cable
For the interface cable, a 25-pair, twisted-pair cable that satisfies the requirements
listed in Table 7.2 should be used.
Table 7.2 Interface cable requirements
Item
Conductor size 28 AWG or bigger
Characteristic impedance
100Ω to 132Ω
In the 25-pair twisted cable, pins n and n + 1 (where n is odd) on the interface
connector must be connected to a pair. Cables having the same characteristic
impedance must be used in the same SCSI bus to reduce signal reflection and
maintain transmission characteristics.
The maximum length of the interface cable is 6 m. But the cable length is
restricted according to the synchronized transfer speed. When an SCSI device is
connected to the interface cable except at one of the ends, the connection to the
SCSI connector must be at a cable branchpoint. When an SCSI device is
connected to an end of the SCSI bus, there must not be any cable wiring after the
SCSI device unless the cable has a terminating resistor. (See Figure 7.7.)