Product manual

Product Manual - Hawk 2 Family (Wide bus) SCSI-2 (Volume 1), Rev. A 53
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11.6.2.2.3 General cable characteristics
In general, cables having the characteristic impedance’s given above are not available; however, impedance’s
that are somewhat lower are satisfactory. A characteristic impedance of 100 ohm ±10% is recommended for
unshielded flat or twisted pair ribbon cable. However, most available cables have a somewhat lower charac-
teristic impedance. To minimize discontinuities and signal reflections, cables of different impedance’s should
not be used in the same bus. Implementations may require tradeoffs in shielding effectiveness, cable length,
the number of loads, transfer rates, and cost to achieve satisfactory system operation. If shielded and
unshielded cables are mixed within the same SCSI bus, the effect of impedance mismatch must be carefully
considered. Proper impedance matching is especially important in order to maintain adequate margin at
FAST SCSI transfer rates.
Cable for "W/WD" model drives
Only nonshielded cable is applicable. A 68 conductor flat cable or two, 34 conductor cables shall be used.
Conductors should be on 50 (1.27 mm) mil centers to be used with connector listed in 11.6.3.1. A minimum
conductor size of 28 AWG should be used to minimize noise effects.
Suggested nonshielded flat cable part numbers are:
Flat cable - 35M-3365-68 Twisted pair - Spectra Twist in flat 455-248-68
Equivalent parts may be used.
Cables for "WC" drive models
The 80 pin connector option is intended for use on drives that plug directly into a wall or bracket mounted
connector in the host equipment. Cable mounted connectors would not be used in such a case. Installations
with cable mounted connectors are not recommended.
11.6.3 Connector requirements
11.6.3.1 Mating connectors for model ST12400W/WD
The nonshielded cable connector shall be a 68 conductor connector consisting of two rows of 34 male
contacts with adjacent contacts 1.27 mm (0.050 inch) apart.
Recommended Mating Connector Part Numbers for above flat cable are:
Closed end Amp Model 749925-5 (50 mil conductor centers for 28 or 30 AWG wire) This
(for cable ends) connector can only be used on cable ends.
Open end Amplimite 88-5870-294-5 W/O Strain Relief, (25 mil conductor centers, 30 AWG wire).
Use either on cable ends or in cable middle section for
daisychain installations.
The disc drive device connector is a nonshielded 68 conductor connector consisting of two rows of 34 female
pins with adjacent pins 1.27 mm (0.050 inches) apart. The connector is keyed by means of its shape (see
Figure 11.6.3-1a).