Product Manual - Hawk 1 Family SCSI-2 (Volume 1), Rev. D
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11.6.2.2.3
General cable characteristics
In general, cables having the characteristic impedance’s given in 11.6.2.2.1 and 11.6.2.2.2 are not avail-
able; 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 characteristic 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 "N" and "ND" models
Only nonshielded cable connectors are applicable. A 50 conductor flat cable or 25 twisted pair cable shall be
used. A minimum conductor size of 28 AWG should be used to minimize noise effects.
Suggested nonshielded flat cable part numbers are:
Flat cable - 35M-3365-50
Twisted pair - Spectra Twist in flat 455-248-50
Equivalent parts may be used.
Cables for "NC" drive models
The 80 pin connector option is intended for use on drives that plug directly into a wall/bracket mounted
connector in the host equipment Cable mounted connectors would not be used in such a case.
For installations requiring an 80 conductor cable connected I/O, only non-shielded connectors are appli-
cable. Two 40 conductor cables or two 20 twisted pair cables are suggested. A minimum conductor size of
30 AWG should be used, with conductors on 50 mil (1.27 mm) centers.
Suggested nonshielded flat cable part numbers are:
Flat cable: 35M-336540
twisted pair: Spectra Twist in flat 455-248-40
Equivalent parts may be used.
11.6.3
Connector requirements
11.6.3.1
Mating connectors for "N" and "ND" drive models
The nonshielded cable connector shall be a 50 conductor connector consisting of two rows of 25 female
contacts with adjacent contents 100 mils apart.
Recommended Mating Flat Cable Connector Part Numbers are:
Closed end
3M-3425-7000
W/O Strain Relief, No Center Key
(for cable ends)* 3M-3425-7050
With Strain Relief, No Center Key
Dupont-66900-290
With Strain Relief, With Center Key
Open end
3M-3425-6000
W/O Strain Relief, No Center Key
(In Daisychain)
3M-3425-6050
With Strain Relief, No Center Key
Dupont-66900-250
With Strain Relief, With Center Key
*See Figure 11.6.3-2.
The drive device connector is a nonshielded 50 conductor connector consisting of two rows of 25 male pins
with adjacent pins 100 mils apart. The connector is keyed (see Figure 11.6.3-1).
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