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Barracuda 18LP Product Manual, Rev. E
9.6.3
SCSI interface cable requirements
The characteristics of cables used to connect SCSI-3 parallel interface devices are discussed in detail in ANSI
Standard T10/1302D and X3T10/1143D. The cable characteristics that must be considered when interconnect-
ing the drives described in this manual in a SCSI-3 parallel, daisy-chain interconnected system are:
• characteristic impedance (see section 6.1)
• propagation delay (see section 6.1)
• cumulative length (see sections 6.4 and 6.5)
• stub length (see sections 6.4 and 6.5)
• device spacing (see sections 6.4 and 6.5)
To minimize discontinuances and signal reflections, cables of different impedances should not be used in the
same bus. Implementations may require trade-offs in shielding effectiveness, cable length, number of loads
and spacing, 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-20 and
FAST-40 SCSI transfer rates.
Note.
For LVD operation, twisted pair cables are recommended. For LVD Fast-40 operation, twisted pair
cables are strongly recommended. For Fast-80 operation, twisted pair cables are required.
For "LC" models:
The 80 pin connector option is intended for use on drives that plug directly into a PCBA or wall/bracket
mounted connector in the host equipment. In such installations, all backplane wiring segments are subject to
the electromagnetic concepts presented in Standard T10/1302D. For "LC" model drives, installations with con-
nectors on cables are not recommended.
9.6.4
Mating connectors
Part numbers for the different type connectors that mate with the various Barracuda 18LP I/O connectors are
given in the sections following.
9.6.4.1
Mating connectors for "LW" models
The nonshielded cable connector shall be a 68 conductor connector consisting of two rows of 34 male contacts
with adjacent contacts 0.050 inch (1.27 mm) apart.
Recommended mating flat cable connector part numbers are:
Amp Model 786096-7
Amp Model 786090-7
Amp Model 749925-5
Amp Model 88-5870-294-5 W/O Strain Relief (25 mil conductor centers, 30 AWG wire).
Amp Model 1-480420-0
Berg 69307-012
[1]
See Figure 10.
The drive device connector is a nonshielded 68 conductor connector consisting of two rows of 34 female pins
with adjacent pins 50 mils apart. The connector is keyed by means of its shape (see Figure 11a).
Female, 68-pin, panel mount
Female, 68-pin, cable mount
(50 mil conductor centers, 28 or 30 AWG wire)
Use two, 34 conductor, 50 mil center flat cable with this connector.
This type connector can only be used on cable ends. [1]
Use either on cable ends or in cable middle section for daisy-chain
installations [1].
Power connector 4 circuit housing
12-position, 2 x 6, 2 mm receptacle housing
55
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