Seagate ST34520N - Medalist 4.55 GB Hard Drive, Product Manual

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Medalist Pro Product Manual, Rev. D 59
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.
For “WC” and “LC” models:
The 80 pin connector option is intended for use on drives that plug directly into a PCB or wall/bracket mounted
connector in the host equipment. In such installations, all backplane wiring segments are subject to the electro-
magnetic concepts presented in Standard X3T10/1142D, section 6. For “WC” and “LC” model drives, installa-
tions with connectors on cables are not recommended.
9.6.3.1 Single-ended I/O circuits (“N” and “W” models)
The maximum total cable length allowed with drives having single-ended I/O driver and receiver circuits
depends on several factors. Table 15 lists the maximum lengths allowed for different configurations of drive
usage. These values are from the ANSI SCSI-3 Fast-20 (also called Ultra SCSI) specification X3T10/1071D.
All device I/O lines must have equal to or less than 25 pf capacitance to ground, measured at the beginning of
the stub.
A stub length of no more than 0.1 meter (0.33 foot) is allowed off the mainline interconnection with any con-
nected equipment. The stub length is measured from the transceiver to the connection to the mainline SCSI
bus.
Single-ended I/O pin assignments are shown in Tables 16, 17, and 19.
9.6.4 Mating connectors
Part numbers for the different type connectors that mate with the various Medalist Pro I/O connectors are given
in the following sections.
9.6.4.1 Mating connectors for “N” models
The nonshielded cable connector shall be a 50 conductor connector consisting of two rows of 25 female con-
tacts with adjacent contacts 0.1 inches (2.54 mm) apart.
Recommended mating flat cable connector part numbers are:
[1] See Figure 19.
The drive device connector is a nonshielded 50 conductor connector consisting of two rows of 25 male pins
with adjacent pins 0.1 inches (2.54 mm) apart. The connector is keyed (see Figure 20).
Mating panel mount connector: 3M-CHE-2050-J01A10-KLE.
Table 15: Cable characteristics for single-ended circuits
I/O transfer rate
Maximum number of
devices on line Maximum cable
length allowed
Transmission line impedance
REQ/ACK Other signals
< 10 M transfers/s 8 (reg. SCSI bus) 6 meters (19.7 ft.) 90 ± 6 Ohms 90 ± 10 Ohms
< 10 M transfers/s
16 (wide SCSI bus) 6 meters (19.7 ft.) 90 ± 6 Ohms 90 ± 10 Ohms
< 20 M transfers/s 4 (reg./wide SCSI bus) 3 meters (9.8 ft.) 90 ± 6 Ohms 90 ± 10 Ohms
< 20 M transfers/s 8 (reg./wide SCSI bus) 1.5 meters (4.9 ft.) 90 ± 6 Ohms 90 ± 10 Ohms
Closed end 3M-3425-7000 W/O Strain Relief, No Center Key
(for cable 3M-3425-7050 With Strain Relief, No Center Key
ends)[1] Dupont-66900-290 With Strain Relief, With Center Key
Open end 3M-3425-6000 W/O Strain Relief, No Center Key
(In daisy chain)[1] 3M-3425-6050 With Strain Relief, No Center Key
Dupont-66900-250 With Strain Relief, With Center Key