Scsi Interface Physical Description; Scsi Interface Cable Requirements; Figure 14. Physical Interface For "W" Model Drives - Seagate ST34555N Product Manual

Hawk 4XL Product Manual, Rev. A
Figure 14. Physical interface for "W" model drives
9.6.2

SCSI interface physical description

The drives may be daisy-chained together or with other compatible SCSI devices. Both ends of the cable must
be terminated. The "N" and "W" model drives implement single-ended drivers and receivers. All signals are
common between all SCSI devices. The drive may be daisy-chained only with SCSI devices having the same
type drivers and receivers. Devices having single-ended interface circuits cannot be on the same daisy chain
with devices having differential interface circuit. A maximum of 8 ("N" models) or 16 ("W" models) SCSI devices
(including the Host) may be daisy-chained together. The SCSI devices at both ends of the daisy chain are to be
terminated. Intermediate SCSI devices shall not be terminated (see Figure 15). Remove the terminator enable
jumper TE on J2 select header, not the terminator power source selector jumper TP (Figure 11).
9.6.3

SCSI interface cable requirements

In general, cables having the characteristic impedances given in Section 9.6.3.1 are not available; however,
impedances that are somewhat lower are satisfactory. A characteristic impedance as listed in Table 11 is rec-
ommended for unshielded flat cable or twisted pair ribbon cable. 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, the number of loads, transfer rates, and cost to achieve sat-
isfactory 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.
Model "N" drives use nonshielded cable connectors. 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
Pin
1P
2P
3P
4P
J1 J1-Auxiliary
Pin 1 Pin 1A
J1-DC Power
J1-Auxiliary
Pin 1P
Pin 1A
J1
Pin 1
68 Pin
SCSI I/O
Connector
J2
Power
+12V
+12V ret
+ 5V ret
+ 5V
J1-DC Power
4P 3P 2P 1P
PCB
J6
51