Product manual

52 Product Manual - Hawk 2 Family (Wide bus) SCSI-2 (Volume 1), Rev. A
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11.6.1 DC cable and connector
The model ST12400W/WD drive receives DC power through a 4 pin connector mounted at the rear of the
main PCB (see Figure 11.6.3-1a). Recommended part numbers of the mating connector are listed below, but
equivalent parts may be used (see Table 11.6.1-1).
Table 11.6.1-1. Mating connector parts
Type of cable Connector Contacts (20-14 AWG)
14 AWG AMP 1-480424-0 AMP 60619-4 (Loose Piece)
AMP 61117-4 (Strip)
The model ST12400WC requires no extra DC power cable since both DC power and SCSI I/O signals are all
in the single 80 pin connector. See Table 11.6.3-1b for pin assignments.
11.6.2 Physical characteristics
This section defines the connectors, cables, signals, terminators and bus timing needed to implement SCSI.
11.6.2.1 Physical description
The model W and WD drives may be daisychained together or with other compatible SCSI devices using a
common cable. Both ends of the cable must be terminated. Model ST12400 wide drives do not have on-
board terminator circuits. The ST12400WD drive implements differential drivers and receivers. The model
ST12400W/WC drive implements single ended drivers and receivers. All signals are common between all
SCSI devices. The drive may be daisychained only with SCSI devices having the same type drivers and
receivers. Devices having single ended interface circuits cannot be on the same daisychain with devices
having differential interface circuit. A maximum of 16 SCSI devices (including the Host) may be daisychained
together. The SCSI Devices at both ends of the daisychain are to be terminated. Intermediate SCSI devices
shall not be terminated (see Figure 11.6.3-1). Remove or disable (whichever is applicable) the terminators.
Do not remove the terminator power source selector jumper TP ( See Figure 10.1-1 and accompanying
notes).
"NC" model drives plug into PCB or bulkhead connectors in the Host. They may be connected in a daisy-
chain by the host backplane wiring or PCB circuit runs that have adequate DC current carrying capacity to
support the number of drives plugged into the PCB or bulkhead connectors. A single 80 pin I/O connector
cannot support the DC current needs of several drives, so no daisy-chain cables should be used. A single
drive connected via a cable to a host 80 pin I/O connector is not recommended.
11.6.2.2 Cable requirements ("W" and "WD" models only)
11.6.2.2.1 Single ended I/O circuits ("W" models)
The maximum total cable length for use with "W" model drives (single ended I/O driver and receiver circuits)
shall be 6 metres (19.7 ft.) when operating at line data transfer rates of 5 MBytes/sec or less, and 3 metres
(9.85 ft.) when operating at transfer rates greater than 5 Mbytes/sec (FAST SCSI). A stub length of no more
than 0.1 metre (0.33 ft.) is allowed off the mainline interconnection with any connected equipment. An ideal
impedance match with cable terminators implies a cable characteristic impedance of 132 ohms (see 11.6.2.2.3).
Model ST12400W/WC single ended I/O pin assignments are shown in Table 11.6.3-1a.
11.6.2.2.2 Differential I/O circuits ("WD" models)
The maximum total cable length for use with drives having differential I/O drivers and receiver circuits shall
be 25 metres (82 ft.). A stub length of no more than 0.2 metre (0.66 ft.) is allowed off the mainline interconnec-
tion with any connected equipment. An ideal impedance match with cable terminators implies a cable charac-
teristic impedance of 122 ohms. Model ST12400WD differential I/O pin assignments are shown in Table
11.6.3-1b.