Product manual

64 Product Manual - Hawk 2 Family (Wide bus) SCSI-2 (Volume 1), Rev. A
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11.6.4.2 Terminator requirements
Drive I/O termination is not provided internally on ST12400WD or ST12400WC drives. Terminator circuits,
must be provided in some manner external to the ST12400WD/WC drives by the user, systems integrator or
OEM manufacturer. It is highly recommended that ANSI SCSI-2 Standard's Alternative 2 termination (active
termination) be used for single-ended ST12400W and ST12400WC applications, especially if the bus will be
operated at transfer rates above 5 Mbytes/sec. The ST12400W provides on-board active termination that
can be disabled by removal of the enable jumper TE (see Figure 10.1-1). Power for the external terminators
may be taken from the drive (see paragraph 11.6.4.3) by installing a jumper plug on one of the J2-TP (see
Figure 10.1-1a). If the TP jumper is not installed terminator power must be supplied by some other source. All
single initiator/single target (nondaisychain) applications require that the Initiator and disc drive be termi-
nated. Daisychain applications require that only the units at each end of the daisychain be terminated. All
other peripherals on the chain should not be terminated. (See Figure 11.6.3-1).
Note. Where terminators are not required, remove external terminator modules or disable terminators on
the model ST12400W by removing the TE jumper from header J2 (see Figure 10.1-1a). Removal of
terminator power source selection jumper TP does not disconnect the terminators from the circuit.
Note. ACTIVE TERMINATORS ARE HIGHLY RECOMMENDED FOR USE IN THE DAISYCHAIN AS DE-
SCRIBED ABOVE. ACTIVE AND PASSIVE TERMINATORS SHOULD NOT BE MIXED ON THE
SAME SCSI BUS.
11.6.4.3 Terminator power
The model ST12400W/WD drives may be configured to provide terminator power via pins 17, 18, 51 and 52
of the SCSI Bus, to supply power to the SCSI bus. See Figure 11.6.3-1 and 10.1-1. The drive can provide
power both to external terminators at the drive end and to the SCSI Bus terminator power lines to provide
power for terminators at the other end of the I/O cable.
SCSI devices providing terminator power (TERMPWR) shall have the following characteristics:
V TERM = 4.50 V to 5.25 V
800 mA min source drive capability
1.0 A maximum
The model ST12400WC drive cannot furnish terminator power, because no pins in the 80 pin I/O connector
are devoted to terminator power.