Seagate ST12400N Product Manual page 72

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11.6.4.3 Terminator requirements
Internal disc drive I/O termination (provided only in single ended I/O model ST12400N drives) consists of active
circuits in an LSI module that is permanently mounted on the PCB. All single initiator/single target (nondaisy-
chain) applications require that the Initiator and disc drive be terminated. Daisy-chain applications require that
only the units at each end of the daisy-chain be terminated. All other peripherals on the chain must not be
terminated. (See Figure 11.6.3-2).
Note. Remove drive terminator enabling jumper TE (see Figure 10.1-1) where terminators are not required.
Removal of terminator power source selection jumper TP (see Figure 10.1-1) does not disconnect the
terminator resistors from the circuit.
It is highly recommended that ANSI SCSI-2 Standard's Alternative 2 termination (active termination) be used for
single-ended ST12400N and ST12400NC applications, especially if the bus will be operated at transfer rates
above 5 Mbytes/sec. The ST12400N provides on-board active termination that can be disabled by rmoval of the
enable jumper TE (see Figure 10.1-1).
Note. Active terminators are highly recommended for use in the daisy-chain as described above. Active and
passive terminators should not be mixed on the same SCSI bus.
Differential I/O ST12400ND does not have terminators on the PCB. The user, systems integrator or host equip-
ment manufacturer must provide a terminator arrangement external to the drive. Model ST12400NC does not
have terminators on the drive PCB and there is no provision for terminator power in the 80 pin I/O connector.
11.6.4.4 Terminator power
The drive may be configured to accept terminator power from pin 26 of the SCSI Bus, to supply power to the SCSI
bus or to provide terminator power for internal termination circuits from the drive power connector. See Figures
10.1-1 and 11.6-1. The drive can provide power both to its own terminators and to the SCSI Bus terminator power
line (Pin 26) if both "TP" jumpers are on (models ST12400N/ND only).
SCSI devices providing terminator power (TERMPWR)* shall have the following characteristics:
*See Figure 10.1-1 for configuration details.
Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. C
V TERM = 4.50 V to 5.25 V
800 mA min source drive capability
1.0 A maximum