82 Barracuda 18XL Product Manual, Rev. A
9.8 Terminator requirements
“N” and “W” models have active, permanently mounted LSI terminator circuits on board the PCB.
All single initiator/single target (non-daisy-chain) applications require that the Initiator and disc drive be termi-
nated. 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 10a).
Note.
Remove drive terminator enabling jumper
TE
where terminators are not required. Removal of termina-
tor power source selection jumper
TP
(see Figure 7d) does not disconnect the terminator resistors
from the circuit.
It is required that ANSI SCSI-2 Standard’s Alternative 2 termination (active termination) be used for applica-
tions with single-ended mode, especially if the bus will be operated at transfer rates above 5 Mbytes/sec.
Note.
ACTIVE TERMINATORS ARE REQUIRED FOR USE IN THE DAISY CHAIN AS DESCRIBED
ABOVE. PASSIVE TERMINATORS SHALL NOT BE USED AT ANY TRANSFER SPEED. ACTIVE
AND PASSIVE TERMINATORS SHALL NOT BE MIXED ON THE SAME SCSI BUS.
Drive models “LW” and “LC” do not have internal terminators available. The user, systems integrator or host
equipment manufacturer must provide a terminator arrangement external to the drive. For “LW” models, termi-
nator modules can be purchased that plug between the SCSI I/O cable and the drive I/O connector or on the
end of a short I/O cable stub extending past the last cable connector.
ANSI Standard X3T10/1143D contains additional details about SCSI bus terminator and terminator power
requirements.
9.9 Terminator power
“LW” model drives
You can configure terminator power in two different ways. See Section 8.1 for illustrations that show how to
place jumpers enabling each of the following terminator power configurations:
1. The external terminator accepts terminator power through SCSI bus pins 17, 18, 51, and 52.
2. Drive supplies terminator power to the SCSI bus on pins 17, 18, 51, and 52.
SCSI devices providing terminator power (TERMPWR) must have the following characteristics:
8-bit SCSI V TERM = 4.25 V to 5.25 V
800 mA minimum source drive capability
1.0 A maximum
16-bit SCSI V TERM = 4.25 V to 5.25 V
1,500 mA minimum source drive capability
3.0 A maximum
“LC” model drives
These drives cannot furnish terminator power because no conductors in the 80-pin I/O connector are devoted
to terminator power.
“N” and “W” model drives
You can configure terminator power in four different ways. See Section 8.1 for illustrations that show how to
place jumpers enabling each of the following terminator power configurations:
1. Drive accepts terminator power through SCSI bus pins:
“N” ModelsPin 26
“W” ModelsPins 17, 18, 51, and 52
2. Drive supplies power to the SCSI bus.
3. Drive provides terminator power for optional internal terminator resistors using the drive’s power connector.
4. Drive provides power to its own terminators and to the SCSI bus terminator power line.
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