Barracuda 4LP Product Manual, Rev. D
71
9.8
Terminator requirements
Internal disc drive I/O termination (provided only in model “N” and “W” drives single ended I/O model drives)
consists of active circuits in an LSI module that is permanently mounted on the PCB. All single initiator/single
target (non-daisy-chain) applications require that the Initiator and disc drive be terminated. Daisy-chain appli-
cations 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 10).
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 highly recommended that ANSI SCSI-2 Standard’s Alternative 2 termination (active termination) be used
for applications with single-ended (“N” and “W” models), especially if the bus will be operated at transfer rates
above 5 Mbytes/sec. The “N” and “W” models provide on-board active termination that can be disabled by
removal of the enable jumper TE (see Figure 7d).
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.
Drive models “WD,” “WC,” and “DC” do not have internal terminators available. The user, systems integrator or
host equipment manufacturer must provide a terminator arrangement external to the drive. For “WD” models,
terminator 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.
9.9
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” Models
Pin 26
“W” Models
Pins 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.
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
“WD” model drives
You can configure terminator power from the drive to the SCSI bus or have the host adaptor or other device
supply terminator power to the external terminator. See Section 8.1 for illustrations that show how to place
jumpers for this configuration.
“WC” and “DC” model drives
These drives cannot furnish terminator power because no conductors in the 80-pin I/O connector are devoted
to terminator power.
