Seagate ST31250N Product Manual page 85

Barracuda 2LP Product Manual, Rev. D
11.7.3.3
11.7.3.4
[3] Total interface cable length should not exceed 82.1 feet (25 meters) from
the host to the end of the daisy chain.
[4] You must provide terminators.
Terminator requirements
ST31250N, ST31250W, ST32550N and ST32550W drives
Internal disc drive I/O termination consists of active circuits contained in
permanently mounted IC terminator packs on the main PCB. All single
initiator/single target (non-daisy-chain) applications require you to terminate
the initiator and drive.
You must terminate both ends of the SCSI bus with ANSI SCSI-2 standard
alternative 2 (active) termination.
Daisy-chain configurations require you to terminate only the units at each
end of the daisy chain. Do not terminate any other peripheral on the chain.
Note. Remove the Enable SCSI Terminator jumper from J1 pins 5 and 6
when terminators are not required.
ST31250WC/DC and ST32550WC/DC drives
SCA connector drives do not have internal terminators available. Provide
external active terminators when termination is required.
ST31250ND, ST31250WD, ST32550ND and ST32550WD drives
Differential I/O Barracuda drives do not have provisions to add terminator
sockets on the PCB. You must provide external termination.
Terminator power
ST31250N, ST31250W, ST32550N and ST32550W drives
You can configure terminator power in four different ways. See Section 10.1
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
ST31250N and ST32550N
ST31250W and ST32550W
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:
• V TERM = 4.50V to 5.25V
• 800 mA minimum source drive capability
• 1.0A maximum
ST31250ND, ST31250WD, ST32550ND and ST32550WD drives
You can configure terminator power only from the drive to the SCSI bus.
Pin 26
Pins 17, 18, 51, and 52
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