Terminator Power - Seagate ST39173N Product Manual

Barracuda 9LP Product Manual, Rev. C
Note. The SCSI protocol chip drives the upper eight data and parity bits of the SCSI bus even when operat-
ing in narrow (eight bit) mode. This is normal operation for this chip. If the unused data bit signals are
connected to conductors that extend out beyond this drive's SCSI connector, correct termination must
be provided for these unused signals at the device/system at each end of the bus onto which this drive
is connected. Termination is required to control radiated emissions and conducted noise on other SCSI
bus signals.
ANSI Standard X3T10/1143D contains additional details about SCSI bus terminator and terminator power
requirements.
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" and "LW" 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 "LC" model drives
These drives cannot furnish terminator power because no conductors in the 80-pin I/O connector are devoted
to terminator power.
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