Seagate ST336938LW, ST318418N manual Terminator requirements, Terminator power N drives, LW drives

72 Barracuda 36ES2 Product Manual, Rev. B

9.8Terminator requirements

N 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 21).

Note. Remove drive terminator enabling jumper TE where terminators are not required. Removal of termina- tor power source selection jumper TP (see Figure 14) 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. Do not use passive ter- minators at any transfer speed. Do not mix active and passive terminators on the same SCSI bus.

Caution: LW models do not have onboard internal terminators. The user, systems integrator or host equip- ment manufacturer must provide a terminator arrangement external to the drive when termination is required. For LW drives, 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.

ANSI Standard X3T10/1143D contains additional details about SCSI bus terminator and terminator power requirements.

9.9Terminator power

N 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 pin 26 on N models.

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

1.0A maximum

16-bit SCSI:

V TERM = 4.25 V to 5.25 V

1,500 mA minimum source drive capability

3.0 A maximum

LW 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.