Quantum DLT 4000 Manual descargar pdf (Pagina 82)

SCSI Description

3-20 Quantum DLT 4000 Tape Drive

3.5.5.1 Asynchronous Data Transfer

Drive to Initiator Transfer Procedure

1. The drive drives the DB (7–0, P) signals to their desired values.

2. Drive delays at least one deskew delay plus a cable skew delay.

3. Drive asserts the REQ signal.

4. Initiator reads the DB (7–0, P) signals.

5. Initiator indicates its acceptance of the data by asserting the ACK signal.

6. When ACK is true at the drive, drive can change or release the DB (7–0, P)

signals.

7. Drive negates the REQ signal.

8. Initiator negates the ACK signal.

9. Drive can continue the transfer by driving the DB (7–0, P) signals and

asserting the REQ signal (Steps 1 – 3).

Initiator-to-Drive Transfer Procedure

1. Drive asserts the REQ signal.

2. Initiator drives the DB (7–0, P) signals to their desired values.

3. Initiator delays at least one deskew delay plus a cable skew delay.

4. Initiator asserts the ACK signal.

5. When ACK is true at the drive, drive reads the DB (7–0, P) signals.

6. Drive negates the REQ signal.

7. Initiator can change or release the DB (7–0, P) signals.

8. Initiator negates the ACK signal.

9. Drive can continue the transfer by asserting the REQ signal (Step 1).

3.5.5.2 Synchronous Data Transfer

Synchronous Data Transfer is optional and is only used in DATA phases and

only if a synchronous data transfer agreement is established. The REQ/ACK

offset specifies the maximum number of REQ pulses that can be sent by the

drive in advance of the number of ACK pulses received from the initiator,

establishing a pacing mechanism. If the number of REQ pulses exceeds the

number of ACK pulses by the REQ/ACK offset, the drive does not assert the

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Quantum DLT 4000 Manual Pagina 82