Quantum DLT 8000 Manual descargar pdf (Pagina 116)

SCSI Description

3-14 Quantum DLT 8000 Tape System

If no higher priority SCSI ID bit is true on the DATA BUS, the SCSI

device wins the arbitration and asserts the SEL signal.

• The winning SCSI device waits at least one bus clear delay plus one bus

settle delay after asserting the SEL signal before changing any signals.

3.5.3 SELECTION Phase

The SELECTION phase allows an initiator to select a drive to initiate a drive function.

The SCSI device that won the arbitration has both the BSY and SEL signals asserted

and has delayed at least one bus clear delay plus one bus settle delay before ending the

ARBITRATION phase. The SCSI device that won the arbitration becomes an initiator by

not asserting the I/O signal.

During SELECTION, the I/O signal is negated so that this phase can be distinguished

from the RESELECTION phase.

Selection Sequence

The initiator:

1. Sets the DATA BUS to the OR of its SCSI ID bit and the drive’s SCSI ID

bit.

2. Asserts the ATN signal (signaling that a MESSAGE OUT phase is to follow

the SELECTION phase).

3. Waits at least two deskew delays.

4. Releases the BSY signal.

5. Waits at least one bus settle delay.

6. Looks for a response from the drive.

The drive:

7. Determines that it is selected when the SEL signal and its SCSI ID bit are

true and the BSY and I/O signals are false for at least one bus settle delay.

8. Can examine the DATA BUS to determine the SCSI ID of the selecting

initiator.

9. Asserts the BSY signal within a selection abort time of its most recent

detection of being selected (this is required for correct operation of the

selection time-out procedure).

The drive does not respond to a selection if bad parity is detected. Also, if

more than two SCSI ID bits are on the DATA BUS, the drive does not

respond to selection.

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Quantum DLT 8000 Manual Pagina 116