Quantum DLTtape DLT 4000, Product Manual

Page: 76 / 300

SCSI Description
3-14 Quantum DLT 4000 Tape Drive
3.5.3.1 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.
Note that the initiator will release the SEL signal and may change the DATA
BUS no less than two deskew delays after it detects that the BSY signal is true.
The drive waits until the SEL signal is false before asserting the REQ signal to
enter an information transfer phase. Other signals (e.g., MSG, C/D) may also
be asserted.
3.5.3.2 Selection Time-Out
Two optional time-out procedures are specified for clearing the SCSI bus if the
initiator waits a minimum of a selection time-out delay and there has been no
BSY signal response from the drive.