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Appendix B. SCSI Bus Signal Timing

B–14 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives

B.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.

7. No less than two deskew delays after the initiator detects that the BSY signal

has been asserted by the target/drive, it releases the SEL signal and can change

the DATA BUS.

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