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SCSI Description
Quantum DLT 7000 Tape System 3-13
NOTE
Step 4 requires that every device complete the arbitration phase to
the point of SEL being asserted (for a SELECTION or RESELECTION
phase) to avoid hanging the bus.
• If a higher priority SCSI ID bit is true on the DATA BUS, the SCSI
device loses the arbitration.
• The losing SCSI device releases the BSY signal and its SCSI ID bit
within one bus clear delay after the SEL signal asserted by the
arbitration winner becomes true.
• The losing SCSI device waits for the SEL signal to become true
before releasing the BSY signal and SCSI ID bit when arbitration is
lost.
• The losing SCSI device returns to Step 1.
• 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.