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SCSI Description
3-12 Quantum DLT 7000 Tape System
If an initiator detects the release of the BSY signal by the drive at any other
time, the drive is indicating an error condition to the initiator. The drive can
perform this transition to the BUS FREE phase independently of the state of the
ATN signal. The initiator manages this condition as an unsuccessful I/O
process termination. The drive terminates the I/O process by clearing all pending
data and status information for the affected nexus. The drive can optionally
prepare sense data that can be retrieved by a REQUEST SENSE command.
Bus Free Sequence
1. BSY and SEL signals are continuously false for one bus settle delay.
2. SCSI devices release all SCSI bus signals within one bus clear delay.
If a SCSI device requires more than one bus settle delay to detect the BUS FREE
phase, then it releases all SCSI bus signals within one bus clear delay minus the
excess time to detect the BUS FREE phase.
The total time to clear the SCSI bus cannot exceed one bus settle delay plus one
bus clear delay.
3.5.2 ARBITRATION Phase
The ARBITRATION phase allows one SCSI device to gain control of the SCSI
bus so that it can initiate or resume an I/O process.
The SCSI device arbitrates for the SCSI bus by asserting both the BSY signal
and its own SCSI ID after a BUS FREE phase occurs.
Arbitration Sequence
1. The SCSI device waits for the BUS FREE phase to occur.
2. The SCSI device waits a minimum of one bus free delay after detection of the
BUS FREE phase before driving any signal.
3. The SCSI device arbitrates for the SCSI bus by asserting the BSY signal and
its SCSI ID.
4. The SCSI device waits at least an arbitration delay to determine arbitration
results.