Arbitration Phase - Quantum DLT 8000 Product Manual

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.
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.
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.
Quantum DLT 8000 Tape System
NOTE
SCSI Description
3-13