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7. The tape drive does not act as an initiator on the SCSI bus.
Therefore, the drive does not 1) generated unsolicited interrupts to
the bus, 2) initiate its own SCSI commands, and 3) assert bus reset.
8. A mini-library subsystem is assigned two logical unit numbers
(LUNs): the tape drive is always LUN 0, and the mini-library
component has a default LUN of 1, but may be reconfigured to any
LUN from 0 to 15 via the SCSI MODE SELECT command.
The COMMAND, DATA, STATUS, and MESSAGE phases are known as the
Information Transfer Phases because they are used to transfer data or control
information.
The C/D, I/O, and MSG signals are used to distinguish between the different
information transfer phases (Table 3−5). The drive asserts these three signals and
so controls all information transfer phase changes. The drive can also cause a BUS
FREE phase by releasing the MSG, C/D, I/O, and BSY signals. The initiator can
request a MESSAGE OUT phase by asserting the ATN signal.
The information transfer phases use one or more REQ/ACK handshakes to control
the information transfer. Each REQ/ACK handshake allows the transfer of one
byte of information. During the information transfer phases, the BSY signal
remains true and the SEL signal remains false. Additionally, the drive continuously
envelopes the REQ/ACK handshake(s) with the C/D, I/O, and MSG signals in such
a manner that these control signals are valid for one bus settle delay before the
assertion of the REQ signal of the first handshake and remain valid after the
negation of the ACK signal at the end of the handshake of the last transfer of the
phase.
After the negation of the ACK signal of the last transfer of the phase, the drive can
prepare for a new phase by asserting or negating the C/D, I/O, and MSG signals.
These signals can be changed together or individually. They can be changed in any
order and can be changed more than once (although each line should change only
once). A new phase does not begin until the REQ signal is asserted for the first
byte of the new phase.