Quantum DLTtape DLT 4000, Product Manual

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Quantum DLT 4000 Tape Drive 4-1
Chapter 4
MESSAGES
The SCSI message system allows communication between an initiator and the drive for interface
management and command qualification. Messages can be originated by either the initiator or the
drive. This section contains a detailed description of the messages supported by the drives.
4.1 MESSAGE FORMAT
A message can be one or more bytes in length. One or more messages can be
sent during a single MESSAGE phase, but a message cannot be split over
MESSAGE phases. The initiator is required to end the MESSAGE OUT phase
(by negating ATN) when it sends certain messages that are identified in Table
4–2.
When a connection to the drive is established (i.e., the drive is selected with
ATN asserted), the first message byte passed by the initiator must be either an
IDENTIFY, ABORT, or BUS DEVICE RESET message. If not, the drive discards
the message, saves no status information, and goes to the BUS FREE phase.
If an initiator supplies an unsupported message (for example, COMMAND
COMPLETE or a reserved or undefined message code), the drive returns a
MESSAGE REJECT message and continues where it left off (possibly returning
to MESSAGE OUT if ATN is raised).
The first byte of the message, as defined in Table 4–1, determines the format of
the message.