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 disk drives.

4.1MESSAGE 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.

Quantum DLT 7000 Tape System

4-1

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Quantum Instruments DLT 7000 manual Messages, Message Format
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DLT 7000 specifications

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