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Messages

4-6 Quantum DLT 4000 Tape Drive

4.2.4 DISCONNECT Message (04h)

The DISCONNECT message is sent from the drive to inform the initiator that

the present connection is going to be broken (the drive plans to disconnect by

releasing the BSY signal) and a later reconnect will be required to complete the

current I/O process. The message does not cause the initiator to save the data

pointer. After sending the message, the drive goes to the BUS FREE phase by

releasing the BSY signal.

The DISCONNECT message can also be sent by the initiator to tell the drive to

suspend the current phase and disconnect from the bus. The drive’s response to

and its handling of a DISCONNECT message are based on when, in the I/O

process, the initiator introduces the DISCONNECT message. Table 4–4

summarizes the drive’s response.

Table 4–4 Drive Response to DISCONNECT Message

BUS Phase Drive Response

SELECTION The drive discards the DISCONNECT message and goes to BUS FREE.

COMMAND The drive discards the DISCONNECT message and goes to BUS FREE. The

ATTENTION request is ignored while the Command Descriptor Block is fetched.

The drive does not switch to MESSAGE OUT until the current DMA completes.

DATA The ATTENTION request is ignored while the current data transfer completes;

that is, the drive does not switch to MESSAGE OUT until after the current DMA

completes. The drive returns a MESSAGE REJECT message and responds with

CHECK CONDITION status, indicating the command aborted because of an

invalid message.

STATUS The drive sends a MESSAGE REJECT message, then sends COMMAND

COMPLETE.

MESSAGE IN The drive sends a MESSAGE REJECT message and switches to the BUS FREE

phase.

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Quantum DLT 4000 Manual Página 94