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4-6 Quantum DLT 7000 Tape System
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.