Quantum DLT 2000, Product Manual

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DLT2000 SCSI Interface
DLT2000/DLT2700 Cartridge Tape Subsystem 8-11
IDENTIFY (80h-FFh)
These messages are sent either by the initiator or by the target to establish (or
reestablish) the physical connection path between an initiator and target for a particular
logical unit. The message byte consists of the following bits:
Bit 7: Always set to one.
Bit 6: Set by initiator if target is allowed to disconnect/reconnect.
Bit 5: Must be set to zero ("Target Routines" not supported).
Bit 4: Reserved. Must be set to zero.
Bit 3: Reserved. Must be set to zero.
Bits 2-0: Logical Unit Number (LUN).
When the Identify message is sent from a target to an initiator during reconnection, a
RESTORE POINTERS message is implied.
INITIATOR DETECTED ERROR (05h)
This message is sent from an initiator to inform a target that an error (for example, a
bus parity error) has occurred that does not prevent the target from trying the operation
again. When received, the DLT2000 attempts to retransfer the last command, data, or
status bytes by using the RESTORE POINTERS message mechanism.
LINKED COMMAND COMPLETE (0Ah)
This message is sent from a target to an initiator to indicate that the execution of a
linked command (with the Flag bit zero) is complete and that status has been sent. The
initiator then sets the pointers to the initial state for the next command.
When received as a target, it is handled as an illegal message; the drive enters the
MESSAGE IN phase and returns MESSAGE REJECT.
LINKED COMMAND COMPLETE, with flag (0Bh)
This message is sent from a target to an initiator to indicate that the execution of a
linked command (with the Flag bit set to one) is complete and that status has been sent.
MESSAGE PARITY ERROR (09h)
This message is sent from the initiator to the target to indicate that one or more bytes in
the last message it received had a parity error.
To indicate that it intends to send the message, the initiator sets the ATN signal before
it releases ACK for the REQ/ACK handshake of the message that has the parity error.
This provides an interlock so that the target can determine which message has the parity
error. If the target receives this message under any other conditions, it proceeds directly
to the BUS FREE state by releasing the BSY signal, signifying a catastrophic error.