Quantum DLT 4000 Product Manual page 171

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 DLT4000 drive 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
DLT4000/DLT4500/DLT4700 Cartridge Tape Subsystem 8-11
DLT4000 SCSI Interface