Optical Drive and Library SCSI-2 Command Reference

SCSI Command Overview
Drive Control Commands
Chapter 11-16
Conditions
Attention Condition
The Attention Condition allows an initiator to inform the target that the
initiator has a message ready. The target gets this message at its
convenience by performing a Message Out Phase as follows:
1. If the ATN signal becomes true during a COMMAND phase, the drive
enters the MESSAGE OUT phase after transferring part or all of the
command descriptor block bytes.
2. If the ATN signal becomes true during a DATA phase, the drive
enters the MESSAGE OUT phase at the drives earliest convenience.
The initiator will continue REQ/ACK handshakes until it detects the
phase change.
3. If the ATN signal becomes true during a STATUS phase, the drive
enters the MESSAGE OUT phase after the status byte has been
acknowledged by the initiator.
4. If the ATN signal becomes true during a MESSAGE IN phase, the
drive enters the MESSAGE OUT phase before it sends another
message.
5. If the ATN signal becomes true during a SELECTION phase and
before the initiator releases the BSY signal, the drive enters the
MESSAGE OUT phase immediately after that SELECTION phase.
6. If the ATN signal becomes true during a RESELECTION phase, the
drive enters the MESSAGE OUT phase after sending its IDENTIFY
message for that RESELECTION phase.
Reset Condition
The drive implements the hard reset alternative, upon detection of the
RESET condition. When the drive creates the reset conditions, it clears
all I/O processes including queued I/O processes, releases all
reservations, returns any SCSI device operating modes (MODE SELECT,
PREVENT/ALLOW MEDIUM REMOVAL commands, etc.) to their
initial conditions, and generates UNIT ATTENTION condition.