Optical Drive and Library SCSI-2 Command Reference

SCSI Command Overview
Drive Control Commands
Chapter 1 1-3
SCSI Command OverviewSCSI Command Overview
Drive Control Commands
This section describes all specifications, except command specifications
of the target. The “SCSI Commands Used by the Target” are described
later in this chapter.
SCSI Bus Phases
The target supports the following phases specified in the SCSI standard.
Arbitration phase
When the drive tries to reconnect to an initiator to continue command
operations, it waits for the BUS FREE phase, then enters the
ARBITRATION phase.
Selection phase
The selection phase allows an initiator to select a target for the purpose
of initiating a target function such as a read or write command. During
the selection phase the I/O signal is negated so that this phase can be
distinguished from the reselection phase. The drive examines the DATA
BUS to determine the selecting initiator SCSI ID. If it cannot detect the
ID, the drive does not respond to the selection.
Reselection phase
The reselection phase allows the target to reconnect to an initiator to
continue the command started by the initiator, but suspended by the
target.
Information transfer phase
The command, data, status, and message phases are all grouped together
as the information transfer phases because they are all used to transfer
data or control information via the data bus.