HP Surestore 28/48-Slot with DLT7000 Digital Linear Tape SCSI-2 Drive and SCSI - Page 28

SCSI Command Overview Library Control Commands Library Control Commands This section describes all specifications, except the target command specifications. The SCSI commands used by the targets are described later in Chapter 2. SCSI Bus Phases The target supports all phases specified in the SCSI standard. This section describes the following phases: • Arbitration • Selection • Reselection • Information Transfer • Data • Command • Message • Status Arbitration Phase The arbitration phase allows one SCSI device to gain control of the SCSI bus so that it can initiate or resume an I/O process. Selection Phase The selection phase allows an initiator to select a target to initiate 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. Reselection Phase The reselection phase allows the target to reconnect to an initiator. The purpose of this phase is to continue the command operation already started by the initiator, but suspended by the target. 1- 4 Chapter 1