Arbitration; Selection; Reselection; Information Transfer - Sun Microsystems storagetek sl500 Reference Manual

Arbitration

The Arbitration phase allows an initiator (or target during reselection) to gain
control of the SCSI bus. All devices requiring use of the bus assert their SCSI IDs to
gain control. If multiple devices attempt to gain control of the bus at the same time,
the device with the highest-priority SCSI ID obtains control over the bus.

Selection

The Selection phase allows an initiator to select a target to perform some operation.
In the Selection phase, the initiator asserts both its SCSI ID and the SCSI ID of the
target being selected on the bus. This selection process informs the device that it is
being selected and identifies the initiator that is performing the selection.

Reselection

The Reselection phase allows the target to reconnect to an initiator after
disconnecting.

Information Transfer

Four Information Transfer phases transfer data or provide status over the SCSI bus:

TABLE 3-1 Information Transfer Data

Command
Data
Data In
Data Out
Message
Message In
Message Out
Status
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The Command phase allows the device to request command
information from the initiator.
Two types of Data phases transfer data in asynchronous modes:
The target sends data to the initiator.
The initiator sends data to the target.
There are two types of Message phases:
The target sends messages to the initiator.
The target receives messages from the initiator. The target invokes
this phase when the initiator asserts the attention (ATN) signal.
The Status phase allows the target to send status information to
the initiator.
Bus Phases
Chapter 3 SCSI Bus Operations 17