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3-26 M3099GX/GH OEM Manual
The order in which phases are used on the SCSI bus follows a
prescribed sequence.
The reset condition can abort any phase and is always followed by
the BUS FREE phase. Also any other phase can be followed by the
BUS FREE phase but many such instances are error conditions.
The additional allowable sequences shall be as shown in Figure 3.5.
The normal progression is from the BUS FREE phase to
ARBITRATION, from ARBITRATION to SELECTION or
RESELECTION, and from SELECTION or RESELECTION to
one or more of the information tranfer phases (COMMAND,
DATA, STATUS, or MESSAGE). The final information transfer
phase is normally the MESSAGE IN phase where a
DISCONNECT, or COMMAND COMPLETE message is
transferred, followed by the BUS FREE phase.
Reset or
protocol
error
BUS FREE
SELECTION
ARBITRATION
RESELECTION
DATA IN or
DATA OUT
COMMAND
MESSAGE OUT
STATUS
MESSAGE IN
Figure 3.5 Phase Sequence
SCSI Bus Phases
Sequences
#03.pm5 98.2.22, 1:31 PM26