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M3099GX/GH OEM Manual 3-17
INTERFACE
d) After waiting at least an arbitration delay (measured from its
assertion of the BSY signal) the SCSI device shall examine the
DATA BUS. If a higher priority SCSI ID bit is true on the
DATA BUS (DB(7) is the highest), then the SCSI devices has
lost the arbitration and the SCSI device may release its signals
and return to Step(a). If no higher priority SCSI ID bit is true on
the DATA BUS, then the SCSI device has won the arbitration
and it shall assert the SEL signal. Any SCSI device other than the
winner has lost the arbitration and shall release the BSY signal
and its SCSI ID bit within a bus clear delay after the SEL signal
becomes true. An SCSI device that loses arbitration may return to
Step(a).
e) The SCSI device that wins arbitration shall wait at least a bus
clear delay plus a bus settle delay after asserting the SEL signal
before changing any signals.
SELECTION Phase
The SELECTION phase allows an initiator to select a target for the
purpose of initiating some target function (e.g., 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 SCSI device that won the arbitration has both the BSY and SEL
signals asserted and has delayed at least a bus clear delay plus a bus
settle delay before ending the ARBITRATION phase. The SCSI
device that won the arbitration becomes an initator by not asserting
the I/O signal.
The initiator shall set the DATA BUS to a value which is the OR of
its SCSI ID bit and the target’s SCSI ID bit and it shall assert the
ATN signal (indicating that a MESSAGE OUT phase is to follow
the SELECTION phase). The initiator shall the wait at least two
deskew delays and release the BSY signal. The initiator shall then
wait at least a bus settle delay before looking for a response from the
target.
The target shall not respond to selection if bad parity is detected.
Also, if more than two SCSI ID bits are on the DATA BUS, the
target shall not respond to selection.
#03.pm5 98.2.22, 1:31 PM17