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4.3.4 RESELECTION phase
RESELECTION is an optional phase that allows a target to reconnect to an
initiator for the purpose of continuing some operation that was previously started
by the initiator but was suspended by the target (i.e., the target disconnected by
allowing a BUS FREE phase to occur before the operation was complete).
— Upon completing the ARBITRATION phase, the winning SCSI device has both
the BSY and SEL signals asserted and has delayd at least a bus clear delay plus
a bus settle delay. The winning SCSI device becomes a target by asserting the
I/O signal.
“ The winning SCSI device shall also set the DATA BUS to a value that is the
logical OR of its SCSI ID bit and the initiatorπs SCSI ID bit.
” The target shall wait at least two deskew delays and release the BSY signal.
‘ The target shall then wait at least a bus settle delay before looking for a
response from the initiator.
’ The initiator shall determine that it is reselected when the SEL and I/O signals
and its SCSI ID bit are true and the BSY signal is false for at least a bus settle
delay. The reselected initiator may examine the DATA BUS in order to
determine the SCSI ID of the reselecting target. The reselected initiator shall
then assert the BSY signal within a selection abort time of its most recent
detection of being reselected; this is required for correct operation of the time>
out procedure. The initiator shall not respond to a RESELECTION phase if bad
parity is detected. Also, the initiator shall not respond to a RESELECTION
phase if other than two SCSI ID bits are on the DATA BUS.
÷ After the target detects the BSY signal is true, it shall also assert the BSY
signal and wait at least two deskew delays and then release the SEL signal.
The target may then change the I/O signal and the DATA BUS. After the
reselected initiator detects the SEL signal is false, it shall release the BSY
signal. The target shall continue asserting the BSY signal until it relinguishes
the SCSI bus.
TARG
deskew
delay ¥ 2
bus clear delay
+ bus settle delay
deskew
delay ¥ 2
RESELECTION phase
I/O
BSY
SEL
DB
TARG INIT
INIT
4 $ 16