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SCSI BUS
7-24 C156-E228-02EN
(4) Timeout procedure
If the INIT cannot detect the response from TARG when the Selection Timeout
Delay (or longer) has passed after starting the SELECTION phase, the timeout
procedure shall be performed through one of the following schemes:
• The INIT asserts the RST signal and creates the RESET condition.
• The INIT maintains SEL signal true and releases the data bus (SCSI IDs).
Subsequently, the INIT waits for the response from TARG for at least
Selection About Time + Deskew Delay × 2. If no response is detected, the
INIT releases the SEL signal allowing the SCSI bus to go to the BUS FREE
phase. If the INIT detects the response from TARG during this period, the
INIT considers the SELECTION phase to have completed normally.
7.6.4 RESELECTION phase
The TARG selects an INIT during the RESELECTION phase. The
RESELECTION phase can only be used in systems with ARBITRATION phase
implemented.
The TARG reconnects the INIT using this RESELECTION phase when the
TARG restarts the command processing that is in the disconnect state on the SCSI
bus.
(1) Start sequence
A TARG performs the RESELECTION phase in the following sequence after
obtaining control of the SCSI bus through the ARBITRATION phase:
1) The TARG waits at least Bus Clear Delay + Bus Settle Delay after asserting
the SEL signal.
2) The TARG sends the SCSI ID of TARG itself and INIT and asserts the I/O
signal. (The TARG can obtain control of the SCSI bus by asserting the I/O
signal.)
3) The TARG releases the BSY signal after waiting at least Deskew Delay × 2,
then wait at least Bus Settle Delay before looking for the response from the
INIT (BSY signal).