Avago Technologies LSI8751D User Manual
Page 120
5-4
SCSI Operating Registers
2. It asserts SBSY/ and its SCSI ID (the highest priority
ID stored in the
register) onto the
SCSI bus.
3. If the SSEL/ signal is asserted by another SCSI device
or if the LSI53C875 detects a higher priority ID, the
LSI53C875 deasserts BSY, deasserts its ID, and waits
until the next bus free state to try arbitration again.
4. The LSI53C875 repeats arbitration until it wins control
of the SCSI bus. When it wins, the Won Arbitration bit
is set in the
register, bit 2.
5. The LSI53C875 performs selection by asserting the
following onto the SCSI bus: SSEL/, the target’s ID
(stored in the
register),
and the LSI53C875’s ID (stored in the
register).
6. After a selection is complete, the Function Complete
bit is set in the
SCSI Interrupt Status Zero (SIST0)
register, bit 6.
7. If a selection time-out occurs, the Selection Time-Out
bit is set in the
SCSI Interrupt Status One (SIST1)
register, bit 2.
START
Start Sequence
5
When this bit is set, the LSI53C875 starts the arbitration
sequence indicated by the Arbitration Mode bits. The
Start Sequence bit is accessed directly in low level mode;
during SCSI SCRIPTS operations, this bit is controlled by
the SCRIPTS processor. Do not start an arbitration
sequence if the connected (CON) bit in the
register, bit 4, indicates that the
LSI53C875 is already connected to the SCSI bus. This bit
is automatically cleared when the arbitration sequence is
complete. If a sequence is aborted, check bit 4 in the
register to verify that the
LSI53C875 is not connected to the SCSI bus.
WATN
Select with SATN/ on a Start Sequence
4
When this bit is set and the LSI53C875 is in the initiator
mode, the SATN/ signal is asserted during selection of a
SCSI target device. This is to inform the target that the
LSI53C875 has a message to send. If a selection