Avago Technologies LSI53C825AE User Manual
Page 109
Operating Registers
4-21
Full Arbitration, Selection/Reselection
1.
The LSI53C825A waits for a bus free condition.
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 LSI53C825A detects a higher priority
ID, the LSI53C825A deasserts BSY, deasserts its ID,
and waits until the next bus free state to try
arbitration again.
4.
The LSI53C825A repeats arbitration until it wins
control of the SCSI bus. When it has won, the Won
Arbitration bit is set in the
register, bit 2.
5.
The LSI53C825A performs selection by asserting
the following onto the SCSI bus: SSEL/, the target’s
ID (stored in the
register), and the LSI53C825A 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
register, bit 2.
START
Start Sequence
5
When this bit is set, the LSI53C825A 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. An arbitration sequence should
not be started if the connected (CON) bit in the
register, bit 4, indicates that the
LSI53C825A is already connected to the SCSI bus. This
bit is automatically cleared when the arbitration sequence
is complete. If a sequence aborts, check bit 4 in the
register to verify that the
LSI53C825A did not connect to the SCSI bus.