LSI LSI53C1000, Technical Manual

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4-24 Registers
Full Arbitration, Selection/Reselection
1. The LSI53C1000 waits for a bus free condition.
2. It asserts SBSY/ and its SCSI ID onto the SCSI bus.
The SCSI ID asserted is the highest priority ID
stored in the
SCSI Chip ID (SCID) register.
3. If the SSEL/ signal is asserted by another SCSI
device or if the LSI53C1000 detects a higher priority
ID, the LSI53C1000 deasserts SBSY/, deasserts its
ID, sets the Lost Arbitration bit, bit 3 in the
SCSI
Status Zero (SSTAT0) register, and waits until the
next bus free state to try arbitration again.
4. The LSI53C1000 repeats arbitration until it wins
control of the SCSI bus. When it wins, the Won
Arbitration bit is set in the
SCSI Status Zero
(SSTAT0) register, bit 2.
5. The LSI53C1000 performs selection by asserting
SSEL/, the target’s ID (stored in the
SCSI
Destination ID (SDID) register), and the
LSI53C1000’s ID (stored in the SCSI Chip ID (SCID)
register) onto the SCSI bus.
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 LSI53C1000 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
SCSI Control
One (SCNTL1) register, bit 4, is set. This bit indicates
that the LSI53C1000 is already connected to the SCSI
bus. This bit is automatically cleared when the arbitration