LSI53C825AJ LSI, LSI53C825AJ Datasheet - Page 113

• Manufacturer Part Number: LSI53C825AJ
• Manufacturer: LSI

Specifications of LSI53C825AJ

• Lead Free Status / RoHS Status: Not Compliant

IARB
SST
Operating Registers
Immediate Arbitration
Setting this bit causes the SCSI core to immediately
begin arbitration once a Bus Free phase is detected
following an expected SCSI disconnect. This bit is useful
for multithreaded applications. The ARB[1:0] bits in
Control Zero (SCNTL0)
selection before setting this bit.
Arbitration is retried until won. At that point, the
LSI53C825A holds BSY and SEL asserted, and waits for
a select or reselect sequence. The Immediate Arbitration
bit is reset automatically when the selection or reselection
sequence is completed, or times out.
An unexpected disconnect condition will clear IARB
without attempting arbitration. See the SCSI Disconnect
Unexpected bit
more information on expected versus unexpected
disconnects.
It is possible to abort an immediate arbitration sequence.
First, set the Abort bit in the
register. Then one of two things eventually happens:
Start SCSI Transfer
This bit is automatically set during SCRIPTS execution
and should not be used. It causes the SCSI core to begin
a SCSI transfer, including SREQ/ and SACK/
handshaking. The determination of whether the transfer
is a send or receive is made according to the value
written to the I/O bit in
(SOCL). This bit is self-clearing. Do not set it for low level
operation.
The Won Arbitration bit
bit 2) is set. In this case, the Immediate Arbitration bit
needs to be reset. This will complete the abort
sequence and disconnect the LSI53C825A from the
SCSI bus. If it is not acceptable to go to Bus Free
phase immediately following the arbitration phase, a
low level selection may be performed instead.
The abort completes because the LSI53C825A loses
arbitration. This can be detected by the Immediate
Arbitration bit being cleared. Do not use the Lost
Arbitration bit
detect this condition. In this case take no further
action.
(SCSI Control Two
(SCSI Status Zero
SCSI Output Control Latch
are set for full arbitration and
(SCSI Status Zero (SSTAT0),
Interrupt Status (ISTAT)
(SCNTL2), bit 7) for
(SSTAT0), bit 3) to
SCSI
4-25
1
0