LSI LSI53C1000, Technical Manual

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SCSI Registers 4-29
An unexpected disconnect condition clears IARB with it
attempting arbitration. See the SCSI Disconnect
Unexpected bit (
SCSI Control Two (SCNTL2) , bit 7) for
more information on expected versus unexpected
disconnects.
It is possible to abort an immediate arbitration sequence.
First, set the Abort bit in the
Interrupt Status Zero
(ISTAT0) register. Then one of two things eventually
happens:
•
The Won Arbitration bit ( SCSI Status Zero (SSTAT0),
bit 2) will be set. In this case, the Immediate
Arbitration bit needs to be cleared. This completes the
abort sequence and disconnects the chip from the
SCSI bus. If it is not acceptable to go to the Bus Free
phase immediately following the arbitration phase, it is
possible to perform a low level selection instead.
•
The abort completes because the LSI53C1000 loses
arbitration. This is detected by the clearing of the
Immediate Arbitration bit. Do not use the Lost
Arbitration bit (
SCSI Status Zero (SSTAT0) ,
bit 3) to detect this condition. In this case take no
further action.
R Reserved 0
Register: 0x02
SCSI Control Two (SCNTL2)
Read/Write
SDU SCSI Disconnect Unexpected 7
This bit is valid in the initiator mode only. When this bit is
set, the SCSI core is not expecting the SCSI bus to enter
the Bus Free phase. If it does, an unexpected disconnect
error is generated (see the Unexpected Disconnect bit in
the
SCSI Interrupt Status Zero (SIST0) register, bit 2).
During normal SCRIPTS mode operation, this bit is set
automatically whenever the SCSI core is reselected, or
successfully selects another SCSI device. The SDU bit
7 6 5 4 3 2 1 0
SDU CHM R WSS VUE0 VUE1 WSR
0 0 0 0 0 0 0 0