bit is cleared automatically when the selection or reselection sequence is completed, or times out. Interrupts do not occur until after this bit is reset.

An unexpected disconnect condition clears IARB without 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 (ISTAT) 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 LSI53C810A from the SCSI bus. If it is not acceptable to go to Bus Free phase immediately following the arbitration phase, it is possible to perform a low level selection instead.

The abort completes because the LSI53C810A loses arbitration. This is detected by clearing 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.

SSTStart SCSI Transfer0

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/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 SCSI Output Control Latch (SOCL). This bit is self-clearing. Do not set it for low level operation.

Note: Writing to this register while not connected may cause the loss of a selection/reselection by clearing the Connected bit.

5-8

Operating Registers

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LSI 53C810A technical manual SSTStart Scsi Transfer0